motion fundamentals

8/12/2019 Motion Fundamentals

1/64

Defining Motion Control

What is Motion Control?a If:

After completing this lesson, you will be able to define motioncontrol.

Motion is an act, process, or instant of changing place

And:

Control is the power or authority to guide, manage,coordinate, or direct . .

Then:

Motion control is a means of directing movement.

What Is a Motion Control System?

A motion control system is a series of high-performance electricaland hardware components working together to precisely controlmovement of an axis or axes. These components are programmed toinitiate or produce motion using a human-machine interface, fieldsensors, or a specific software package.

What Is an Axis?

An axis is a principal direction along which movement of the tool or workpiece occurs. Axes have the following characteristics:l An axis can be a motor turning a shaft.

l An axis can be a motor attached to a piece of hardware.l One motor and feedback device control the movement of one

axis.l Movement and motion are performed on a motion control system

by axes.

Depending on the complexity of the motion control application andthe motion control system, one axis can perform motionindependently or many axes can control motion together.

1


2/64

What Does a Motion Control System Control?

There are five main control parameters of axis motion that a motioncontrol system precisely controls:l Velocityl Acceleration/decelerationl Position

l Inertial Torque

Velocity

Velocity is the speed at which a move is made. A motion controlsystem regulates the speed at which an axis moves. Velocity has thefollowing characteristics:

l The amount of electrical current sent from the motion controlsystem to the motor is regulated.

l The electrical current is controlled by performing a logicalcomparison inside the motion control system of the motorsrequired speed to the motors actual speed.

The following graphic shows velocity in a motion event. The initialvelocity is the speed at which the motion is started. The finalvelocity is the maximum speed reached during the move.

Final Velocity Time InitialVelocity

Time

Acceleration

Acceleration is an increase in velocity as a function of time. Amotion control system controls the speed at which an axis move isstarted. This is done by applying a predetermined acceleration settingto the axis being controlled.

2

Distance

Area =Acceleration

Final Velocity

Velocity

Initial Velocity


3/64

. Deceleration

Deceleration is a decrease in velocity as a function of time. A motioncontrol system controls the speed at which an axis slows down andstops. As with acceleration, a predetermined deceleration settingcontrols the axis that is being decelerated and stopped.

Position

Position is the location of a specific place with respect to one or more fixed references. A motion control system controls the positionof an axis by performing the following actions:

Comparing where the axis needs to be to where it actually is onthe motion control application

l Compensating for the difference between where the axis needs to be and where it actually is on the motion control system

l Minimizing the difference between where the axis needs to beand where it actually is on the motion control system. Bycomparing these two factors and correcting the difference

between them, the motion control system can achieve pinpointaccuracy in positioning an axis.

I nertia

Inertia is a measure of a bodys resistance to changes in velocity,whether the body is at rest or moving at a constant velocity. Thevelocity can be either linear or rotational.

Inertia has the following characteristics:l Is typically expressed in units of or lb-in-sec2kg-m 2

l Must be calculated for each component in the motion controlapplication prior to determining the amount of torque required to

perform motion

3


4/64

Example: Inertia Calculation for an Aluminum Pulley

In this example, a motion control application includes onealuminum pulley with the following dimensions:l Radius is 40 mm.

. Length is 50 mm.l Material is aluminum (density of 2700kg/m 3 ).

The pulley dimensions are shown in the following graphic:

Side View Top View

40 mm

Lc l l

Given the dimensions and the material, the pulley volume iscalculated as follows:l r 2 L = volumel 3.142 x (0.04)2 x 0.05 = 0.000251m 3

Next, the pulley mass is calculated as follows:l volume x density = mass. 0.000251 x 2700 = 0.6777 kg (round up to 0.7 kg)

Finally, the pulley inertia is calculated as follows:l mass x radius2/2 = inertia (of a solid round object)l 0.7 x (0.04)2/ 2 = 0.0056 kg-m2

In some instances, the component manufacturer will provide a precalculated inertia value for a component.

4

50 mm

For a hollow circular cylinder:Inertia = mass x (outer radius + inner radius )/2

2 2

Caclulate inertia of a pulley with mass of 0.7 kginner radius of 30 mm and outer radius of 40 mm

Exercise


5/64

24-28

Torque

Torque

Torque is the turning force applied to an object, tending to causerotation. Torque is required to overcome the mechanical forces of friction, gravity, and inertia when moving a load.

Torque is the product of force times lever arm length (radius). Thiscan be expressed as follows:

T = F R, where:l T = torquel F = force

R = radius (lever arm length)

This concept is shown in the following graphic:

Force

In a motion control system, torque is produced by the rotational forceof a turning motor. There are four types of torque that apply tomotion control:l Acceleration torquel Loss torque

l Load torque

Gravity torque

In addition to the total inertia of the motion control system, a motioncontrol application must have all four of these torques factored intothe motion control systems movements to perform motionsuccessfully in an application.

5


6/64

acceleration value.

4

Acceleration Torque

The torque required to overcome the total inertia of the systemcomponents and start the load moving is called accelera t ion torq ue.Acceleration torque can be expressed as follows:

T = Ja, where:l T = accelerating torquel J = polar moment of inertia (load inertia)l a = angular acceleration

The angular acceleration value is obtained by adding together all of the moving component inertia values in the motion controlapplication.

Loss Torque

The torque that is required to overcome static forces of machinefriction is called loss t o r q u e .

Friction losses are caused by the following:l Sliding frictionl Gear tooth resistancel Bearing resistancel Ballnut resistancel Machine component weight

Friction loss points in a typical motion control system are shown in

the following graphic:

Ballnut Assembly

Ball Bearing Ball Bearing

Ball Bearing

6


7/64

Loss torque has the following characteristics:l Is often precalculated and established by machine manufacturer,

e.g., ballscrew preloadl Is active during motion only

l Must be added to the torque calculations in the motion controlapplication to overcome the loss

Changes direction with motion, so loss torque always opposes

motion

Load Torque

The torque that is required to perform the actual work in the motioncontrol application is called l o a d t o r q u e. Load torque is applicablewhenever work must be performed after acceleration.

Load torque has the following characteristics:l Is usually constant for an applicationl

Is often not present for the entire motion actionl Is zero if there is no loadl Changes with the direction of applied load

Example: Load Torque in a Drilling Application

In the following example, castings are being drilled as a step in amanufacturing process.

Load torque is shown in the following graphic:

7


8/64

The load torque in the drilling operation is described as follows:l The conveyor pauses as each casting is positioned under the

drill head. The drill head is raised and lowered by motor 1, which is

connected to a ballscrew by a gearbox.l Motor 2 rotates the drill bit.l When the casting is in position, motor 1 turns the ballscrew

and lowers the drill head, providing load torque to press therotating drill bit into the casting.

l Motor 2 then provides the load torque required to drill into themetal surface of the casting and create the hole.

l Both motors in the application must provide the required loadtorque to push the drill head down and drill the hole in thecasting.

Gravity Torque

The torque that is required to perform non-horizontal work in themotion control application is called gravity torque. This is applicabwhenever the force of gravity must be overcome to lift a load or perform work.

Gravity torque has the following characteristics:l Applies to any motion other than horizontal motionl Is zero if there is no lifting being performed

Example: Gravity Torque in a Lifting Application

In the following example, a load is lifted vertically by a motor turning a ballscrew. Gravity torque is shown in the followinggraphic:

8


9/64

Exercise 0

15 minutes

The gravity torque in the lifting operation is described as follows:l The motor is connected to the ballscrew by a gearbox.l As the motor turns, the ballscrew rotates and raises or lowers

the load, depending on the direction the motor is turning.l The motor must provide the required gravity torque to

overcome the force of gravity and lift the load.

In this exercise, you will define motion control.

Directions:

Answer the following questions:

1 . How does a motion control system produce motion?

2. What is an axis?

3. How does a motion control system control velocity?

4. In a motion event, what is the difference between initial velocityand final velocity called?

5. How is deceleration controlled in a motion control application?

9


10/64

6. How does a motion control system achieve pinpoint accuracywhen controlling position?

7. What are the factors that determine the amount of inertia a motioncontrol system will have?

8. Why is torque such an important factor in motion control?

9. Determine the type of torque required for each applicationdescribed:

A. A large conveyor system with a length of 150 metersregularly starts and stops to allow workers to place heavy

packages at one end of the belt and remove them at the

opposite end. What kind of torque is required start theconveyor moving?

B. An application has numerous gearboxes, ball bearings, and alarge ballscrew that moves a heavy load. What kind of torqueis required for the machine to perform motion?

10


11/64

C. A stamping machine is operating in a manufacturing facility.The machine stamps serial numbers on metal castings as theymove past the machine on a conveyor. What kind of torque isutilized to make sure the stamping machine makes a readableimpression in the castings?

D. A motion control application raises and lowers a heavy craneunit in a fabrication shop. What kind of torque must beutilized in order to perform the motion required?

How Did You Do? Turn to the end of the lesson for the answers. If you have anyquestions, ask your instructor for assistance.

11


12/64

Answers Exercise

1 . Motion is produced through application software, sensors, or through a human-machine interface.

2. An axis can be a motor turning a shaft or a motor attached to a piece of hardware.

3. Velocity is controlled by regulating the amount of current sentfrom the motion control system to the motor.

4. Acceleration is the difference between initial velocity and finalvelocity.

5. Deceleration is controlled by a predetermined setting in themotion controller, which controls the axis that is beingdecelerated and stopped.

6. Pinpoint accuracy is achieved by minimizing the difference

between where the axis needs to be and where it actually is on themotion control system.

7. Inertia is determined by the size, quantity, and materialcomposition of system components that move and performmotion.

8. Torque is required to overcome mechanical forces of friction,gravity, and inertia.

9.

A. Acceleration torque

B. Loss torque

C. Load torque

D. Gravity torque

12


13/64

Identifying Motion Control SystemComponents and Functions

After completing this lesson, you will be able to identify motioncontrol system components and functions.

Key Terms

Asynchronous Motion : One or more AC or DC motors operatingindependently on a single motion control system.

Digital Servo Motion Controller: A processing device that controlsthe entire motion control system.

Feedback Element: An element of a control system that convertslinear or rotary motion to an electrical signal for comparison to theinput signal.

Servo: A system of several devices that continuously monitors andcompares actual position and velocity values to the desired outcome.

Digital Motion Control

Digital motion control is the process of using microprocessors tocontrol the following motion control parameters:l Velocityl Acceleration/decelerationl Positionl Torque

Digital motion control can be broken down into two categories:l Open-loop digital control systemsl Closed-loop digital servo control systems

13


14/64

6 Open-Loop Digital Control Systems

A control system that uses a controller to generate commands tomove a motor the required number of revolutions without feedbackfrom a sensor is called an open-loop digital control system.

Use the following graphic to show thatthere is no feedback connectionbetween the motor and the motion

controller.

An open-loop digital control system schematic is shown in thefollowing graphic:

MotionCommand

MotionController -

Input -

Mecha- Motion

?. Can anyone think of an applicationwhere an open-loop digital controlsystem may be used?

Answer: One possible application is ablower motor application, where error between the input command and actualmechanical motion is not critical.

7 - 11

?. Does it matter if the conveyor runs alittle faster or slower than the targetspeed?

Answer: No, as long as the passengershave the time to identify and pick uptheir baggage as it moves past on theconveyor.

The characteristics of an open-loop digital control system include:l Errors between the input command and the actual mechanical

motion are not corrected.l Performance is lower than a closed-loop system.l Price is lower than a closed-loop system.

Example: Open-Loop Digital Control System Application

In the following example, baggage is being unloaded from anincoming aircraft and transported inside an airport terminal. The

baggage unloading operation is described as follows:l The motor is connected to the conveyor by a reduction

gearbox.l The input command is predetermined and is constant.l The bags are physically placed on the conveyor by an airport

employee.l Inside the airport terminal, passengers identify and pick up

their baggage as it moves past on the conveyor.l The conveyor moves at a constant velocity and is either on or

Off.

14

Drive amplifier Motor


15/64

In the following graphic, point out thefact that there is no feedback element tocompare the actual position to thecommand input.

An open-loop digital control system application is shown in thefollowing graphic:

12-18 Closed-Loop Digital Servo Control SystemsA servo system that uses a controller to generate commands to movea motor the required number of revolutions by using feedback fr position and/or velocity sensors is called a closed-loop digital servocontrol system.

15


16/64

In the following graphic, point out thefeedback element connection from themotor to the digital servo motioncontroller.

A closed-loop digital control system schematic is shown in thefollowing graphic:

Computer Terminal

. Can anyone say why it is critical to

correct errors between the inputcommand and actual mechanicalmotion?

Answer: If there is no correctionbetween the input command and theactual mechanical motion, thenequipment damage, personnel injury,and material loss are possible.

19-22

?. What would happen if the conveyor sped up slightly?

Answer: The rotary knife would need tospeed up. If the material cutoff lengthmust be within a specific tolerance, thenboth axes must run at the samesynchronized velocity, fast or slow.

MechaniMotion Ou

The characteristics of a closed-loop digital servo control systeminclude the following:l Errors between the input command and the actual position are

corrected.l Performance is enhanced.l Price is higher than an open-loop system.l High-performance servo control is provided.l Setup adjustments are reduced.

Example: Closed-Loop Digital Control System Application

In the following example, material on a moving conveyor is cutusing a rotary knife. The cutting operation is described asfollows:l The rotary knife motor and the conveyor motor are both

connected to the same motion controller.l The conveyor motor is connected to the conveyor by a

reduction gearbox.l As the material passes beneath on the conveyor, the rotary

knife cuts the same length of material each time.l A feedback element is mounted on the conveyor and is

connected to the motion controller.l The motion controller monitors the feedback element signal

and adjusts the speed of the rotary knife to keep up with theconveyors actual speed, ensuring that all pieces of materialare cut at the same interval.

16


17/64

In the following graphic, point out thefeedback element and explain brieflyhow the actual position is compared tothe command input in order to keep theapplication cutting correctly.

A closed-loop digital control system application is shown in thefollowing graphic:

Side View

Direction of Motion-

Top View Rotary Knife

FeedbackElement

Conveyor

Operator Interface

Motor

Gearbox

MotionController

23 Components of a Closed-Loop Digital Servo Control SystemA typical closed-loop digital servo control system consists of the

If you are using a workstation with thislesson, point out these components andwhere they are located on theworkstation.

following components:l Digital servo motion controller l Drive/amplifier l Motor l Feedback element

17


18/64

37 Motion Controller Architectures

As you go through the differentarchitectures, students may express aninterest in obtaining more informationabout some of the products.

Be prepared to supply the students withproduct literature as required for theproducts that Rockwell Automationmanufactures and supports.

There are several different motion controller architectures available.Each of these architectures serves a different application need. Thesearchitectures are as follows:l Rack-mounted motion controllers

l Bus-based motion controllersl Stand-alone motion controllersl Integrated motion controllersl Open-architecture motion controllers

4 38-39

?. Can anyone think of applications for a rack-mounted motion controller?

l A plant with limited motion controlfunctions

l An assembly line that is moving car frames slowly along as workersassemble them

Rack-Mounted Motion Controllers

Rack-mounted motion control has the following characteristics:l Ladder logic programming is used to program motion.l The motion controller is actually a module in the PLC or SLC

processor rack.l Operator interface, inputs, outputs, and communications are

merged in the controller backplane.l Dedicated motion modules use separate microprocessors for

faster response time.

Applications for rack-mounted motion controllers include largeautomation applications and the automotive industry. A schematicview of two rack-mounted motion controllers is shown in thefollowing graphic:

PLC or SLCT Processor Chassis Remote PLC or SLC Chassis

Motion Control Modules

Inputs/Outputs Inputs/Outputs

Servo Controller

18


19/64


20/64

Tell the class that CNC will not becovered in this training course, but other CNC-specific courses are available fromRockwell Automation.

46-47

If workstations are used for this course,mention that the workstations will beeither integrated or stand-alone motioncontrollers.?. Can anyone think of other applications?

. A manufacturing operation that isplacing labels on packages as theypass on a conveyor belt. The labelsmust all be placed in the samelocation on the packages as theypass.

One axis that is following a feedbackelement or another axis duringmotion

CNC stand-alone motion controllers have the followingcharacteristics:l Highly complex, precise motion can be programmed.l Programming software is proprietary in nature.l Special program routines are required for operation.

Applications for CNC include dedicated machine tool applications,automotive manufacturing and machining, and specialized

applications requiring multiple tool operations.

Integrated Motion Controllers

Integrated motion controllers have the following characteristics:l The motion controller and the servo drive are packaged together.l The motion controller is configured for multiple axis control.l The motion controller processes velocity, position, motion

program, inputs and outputs, and communications.l

The motion controller follows stand-alone architecture.Applications for integrated motion controllers include packaging,

pick-and-place, and applications where several axes are movingtogether in synchronized motion. An integrated motion controller isshown in the following graphic:

Computer Terminal

1394 GMC

Mo

Mo

20


21/64


22/64

54-59

3. Do any of you currently work with or have experience working with any of these motion controller systems?

Allen-Bradley Motion Controller Families

Allen-Bradley motion controllers are available in the followingconfigurations:

l Rack-mounted motion controllers (for use with a 1771 I/Ochassis):

- IMC 120- IMC 120AR - IMC 121- IMC 123- IMC123 CR

l Rack-mounted motion controllers (for use with a SLC 5/01 processor or later):

- IMC 110- 1746-HSRV- 1746-HSTP1

l Stand-alone motion controllers:

- 1398 Ultra 100/200 Series- 1398 Ultra Plus- S-Class Basic (IMC 20x)- S-Class Integrated (IMC 21x)

- S-Class Compact (IMC 23x)

l Integrated motion controllers:

- 1394 Servo system (Digital servo with traditional interface)

- 1394 GMC system (Embedded IMC S-Class)- CNC system (9/Series CNC interface)

l Open-architecture motion controllers - ControlLogix system

Heres How(1394 GMC System or 1398Ultra 100/200)

To identify motion control system components and functions:

Follow along as your instructor points out and describes the motioncontrol system components and their functions on your workstation.

If you are using a workstation with theclass, have the students gather around aworkstation while you point out all major components. Explain each componentsfunction in the motion control system. Besure to include LEDs, inputs, andoutputs.

22


23/64


24/64

6. How does the controller close the position loop in a controlsystem?

7. Why is it necessary to have a drive/amplifier in a control system?

8. What role does the motor play in a control system?

9. Why is it important to have a feedback element in a closed-loopsystem?

10. Provide the best type of motion controller architecture to use for each application listed:

A. A machine that is grinding crankshafts to precise tolerances,using several separate tool movements for each operation.

B. A large conveyor system with numerous operator interfacesthat is moving parts to be spray painted through a paint

booth.

24

C. A machine that is moving packages from one conveyor belt to another conveyor belt using an armature to pick up and move items.


25/64

Answers Exercise A

1 . An open-loop system does not have a feedback element, while aclosed-loop system has a feedback element.

2. An open-loop digital control system

3. A closed-loop digital control system

4. A servo continuously monitors and compares actual position andvelocity values to the desired outcome.

5. Errors between the input command and the actual position arecorrected.

6. The controller closes the position loop by processing the inputand feedback signals into a form that will actuate thedrive/amplifier.

7. The drive/amplifier amplifies a small command signal that iscapable of driving a motor and controls the input voltage andcurrent to the motor.

8. The motor converts the electrical signal from the drive/amplifier into mechanical motion/power.

9. The feedback element converts the dynamic conditions, position,and velocity to an electrical signal for use by the controller.

10 .

A. CNC motion controller

B. Rack-mounted motion controller

C. Integrated or stand-alone motion controller

25


26/64

What You Will Learn

a 2-10

?. Who can think of examples of eachtype of axis?

. An example of a rotary axis is arotary table that moves containers

under a filling head.l An example of a linear axis is a

ballscrew moving a glue gun acrossthe flaps of boxes as they passbeneath on a conveyor.

Applying Basic Motion ControlConcepts

After completing this lesson, you will be able to apply basic motioncontrol concepts.

Axis Types

Axis: The principal direction along which movement of a tool or workpiece occurs.

There are two different types of axes used in motion control:l Rotary axesl Linear axes

Rotary Axes

A rotary axis has the following characteristics:l Rotation occurs around a central shaft.l Axis motion occurs when the shaft, usually in a motor, rotates.l Rotary axes are used in applications for conveyor belts and

machining tools.

A rotary axis example is shown in the following graphic:

:.I.AXis 0

=z

Axis

Rotary Axis

Linear AxesA linear axis has the following characteristics:l Movement occurs in a point-to-point line.

l Axis motion occurs when the motor turns a gearbox and in turn,rotates a ballscrew and ballnut assembly.

l Linear axes are used in applications for moving loads and for pick-and-place operations.

26


27/64

A linear axis example is shown in the following graphic:

11-14Potential Learning Problem: Makesure that students understand thedifference between an incremental moveand an absolute move.

Two examples of each type of move areprovided - one linear and the other rotary.

Use additional examples as required toensure that students can clearly discernbetween the two types of moves.

3. What would happen if we specified athird incremental move of -10 units fromthe 20-unit position?

Answer: Motion would occur in anegative direction, with the ballscrewmoving the ballnut back to the 11 O-unitposition.

Linear Axis

Axis Movements

For both rotary and linear axes, there are two types of movementsthat can be performed on a motion control system:l Incremental motionl Absolute motion

Incremental Motion

Incremental motion is measured from the current position of the axiswhen the motion command, or desired position of the axis asgenerated by the motion controller, is performed. Refer to thefollowing examples:

Example: Incremental Motion on a Linear Motion System

In the following example, a linear motion control applicationmust make two incremental moves:l The first move is 10 units, starting at the zero position.l The second move is also 10 units.

27


28/64

Incremental motion on a linear motion system is shown in thefollowing graphic:

0

Move 110 Units

10

Axis Position

Move210 Units

20

Therefore, the total incremental move is 20 units from positionzero, a sum total of two lo-unit moves.

15-24

Tell the class that incremental motion isthe same principle for both linear and for rotary axes.

Example: Incremental Motion on a Rotary Motion System

In the following example, a rotary motion control applicationmust make two incremental moves:l The first move is 90 degrees clockwise, starting at the zero

position.l The second move is 45 degrees clockwise.

Incremental motion on a rotary motion system is shown in thefollowing graphic:

28


29/64

?. What would happen if we specified a The final incremental position of the rotary motion application isthird incremental move of -30 degreesfrom the 135-degree position?

135 degrees from the zero position, a sum total of a 90-degreemove and a 45degree move.

Answer: Motion would occur in acounterclockwise direction, with therotary axis moving back to the Absolute Motion105-degree position. Absolute motion is measured from an established position or a zero

point on the motion controller. Refer to the following examples:

Example: Absolute Motion on a Linear Motion System

In the following example, a linear motion control applicationmust make two absolute moves as follows:l The first move is 10 units, starting at the zero position.l The second move is 20 units.

Absolute motion on a linear motion system is shown in thefollowing graphic:

Move 110 Units

10

Axis Position

Move 220 Units

?. What would happen if we specified asecond move of 10 units instead of 20units?

Answer: No motion would occur,because the ballscrew is already at the10-unit position.

Tell the class that absolute motion is thesame principle for both linear and for rotary axes.

Therefore, the final absolute position of the ballnut is 20 unitsfrom position 0, with the first move to the lo-unit position andthe second move to the 20-unit position on the ballscrew. For

both moves, the specified number of units to move is referencedto the zero position.

Example: Absolute Motion on a Rotary Motion System

In the following example, a rotary motion control applicationmust make two absolute moves as follows:l The first move is 20 degrees clockwise, starting at the zero

position.l The second move is 35 degrees clockwise.

29


30/64

?. What would happen if we specified athird incremental move of -30 degreesfrom the 35-degree position?

Answer: Motion would occur in acounterclockwise direction, with therotary axis moving back to the 5-degreeposition.

25-31 As an everyday application for homingand its functionality, mention that a pair of windshield wipers on a car homes toa position at the bottom of thewindshieldwhen they are not being used

Another example is an elevator thatalways goes to a specific floor when it isnot in use.

Compare homing to calibrating a set of calipers before taking a measurement.

Absolute motion on a rotary motion system is shown in thefollowing graphic:

Move 120 Degrees Move 2

20

35 Degrees

35

The final absolute position of the rotary motion application is 35degrees from the zero position, with the first move to the20-degree position and a second move to the 35-degree posiFor both moves, the specified number of degrees to move isreferenced to the zero position.

Homing

Homing is the process of establishing a unique position at power upfor the purpose of axis calibration. Most motion applications arehomed before motion begins.

Home position is the base reference for all absolute moves. Thehome position in a motion control application has the followingcharacteristics:

. Establishes a reference point (zero point) for each axisl Is usually defined by a home limit switch, feedback element

pulse, or both for linear axesl Is usually defined by a feedback element pulse for rotary axesl Serves as a reset marker for the feedback devices

3 0


31/64

Point out the home position in thefollowing graphic. Tell the class thathome position is not always in the center of the machine, but is determined by theapplication requirements.

Home position on a linear motion control system is shown in thefollowing graphic:

Load

Home Position

Point out the home position in thefollowing graphic. Tell the class thathome position on a rotary axis dependson the configured location of thefeedback element pulse.

Home position on a rotary motion control system is shown in thefollowing graphic:

Home Position as Defined byFeedback Element Pulse

Feedback Element Pulse DetectedWhen Axis Turns Past Home Position

Axis Performs Motion UsingHome Position as Reference

32 Overtravel

?. What kinds of over-travel does your application use?

Overtravel in a motion control system must be carefully controlled toavoid damage to equipment, personnel injury, and economic loss.

The following methods may be used for overtravel protection:l Hardware overtravel controll

Software overtravel control3 1


32/64

33-37

A hard stop can also serve as a

hardware overtravel control.

Explain that some motion controllersoffer other response options to hardovertravel besides turning off axis power,but turning off the axis is the safest wayto respond.

Other responses include:

l A status message sent to theoperator terminal

l Stopping motion, but allowing motionto occur in the opposite directionaway from the direction of overtravel

38-42

Motor

Hardware Overtravel Control

Overtravel is a condition that occurs when an axis moves beyond the physical limits of the machine.

Hardware overtravel control is usually enforced by limit switches ateach end of the travel range on a motion control system. The limitswitches shut down the drive before the axis comes into physicalcontact with the machine limits.

Hardware overtravel control has the following characteristics:l Limit switches are hard-wired to the digital servo motion

controller as discrete inputs.l The digital servo motion controller turns off the axis motion

when the axis comes into contact with the limit switches.l The axis cannot be reactivated until it is moved back within the

acceptable travel range of the motion control system.

Hardware overtravel control on a linear motion system is shown inthe following graphic:

Load

m t Switc

Software Overtravel Control

Software overtravel control occurs within the axis travel rangedefined by the hardware overtravel limit switches on the motioncontrol system.

3 2


33/64


34/64

Following Error

Following error is the difference between commanded position andactual position, while the axis is in motion. When the axis is notcommanded to move, following error is zero.

Using the illustration you created for position error, show how following error affects the positioning accuracy whenthe axis is in motion.

Following error is measured and calculated at three critical pointswhen motion is occurring:l When the axis is at the end of the acceleration rampl When the axis is moving at full speedl When the axis is decelerating

The minimum time that a motion control system requires to respondto a motion command is called response time. An increase inresponse time will reduce following error.

Discuss some of the causes of following Following error is shown in the following graphic:error on a motion control application:

l The axis not keeping up with the

commanded position, due to speedrequirements beyond the limits of the motor

l The load being too heavy to move inthe time and distance required

Commanded PositionVelocity- - - - - - - -

Actual Posit ion

0.5 1 1.5 2

Time in Seconds

54-55 ResolutionResolution is the smallest distinguishable increment into which asignal or quantity can be divided. Resolution is also the degree towhich nearly equal values of a quantity can be discriminated.

3 4


35/64

Axis Positioning

Analoav: How fast an automobile isbeing propelled by the driver pressing onthe accelerator and how fast the

There are two aspects of axis positioning:l Commanded Position: The desired position of the axis. as1

generated by the motion controller.

automobile is actually moving. l Actual Position: The true position of the axis.

The goal of axis positioning is to minimize the difference between

the commanded axis position and the actual axis position.

44-53 Axis Positioning ErrorsThere are two types of axis positioning errors that can occur whenthere is a difference between the commanded axis position and theactual axis position:l Position error l Following error

Position error can never be completely eliminated from a closed-loopservo system. However, specific tolerances can be configured so thatthe system will operate within an acceptable range of values.

Position Error

Position error is the difference between the axis commanded position and the actual position on the motion controller.

Using the board, create a simple motiondiagram and show how the introductionof position error affects the positioningaccuracy.

Position error tolerances can be set in motion controllers to permit a predetermined amount of difference between the actual position andthe commanded position of the axis, when it is not in motion.

Discuss some of the causes of positionerror, such as friction, gravity, and theinertia a machine needs to overcome onstartup.

Position error is shown in the following graphic:

Commanded ActualPosition Position

I

ICI

-.0002 -.0001

BI

A BI I

+.0001

Error I

35


36/64

?If the motion controller cannot distinguish a difference in axis

. How many of you are familiar with position from A to B, but it can distinguish a difference from A to C,the term hunting? then the positioning resolution of the system is +/-0.0002.

Hunting refers to a motion controller axisseeking a position that is too small a An example of resolution is shown in the following graphic:number for it to detect. Hence, the axiswill hunt for the commanded positionindefinitely. C B A B

I I I I

-.0002 -.0001 .0000 +.0001 +

56-58 Lead and PitchOn a ballscrew assembly, lead and pitch must be taken into accountwhen performing motion control. Lead and pitch have the followingcharacteristics:l Lead is the distance, in meters, mm, or inches, of linear travel

that a ballnut moves for each revolution of a ballscrew.l Pitch is the number of threads for each inch (or other unit of

measure) on the ballscrew. This number, measured as 1inch/Lead, is factored into the number of turns the motor mustmake to complete one unit of motion.

In the following graphic, show the classhow pitch is calculated for the ballscrew.

Lead and pitch are shown in the following graphic:

1 2 3 4Lead

0.02540Pitch =- =40.00635

36

0.0254 m


37/64

?. Why would there be trade-offs withspeed and resolution here?

Answer: Because the motion controller is expendingresources ( C

so much of its internalPU, memory, etc.) that

other aspects of its operation must besacrificed.

60-61

Tell the students that backlash iscommonly found in mechanically gearedmotion control applications.

Bandwidth is the range of frequencies over which a motion controlsystem is designed to operate.

Bandwidth has the following characteristics:l A higher bandwidth allows the motion controller to count encoder

pulses at a higher rate.

l A higher bandwidth minimizes speed/resolution trade-offs.

Backlash

Backlash is the relative movement between interacting mechanical parts, resulting in lost motion. Backlash occurs as a result of thefollowing conditions:

l In a rotary axis or gearbox, backlash is caused by the smallamount of extra space between gear teeth where they do notcontact.

l In a linear axis or a ballscrew, backlash is caused by the smallamount of space between the balls and the screw assembly wherethey do not contact.

Backlash is shown in the following graphic:

3 7

Bandwidth


38/64

62-67?. Why would backlash compensationbe an important factor in motion control?

Answer: An applications hardwarebacklash must be accounted for in order to ensure accurate positioning.

Use the markerboard to illustrate thisexample, drawing the two gears andpointing out the backlash. Then, usearrows to show the direction of movement and how the unidirectionalapproach works.

Backlash Compensation

Backlash compensation is the elimination of the extra space betweencontacting components. Backlash compensation can be accomplishedin the following ways:l Equipment manufacturers can design and manufacture preloaded

components, in which contacting parts are always touching eachother, with no free space between them.

l If the exact amount of backlash is known, the motion controller can be programmed to move slightly to compensate for the freespace between the components when motion is performed.

Unidirectional approach is a form of backlash compensation. Thismeans that the axis always approaches the destination position fromthe same direction.

Example: Unidirectional Approach for Backlash Compensationin a Rotary Motion Application

In the following example, a rotary motion application uses twogears with a given backlash offset of 0.200 mm between them.Two moves must be made, both the same distance, one a forwardmove and the other a reverse move:l For the forward move, backlash is not a factor.l For the reverse move, backlash compensation occurs after the

move, by a short forward move equivalent to the amount of backlash offset.

With the unidirectional approach, the axis always approaches thedestination position from the same direction. The unidirectionalapproach concept is shown in the following graphic:

Velocity

Destination Position

3 8

0.2 mm

BacklashCompensation


39/64

Exercise A 30 mi nutes

In this exercise, you will apply basic motion control concepts.

Directions:


1 . An application that is using a grinding tool to shape a roughcasting is probably using what kind of an axis?

2. An application that is moving a load from Point A to Point B is probably using what kind of an axis?

3. A motion controller is performing incremental motion on a linear axis. If the first incremental move is 10 units, and the secondmove is 20 units, what is the final position of the axis after the

second incremental move?

4. A motion controller is performing absolute motion on a rotaryaxis. If the first absolute move is 25 units, and the second move is30 units, what is the final position of the axis after the secondmove is completed?

5. Why is homing important in a motion control application?

6. What must happen when a hardware overtravel condition occurson a motion control application?

3 9


40/64

7. What must happen when a software overtravel condition occurson a motion control application?

8. If a motion controller cannot distinguish a difference in axis position from point X to point Y, but can distinguish a differenin axis position from point X to point Z, then what is the

positioning resolution of the system? Refer to the followinggraphic:

z Y X Y

- . 005 . 000 - . 005

9. What is the pitch of the following ballscrew? Refer to thefollowing graphic:

25. 4mm(1 I nch)

10. Using the preceding graphic as a reference, if the ballscrewmoves 5 mm for each motor revolution, how many motor revolutions are required to make the ballscrew move .22 m?

- . 010

40


41/64

11. A motion control application has .254 mm of backlash for which compensation must be made in each move. Using theunidirectional approach, how will the backlash compensationoccur for each type of move below?

A. A forward move:

B. A reverse move:

How Did You Do? Turn to the end of the lesson for the answers. If you have anyquestions, ask your instructor for assistance.

41


42/64

Answers Exercise A

1 . Rotary axis, since the tool is turning in a rotational direction.

2. Linear axis, since the load is moving in a point-to-point direction.

3. 30 units

4. 30 units

5. Homing establishes a reference point (zero point) for each axisand serves as a reset marker for the feedback devices.

6. The axis must be moved back within the defined travel limits of the application before further motion can occur.

7. The axis must be moved back within the defined travel limits of the application before further motion can occur.

8. +/-0.010

9. 7 threads per inch

10. 44 turns

11. The axis always approaches the destination position from thesame direction.

A. Compensation will not occur during the forward move, aslong as the axis continues in a forward direction.

B. Compensation will occur at the end of the reverse move by ashort forward move of .254 mm.

Exercise B

3. The axis position should be 10 units.



8. The axis position should be -10 units.

9. No axis motion occurred, because the axis was already at the20-unit position in relation to the home position.

42


43/64

Applying Motion Profiles

What You Will Learn

4-6Tell the students that an example of aspindle control application is a rotating

tool that is performing a grindingprocedure on a casting.

?. Can anyone think of other applications?

?. How could wear be reduced on theequipment using this profile?

Answer: Establish a longer ramp up tospeed.

After completing this lesson, you will be able to apply motion profiles.

Motion Profiles

Motion is generated by a digital servo motion controller byconverting a command signal, which is an electronic signal produced

by the motion controller, into an output voltage that turns a motor.

During the conversion process, there are several different motion profiles that can be created and executed by the motion controller:

l Jog motion profilel Trapezoidal motion profile

l Triangular motion profilel Parabolic motion profilel S-curve (sinusoidal) motion profilel Customized motion profile

J og Motion Profile

A jog motion profile moves the axis at a specified speed in aspecified direction, either positive or negative. Typical applicationsfor a jog motion profile include spindle control, in which a constantspeed must be maintained in a positive or negative direction, or aconveyor, in which a belt is moving at constant speed.

Characteristics of a jog motion profile include the following:l Ramps up to speed, ramps down to stopl Induces high wear on equipmentl Is event-driven (release button, trip switch, etc.)l Defines end position of axis after stop

4 3


44/64


45/64

IO-11

?jerk means?

Answer: Jerk is the physical effect themachine hardware experiences fromacceleration and deceleration.

Explain to students that when this profile

is used in moving a heavy load, a largeamount of torque is required to get theload moving.

Mention to students that an applicationthat can use this type of motion profile isa pick-and-place application, in which arobot arm is rapidly picking finishedparts from a tray and placing them inpackages.


Triangular Motion Profile

A triangular motion profile has the following characteristics:

Acceleration is a steady ramp up to speed.

Deceleration occurs as soon as the peak acceleration velocity isreached.

Deceleration is a steady ramp down to stop.

Equipment suffers high wear, due to rapid acceleration and

deceleration.

Typical applications for a triangular motion profile includeapplications where an axis must be accelerated and deceleratedquickly, without reaching a steady speed.

An example of a triangular motion profile is shown in the followinggraphic:

Velocity

0 Time

45


46/64

12-13 Parabolic Motion ProfileA parabolic motion profile has the following characteristics:l Makes the most efficient use of the drive/motor

l Reduces acceleration and deceleration strain on hardware

l Locks in acceleration and deceleration velocity once profile begins

l Cannot be modified except to zero

Typical applications for a parabolic motion profile includeapplications where a tight conformity to the motion controllerscommanded position must be maintained.

Using the board, illustrate how aparabolic motion profile can tightly followthe motors torque requirements.

An application that uses this type of motion profile is one axis following theposition of another axis (in an X-Yconfiguration).

Example: An example of an applicationthat uses a parabolic motion profile isone where labels are being applied topackages as they pass on a conveyor. Insuch an application, the coordination of movements is critical.


14-15 An example where an S-curve motionprofile is used is an amusement parkride, where there may be largequantities of riders and equipmentmaintenance must be kept to aminimum.

Another example is a bottlingapplication, where the S-curve profilereduces mechanical jerk on the line.


An example of a parabolic motion profile is shown in the followinggraphic:

Constant Velocity

Velocity

0Time

S-Curve (Sinusoidal) Motion Profile

An S-curve (sinusoidal) motion profile has the followingcharacteristics:l Provides smooth start/stop transitions that are ideal for delicate

applicationsl Reduces acceleration and deceleration strain on hardware

l Is easiest on the mechanical system, due to the long accelerationand deceleration

Typical applications for an S-curve motion profile includeapplications where a heavy load must be moved with minimalexertion and wear on equipment.

46


47/64

16-17

Explain that customized motion profilescan be configured by using a camprofile. Tell the students that this will becovered in an upcoming lesson.

If you are using this lesson in TailoredTraining, and the Applying ElectronicGearing and Camming Profiles lesson isnot included, be ready to explain more

about how a customized motion profilecan be created using a camming profile.

Example: A machine that is picking uploaded containers from a belt, movingthem to another belt, and is returningwithout a load to pick up another loadedcontainer.


Velocity

An example of an S-curve motion profile is shown in the followinggraphic:

Constant Velocity

Velocity

T i m e

Customized (Blended) Motion Profile

A customized motion profile has the following characteristics:l Is configured for a specific application need

l Can combine elements of several motion profilesl Is programmed into the command position input by the motion

control softwarel Is limited to the functionality of the motion controller

Typical applications for a customized motion profile includeapplications that require complex material handling and

pick-and-place operations.

An example of a customized motion profile is shown in thefollowing graphic:

Constant Velocity

0 T i m e47


48/64

1 8 - 2 1?. Where would indexing be most

useful?

Answer: In an application that can usemany different motion profiles on thesame axis, such as a pick-and-placemachine that handles several different

types of containers, each with a differentweight.

2 2

Confirm that students are clear aboutwhat incremental motion is. If studentsare not clear about this, recap theconcept of incremental motion.

23-25Confirm that students are clear aboutwhat absolute motion is. If students arenot clear about this, recap the concept of absolute motion.

Use the following graphic to point outhow the rotary table performs oneincremental move for each can to befilled.

Also, show how the pick-and-place armperforms absolute indexing by pickingup a can at its home position, movingthe can to the conveyor, and thenreturning to the home position to pick upanother can.

Direct ion of Motion

Filling

Motion Profile Indexing

Indexing is a series of repeated, predefined moves on a motioncontrol system.

Indexing has the following characteristics:l Can be an incremental, absolute, or registration movel Can be performed as a linear movel Can be performed as a rotary movel Can be configured as a part of a series of moves

Incremental Indexing

Incremental indexing is motion that is performed by a motioncontroller executing a series of incremental moves. This is mostcommonly used on a rotary axis, where there is no home or zero

position to use as a reference.

An example of incremental indexing is an application in which cansare being filled with product on a rotary table.

Absolute Indexing

Absolute indexing is motion that is performed by a motion controller executing a series of absolute moves, in which a home or zero

position is used as a reference for motion.

An example of absolute indexing is an application in which filledcans are being picked up from a rotary table and placed on aconveyor belt.

An example of incremental and absolute indexing, utilizing the canfilling and pick-and-place application, is shown in the followinggraphic:

Pick-and-Place Arm(Absolute Indexing)

Direction of Mot

Conveyor

Rotary Table (Incremental Indexing)48


49/64

Exercise 15 minutes

In this exercise, you will apply motion profiles.

Directions:


1 . A motion control application is moving a conveyor belt thatcarries parcels from an incoming express delivery truck to theinside of a large terminal, where the packages are sorted anddistributed. When there are no packages on the belt, an operator turns off the conveyor by pressing a button. Which motion profileis the application using?

2. A motion application needs to complete its motion sequence inthe shortest amount of time possible. What is the best motion

profile to use?

3. If a motion control application required a smooth acceleration anddeceleration to move a heavy, fragile component from one pointto another, which motion profile would be the best one to use?

4. A motion control application is rapidly moving a cutting toolacross a workpiece. The axis decelerates as soon as the peak acceleration velocity is reached. Which motion profile is theapplication most likely using?

5. A motion controller needs to make the most efficient use of amotor but must also maintain a tight conformity to the motioncontrollers commanded position. Which motion profile would

best accomplish this?

49


50/64

Answers Exercise

1. Jog motion profile

2. Trapezoidal motion profile

3. S-curve (sinusoidal) motion profile

4. Triangular motion profile

5. Parabolic motion profile

6. Customized motion profile

7. Indexing

A. Absolute indexing

B. Incremental indexing

50


51/64

What You Will Learn

a

a 2

Electronic Gearing andCamming Profiles

After completing this lesson, you will be able to apply electronicgearing and camming profiles.

Key Terms

Cam: An eccentric wheel mounted on a rotating shaft and used to produce variable or reciprocating motion in another engaged or contacted part.

Electronic Camming: A technique used to electronically simulate amechanical relationship between a cam and a follower. Causes oneclosed-loop axis to move with another open-loop or closed-loop axis

by following a user-defined position point array.

Point the students to the Motion ControlGlossary for reference to these andrelated definitions.

Electronic Gearing: A technique used to electronically simulate amechanical link between two axes. Causes one closed-loop axis to beslaved to another open-loop or closed-loop axis at a user-definedratio.

4 3-5 Electronic Gearing

Go to the board and create anapplication drawing for these concepts,such as a two-axis rotary cutoff application.

Potential Learning Problem: Electronicgearing and camming share some of thesame characteristics, and students mayconfuse the two.

In a motion control application, electronic gearing has the followingcharacteristics:l Movement of two or more separate axes is coordinated without a

mechanical connection between them.

l A ratio between a master and a slave axis is established.l The slave axis follows the master axis at the specified ratio.l A command signal for the motors is produced.

51


52/64

The concept of electronic gearing is shown in the following graphic.

Not Mechanically Coupled

Master AxisPosition

? Can anyone think of other possible

advantages?Answer: Changes can be made to thegear ratio without physically retooling anapplication, therefore saving largeamounts of time and money.

Go to the board and draw a simpleelectronic gearing application, using oneof the examples mentioned here.

Master : Slave-Gear Rat io

_____

Position-Command

ElectronicGearing

Advantages of electronic gearing include the following:

Master/slave operation can be enabled.

No mechanical coupling exists between the master and slave,

meaning no additional loss, friction, or gravity torques toovercome on the hardware.

Software control of gear ratio and motion direction is highly precise, resulting in reduced setup and changeover times.

Applications for Electronic Gearing

Typical electronic gearing applications include the following:l Coil winding

l Tappingl Flying cutoffs and shearsl Stampingl Gantry cranes and robots

52


53/64

Explain how an indexing function can be joined with an electronic gearingapplication. For example, an applicationthat must handle more than one size or type of material, such as:

Indexed Motion Commands and Electronic Gearing

Electronic gearing utilizes an indexing function that contains predefined motion profiles with the functionality of master/slave position synchronization. This concept is shown in the followinggraphic:

l A cutoff application that cuts

different lengths of plastic sheeting. Indexer l A plastic cup manufacturing

application, in which different sizesof cups can be made.

Add this to the application illustrationyou previously created on the board.

A

Move

Not Mechanically Coupled

ElectronicGearing

Position

Command

?

Combining the indexed motion commands and electronic gearing provides the following advantages:

. Why would on-the-fly master/slaveposition synchronization be an importantfeature?

l On-the-fly master/slave position synchronization, in which themovements of the master and the slave axes can be coordinatedwithout stopping the axes

Answer: When an application is runningand cannot be easily or effectivelystopped to home or synchronize the

motion of the two axes, on-the-flymaster/slave position synchronizationcan be used to correct the positioning of the two axes without stopping them.

An example of this would be a flyingcutoff or a rotary knife operating at highspeed that needs to maintainsynchronization with a conveyor beltmoving material under the knife.

l Phase advance/retard, in which the slave axis can be movedforward or backward relative to the master

53


54/64

10

I I -1 2

Applications for Indexed Motion Commands and ElectronicGearing

Typical applications that combine indexed motion commands andelectronic gearing include the following:l Slip compensation for feedersl Converting operations, such as aligning material to printed

registration marks

l Packaging, such as loading and unloading product conveyors

Mechanical Camming

Mechanical camming has the following characteristics:

Tell students that the mechanical cammust be physically changed in theapplication in order for follower motion tobe changed.

l An oval-shaped cam drives a follower assembly.l A follower conforms to the cam shape as the cam unit rotates.

l Motion is limited by the cam shape.

A mechanical cam is shown in the following graphic:

Follower

Cam

JJ 13-24 Electronic CammingIn a motion control application, electronic camming has thefollowing characteristics:l Is an electronic replacement for mechanical cam and follower

assembliesl Allows arbitrary move profiles

l Creates coordinated motion profiles that are functions of time or the relative position of another axis

?. Does your companys application use l Coordinates movement of two separate axes without a mechanicala camming operation? connection between them

54


55/64

Explain that in this part of the lesson, theterms follower and slave are usedinterchangeably and mean the samething.

l Allows higher cam velocities to be configuredl Is defined using a point pair table of values - this is a master

axis set of point positioning values and a corresponding set of slave axis point positioning values

Take the students step-by-step throughthe cam motion sequence in thefollowing graphic.

A comparison of a mechanical cams functionality and an electroniccams functionality is shown in the following graphic:

Mechanical Cam ElectronicCam

Follower

Direction of

Axis 2

Rotation Master (Follower)

Axis 1 (Master)

55


56/64

25-29

Example: A two-axis machine thatsprays paint on metal parts movingthrough the paint booth on a conveyor.

?. In the paint spraying application justmentioned, which axis would be themaster axis and which axis would be theslave axis?

Answer: Although there are manypossibilities for this type of application,the master axis would be the conveyor belt and the slave would be the axis thatmoves the paint sprayer over the parts.

In a motion control application, electronic camming is accomplished by using two different types of cam profiles:

l Time-lock caml Position-lock cam

Time-Lock Cam

A time-lock cam functions similarly to a cam drum driven by a

constant speed motor.

A time-lock cam has the following characteristics:

Is an arbitrary move profile

Is defined using a table of values, which consists of the followinginformation:

- An array of master axis time values (usually in seconds)- An array of slave axis position valuesEach master axis time value has a corresponding slave axis

position value.A time-lock cam profile is shown in the following graphic:

Using the paint spraying applicationexample provided on the previous page,explain to the class how the master andslave axes can be represented in thisgraphic.

Slave Axis PositionReference

Master Axis Time Reference

30-35

An example of a position-lock camapplication is a drywall sheet cuttingapplication, in which finished sheets of drywall are cut to a predeterminedlength. Cutting occurs while materialpasses beneath the cutting tool in acontinuous run.

Position-Lock Cam

A position lock cam has the following characteristics:l Provides the capability of implementing non-linear electronic

gearing relationships between two axesl Positions slave axis as an arbitrary function of master

axis position

l Does not use maximum velocity, acceleration, or decelerationlimits

56


57/64


58/64


59/64

Fundamentals of Motion Control:Integrated Practice

Exercise A

After completing this lesson, you will be able to demonstratefundamental motion control concepts and perform motion controlfunctions by applying the combined skills learned in the course.

In this exercise, you will apply skills learned in the course to answer the following questions.

Directions:

Circle the correct answer for the following questions:

1. What application requirements suggest the most likely need for amotion controller?

A. Speed regulation better than 1%

B. Position control less than 0.5 mm

C. High duty cycle

D. Regeneration and dampened response

E. All of the above

2. When position must be controlled, a servo drive is required to

achieve this.A. True

B. False

3. Which of the following is true of an absolute move?

A. Always referenced to where you are

B. Always referenced to home

C. Cannot be in negative direction

D. Cannot be a rotary move

E. None of the above

59


60/64

4. The difference between commanded position and actual positionis called:

A. Acceleration factor

B. Position compensation

C. Position error

D. Velocity error


5. A closed-loop system is defined as:

A. A system without feedback devices

B. A stepper system

C. A system where velocity and position are both fed back andused for correction

D. A system that always operates with absolute moves


6. Excess integral gain can cause axis instability.

A. True

B. False

7. Torque is defined as:

A. A specific amount of axis rotation

B. A measure of resistance to a change in velocity

C. Turning force applied to an object, tending to cause rotation

D. The speed at which a move is made

E. Both B and C

60


61/64

8. When two axes are ratioed, this means:

A. The master axis rotates the same speed as the slave axis.

B. The axes rotate in different directions.

How Did You Do?

C. The slave axis rotates in fixed ratio to the master.

D. The slave axis always rotates twice as fast as the master.

E. The master and slave act independently.9. You are designing a servo application in your factory. The

motors speed on a leadscrew driven shuttle is 3000 RPM, and ithas a ballscrew with a lead of 6.35000 mm and 250 line encoder (in quadrature).

You need to calculate the maximum slide speed (m per sec)and the maximum resolution that the encoder can see in mm(assume the encoder is on the ballscrew).

The maximum slide speed and the maximum resolution are:

A. Speed = 0.31750 m/sec and resolution = 0.00635 mm/pulse

B. Speed = 3.1750 m/sec and resolution = 0.0635 mm/pulse

C. Speed = 0.3175 m/sec and resolution = 0.0127 mm/pulse

D. Speed = 1.9050 m/sec and resolution = 0.0240 mm/pulse


Turn to the end of the lesson for the answers. If you have anyquestions, ask your instructor for assistance.

61


62/64

Exercise B In this exercise, you will apply skills learned in the course to answer the following questions.

Directions:

Circle the correct answer for the following questions:

1 . A digital servo motion controller closes the position loop bydoing which of the following?

A. Generating the command signal to the drive

B. Accepting and conditioning feedback from the motor

C. Calculating the compensation factors for error between theinput command position and the actual position of the drive

D. Correcting errors between the input command position andthe actual position by modifying the command signal to thedrive

E. All of the above

2. An open-loop system is most useful when the application doesnot require specific motor velocity control.

A. True

B. False

3. Which of the following is true of an incremental move?

A. Always referenced to where you are

B. Always referenced to home

C. Cannot be in negative direction

D. Cannot be a rotary move


4. Which of the following defines following error?

A. Not affected by position error

B. The amount of error incurred when the axis is movingC. The amount of error incurred when the axis is not moving

D. There is no difference between the actual position and thecommanded position of the axis


62


63/64

How Did You Do?

5. In electronic gearing, phase advance/retard means:

A. A master axis can be made to follow the slave axis.

B. A slave axis can be accelerated or decelerated to coordinatemovement with a master axis.

C. Homing a slave axis to a master axis position while themaster axis is not moving.

D. The system always operates with absolute moves.


6. In AC motor operation, torque will vary as the motor reachessynchronous speed:

A. True

B. False

7. Pulse-width modulation is defined as:

A. The electronic output signal of a resolver as seen by a motioncontroller

B. A measure of resistance to a change in velocity

C. A method of varying the on/off times of a voltage bus as seenfrom the load

D. Flipping an electronic switch on and off


8. Which motion profile would best be used to move a heavy loadwith minimal strain on motion control hardware?

A. Trapezoidal profile

B. S-curve (sinusoidal) profile

C. Triangular profile

D. Parabolic profile

E. All of the above

Turn to the end of the lesson for the answers. If you have anyquestions, ask your instructor for assistance.

63


64/64

Answers Exercise A

1 . E

2. False

3. B

4. C

5. C

6. A

7. C

8. C

9.

A. Speed = 0.31750 m/sec and resolution = 0.00635 mm/pulseThis was calculated as follows:

3000/60 rev/sec x 6.35/1000 m/rev = 0.31750 m/sec

250 lines/rev x 4 pulses/line = 1000 pulses/rev x1rev/6.35 mm = 157.48 pulses/mm = 0.00635 mm/pulse

Exercise B

1 . E

2. A

3. A

4. B

5. B

6. A

motion fundamentals

Documents