# positioner selection and motor sizing ... positioner selection criteria positioner selection and...

Post on 05-May-2020

13 views

Embed Size (px)

TRANSCRIPT

Positioner Selection and Motor Sizing

Jim Wiley Product Manager

Parker Hannifin

Overview

Positioner Selection

Motor & Drive Sizing

Positioner Selection Criteria

Precision

Loading

Environm ent

Geometr y

Motion

Positioner Selection Criteria

Positioner Selection and motor sizing is not a strictly linear process.

One set of criteria might restrict another, for example travel distance v. precision or load v. motion profile.

Selection often requires compromise and reassessment of needs based on budget, size constraints and other goals.

In many cases there is more than one right answer

Precision

Loading

Environm entGeometry

Motion

Application Categories

Making

• Transform

• Welding, Cutting, Etching, Dispensing, Bending

Moving

• Transfer

• Pick & Place, Storage & retrieval, palletize, Shuttle

Measuring

• Test

• Inspection, Vision, Gauging, Sampling

Positioner Selection : Precision

Accuracy is “more expensive” than repeatability so be sure to understand the difference and machine requirements

Making

Moving

Measuring

Precision

Accuracy

Repeatability

Accuracy

Positioner Selection : Geometry

Rod Style

• Electric Cylinder

• Rodded Actuator

• PistonRodless Actuator

• Electric Actuator

• Linear Actuator

Linear Positioner

• Linear Table

• Linear Stage

Positioner Selection : Geometry

Rod Style Defining characteristics:

Non-constant support geometry

Packaged drivetrain, guidance and moving rod

Similar functionality to pneumatic and hydraulic

cylinders

Applications:

Push/pull

Push to force

Pressing

Forming

Clamping

Vertical axis in gantry

Good for-

High thrust force applications

Vertical applications

Fluid power conversion

Reach in and retract applications

Positioner Selection : Geometry

Rodless Actuator

Defining characteristics:

Constant support geometry

Packaged drivetrain, guidance and moving

carriage assembly

Single linear guide

Applications:

Pick and place

Push to force

Indexing

Cutting/feeding

Material Handling

Good for-

Low Cost

Flexibility- drive trains/guides

Scalability- multiple frame sizes

Long stroke

Moderate payloads

Industrial applications

Positioner Selection : Geometry

Linear Positioner

Defining characteristics:

Constant support geometry

Packaged drivetrain, guidance and moving

carriage assembly

Dual linear guides

Applications:

High precision positioning

Dynamic control

Multi-axis

Scanning

Metrology

Electronics mfg

Good for-

Precision positioning

High moment loading

Multi-Axis Stacking

Straightness/flatness

Positioner Selection : Travel

Determine Overall Travel Distance/Stroke Drive Train Guidance System Mounting Considerations

Review how the overall length of the positioner impacts the machine constraints

Positioner Selection : Precision

Positioner Specifications will typically call out a repeatability as a +/- value.

Positional Accuracy, straightness is generally travel length dependent.

Positioner Selection : Precision

Straightness and Flatness are generally travel length dependent.

Positioner Selection : Precision

Errors can occur in 6 different ways in a linear positioning device:

Guidance system, drive train, machined surfaces, assembly techniques all contribute the accuracy specification.

X Z Y

YAW

PITCH

Positioner Selection : Motion Profile

Review Motion profile requirements to determine maximum speed and acceleration

Motion

Positioner Selection : Motion Profile

Trapezoidal Move Profile: 𝑽𝒆𝒍𝒐𝒄𝒊𝒕𝒚𝑴𝒂𝒙𝒊𝒎𝒖𝒎 = 1.5∗𝐷

𝑡

𝑨𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏𝑴𝒂𝒙𝒊𝒎𝒖𝒎 = 4.5∗𝐷

𝑡2

17

Positioner Selection : Motion Profile

Positioner Specifications will typically rate a maximum allowable velocity and acceleration based on the drive train and guidance system limits.

Maximum velocity will vary based on overall travel distance and in the case of ballscrew, the lead (or pitch of the screw.

Load Selection Criteria

Select Positioner based on

Normal Load capacity

Moment load capacity

Axial load capacity

Load Selection Criteria

Consider

Mounting Orientation

Load Center of gravity

Axial load capacity

Load Selection Criteria

Moment Load Capacity

Load Selection Criteria

Load Selection Criteria

Load Selection Criteria

Maximum Load Rating

Load/Life Charts based in cumulative travel distance

Load Selection Criteria

Environmental

Environmental conditions may lead to additional design considerations

Dust/Dirt/Debris>>> > Sealing/Bellows

Clean room/Vacuum/Explo sion>>>Special preparation

Overview

Positioner Selection

Motor & Drive Sizing

Motor Sizing

Speed

Peak Torque

AmplifierInertia

Continuo us Torque

Motor Sizing

Convert required linear speed to rotational speed

Simple rotational velocity equation for a screw device:

𝜔 = 𝑉 ∗ 𝑅

𝐿

𝜔 = rotational velocity required (RPM, RPS)

𝑉 = linear velocity (in/s, m/s)

𝑅 = any gear reduction ratio

𝐿 = Lead of the screw (mm, in)

Example: 𝑉 = 300 𝑚𝑚/sec 𝐿 = 12 mm screw

𝜔 = 300 𝑚𝑚/𝑠

12 𝑚𝑚 𝑟𝑒𝑣

= 25RPS

or 1500 RPM

Motor Sizing

Convert required linear acceleration to rotational acceleration

Simple rotational acceleration equation for a screw device:

𝛼 = 𝐴 ∗ 𝑅

𝐿

𝛼 = rotational acceleration required (RPS)

𝐴 = linear acceleration (in/s2, m/s2)

𝑅 = any gear reduction ratio

𝐿 = Lead of the screw (mm, in)

Example: 𝐴 = 3 m/sec2

𝐿 = 12 mm screw

𝛼 = 3 m/sec2

12 𝑚𝑚 𝑟𝑒𝑣

= 250 𝑟𝑒𝑣/𝑠𝑒𝑐2

α = 2𝜋 ∙ 𝑟𝑎𝑑/ rev ×250 𝑟𝑒𝑣/𝑠𝑒𝑐2

α = 1570 𝑟𝑎𝑑/𝑠𝑒𝑐2

Motor Sizing

Peak Torque

The total torque required from the motor to move itself and the load

𝑻𝒕 = 𝑻𝒂 + 𝑻𝒇 + 𝑻𝒐𝒕𝒉𝒆𝒓

𝑇𝑡 = 𝑡𝑜𝑡𝑎𝑙 𝑝𝑒𝑎𝑘 𝑇𝑎 = 𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑡𝑜𝑟𝑞𝑢𝑒 𝑇𝑓 = 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛 𝑡𝑜𝑟𝑞𝑢𝑒 𝑖𝑛 𝑁 −𝑚

𝑇𝑜𝑡ℎ𝑒𝑟 = 𝑡𝑜𝑟𝑞𝑢𝑒 𝑓𝑟𝑜𝑚 𝑔𝑟𝑎𝑣𝑖𝑡𝑦, 𝑝𝑟𝑒𝑙𝑜𝑎𝑑𝑠, 𝑝𝑢𝑠ℎ/𝑝𝑢𝑙𝑙 𝑓𝑜𝑟𝑐𝑒𝑠 𝑇𝑔 = 𝑔𝑟𝑎𝑣𝑖𝑡𝑦 𝑡𝑜𝑟𝑞𝑢𝑒 𝑖𝑛 𝑁 −𝑚

Motor Sizing

Acceleration Torque

𝑇𝑎 = 𝐽𝑡𝑜𝑡𝑎𝑙 × 𝛼

𝐽𝑡𝑜𝑡𝑎𝑙 = 𝐽𝑚 + 𝐽𝐿 + 𝐽𝑝

𝑇𝑎 = acceleration torque

α = angular acceleration, rad/sec2

𝐽𝑚 = inertia of motor

𝐽𝐿 = reflected inertia of load thru mechanics

𝐽𝑝 = inertia of positioner mechanics

𝛼 = angular acceleration, rad/sec2

Motor Sizing : Inertia

Determine the reflected inertia of the load back to the motor

For ballscrew:

𝐽𝐿 =𝑚𝑙𝑜𝑎𝑑 ∗ ( 𝐿

2𝜋 )2

JL = reflected inertia of load thru mechanics 𝑚𝑙𝑜𝑎𝑑= payload in kg L= Lead of screw (mm, in)

Example: 𝑚𝑙𝑜𝑎𝑑 = 50𝑘𝑔 𝐿 = 12𝑚𝑚/𝑟𝑒𝑣

𝐽𝐿 = 50𝑘𝑔 ∗ ( 0.012𝑚

2𝜋 ) 2

𝐽𝐿 =0.00018 𝑘𝑔 ∙ 𝑚 2

Motor Sizing : Torque

Use reflected inertia to approximate acceleration torque

𝑇𝑎 = (𝐽𝐿 + 𝐽𝑝) × 𝛼

Example: 𝑚𝑙𝑜𝑎𝑑 = 50𝑘𝑔 𝐿 = 12𝑚𝑚/𝑟𝑒𝑣

𝐽𝐿 = 50𝑘𝑔 ∗ ( 0.012𝑚

2𝜋 ) 2

𝐽𝐿 =0.00018 𝑘𝑔 ∙ 𝑚 2

α = 1570 𝑟𝑎𝑑/𝑠𝑒𝑐2

𝐽𝐿 = 0.000182 𝑘𝑔 ∙ 𝑚 2

𝐽𝑝 = 0.0000042 𝑘𝑔 ∙ 𝑚2

𝑇𝑎 = 0.000186 𝑘𝑔 ∙ 𝑚2 × 1570 𝑟𝑎𝑑/