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  • 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/

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