Assembly Components: End Effectors

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Assembly ComponentsEnd Effectors

• Spencer Shore
• October 13, 2008

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Actuators
Definition a transducer that changes some form
of input into an output of physical movement
(i.e. electrical current to rotational
displacement, such as an electric motor).
-Rotational -Linear
Current state of actuators Everything today that
has any type of robotic or automated process
requires actuators. If you want it to move, it
better have an actuator. Applications End
effectors, part sorters, robot arms, controls

• Electrical
• DC Motors
• Step Motors
• Pneumatics
• Hydraulics
• Solenoids
• Electro-mechanical linear actuators

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Electric DC Motors

• Rated at most efficient voltage (Typically 6-12
  V)
• Operating current average amount drawn for
  typical torque
• Stall current max current your motor will draw
• Support circuitry must be rated this high
• Heat sink motor if running above rated voltage
• Wattage rating on spec sheet
• Power spikes when reversing directions due to
  inductance
• Most efficient at high torque gear down for
  reduced speed

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Stepper Motors
-Brushless -Open-loop (no feedback) -Need to be
over engineered to avoid losing steps (oversized
but cheap) -Cutting Edge Addition of rotor
positions feedback (encoder or resolver) to
improve torque generation
Industrial applications high speed pick and
place equipment, multi-axis machine CNC machines,
scanners, printers, plotters and many more
devices.
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Pneumatic Actuators

• Quick and low force
• Used frequently to open and close grippers
• Compressed air readily available
• Compressibility of gas makes control difficult
  but allows energy storage
• Good for end effectors and tools
• Bad for high precision applications

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Pneumatic Gripper Example

• Capabilities/Specifications
• Model P-3100
• Vendor RAD
• 2 Jaw parallel motion
• Up to 500 lb grip force
• Temp range -25 200 F
• Pneumatic
• Control Regulator and your robots logic and
  valve system
• Internally lubricated
• Internal magnetic piston can actuate sensors for
  position sensing.
• Pneumatic air ports can rotate 90
• Adapter plates allow you to connect to the robot
• Max grip 7 lb (Friction) 27.0 lb (Encompassing)

• Helpful Hints
• Four way solenoid valve required to control the
  gripper
• Design fingers as short as possible maximizes
  life and gripping force
• Always key or dowel the fingers into the jaws

• Sizing Considerations
• Part weight, dimensions, COG
• Orientations
• Acceleration of robot
• Available air pressure
• Length of fingers
• Robot payload restrictions
• Environmental conditions
• Friction or encompassing grip

http//www.rad-ra.com/robot-grippers-robotic-gripp
er-robot-end-effector-robotic-arm_2-jaw_general_sp
eng.htm
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Cutting Edge Vacuum Gripper

• VGS 3010 by Piab
• Localized vacuum generation
• Greater gripping power
• More energy efficient
• Independent grips

http//www.coaxtechnology.com/Templates/Normal.asp
x?id103
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Hydraulic Actuators

• Very high forces possible
• Piston types most common
• Leaks
• External hydraulic pumps required
• Some designs good in compression only
• Requires position feedback for repeatability
• Commonly used for heavy equipment

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Solenoids

• Linear motion push vs. pull
• Electromagnetically inductive coil wound around a
  movable steel or iron slug (armature)
• Interface between electronic controllers and
  pneumatic or hydraulic systems
• Transistor analog small signal controls a large
  device
• Pneumatic up to 100 psi
• Hydraulic up to 3,000 psi
• Controls the flow of air or oil to rams or
  actuators
• Power issues similar to DC motors

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Electro-Mechanical Linear Actuators

• Lead screw continuous inclined plane (large
  load over a short distance)
• Built for high speed or high force
• Important specifications
• Travel
• Speed
• Force
• Lifetime
• Cheap, repeatable and self-contained
• Identical extending and retracting behavior
• Many moving parts prone to wear

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Cutting Edge Piezoelectric

• Description and Performances of a
  Four-Degrees-of-Freedom Piezoelectric Gripper
• Agnus, Joel et al. International Symposium on
  Assembly and Task Planning, July 2003.
• Inverse piezolelectric effect deformation of
  material due to an applied electric field
• Two fingers, independently deform in x and y
• Whole actuation system integrated with electrical
  connection system in case
• End effectors protrude
• Total mass 6 grams

Agnus2003.pdf
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Cost and Vendors
Cost of Actuators Typical 100-300 .05 to
25,000 (from piezo-electric to industrial
hydraulics Requires supporting Technology?
Yes Vendors HUGE variety Electric Motor
Superstore Precision Fluid Power
(hydraulics) MSC Industrial Supply
(pneumatics) SMAC LINAK (electric
rotary/linear) Exlar (linear)
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Standards

• ISO-14001 Environmental Management System
  Standard
• ISO-9001 Quality Management Systems
• UKAS
• Underwriters Laboratory (UL)
• National Electric Manufacturers Association (NEMA)

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References
http//en.wikipedia.org/wiki/End_effector Groover,
Mikell P. Robot Grippers Third Edition, pp
223-224. Robot Grippers http//en.wikipedia.org/w
iki/Stepper_motor http//en.wikipedia.org/wiki/Lin
ear_actuator http//www.robotics.utexas.edu/rrg/le
arn_more/low_ed/actuator/ http//www.societyofrobo
ts.com/actuators_solenoids.shtml http//www.engine
ersedge.com/hydraulic/hydraulic_actuator.htm http
//en.wikipedia.org/wiki/Solenoid
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In-Class Problem

• Determine an appropriate actuator needed to
  rotate a 10 lb cylindrical part (radius 5
  in, length 10 in) 45 degrees in 3 seconds.
  Neglect acceleration.

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Sorters

• Vision system (e.g. colored pencils)
• Laser sorting
• Electronic ID tags
• Linear vibrators
• Bowl feeders
• Vibratory centrifugal

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Vibratory bowl feeders

• Self-contained systems consisting of a a
  vibrating drive unit, upon which a bowl is
  mounted. The drive unit (usually has a
  variable-amplitude controller) vibrates the bowl,
  forcing the parts to move up a circular, inclined
  track. Along the track is custom designed tooling
  that sorts and orients the parts in consistent,
  repeatable positions.

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Specifications

• Steel vs. cast aluminium
• Benefits to Stainless Steel
• More Durable than Aluminum
• FDA Approved
• Cleaner than Aluminum
• More versatile for welding and custom tooling
• Benefits to Cast Aluminum
• Low-Cost alternative to Stainless
• Quick Delivery
• Adequate for simple parts
• Ideal for mass production
• an cast tooling

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Coatings
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Limitations

• Part size limited by bowl size
• Vibratory 3-42 dia.
• Centrifugal 20 50
• Part weight
• Speed (maximum frequency)

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Applications

• Pharmaceutical
• Food Handling
• All 316 S.S. Construction
•  Alignment for Vision Part Selection
•  High Tolerance Gauging
•  Automotive

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Cost

• Since most bowls and their accompanying tooling
  are custom made the price really varies and
  quotes must be requested.
• 400 (used) 25,000

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Important rules

• Frequency is crucial!
• They are usually custom built.
• Once built, frequency tooling are about the
  only things that can be adjusted.

Troubleshooting http//www.vibratoryfeeders.com/af
ter.htm
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Capabilities

• Five tracks that collectively feed over 1600
  parts per minute, 140 parts per minute, 50 per
  minute, http//www.autodev.com/products/feeder-bo
  wls/custom-tooled-vibratory/
• 3000 parts per minute, with 100 of them oriented
  for proper assembly! http//www.vibromatic.net/Fe
  eder-Bowls.html
• Large parts http//www.mgsmachine.com/products/pro
  dvideo.php?id14.0vididvideo2

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Integration with other components or products

• Typical integration includes, but is not limited
  to the following
• Pneumatic
• Optical inspection
• Conveyors
• Lathes

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Primary vendors

• Feed Rite http//www.feedriteautomation.com/vibrat
  or_feeder.html
• Automation Devices, INC http//www.autodev.com/pro
  ducts/feeder-bowls/how-to-tool-a-bowl/
• Vibromatic Co. http//www.vibromatic.net/Feeder-Bo
  wls.html
• Elscint automation http//www.elscintautomation.co
  m/vibratorybowlfeeders(vast).html
• California Vibratory Feeders http//www.thomasregi
  ster.com/olc/11487501/pr01.htm
• Jerhen Industries http//www.jerhen.com/feedbowls.
  htm

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Other interesting links

• http//www.spectrumautomation.com/vid1.htm
• http//www.autodev.com/assets/products/bowls/multi
  purpose-diagram.gif
• Vibratory vs. centrifugal http//www.feederdynamic
  s.com/videos.html

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Interesting links continued

• Statistical analysis for part feeders Theory -
  http//www.ieor.berkeley.edu/goldberg/feeder/sec_
  1_2.html
• Mathematical model - http//findarticles.com/p/art
  icles/mi_qa3685/is_199701/ai_n8757163

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• Thanks!