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Assembly Components: End Effectors

Assembly Components: End Effectors. Spencer Shore October 13, 2008. 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.

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Assembly Components: End Effectors

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  1. Assembly Components:End Effectors Spencer Shore October 13, 2008

  2. 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

  3. 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

  4. 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.

  5. 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

  6. Pneumatic Gripper Example • 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 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 robot’s 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) • 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-gripper-robot-end-effector-robotic-arm_2-jaw_general_speng.htm

  7. 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.aspx?id=103

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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)

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

  14. References http://en.wikipedia.org/wiki/End_effector Groover, Mikell P. “Robot Grippers” Third Edition, pp 223-224. Robot Grippers http://en.wikipedia.org/wiki/Stepper_motor http://en.wikipedia.org/wiki/Linear_actuator http://www.robotics.utexas.edu/rrg/learn_more/low_ed/actuator/ http://www.societyofrobots.com/actuators_solenoids.shtml http://www.engineersedge.com/hydraulic/hydraulic_actuator.htm http://en.wikipedia.org/wiki/Solenoid

  15. 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.

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

  17. 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.

  18. 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

  19. Coatings

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

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

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

  23. 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/after.htm

  24. Capabilities: • Five tracks that collectively feed over 1600 parts per minute, 140 parts per minute, 50 per minute, http://www.autodev.com/products/feeder-bowls/custom-tooled-vibratory/ • 3000 parts per minute, with 100% of them oriented for proper assembly! http://www.vibromatic.net/Feeder-Bowls.html • Large parts http://www.mgsmachine.com/products/prodvideo.php?id=14.0&vidid=video2

  25. Integration with other components or products: Typical integration includes, but is not limited to the following: • Pneumatic • Optical inspection • Conveyors • Lathes

  26. Primary vendors: • Feed Rite http://www.feedriteautomation.com/vibrator_feeder.html • Automation Devices, INChttp://www.autodev.com/products/feeder-bowls/how-to-tool-a-bowl/ • Vibromatic Co. http://www.vibromatic.net/Feeder-Bowls.html • Elscint automation http://www.elscintautomation.com/vibratorybowlfeeders(vast).html • California Vibratory Feeders http://www.thomasregister.com/olc/11487501/pr01.htm • Jerhen Industries http://www.jerhen.com/feedbowls.htm

  27. Other interesting links • http://www.spectrumautomation.com/vid1.htm http://www.autodev.com/assets/products/bowls/multipurpose-diagram.gif • Vibratory vs. centrifugal http://www.feederdynamics.com/videos.html

  28. 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/articles/mi_qa3685/is_199701/ai_n8757163

  29. Thanks!

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