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Gripper Designs

Gripper Designs. By Pragnay Choksi. INTRODUCTION. Hands of robots referred to as Grippers No single design is ideal for all applications. TYPES OF GRIPPERS. 6 different types described here The Clapper Two-Pincher Gripper Basic Model Advanced Model Number 1 Advanced Model Number 2

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Gripper Designs

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  1. Gripper Designs By Pragnay Choksi

  2. INTRODUCTION • Hands of robots referred to as Grippers • No single design is ideal for all applications

  3. TYPES OF GRIPPERS • 6 different types described here • The Clapper • Two-Pincher Gripper • Basic Model • Advanced Model Number 1 • Advanced Model Number 2 • Flexible Finger Grippers • Wrist Rotation

  4. The Clapper • Can be built using • Metal • Plastic • Wood • This section describes a metal and plastic clapper

  5. The Clapper • Parts List

  6. The Clapper • Consists of a wrist joint (assume permanently attached to forearm of robot) • Connected to the writ are 2 plastic plates • Bottom plate is secured to the wrist • Top plate is hinged • Small spring-loaded solenoid is positioned between the two plates • When solenoid is active, gripper is closed • When solenoid is not active, gripper is open

  7. The Clapper (construction) • Cut both acrylic plastic to 1.5” x 2.33” pieces • Attach the lower flap to both corner brackets • Place bracket ~ (1/8)” from either side of the flap • Secure the pieces using (6/32)” bolts

  8. The Clapper • Choice of solenoid is important • Must fit between the 2 flaps • Must have a flat bottom to facilitate mounting • Must operate within the voltage used in your robot (usually 6V or 12 V) • If solenoid doesn’t have mounting flanges opposite the plunger, mount it in the center of the bottom flap using household cement

  9. Two-Pincher Gripper • Two movable fingers • Three types: • Basic • Advance model # 1 • Advance model # 2 • Basic Model: • Made from extra Erector Set (similar construction kits may be used)

  10. Two-Pincher GripperBasic Model (parts)

  11. Two-Pincher Gripper(Basic Model) construction • Connect the 4.5” grinders and the 3.5” grinder using (6/32)” x ½” bolts and nuts to make two pivoting joints • Shown on page 407 • Cut two 3” lengths and mount them • Sand off the ends at an angle to prevent them from touching • Cut through two or three holes on one end to make a slot

  12. Two-Pincher Gripper(Basic Model) construction • (6/32)” x ½” bolts and nuts to make pivoting joints in the fingers • You can actuate it in a number of ways • Mount a small eyelet between the two pivot joints on the angle grinder. • Thread two small cables through the eyelet and attach the cable • Connect to other end of the cables to a solenoid or a motor shaft

  13. Two-Pincher Gripper(Advanced Model 1) • Use a readily available plastic toy and convert it into a useful two-pincher gripper for your robot arm • Toy is a plastic “extension arm” • Inexpensive contraption • Usually under $10.00 • Available at many toy stores

  14. Two-Pincher Gripper(Advanced Model 1) construction • Chop off the gripper three inches below the wrist • Cut through the aluminum cable • Cut another 1.5” of tubing • Just the arm not the cable • Fashion a 1.5” length of ¾” diameter dowel to fit into the rectangular arm

  15. Two-Pincher Gripper(Advanced Model 1) construction • Drill a hole in the dowel for the cable to go through • Cable maybe of center, compensate for that • Place the cable through the hole then push the dowel at least ½” into the arm • Drill 2 small mounting holes to keep the dowel in place • Use (6/32)” x ¾” bolts and nuts to secure it

  16. Two-Pincher Gripper(Advanced Model 1) construction • Use the dowel to mount the gripper on an arm assembly • Flatten one end of the dowel and attach it directly to the arm • Gripper opens with only (7/16)” pull • Attach one end of the cable to a 1/8” round aircraft cable • Crimp-on connector designed for 14 to 16 gauge electrical wire to connect them end to end

  17. Two-Pincher Gripper(Advanced Model 1) construction • Attach the aircraft cable to a motor or rotary solenoid shaft • Activate the motor or solenoid to pull the gripper closed • Spring built into the toy arm opens the gripper when power is turned off

  18. Two-Pincher Gripper(Advanced Model 2) • Uses a novel worm gear approach • Without requiring a hard-to-find worm gear • Worm is a length of ¼” 20 bolt • Gears are standard 1” diameter 64-pitch aluminum spur gears • Hobby stores have these for about $1 a piece • Turning the bolt opens or closes the fingers of the grippers

  19. Two-Pincher Gripper(Advanced Model 2) Parts

  20. Two-Pincher Gripper(Advanced Model 2) construction • Cutting two 3” aluminum channel stock • Use the 3” flat mending “T” plates as the base • Attach the fingers and gears to “T” plates as shown on page 410 • The distance of the holes is critical • It depends entirely on the diameter of the gears you use

  21. Two-Pincher Gripper(Advanced Model 2) construction • Secure the shaft using a 1.5” x ½” corner angle bracket • Mount it to the stem of the “T” using (8/32)” x 1” bolt and nut • Add # 10 washer between the “T” and the bracket to increase the height of the bolt shaft • Mount a 3.5” long ¼” 20 machine bolt through the bracket

  22. Two-Pincher Gripper(Advanced Model 2) construction • Use double nuts or locking nuts to form a free spinning shaft • Reduce the play as much as possible without locking the bolt to the bracket • Align the finger gears to the bolt so they open and close at the same angle

  23. Two-Pincher Gripper(Advanced Model 2) construction • To actuate the fingers • Attach a motor to the base of the bolt shaft • The prototype gripper used a ½” diameter 48-pitch spur gear • a matching 1” 48-pitch spur gear on the drive motor • Operate the motor in one direction the fingers open • the motor spins in the opposite direction, the fingers close

  24. Flexible Finger Grippers • Clapper and two-pincher grippers are not like human fingers • They lack a compliant grip • The capacity to contour the grasp to match the object • You can approximate the compliant grip by making articulated fingers for your robot • At least one toy id available that uses this technique • Opposing thumb is not articulated, but you can make a thumb that moves in a compliant griper of your own design

  25. Flexible Finger Grippers • Use the same method as for the two-pincher gripper

  26. Wrist Rotation • Human hand has three degrees of freedom: • Twist on the forearm • Rock up and down • Rock side to side • Can add all or some of these degrees of freedom to the robotic hand

  27. Wrist Rotation • Most arm designs just want to rotate the gripper at the wrist • Usually preformed by a motor attached at the end of the arm or at the base • A cable or chain joins the motor shaft to the wrist • The gripper motor shaft are outfitted with mating spur gears • Can also use chains or timing belts to link the gripper to the drive motor

  28. Wrist Rotation • You can also use a worm gear on the motor shaft • Another approach is to use a rotary solenoid • Have a plate that turns 30 to 50 degrees in one direction when the power is applied • It return to its normal position when the power is removed • Mount the solenoid on the arm and attach the plate to the wrist of the gripper

  29. EXPERIMENT WITH GRIPPER DESIGNS ?

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