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Wright State University. Jenny Broering Mike Hill Rahul Shah Michael Wasco. Problem Statement. The purpose of this project is to design and manufacture robotic manipulator to assist younger patients with daily activities, such as retrieving things from the ground or immediate environment.

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Wright State University

  • Jenny Broering

  • Mike Hill

  • Rahul Shah

  • Michael Wasco


Problem Statement

The purpose of this project is to design and manufacture robotic manipulator to assist younger patients with daily activities, such as retrieving things from the ground or immediate environment.

  • Basic Requirements

    • 0.75 m reach from front of wheelchair

    • Each linkage must move no more than 0.25 m/s

    • Lift 0.5 kg mass (1.1 lbs.) with 7.5 cm in diameter

    • Maximum cost of $4,500 (excluding controllers)


Agenda

  • Design Constraints

  • Robotic Arm Design (detailed)

  • Conclusions

  • Questions


Design Constraints

  • Arm, including motors, must weight less than 30 lbs.

    • Keeps wheelchair balanced

  • Dimensions of arm/base must not exceed 6 inches

    • Wheelchair must be able to fit through standard doorways


Design Constraints

  • Keep shoulder and elbow motors at the base

    • reduces weight on arm itself

    • transmit power to elbow via shaft

  • Aluminum 2024

    • High Strength-to-Weight ratio

    • Lightweight compared to steels (2770 vs. 8030 kg/m3)


WSU Arm Design


Orientation of Base Motors

  • Mounting position

    • Length along chair allows space for base plate

    • Straight layout allows for easy mounting possibilities

  • Two large motors displaced from arm

    • Reduces torque

    • Makes links slimmer and lighter


Base Configuration


Shoulder Motor

  • Required Torque: 465 in-lbs (7433 oz-in)

  • Speed Requirement: 2.65 RPM

  • Suggested motor and gearhead:

    • K & D Magmotor servo motor (model # C33-I-200E08)

    • Carson 34EP100 NEMA 34 gearhead (100:1)

    • 477 in-lbs provided


Shoulder Motor

  • Servo amplifier suggested to slow speed down to required speeds

    • connecting directly to 24 VDC will give an output of 10 RPM

    • connecting 24 VDC to a servo amplifier, we can set a speed from 0-10 RPM


Gearhead

5.43” length

3.25” diameter

9.68 lbs

$700.00

Shoulder Motor Dimensions and Costs

  • Motor

    • 5.15” length

    • 3.38” diameter

    • apr. 5 lbs.

    • $134.00

  • Amplifier

    • $439.00


Elbow Motor

  • Required Torque: 237 in-lbs (3797 oz-in)

  • Speed Requirement: 4.4 RPM

  • Suggested motor and gearhead is the same as shoulder motor:

    • K & D Magmotor (model # C33-I-200E08)

    • Carson 34EP100 NEMA 34 gearhead (100:1)

    • 477 in-lbs provided


Gearhead

5.43” length

3.25” diameter

9.68 lbs

$700.00

Elbow Motor Dimensions and Costs

  • Motor

    • 5.15” length

    • 3.38” diameter

    • apr. 5 lbs.

    • $134.00

  • Amplifier

    • $439.00

  • Same as Shoulder motor choices


Upper Arm

  • Comprises of two links

  • Dimensions:410 x 50 x 5 mm.

  • Weight:0.8772 lbs.

  • Advantages:

    • slots cut to reduce the weight

    • Provide support for the shaft and the lower arm

    • encompasses the parts


Upper Arm


Bearing Plate

  • Provides structural support

  • Slot provided for compact closing of the arm

  • Dimensions:100 x 50 x 10 mm.

  • Weight:0.23 lbs.


Elbow Joint

  • Elbow motion using the shaft, bevel gears and rod.

  • Weight:

    • Rod: 0.045 lbs.

    • Shaft : 0.614 lbs.

    • Bevel Gears: 0.0278 lbs. each


Elbow Joint

  • Advantages:

    • eliminates the motor-on-joint assembly.

    • reduces torque on the shoulder motor.


Lower Arm

  • Single shaft design

  • Two slots

    • decrease weight

  • Symmetric placement between the two upper arm links reduced unwanted torsion.


Lower Arm

  • Dimensions:320 x 50 x 5 mm.

  • Weight:0.3498 lbs.


Differential Assembly(wrist)

  • Motor-on-Gear Design

  • Off the Shelf vs. Machined

  • Dimensions


Design

  • Two Axes Movement

    • Gears spin in same direction, gripper pitches up/down

    • Gears spin in opposite directions, gripper rolls cw/ccw

  • Motor-on-Gear Design

    • Gear is attached to motor shaft

    • Motor shaft/gear have same axis of rotation


Off-the-Shelf vs. Machined

  • Currently searching for off-the-shelf models that can be incorporated into the design space

  • Machined differential will drive the cost up significantly


Dimensions

  • Approx. Size (w/o motors) : 162x120x50 mm

  • Weight (w/o motors) : 1.7 lbs


Differential Assembly(wrist)


Differential Motors

  • Orientation of motors provide a direct application of the gear movement

  • Differential design allows motors to work together thus reducing the size and cost of motors


Differential Motors

  • Torque requirement: 107.2 oz-in

  • Speed Requirement: 15.7 RPM

  • Suggested motor:

    • Barber-Colman permanent magnet DC Motor with gearhead (model # EYQF-33300-661)

    • 12 VDC

    • 160 oz*in

    • 9 RPM


Differential Motor Dimensions and Costs

  • Motor

    • 2.5” length

    • 1.5” diameter

    • weighs 9 oz.

    • $74.00 ea.


End Effecter(Gripper)

  • Motor-screw powered movement

  • Three Fingers

  • Dimensions


Gripper


Motor-Screw

  • Powers the closing action

  • Will weigh less then 1.5 pounds

  • open/close control

  • variable closing pressure


Three Fingers

  • Better stability

  • Pick-up a wide variety of sizes 7.5cm-.5cm

  • Middle finger has lip for round objects

  • Fork lift design

  • Non-slip cork/rubber padding


Dimensions

  • Each finger is 95 x 25 x 2 mm

  • Weighs only .333 kg w/o motor-screw

  • Hollow casing 50 x 95 mm

    • 2 mm wall thickness


Note that theweight of the materials were taken to act at the farthest distance possible

c

a

d

b

Torque Calculations


Motor Speed Calculations

 = L/V

0.1524 m

0.542 m

0.902 m


Summary

  • Main motors placed at base

  • Design uses 5 motors

  • Design gives 5 axes of motion.

  • Upper arm is slightly longer than lower arm

  • Differential Design

  • Three finger Gripper


Summary

  • Motor cost:$2768.00

  • Material cost:$ 150.00 (est.)

  • Machining cost:

  • Total weight. 36 lbs


Disadvantages

  • Improper folding of arm

    • not certain if folding is within 6 in.

    • motor placement on differential makes wrist bulky

  • Overall assembly is overweight by 6 lbs.


Advantages

  • Meets nearly all of the constraints / requirements.

  • Shaft

    • allows transfer of more power to the lower arm

    • allows reduction of torque on the shoulder motor.

  • Use of plates instead of tube reduces overall weight considerably


Advantages

  • Can lift objects from the floor or from table-tops.

  • Torque requirements met by motors.

  • Versatile gripper.

  • Use of Aluminum 2024 in most parts

    • consistency in material

    • high strength to weight ratio (used in airframes)


?? Questions ??


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