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Servo-controlled Friction Drive Rotary Motor

IP.com Disclosure Number: IPCOM000050926D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 4 page(s) / 66K

Publishing Venue

IBM

Related People

Stuckert, PE: AUTHOR

Abstract

Certain robots require a motor that converts the constant rotation of an input drive shaft to linear motion to effect positioning. The device is functionally a lead screw whose pitch is not only infinitely variable but is controllably right hand, zero, or left hand.

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Servo-controlled Friction Drive Rotary Motor

Certain robots require a motor that converts the constant rotation of an input drive shaft to linear motion to effect positioning. The device is functionally a lead screw whose pitch is not only infinitely variable but is controllably right hand, zero, or left hand.

In addition to linear motion, robots require rotary motion (for pitch, roll, and yaw and for the armlike joint motions that replace linear motion in some designs). The following describes a servo-controlled friction drive rotary motor.

Throughout the following, identifying numbers are used in groups:

- the 1xx group applies to parts that are fixed relative to the

fixed member of the rotary joint.

- the 2xx group applies to parts that are fixed relative to the

moved member of the rotary joint.

- the 3xx group applies to moving parts that link the 1xx and

2xx groups.

"Fixed" and "moved" are, of course, used in a relative sense; the fixed group may, itself, be moved by other parts that are neither shown nor discussed.

Fig. 1.1 shows a coaxial rotary joint between cylindrical members; Fig. 1.2 shows a rotary joint between armlike members. In both figures, 100 is the fixed member and 200 is the moved member. Other combinations exist. Both types of rotary joint employ the same motor.

The Ball/Disc Integrator Mechanism.

Graham Transmission Company manufactures an adjustable speed drive that is based on the ball/disc integrator. Fig. 2.1 shows the Graham device, and Fig. 1.2 shows its functional equivalent. Relative to Fig. 2, note that: - the output speed is variable from zero to some maximum in one direction, - no reversal of the direction of rotation is provided, and - a rotating assembly of caged balls is functionally equivalent to a single caged ball. Multiple balls permit the transfer

of more torque.

The servo-controlled friction drive rotary motor described below is also based on the ball/disc integrator; however: - It provides output rotation of a joint, not a shaft, from a maximum speed in one direction, through zero, to a maximum

speed in the opposite direction. The equivalent may be

visualized with reference to Fig. 2. If the ball shown at A

in Fig. 2.2 is moved downward so that it is tangent to the

bottom of the circle on the input disk, the direction of

rotation of the output disk is reversed. - All balls in the rotating cage assembly need not be present. In the motor described below, all balls in the central region

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are removed and a central cylindrical hole provided in the

space they occupied. All peripheral balls are retained.

(This is equivalent to removing the three central balls at B

in Fig. 2.1. Except for slight reduction in output torque,

the operation is unaffected.)

Motor Description.

Fig. 3 shows six sectional views of the servo-controlled friction friction drive rotary motor. Fig. 3.1 is a sectional view through the axis of rotation of the input drive shaft. Figs. 3.2 through 3.6 are sectional...