Browse Prior Art Database

SPEED SENSING SCHEME FOR MOTION CONTROL

IP.com Disclosure Number: IPCOM000026516D
Original Publication Date: 1992-Aug-31
Included in the Prior Art Database: 2004-Apr-06
Document File: 6 page(s) / 187K

Publishing Venue

Xerox Disclosure Journal

Abstract

In high quality and grey level printing systems, accurate control of the relative motion between the print media and the marking device is critical. A number of such printing systems employ encoders or equivalent devices to monitor the motion. In operation, the encoders generate short pulses indicative of the incremental relative motion being monitored. Moreover, the relative speed may also be monitored by timing the pulse intervals, to determine an average speed over one or more intervals. The response of these monitoring systems, and hence the accuracy, may be improved by shortening the intervals. Unfortunately, this usually requires more expensive encoders.

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Page 1 of 6

XEROX DISCLOSURE JOURNAL

SPEED SENSING SCHEME FOR MOTION CONTROL Frank C. Genovese

Proposed Classification
U.S. C1.341/002 Int. C1. H03M 1/22

               90' PHASE SEGMENT 14 DISK I

\

I I I 1

I I I I I

I I

I I I I

I I I I 1

I

I I I I I

LIGHT

____)

I

4

RELATiVE MOVEMENT

FIG. 1

XEROX DISCLOSURE JOURNAL - VoI. 17, So. 4 July/August 1992 205

ZERO PHASE SEGMENT

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Page 2 of 6

SPEED SENSING SCHEME FOR MOTION CONTROL(Cont'd)

CLOCK

FIG. 2

206 XEROX DISCLOSURE JOURNAL - Vol. 17, KO. 4 Juiy/August 1992

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Page 3 of 6

SPEED SENSING SCHEME FOR MOTION CONTROL(Cont'd)

PORT1 ON OF TRIANGLE =@

DERIVATIVE = d @/dt I

           I SEGMENT A I

\ I

SEGMENT B

/

A' - B' STITCHED

I

TIME

FIG. 3

XEROX DISCLOSURE JOURNAL - Vol. 17,Xo. 4 July/August 1992 207

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Page 4 of 6

SPEED SENSING SCHEME FOR MOTION CONTROL(Cont'd)

In high quality and grey level printing systems, accurate control of the relative motion between the print media and the marking device is critical. A number of such printing systems employ encoders or equivalent devices to monitor the motion. In operation, the encoders generate short pulses indicative of the incremental relative motion being monitored. Moreover, the relative speed may also be monitored by timing the pulse intervals, to determine an average speed over one or more intervals. The response of these monitoring systems, and hence the accuracy, may be improved by shortening the intervals. Unfortunately, this usually requires more expensive encoders.

Accordingly, the present invention is directed to a scheme for optimizing an optical or similar encoder, so as to increase the information content of the signal produced by such encoders. Referring to Figure 1, optical encoders generally use a ruled disk, 14, mounted on a shaft and in close proximity to a stationary mask, 16, so that light may pass through the disk and mask and contact photodetectors A or B. In operation, the combination of ruled disk 14 and mask 16 form a light modulator, the throughput of which is a periodic function indicating the relative mask-disk angular position. For a constant shaft velocity, the mask-disk combination of Figure 1 will produce triangular output signals, Out A and Out B, from the A and B photodetectors, respectively, as illustrated at the top of Figure 2. Generally, threshold triggering digital circuitry is used to produce the more familiar square-wave output from the two encoder mask segments. However, the present invention utilizes the "raw" triangular signal in a differentiated fashion, where the amplitude of the waveform produced is representative of the instantaneous slope of the triangle, or more appropriately, the shaft rotation speed. Although the sign of the slope reverses for each leg of the triangle, the signal is symmetric and the absolute value equals the shaft speed for either sign. While the reversa...