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Digital Speed Detection Disclosure Number: IPCOM000078839D
Original Publication Date: 1973-Mar-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 54K

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This apparatus detects motor speed or velocity using digital or sampled data techniques and provides an improved=high-data rate.

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Digital Speed Detection

This apparatus detects motor speed or velocity using digital or sampled data techniques and provides an improved=high-data rate.

Motor 10 of Fig. 1 rotates at a variable speed and drives both load 11 and digital tachometer or encoder 12. The tachometer is a digital device, for example magnetic or optical, and provides an output pulse for each distance unit of motor rotation.

The tachometer's electrical output signal appears at conductor 13 and is ideally of the symmetrical form shown in the upper waveform of Fig. 2, labeled "ideal". This waveform consists of alternate positive transitions 14 and negative transitions 15. This idealized waveform is shown for constant-motor speed, since the time interval between adjacent-positive transitions is equal. The length of this time interval is a measure of the motor's speed, and this interval increases as the motor's speed decreases. actual practice more likely that the tachometer output will be asymmetrical, as shown in the lower waveform of Fig. 2, labeled "actual".

The apparatus of Fig. 1 accommodates this asymmetry and alternately measures the interval between adjacent positive transitions and adjacent negative transitions, in overlapping fashion, to provide a high data rate.

Positive transition detector 16 detects only the positive transitions on conductor 13, and controls both switching logic network 17 and interval timer 18. When a positive transition occurs, network 17 is controlled to transfer the content of timer 18 to motor speed output network 19. Once this transfer is accomplished, network 17 is effective to reset timer 18 to an initial state, for example zero, by way the interval between positive transitions, and the contents of the timer are transferred to network 19, as a measure of motor speed, at the time of a positive transition.

Likewise, negative transition detection 21 controls network 17 and interval timer 22, to continuously time the period between negative transitions. In this manner, network 19 is always operating upon the motor speed information as computed in accordan...