Browse Prior Art Database

Closed-Loop Step Servo System

IP.com Disclosure Number: IPCOM000052118D
Original Publication Date: 1980-Jan-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 85K

Publishing Venue

IBM

Related People

Wooton, RM: AUTHOR

Abstract

Disclosed herein is a DC motor-based closed-loop step servo system with inherent detent positions without an expensive optical encoder for position detection. A high-speed optical synchro decoder is disclosed in IBM Technical Disclosure Bulletin 20, 257 (June 1977). From the system as displayed, position and velocity information may be recovered as from, for example, rotary shafts, gears, cams, motors or other rotary actuators.

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Closed-Loop Step Servo System

Disclosed herein is a DC motor-based closed-loop step servo system with inherent detent positions without an expensive optical encoder for position detection. A high-speed optical synchro decoder is disclosed in IBM Technical Disclosure Bulletin 20, 257 (June 1977). From the system as displayed, position and velocity information may be recovered as from, for example, rotary shafts, gears, cams, motors or other rotary actuators.

The recovered signals are smooth and continuous in nature and permit the easy and inexpensive fabrication of a closed-loop step servo system employing conventional DC motors, such as a motor 10 illustrated in Fig. 1. To the shaft of the motor 10 is coupled a polarized disc 11. Three light-sensitive devices, such as silicon photovoltaic diodes 12, 13 and 14, are positioned on one side of the disc 11, and a light source 15 is positioned on the opposite side of the disc so as to cause light passing through the disc to strike the photovoltaic diodes causing a current to be generated by each diode in proportion to the light falling thereon. Intermediate the disc 15 and the diode sensors are polarized filters 12a-14a having differing axis of optical polarizations such that the sensors effectively output a balanced three phase system of electrical currents which contain instantaneous position information. Obviously the frequency (f(d)) of the rotational phase sequence is related to the rotational velocity of the motor shaft. In the system shown, one rotation of the disc 11 results in two complete cycles of photocurrent.

As illustrated in Fig. 2, the outputs of the photosensors 12, 13 and 14 are applied as modulation signals to amplitude modulators 16, 17 and 18, respectively, amplitude modulator 16 receiving an input reference carrier signal omega c from the output of a divide-by-16 counter 19 which is driven by a reference oscillator 20 (Fig. 1). The modulators 17 and 18, in turn, are driven by the reference carrier signal omega c but through phase-shift amplifiers 21 and 22 so that the outputs of the modulators, taken through resistors R1, R2 and R3 may be summed in a summing amplifier 23, giving an output or composite signal omega c +/- omega r, omega r being the modulation frequency in angular units (2 pi f(d)).

Turning back now to Fig. 1, the reference oscillator 20 is used to provide a clock signal for a delay line comprising a 16-bit shift register 24 as well as the source signal, as has already been described, for the divide-by-16 counter. After the signal is divid...