Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1987-03-18
1988-10-04
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250237G, G01D 534
Patent
active
047757876
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a motor equipped with a pulse encoder, more particularly to a motor equipped with a pulse encoder used for detecting the speed or position (rotational angle) of the motor. It is used for control of the movement of robot arms, control of the feed of machine tool work tables, etc. and further for the positioning of the wire in a wire cut electric discharge machine tool.
BACKGROUND ART
The conventional version of this type of pulse encoder comprises a light emitting diode or other light emitting unit, a light receiving element unit having a PN type photodiode or other light receiving element for receiving light from the light emitting unit, a rotary encoder disc and a fixed encoder disc having signal patterns which pass or interrupt light sent from the light emitting unit to the light receiving element unit. A fixed slit plate has the fixed encoder disc and the light receiving element unit affixed. A housing has the fixed slit plate affixed, and a printed circuit board on which is formed the signal processing circuit (comparator, driver, TTL, etc.) to which the signal output from the light receiving element unit is input through connection lines.
However, in this type of pulse encoder, the signal output from the light receiving element unit is on the high order of several hundred mV, so the signal, in the process of passing from the light receiving element to the amplifier on the printed circuit board (for example, the comparator) is particularly susceptible to noise. Therefore, the signal output to the outside of the pulse encoder often is not correct and thus mistaken operations are caused.
However, the major reason why noise easily superposes on the output signal output from the light receiving element unit is that the fixed slit plate, to which the light receiving element unit is affixed, is made of metal (usually, a metal the same as that of the housing to which said fixed slit plate is affixed). Therefore, the high frequency noise from the circuit for supplying power to the motor, in particular from a circuit controlled by chopping, passes via the case of the motor, the housing, which abuts against an end of the motor case and in which is mounted the bearings supporting the rotary shaft of the motor, to reach the fixed slit plate affixed to the housing. Thus, the fixed slit plate serves as a source of noise.
As a means for reducing the noise, in the prior art, as for example illustrated in FIG. 1, the means has been adopted of connecting a capacitor 104 to the portion (portion of input circuit of comparator 105 in FIG. 1) of the signal processing circuit (comprised of comparator 105, driver 106, etc.) on the printed circuit board 10, to which portion the signal is input from the light receiving element unit 8, where the light receiving elements 82 and 83 are provided, through the connection lines 103, the capacitor 104 absorbing noise included in the signal output from the light receiving element unit 8.
However, with the capacitor 104, both the noise and also the regular output signal are absorbed. In cases, for example, where the motor is rotating at a high speed or where the slits for the signal patterns formed on the rotary encoder disc are narrow (i.e., there are a large number of pulses), when the frequency of the output signal is high, there is a conspicuous rounding of the output signal due to the influence of the capacitor and there is thus the problem of possible failure to obtain a correct signal as the rectangular wave signal on the comparator output side.
Further, even when the fixed slit plate is not made a metal, but of an insulator, about the same thing happens as when it is made of metal, i.e., an electric field created by the high frequency noise is formed through the insulator on the light receiving element unit side. There is a problem in that this type of noise reduction measure is not sufficiently effective.
To solve the above-mentioned problems, the present applicant previously proposed a pulse encoder provided, as shown in FIG.
REFERENCES:
patent: 3790858 (1974-02-01), Brancaleone et al.
patent: 4342909 (1982-08-01), Accattino
patent: 4389902 (1983-06-01), Kataoka et al.
patent: 4654636 (1987-03-01), Rusk
patent: 4661698 (1987-04-01), Cappio et al.
Fanuc Ltd.
Nelms David C.
Oen William L.
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