Electricity: motive power systems – Braking – Automatic and/or with time-delay means
Patent
1985-03-06
1985-11-05
Shoop, Jr., William M.
Electricity: motive power systems
Braking
Automatic and/or with time-delay means
318314, 318327, 318341, 318466, H02P 500, G05B 500
Patent
active
045516626
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a motor speed detecting device, and more particularly, to a motor speed detection device utilizing a magnetic sensor and a slotted disc having an undercut notched wedge and mounted on the rotational shaft of the motor.
BACKGROUND ART
In the prior art, a motor speed detecting device comprises a coded disc composed of a glass plate mounted on the rotational shaft of the motor, and as an opaque portion of the coded disc passes between a light source and a light sensor, an electrical signal is obtained from the light sensor. The electric signal is then amplified to shape the waveform, thus providing a series of pulses in response to the rotational speed of the shaft. Usually, this device outputs two types of pulses, that is to say, one pulse per one revolution of the coded disc and a plurality of pulses per one revolution of the coded disc. The device counts the number per hour of these pulses, and thus detects the rotational speed of the motor.
There is an unavoidable problem wherein, when the detected rotational shaft is hollow, the above-described speed detection device cannot be applied. When a motor is used for driving a machine tool such as a lathe and the like, it is necessary to render a drive rotational shaft hollow and to make a cylindrical workpiece pass therethrough, on the basis of the mechanism for delivering the workpiece. In such a case, the apparatus using the coded disc cannot be adapted from the structural point of view, although it is recognized that the interference from other sources of light considerably affects for the worse the apparatus using the coded disc, and there remains a problem in that the precision of the device cannot always be maintained.
The present invention is intended to solve the problems described in the above prior art devices.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a speed detection device that, when used for a hollow rotational shaft such as in a lathe, it is possible to improve the precision of detection in response to the number of slots of the slotted disc by approximately four times without increasing the number of slots.
According to a feature of the present invention, there is provided a motor speed detecting device comprising, a first disc composed of ferromagnetic material, having one slot and mounted on the rotational shaft of a motor driven by a motor drive unit; a second disc composed of ferromagnetic material, having a plurality of slots; a first magnetic sensor mounted in close proximity to the first disc, for outputting two signals having a phase difference responsive to the width of the notched disc by one half; a second magnetic sensor mounted in close proximity to the second disc, for outputting two signals having the phase difference responsive to the width of the slot by one half, and two other signals in phase with the signals inverted by the first two signals; and a detector circuit for receiving the outputs of the first and second magnetic sensors and detecting those outputs.
The detector circuit comprises, a first differential amplifier circuit for counting the difference between the two signals from the first magnetic sensor, a first comparator circuit for comparing the output from the first differential amplifier circuit with a reference voltage, a second differential amplifier circuit and a third differential amplifier circuit for receiving respectively two sets of signals having an opposite phase relationship to each other from the second magnetic sensor and counting the difference therebetween, a vector synthetic comparator circuit for receiving the outputs of the second and third differential amplifier circuit and searching for the signals having each phase of 0, 22.5, 45, 67.5, 90, 112.5, 135 and 157.5 degrees, at a phase difference of 22.5 degrees, separately, and when the phase angle of the output waveform of the magnetic sensor in response to the width of the slot is 180 degrees, then comparing the signals with the reference voltage to m
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patent: 4468597 (1984-08-01), Baumard et al.
Ishida Hiroshi
Taniguchi Mitsuyuki
Fanuc Ltd
Ip Shik
Shoop Jr. William M.
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