Electricity: motive power systems – Positional servo systems – With particular 'error-detecting' means
Patent
1990-01-19
1992-07-14
Ro, Bentsu
Electricity: motive power systems
Positional servo systems
With particular 'error-detecting' means
318663, G05B 106
Patent
active
051306271
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method of positioning a part and on a device for carrying out the method wherein operation of an electric motor drive is controlled in accordance with a nominal position of the part. It is generally known prior art to detect mechanical end stops by limit switches in a positioning device. When a stop is reached, the positioning device or the part to be positioned actuates a limit switch which stops the positioning drive. The limit switches must be accurately aligned since a faulty end stop can result, on one hand, in damaging the positioning device and, on the other hand, in overloading the positioning drive.
An integrated circuit for pulse-duration-modulated driving of direct-current motors is known from the in-house document "Silicon general, linear integrated circuits, voltage regulator with applications", Product Selection, 1982/83, Messrs. Astonik, Winzererstr. 47d, 8000 Munich 40, pages 111-118. The circuit is suitable for driving positioning device drive motors. The electric motor, which can be switched on by a control circuit via a driver circuit, is connected via a coupling to a part to be positioned and to an actual position value transmitter. The electric motor is switched on in dependence on the difference between a nominal position value and the actual position value until the system deviation drops below an adjustable value. The control circuit exhibits a connection, designated by "shut down", via which the driver circuit or the electric motor, respectively, can be switched off.
SUMMARY OF THE INVENTION
The object of the invention is to provide part positioning method and device in which limit switches are not required for detecting the mechanical stops. The object of the invention is achieved by providing method and device wherein the signal generated by an actual position value transmitter is compared with a threshold value, and a switch-off signal is generated in response to the threshold value being exceeded. There is no cost-intensive alignment of the limit switches hitherto used. The drive circuit of the electric most or has a control input which is supplied with a signal in dependence on the actual position value emitted by the position transmitter. This signal can be used, for example, to switch the drive motor off at a predetermined actual position value or to change its direction of rotation.
It is particularly advantageous to supply the control input with a signal in dependence on at lest one predetermined position limit value. Both mechanical stops are detected by predetermining first and second position limit values. When a position limit value corresponding to the stop is reached, the drive motor is switched off. In a particularly advantageous development of the method according to the invention, it is provided to inhibit the driver circuit, or the drive motor, respectively, when a position limit value is reached, in such a manner that the direction of rotation of the motor for adjusting the position in the direction of the position limit value reached is inhibited and that the opposite direction is not inhibited, so that the position limit value that was reached can be reduced again in the opposite direction.
In the device according to the invention for carrying out the method, the actual position value signal emitted by the position transmitter is advantageously supplied to a comparator with a predetermined threshold, which emits a switch-off signal to the at least one control input of the control circuit when the threshold is exceeded. In a second embodiment of the device according to the invention, a comparator having first and second thresholds is provided which in each case emits a switch-off signal to the control circuit when the thresholds are exceeded or dropped below, respectively.
In the third embodiment, two separate comparators having thresholds which are in each case predetermined are provided, with each comparator emitting a switch-off signal to the control circuit by which one or the other direction of rot
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Frommholz Wilfried
Hoppe Willi
Vohringer Klaus
Ro Bentsu
Robert & Bosch GmbH
Striker Michael J.
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