Electrical pulse counters – pulse dividers – or shift registers: c – Applications – Position determining
Patent
1989-09-29
1991-09-10
Heyman, John S.
Electrical pulse counters, pulse dividers, or shift registers: c
Applications
Position determining
377 39, 377 43, 377 55, 34087019, 318638, G06K 1100, H03K 2102, G05B 1106
Patent
active
050480634
DESCRIPTION:
BRIEF SUMMARY
RELATED APPLICATION
This application is related to U.S. Ser. No. 382,784, filed June 23, 1989.
BACKGROUND OF INVENTION
This invention relates to a machine position detecting apparatus for detecting the absolute position of a machine by a pulse coder or the like attached to a movable element.
BACKGROUND ART
In a machine tool equipped with an absolute position detector and controlled by a Computerized Numerical Controller (CNC) unit, absolute position stored on the position detector side is transferred to the CNC unit at the moment power is introduced, and the absolute position is stored in a register within the CNC unit. When the movement of the movable element is controlled by a move command from the CNC unit, the absolute position detector acts as a relative position detector and the register is updated based solely on the amount of movement to control the machine. More specifically, return to the origin required at introduction of power is no longer necessary, absolute position is read out of the absolute position detector only once when the power supply is turned on, and the amount of relative movement obtained from the position detector is subsequently grasped as an electric signal to control the machine position.
With this conventional method of verifying absolute position, the accuracy of the machine stopping position is confirmed based solely on the absolute position data stored in the register within the CNC unit when the machine is stopped. Consequently, reliability is enhanced as problems associated with a decline in precision due to gear wear or the like do not arise. However, if an error should happen to develop in the contents of the register for some reason, such as an error produced by noise when reading in command data, there is no way to check this. The occurrence of such an error in the contents of the register can lead to machine malfunction. In addition, if it is necessary to verify the machine stopping position, as when tools are changed, the movable element must be returned to the origin. Various other problems arise as well.
SUMMARY OF THE INVENTION
The present invention has been devised in order to solve these problems and its object is to provide a machine position detecting apparatus in which it is possible to check the contents of data related to the absolute position of a movable element stored in a CNC unit.
In accordance with the present invention, there can be provided a machine position detecting apparatus for detecting a machine position of a movable element by a rotational position signal and a one-revolution signal from an absolute position detector circuit attached to the movable element, characterized by comprising position memory means for reading absolute position from the absolute position detector circuit when power is introduced, and for being updated subsequently by a movable element move command, counting means for counting an amount of shift of the absolute position detector circuit in one revolution based on the rotational position signal, and collating means for collating contents of the counting means with contents of the position memory means and checking stored contents of the position memory means when the movable element is stopped.
Accordingly, the machine position detecting apparatus of the present invention is such that absolute position stored by the position memory means and the count recorded by the counting means are collated, whenever the movable element is stopped, to check the data stored by the position memory means, whereby the presence of a malfunction can be determined with regard to reading of machine position.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating an embodiment of the present invention, and FIG. 2 is a view illustrating a pulse signal from an absolute encoder during movement.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will now be described in detail with reference to the drawings.
FIG. 1 is a block diagram illustrating a machine position detecting appara
REFERENCES:
patent: 4155003 (1979-05-01), Grassme
patent: 4566111 (1986-01-01), Tanacawa
patent: 4779075 (1988-10-01), Zagelein et al.
patent: 4805199 (1989-02-01), Muramatsu
Ikeda Yoshiaki
Isobe Shin-ichi
Fanuc Ltd
Heyman John S.
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