Electricity: motive power systems – Positional servo systems – Digital or numerical systems
Patent
1989-06-23
1991-05-07
Ro, Bentsu
Electricity: motive power systems
Positional servo systems
Digital or numerical systems
318565, 318480, G05B 2302
Patent
active
050139886
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a position encoder, and more particularly, to an absolute position encoder capable of complying with high speed rotations.
2. Background Art
Position encoders have been extensively employed as a position detector in a computerized numerical controller (CNC) or a robot controller. Absolute position encoders have particularly been extensively employed as they are capable of accurately detecting position data even after a power supply is again turned on.
Conventional absolute position encoders which detect absolute positions are supplied with absolute data only from absolute code pattern formed in a code disk. The absolute code pattern requires a plurality of parallel patterns and is thus complex as compared with an incremental code pattern.
Accordingly, with the conventional absolute position encoders, it has been difficult in the case of high speed rotations to simultaneously read all the codes due to variations in delay time of detection circuits for detecting the plurality of parallel code patterns, hence a problem exists in that those encoders cannot comply with high speed rotations.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to solve the above-mentioned problem and provide an absolute position encoder capable of complying with high speed rotations in which an absolute position detecting function is used in combination with an incremental position detecting function.
In order to solve the above problem, there is provided an absolute position encoder for outputting a position data as an absolute data, comprising:
a code member having an absolute code pattern and an incremental code pattern;
a counter for counting incremental pulses extracted from the incremental code pattern, said counter presetting an absolute position data extracted from the absolute code pattern; and
an output circuit for outputting contents of said counter as the absolute data.
When a power supply is turned on, the absolute position data extracted from the absolute code pattern is set to the counter, whereby the counter is loaded with the absolute data.
After the absolute data has been set, the incremental pulses extracted from the incremental code pattern are counted and the contents of the counter are updated.
Accordingly, the counter retains the absolute data. This data is output to a computerized numerical controller (CNC) or a robot controller as absolute data.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating an absolute rotary encoder according to one embodiment of the invention;
FIG. 2 is a schematic diagram illustrating an arrangement of the absolute rotary encoder according to the embodiment of the invention;
FIG. 3(a) shows an example of a code pattern;
FIG. 3(b) shows light receiving windows of detecting elements;
FIG. 3(c) shows an output signal from the absolute pattern;
FIG. 4 shows changing absolute codes; and
FIGS. 5(a) and 5(b) are diagrams illustrating relationships between incremental codes and incremental pulses.
DETAILED DESCRIPTION OF THE INVENTION
Embodiment of the present invention will now be described with reference to the accompanying drawings.
FIG. 1 is a block diagram showing an absolute rotary encoder according to the embodiment of the invention. In FIG. 1, a code disk 5 has a lower surface on which an absolute code pattern 6 and an incremental code pattern 7 are printed. Lights emitted from LEDs 8a, 8b are irradiated onto the code disk 5 and the lights which have passed through the code patterns 6, 7 are received respectively at detecting elements 3, 4, each comprising, for example, a photodiode. An absolute code signal (AC signal) and an incremental code signal (IC signal) are output from the detecting elements 3, 4, respectively. Details of the code disk 5, absolute code pattern 6, etc. will be described later.
A detection circuit A denoted by reference numeral 11 receives a minute absolute code signal (AC signal), in which the minute signal is amplified and is then subjected to w
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Fanuc Ltd
Ro Bentsu
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