Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-12-26
1991-11-05
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250237G, G01D 534
Patent
active
050632957
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a slit disposition structure of a fixed slit disk in a pulse encoder for detecting the rotational position or rotational speed of a motor or a spindle of a machine tool or the like.
BACKGROUND ART
In the past, use has been made of pulse encoders combining the use of absolute type slits and increment type slits, as represented by the Gray code, to detect the rotational position or rotational speed of a servo motor for driving and controlling industrial robots, machine tools, etc.
In the past, however, to further raise the resolution of detection of the rotational position by the increment type slits in the fixed slit disk, the slits have been divided into a plurality of increment type slit groups, and these groups have been disposed around the optical axis of one light emitting diode so that the slit groups receive a substantially equal irradiation by the light emitting diode. Therefore, there has been no room for an irradiation of absolute type slits as well, and therefore, these absolute type slits had to be irradiated by using another light emitting diode.
DISCLOSURE OF THE INVENTION
Therefore, an object of the present invention is to provide a slit disposition structure of a fixed slit disk enabling an efficient irradiation of increment type slits and absolute type slits by using of a single light emitting diode.
In view of the above object, the present invention provides a slit disposition structure of a fixed slit disk in a pulse encoder having a light emitting diode, a rotary slit disk, a fixed slit disk, and a light receiving device, having absolute type slits and a plurality of increment type slit groups, and detecting the angular position or rotational speed of a rotary body, characterized in that the plurality of increment type slit groups are disposed radially on said fixed slit disk around the optical axis of the one light emitting diode, and in that the absolute type slits are disposed around the optical axis and inside an arc formed by the extension of the outer circumference of said plurality of increment type slit groups.
In a fixed slit disk, by disposing the increment type slit groups at radial positions about the optical axis of a single light emitting diode and disposing the absolute type slits at the remaining regions about the optical axis and in an arc formed by an extension of the outer circumference of the slit groups, it becomes possible to evenly irradiate the slits without the use of a plurality of light emitting diodes and thus it becomes possible to provide a more compact pulse encoder.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an enlarged front view of a slit disposition structure of a fixed slit disk according to the present invention;
FIG. 2 is a frontal view of the slit disposition structure of a conventional fixed slit disk; and
FIG. 3 is a side view of a pulse encoder.
BEST MODE OF CARRYING OUT THE INVENTION
The present invention is now described in more detail in accordance with the embodiments shown in the attached drawings. Referring to FIG. 3, bearings 42 are housed in a detector housing 44, and a rotary shaft 41 for a detector connected to an output shaft 40 of a motor is held thereby. A rotary slit disk 48 is fixed on the rear end of the rotary shaft 41, to be rotated with the output shaft 40. A light emitting diode 46 is attached at an appropriate position of the detector housing 44, and a fixed slit disk 10 is attached in the front thereof. Furthermore, a light receiving device 50 of a phototransistor is fixed on the detector housing, opposite to the light emitting diode 46, and interposing the rotary slit disk 48.
Below, a slit disposition structure of the fixed slit disk 10 of the above-mentioned elements of the pulse encoder is described. First, FIG. 2 shows the slit structure of a conventional fixed slit disk 10', wherein the two chain-dot lines 12' and 12" show the outer limits of irradiation regions of two LED light emitting diodes. Four substantially quadrilateral slit groups 14', 16', 18', an
REFERENCES:
patent: 4678908 (1987-07-01), LaPlante
patent: 4700062 (1987-10-01), Ernst
patent: 4906838 (1990-03-01), Sogabe et al.
Asaba Eiki
Tagami Kiyoshi
Tanabe Yoshihito
Fanuc Ltd.
Nelms David C.
Shami K.
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