Patent Description:
Transmissive and reflective optical rotary encoders are known as types of optical rotary encoders. As disclosed in <CIT> (<FIG>), in transmissive optical rotary encoders, a light-emitting element is disposed on one side of a rotating disc attached to a rotating shaft to be measured, and a light-receiving element is disposed on the other side of the rotating disc. Detection light emitted from the light-emitting element passes through a slit pattern formed in the rotating disc and a slit pattern formed in a fixed slit plate, whereby a plurality of optical signals are generated. These optical signals are received by the light-receiving element and photoelectrically converted, after which the signals are supplied to a signal processing circuit and, inter alia, two-phase signals having an A phase and a B phase that have a phase difference of <NUM>° are formed. In the optical rotary encoder disclosed in <CIT>, two sets of light-emitting elements and light-receiving elements are provided, and optical signals are generated via two slit patterns formed in a rotating disc and a fixed slit plate. The precision of detection is thereby raised without reducing the size of the slit patterns. <CIT> discloses a rotary encoder comprising: a light source device that includes a light emitting diode radiating light, and a lens collimating the light of the light emitting diode; a rotary slit plate that includes a first slit forming a diffraction grating in a circumferential direction radially from a center; a stationary slit that includes a second slit forming the diffraction grating in the circumferential direction radially from the center; and light reception unit that receives the light passing through the first and second slits and coming from the light source. A distance between the rotary slit plate and the stationary slit plate is a distance where the light passing through the first slit or second slit interferes due to diffraction, and a slit image is formed on the rotary slit plate or stationary slit plate, and a light emitting diameter of the light emitting diode is configured to be greater than six times, and less than <NUM> times an interval among the first slits or the second slits. <CIT> provides an optical encoder capable of using the recesses and convexes of a movable plate and a fixed plate to accurately generate a Z phase signal in synchronism with an A/B phase signal. Phase type diffraction gratings on the moving and fixed plates including a plurality of tracks with different grating pitches cause parallel coherent beams to interfere with one another, and a light receiving part detects the intensity of light to obtain a plurality of synchronous signals with different periods. On the other hand, the light receiving part detects light spots formed by condensing elements on the movable plate to generates a single pulse per rotation as a reference position. One of the plurality of synchronous signals that has the shortest period is selected as an A/B phase signal that depends on the movement of the movable plate. The conjunction of the reference position signal and the plurality of synchronous signals is determined as a Z phase signal indicating the origin of the movable plate, thereby obtaining a Z phase signal in synchronism with one pulse of the A/B phase signal.

In order to raise the detection precision in an optical rotary encoder and also reduce the size and costs of the optical rotary encoder, it is desirable to make it possible to detect a plurality of slit patterns using a single set of a light-emitting element and a light-receiving element. For example, in the optical rotary encoder <NUM> shown in <FIG>, when a light-emitting diode (LED) <NUM> is used as a light source, the shape of an effective spot of detection light <NUM> emitted from the LED <NUM> is round. A plurality of slit patterns <NUM> (detection tracks) are formed in a rotating disc <NUM>, and a plurality of slit patterns <NUM> are formed in a fixed slit plate <NUM> as well.

In <FIG>, the empty rectangles indicate slits 103a that constitute the plurality of slit patterns <NUM> in the rotating disc <NUM>, the gray rhombuses indicate slits 105a that constitute the slit patterns <NUM> in the fixed slit plate <NUM>, and the rectangles marked with diagonal lines indicate light-receiving surfaces 104a that constitute a light-receiving-surface pattern <NUM> on a light-receiving element <NUM>. The detection light <NUM> from the LED <NUM> passes through the slit patterns <NUM> in the rotating disc <NUM> and the slit patterns <NUM> in the fixed slit plate <NUM>, and then is received by the light-receiving surfaces 104a of the light-receiving element <NUM>. As shown in <FIG>, an effective spot <NUM> of the detection light <NUM> from the LED <NUM> must be made large enough to encompass the slit patterns in the fixed slit plate <NUM>, which are formed from the plurality of rhomboid slits 105a.

For example, when the effective spot <NUM> of the LED <NUM> is formed as a small-diameter effective spot 7a as shown by virtual lines in <FIG>, a pair of slits 105a(<NUM>), 105a(<NUM>) within the slit patterns in the fixed slit plate <NUM> partially jut out beyond the effective spot 7a. As a result, the amount of received light of the two-phase optical signals obtained via the pair of slits 105a(<NUM>), 105a(<NUM>) decreases, and it is impossible to obtain two-phase signals having a high S/N ratio. It is necessary to select a large-scale LED <NUM> provided with a large effective spot <NUM> so that the slits 105a that constitute the slit patterns in the fixed slit plate <NUM> completely fit within the range of the effective spot. If the required effective spot diameter of the LED <NUM> could be reduced, such a reduction would be advantageous for increasing the degree of freedom in design, reducing costs, and reducing the size of the device.

It is an object of the present invention to provide an optical rotary encoder provided with a fixed slit plate in which is formed a slit pattern that is suitable for being disposed within the range of an effective spot of detection light, the optical rotary encoder being advantageous for improving the degree of freedom in design, reducing costs, and reducing the size.

It is also an object of the present invention to provide a servo motor into which this new optical rotary encoder is incorporated, and an actuator configured from a reducer and a motor into which this new optical rotary encoder is incorporated.

In order to solve the abovementioned problems, an optical rotary encoder of the present invention is characterized in being provided with.

The shape of an effective spot of detection light emitted from an LED or other light-emitting element is typically round. If the number of detection tracks increases, the slit rows of the slit pattern in the fixed slit plate also increase in number, and therefore the size of the light-emitting element in the direction in which the slit rows are lined up increases. In the present invention, the first slit rows, which have a small length, are disposed on both sides in the direction in which the slit rows are lined up. It is possible for the entirety of the slit pattern to be fitted within the range of a smaller effective spot than is the case when the long second slit rows are disposed on both sides in the direction in which the slit rows are lined up. This makes it possible to use an LED or other light-emitting element having a smaller size, and is advantageous for reducing the size of the optical rotary encoder.

Embodiments of an optical rotary encoder to which the present invention is applied are described below with reference to the accompanying drawings.

<FIG> is a schematic diagram showing a summarized configuration of a transmissive optical rotary encoder according to the present embodiment. The optical rotary encoder <NUM> is provided with a light-emitting element <NUM>, a rotating disc <NUM>, a fixed slit plate <NUM>, and a light-receiving element <NUM>. In the present example, an LED is used as the light-emitting element <NUM>. The rotating disc <NUM> is attached to a rotating shaft <NUM> to be measured and rotates integrally with the rotating shaft <NUM>. The light-emitting element <NUM> and the light-receiving element <NUM> are disposed at fixed positions and face each other, in a direction of the rotational center axis 3a of the rotating disc <NUM>, so as to sandwich the rotating disc <NUM>. The fixed slit plate <NUM> is disposed between the light-receiving element <NUM> and the rotating disc <NUM>.

<FIG> is a schematic diagram showing detection tracks in the rotating disc <NUM>, a slit pattern in the fixed slit plate <NUM>, and a light-receiving-surface pattern on the light-receiving element <NUM>, and <FIG> is an enlarged view of the same portion. Detection light <NUM> emitted from the light-emitting element <NUM> impinges perpendicularly on the rotating disc <NUM>, and the plurality of detection tracks formed in the rotating disc <NUM> are irradiated with the detection light <NUM>. In the present example, six detection tracks <NUM>-<NUM> are formed concentrically about the rotational center of the rotating disc <NUM>. Two outer-peripheral-side detection tracks <NUM>, <NUM> are Vernier-scale signal detection tracks in which, e.g., <NUM> rectangular slits 11a, 12a are formed at regular angular intervals. Two detection tracks <NUM>, <NUM> on the inner side of the aforementioned detection tracks <NUM>, <NUM> are main signal detection tracks in which, e.g., <NUM> rectangular slits 13a, 14a are formed at regular angular intervals. Two rotational-center-side detection tracks <NUM>, <NUM> are correction signal detection tracks in which, e.g., <NUM> rectangular slits 15a, 16a having the same shapes (same width and same length) are formed at regular angular intervals. The slits 11a-16a are parts formed in the rotating disc <NUM> that either fully or partially transmit light.

A slit pattern formed from six slit rows <NUM>-<NUM> is formed in the fixed slit plate <NUM>, correspondingly with respect to the detection tracks <NUM>-<NUM>. The slit rows <NUM>-<NUM> are lined up in the radial direction y of the rotating disc <NUM> (the direction in which the slit rows are lined up). The slit rows <NUM>-<NUM> are respectively configured from a pair of slits 21a, a pair of slits 22a, a pair of slits 23a, a pair of slits 24a, a pair of slits 25a, and a pair of slits 26a, the pairs of slits 21a-26a being disposed at regular intervals in the circumferential direction x of the rotating disc <NUM> (the direction in which the slits are arranged). The slits 21a-26a are parts that either fully or partially transmit light and that have the same shapes (rhombuses in the present example).

The detection light <NUM> with which the detection tracks <NUM>-<NUM> are irradiated forms a round effective spot 7a as an effective irradiation region on the surface of the rotating disc <NUM>. The detection light <NUM> that has passed through the slits 11a-16a in the detection tracks <NUM>-<NUM> positioned within the range of the effective spot 7a becomes optical signals respectively corresponding to the detection tracks <NUM>-<NUM>, and the fixed slit plate <NUM> is irradiated with the optical signals. The optical signals that have passed through the slit pattern in the fixed slit plate <NUM> are received by light-receiving surfaces 5a of the light-receiving element <NUM>.

In <FIG>, the solid circle indicates the effective spot 7a, the empty rectangles indicate the slits 11a-16a in the six detection tracks <NUM>-<NUM> formed in the rotating disc <NUM>, the gray rhombuses indicate the slits 21a-26a in the six slit rows <NUM>-<NUM> formed in the fixed slit plate <NUM>, and the rectangles marked with diagonal lines indicate the light-receiving surfaces 5a of the light-receiving element <NUM>.

In the fixed slit plate <NUM>, the slits 21a (first slits) in one slit row <NUM> among the slit rows <NUM>, <NUM> for generating Vernier-scale signals are arranged at a narrow first angular interval p1 in the circumferential direction x (direction in which slits are arranged). An A-phase signal is generated from an optical signal obtained via one slit 21a, and a B-phase signal is generated from an optical signal obtained via the other slit 21a, in association with rotation of the rotating disc <NUM>. The slits 22a (second slits) in the slit row <NUM> are arranged at a wide second angular interval p2 and are offset from the slits 21a by a prescribed angle in the circumferential direction x (direction in which slits are arranged), whereby an A-phase inverted signal is generated from an optical signal obtained via one slit 22a, and a B-phase inverted signal is generated from an optical signal obtained via the other slit 22a.

The slit rows <NUM>, <NUM> for generating main signals are also configured in a similar manner. The slits 23a (first slits) in the slit row <NUM> are arranged at the first angular interval p1, and two-phase signals having an A phase and a B phase are generated. The slits 24a (second slits) in the slit row <NUM> are arranged at the second angular interval p2, and an A-phase inverted signal and a B-phase inverted signal are generated.

However, in the slit rows <NUM>, <NUM> for generating correction signals, the slits 25a (second slits) in the slit row <NUM>, which is positioned on the outer side in the radial direction y, are arranged at the wide second angular interval p2 in the circumferential direction x. The slits 26a (first slits) in the other slit row <NUM> are arranged at the narrow first angular interval p1 in the circumferential direction x. As described below, inter alia, the wiring on the light-receiving-element <NUM> side is changed so as to adopt a configuration in which two-phase signals having an A phase and a B phase are generated from an optical signal obtained from the slits 25a in the slit row <NUM>, and in which an A-phase inverted signal and a B-phase inverted signal are obtained from an optical signal obtained from the slits 26a in the slit row <NUM>.

A light-receiving-surface pattern on the light-receiving element <NUM> includes twelve light-receiving surfaces 5a, correspondingly with respect to the slits 21a-26a. Optical signals received by the light-receiving surfaces 5a are converted to electrical signals and are then supplied to a signal processing unit <NUM>. In the signal processing unit <NUM>, a main signal formed from two sets of two-phase signals, a Vernier-scale signal formed from two sets of two-phase signals, and a correction signal formed from two sets of two-phase signals are generated through well-known signal processing.

In the slit pattern in the fixed slit plate <NUM> of the optical rotary encoder <NUM> in the present example, the pair of slits 21a and the pair of slits 26a in the slit rows <NUM>, <NUM> that are respectively positioned at the outer end and the inner end in the radial direction y (direction in which slit rows are lined up) are each arranged at the narrow first angular interval p1. All of the slits 21a, 26a thereby fit within the range of the round effective spot 7a of the detection light <NUM>. In the case of the slit patterns in the fixed slit plate <NUM> shown in <FIG>, it is necessary to use an LED <NUM> that has an effective spot <NUM> having a larger diameter than the effective spot 7a so as to fit the slit patterns within the range of the effective spot. In the present example, it is possible to use a light-emitting element <NUM> having a smaller effective spot diameter.

In the present example, the slit patterns in the slit rows <NUM>, <NUM> in the fixed slit plate <NUM> are reversed with respect to those in the slit rows <NUM>, <NUM> and in the slit rows <NUM>, <NUM>. The slit rows are designed so that two-phase signals having an A phase and a B phase are generated from the slits having the narrow first angular interval p1, and so that inverted signals of these two-phase signals are generated from the slits having the wide second angular interval p2. In this case, the wiring should be changed so that the output from the light-receiving surfaces 5a that receive optical signals obtained via the slits 25a disposed at the wide second angular interval p2 and the output from the light-receiving surfaces 5a that receive optical signals obtained via the slits 26a disposed at the narrow first angular interval p1 are switched and then supplied to the signal processing unit <NUM>. Alternatively, if the light-receiving element is programmable, it is permissible to change only internal resistors (allocation of signals) without changing the signal wiring. Thus, it is easy to change the slit pattern in the fixed slit plate <NUM> and to fit the slits 21a-26a within the range of the effective spot 7a without changing the detection tracks <NUM>-<NUM> in the rotating disc <NUM>, the light-receiving-surface pattern in the light-receiving element <NUM>, etc..

The present invention can moreover be applied in a similar manner to a reflective optical rotary encoder. <FIG> shows a summarized configuration of a reflective optical rotary encoder. The basic configuration of the optical rotary encoder <NUM> is the same as that of a typical reflective optical rotary encoder. The optical rotary encoder <NUM> is provided with a light-emitting element <NUM>, a rotating disc <NUM>, a fixed mask <NUM>, and a light-receiving element <NUM>. The rotating disc <NUM> is attached to a rotating shaft to be measured (not shown) and rotates integrally with the rotating shaft. The light-emitting element <NUM> and the light-receiving element <NUM> are disposed at fixed positions and are disposed on the same side with respect to the rotating disc <NUM>. Detection light <NUM> emitted from the light-emitting element <NUM> is reflected by detection tracks 53a in the surface of the rotating disc <NUM>, the detection tracks 53a being formed from reflective zones that are arranged concentrically, and the reflected detection light <NUM> is received by light-receiving surfaces 55a of the light-receiving element <NUM> via a slit pattern 54a formed in the fixed mask <NUM>. The slit pattern formed in the fixed mask <NUM> is formed so that the slits fit within the range of an effective spot of the detection light reflected by the detection tracks 53a.

<FIG> is a schematic diagram showing a servo motor to which the present invention is applied. The servo motor <NUM> is provided with: a motor body part <NUM>; an encoder <NUM> for detecting rotation information such as the rotation position and the rotation speed of a motor output shaft <NUM>; and a motor control unit <NUM>. The optical rotary encoder <NUM>, <NUM> shown in <FIG> or <FIG> is used as the encoder <NUM>.

<FIG> is a schematic diagram showing one example of an actuator to which the present invention is applied. The actuator <NUM> is provided with: a motor <NUM>; a reducer <NUM> that reduces the speed of the output rotation of the motor <NUM> and then outputs said reduced-speed rotation; an encoder <NUM> that detects rotation information such as the rotation position and the rotation speed of an output shaft <NUM> of the reducer <NUM>; and a control unit <NUM>. The optical rotary encoder <NUM>, <NUM> shown in <FIG> or <FIG> is used as the encoder <NUM>.

There are cases where the slit patterns in the optical rotary encoder described above are formed through a Vernier-scale scheme. The present invention can be applied in a similar manner to an incremental-scheme optical rotary encoder provided with a plurality of slit rows having different numbers of slits, or to an optical rotary encoder in which a plurality of slit rows are formed in accordance with an M-serial arrangement pattern.

Claim 1:
An optical rotary encoder (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>) comprising:
a rotating disc (<NUM>; <NUM>; <NUM>) provided with a plurality of detection tracks (<NUM>-<NUM>) that are formed concentrically;
a light-emitting element (<NUM>; <NUM>; <NUM>) that irradiates the detection tracks (<NUM>-<NUM>) with detection light (<NUM>; <NUM>; <NUM>);
a fixed slit plate (<NUM>; <NUM>; <NUM>) provided with a slit pattern (54a; <NUM>) that allows passage of optical signals obtained from regions irradiated with the detection light (<NUM>; <NUM>; <NUM>) in each of the detection tracks (<NUM>-<NUM>); and
a light-receiving element (<NUM>; <NUM>; <NUM>) that receives each of the optical signals that have passed through the slit pattern (54a; <NUM>),
wherein each of the detection tracks (<NUM>-<NUM>) is configured from a plurality of slits or reflective zones arranged at regular angular intervals;
the slit pattern (54a; <NUM>) in the fixed slit plate (<NUM>; <NUM>; <NUM>) is configured from slit rows, the number of slit rows (<NUM>-<NUM>) corresponding to the number of detection tracks (<NUM>-<NUM>);
the slit rows (<NUM>-<NUM>) include a plurality of first slit rows (<NUM>, <NUM>, <NUM>) and a plurality of second slit rows (<NUM>, <NUM>, <NUM>), the first and second slit (<NUM>-<NUM>) rows being lined up in the radial direction (y) of the rotating disc (<NUM>; <NUM>; <NUM>);
the slits (21a, 23a, 26a) of the first slit rows (<NUM>, <NUM>, <NUM>) are arranged at an interval (p1) in the circumferential direction that is shorter than the interval (p2) of the second slit rows (<NUM>, <NUM>, <NUM>); and
the slit pattern (54a; <NUM>) is formed so that those slit rows (<NUM>, <NUM>) that are located at an innermost and at an outermost position in the radial direction (y) of the rotating disc (<NUM>) belong to the first slit rows (<NUM>, <NUM>, <NUM>), the radial direction (y) being a direction in which the slit rows (<NUM>-<NUM>) are lined up, and the slit pattern (54a; <NUM>) being positioned within an effective irradiation region of the detection light (<NUM>; <NUM>; <NUM>) in the fixed slit plate (<NUM>; <NUM>; <NUM>).