Optical encoder

An optical encoder comprising a light-receiving part having photodiodes equal in number to the common multiplier of a number of slits facing the light-receiving part and a number of movement information signals. Output terminals of the photodiodes are connected so that the movement information signals are respectively obtained by adding output signals of the plurality of photodiodes out of the photodiodes equal in number to the common multiplier. The twelve photodiodes are balancedly arranged corresponding to three slits and a light-receiving area of each photodiode is made smaller by subdiving each photodiode. The optical encoder suppress difference, distortion and variance of the movement information signals or the like obtained from the light-receiving part with the result that accurate movement information is obtained.

This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. P2003-289817 filed in Japan on Aug. 8, 2003, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to optical encoders which detect a position, moving speed, and moving direction of a moving body using a photodiode as a photodetector, and more particularly to an optical encoder which is suitable for uses including printing apparatuses such as printers and copiers, and factory automation equipment by way of an example.

An example of a conventional optical encoder will be described by way of the optical encoder disclosed in JP 2001-99684 A.

As shown inFIG. 10, the optical encoder is provided with a light-emitting part (not shown) and a light-receiving part302across a moving body301. The moving body301is provided with a plurality of slits305which are formed with a prescribed pitch and moves along a moving direction Z shown as arrow Z. The light-receiving part302receives lights which are emitted from the light-emitting part and transmitted through the slits305of the moving body301. The light-receiving part302is provided with a plurality of photodiode groups, each of which is composed of four photodiodes3061to3064. The photodiode groups arranged along the moving direction Z. The four photodiodes3061to3064face three slits305of the moving body301.

When the moving body301moves along the moving direction Z relative to the light-emitting part and the light-receiving part302, the light-receiving part302receives lights which are emitted from the light-emitting part and transmitted through the slits305and outputs four independent optical modulation signals, namely, movement signals A+, B+, A− and B− from four photodiodes3061,3062,3063and3064, respectively.

When the optical encoder reads movement information of the moving body301, the equal light quantity distribution on the light-receiving surface of the light-receiving part from a light source for the light-emitting part shown in property A ofFIG. 7is ideal. In this case, only the information of the moving body301is accurately read as an optical modulation signal.

In reality, however, lights which are incident on the light-receiving surface of the light-receiving part show a light quantity distribution like that in property B ofFIG. 7. Examples of the reasons for this distribution are light quantity distribution variance from the light source itself; light quantity distribution variance caused by a converging lens of the light source; diffraction and refracted lights caused by a moving body or the like; irregularities in positional relationship caused by assembly irregularities such as parallelism of the moving body to the light-receiving surface; irregularities in the slit sizes of the moving body; irregularities in the light source, the moving body and the light-receiving surface caused by staining and the like; and light receiving sensitivity variance caused by the variation of the moving speed of the moving body.

Therefore, a plurality of the movement information signals obtained from the light-receiving part are subject to factors such as DC voltage offset between signals, amplitude fluctuation of signals, signal waveform distortion, and phase distortion among signals, so that the movement information obtained is made inaccurate.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an optical encoder which suppresses factors such as difference, distortion and variance of the movement information signals obtained from the light-receiving part so as to obtain accurate movement information signals from a light-receiving part.

In order to achieve the above object, there is provided an optical encoder which comprises a moving body wherein light transmission areas and non-light transmission areas are alternately formed along a moving direction, a light-emitting part for emitting lights toward the moving body, and a light-receiving part for receiving lights emitted from the light-emitting part and transmitted through the light transmission areas and outputting movement information signals which represent the movement information of the moving body, wherein

the light-receiving part which is arranged so as to face a plurality of the light transmission areas, outputs a plurality of the independent movement information signals and comprises photodiodes equal in number to a common multiplier of a number of the light transmission areas facing the light-receiving part and a number of the independent movement information signals; and

output terminals of a plurality of the photodiodes are connected so that the plurality of the movement information signals are respectively obtained by adding output signals of the plurality of photodiodes out of the photodiodes equal in number to the common multiplier.

According to the optical encoder of the present invention, the light-receiving part is provided with photodiodes equal in number to the common multiplier of a number of the light transmission areas facing the light-receiving part and a number of the independent movement information signals. A plurality of output terminals of the photodiodes are connected so that a plurality of the movement information signals are respectively obtained by adding output signals of a plurality of photodiodes out of the photodiodes equal in number to the common multiplier.

Therefore, by arranging balancedly the common multiplier number of photodiodes corresponding to the light transmission areas and by subdiving each photodiode, a light-receiving area of each photodiode is made smaller, as compared with the case in which the light-receiving part has the same number of photodiodes as the number of movement information signals. As a result, factors such as difference, distortion and variance of the movement information signals obtained from the light-receiving part are suppressed and the resolution of the optical encoder is improved with the result that accurate movement information is obtained.

In one embodiment of the present invention, a size of the light transmission area of the moving body in a widthwise direction orthogonal to the moving direction and a size of the photodiode in the widthwise direction are made equal.

According to the present embodiment, the light quantity which each photodiode receives from each light transmission area is increased to maximum, with the result that the light receiving sensitivity is improved.

In one embodiment of the present invention, the photodiodes equal in number to the common multiplier have same sizes along the moving direction; and

each of the movement information signals is outputted by adding output signals of the photodiodes of a number which is obtained by dividing the common multiplier by a number of the independent movement information signals.

In the present embodiment, since the total area of the photodiodes corresponding to each movement information signal is equal to the area of the light-receiving surfaces corresponding to each movement information signal, the balance among movement information signals is maintained with the result that accurate movement information is obtained.

In one embodiment of the present invention, the optical encoder further comprises a plurality of the light-receiving parts having the photodiodes equal in number to the common multiplier. In the present embodiment, a plurality of movement information signals are outputted from each of the light-receiving parts, with the result that more accurate movement information is obtained.

In one embodiment of the present invention, the photodiodes provided for the light-receiving part are arranged along the moving direction; and

the plurality of the light-receiving parts are arranged along the widthwise direction. In the present embodiment, the photodiodes are arranged in two directions, namely, the moving direction and the widthwise direction, with the result that the accuracy of movement information is further improved.

In one embodiment of the present invention, at least two light-receiving parts of the plurality of the light-receiving parts, wherein

arrangement orders of the plurality of photodiodes for obtaining each of the movement information signals are different from each other.

In the present embodiment, the light quantity distribution variance to the photodiodes for obtaining each movement information signal is suppressed with the result that dispersion among movement information signals is suppressed.

In one embodiment of the present invention, a number of the light transmission areas facing each of the light-receiving parts is three, a number of the independent movement information signals is four, and each of the light-receiving parts comprises 12 photodiodes;

when the moving direction of the moving body is considered as a longitudinal direction and an arrangement pitch in the light transmission area is considered as one pitch, the 12 photodiodes are arranged along the longitudinal direction, having a length equal to one-sixth of the pitch respectively;

each of the light-receiving parts comprises three photodiode groups, each of which is composed of the four photodiodes, distance between each of the photodiodes in each of the photodiode groups is 1/12 of the pitch, in two adjacent photodiode groups, a photodiode in one photodiode group closest to the other photodiode group and a photodiode in the other photodiode group closet to the one photodiode group are adjoined at a pitch 5/12 of the pitch; and

four photodiodes in each of the photodiode groups respectively output output signals corresponding to four independent different movement information signals, and output one movement information signal by adding output signals of the three photodiodes corresponding to one movement information signal out of four movement information signals outputted from the three photodiode groups.

According to the present embodiment, each light-receiving part is provided with 12 photodiodes corresponding to three light transmission areas. Each of four movement information signals is obtained by adding the output signals from three photodiodes. Thus, by balancedly arranging the 12 photodiodes corresponding to the light transmission areas and by subdiving each photodiode, factors such as difference, distortion and variance of the movement information signals obtained from the light-receiving part are suppressed and the resolution of the optical encoder is improved with the result that accurate movement information is obtained.

In one embodiment of the present invention, four photodiodes of the three photodiode groups provided for each of the light-receiving parts comprises a first photodiode for outputting an output signal corresponding to a first movement information signal, a second photodiode for outputting an output signal corresponding to a second movement information signal, a third photodiode for outputting an output signal corresponding to a third movement information signal and a fourth photodiode for outputting an output signal corresponding to a fourth movement information signal; and

in each of the three photodiode groups in one light-receiving part out of two adjacent light-receiving parts, the first photodiode, the second photodiode, the third photodiode and the fourth photodiode are arranged along the moving direction in order, and in each of the three photodiode groups of the other light-receiving part out of two adjacent light-receiving parts, the third photodiode, the fourth photodiode, the first photodiode and the second photodiode are arranged along the moving direction in order.

According to the present embodiment, since the arrangement order of photodiodes corresponding to movement information signals is changed in the two adjacent light-receiving parts, the light quantity distribution variance to the photodiodes for obtaining each movement information signal is suppressed with the result that dispersion among movement information signals is suppressed.

In one embodiment of the present invention, a number of the light transmission areas facing the light-receiving part is three, a number of the independent movement information signals is four, and the light-receiving part comprises 24 photodiodes;

when the moving direction of the moving body is considered as a longitudinal direction and an arrangement pitch in the light transmission area is considered as one pitch, the 24 photodiodes are arranged along the longitudinal direction, having a length equal to 1/12 of the pitch respectively;

the light-receiving part comprises eight photodiode groups each of which is composed of the three photodiodes, and the three photodiodes in each of the photodiode groups arranged at a pitch 1/12 of the pitch;

the eight photodiode groups is composed of the first to the eighth photodiode groups arranged along the moving direction in order;

a pitch between the first photodiode group and the second photodiode group, a pitch between the third photodiode group and the fourth photodiode group, a pitch between the fifth photodiode group and the sixth photodiode group and a pitch between the seventh photodiode group and the eighth photodiode group are 1/12 of the pitch;

a pitch between the second photodiode group and the third photodiode group, a pitch between the fourth photodiode group and the fifth photodiode group, and a pitch between the sixth photodiode group and the seventh photodiode group are one-sixth of the pitch; and

three photodiodes in each of the photodiode groups respectively output output signals corresponding to different movement information signals from one another, and output one movement information signal by adding output signals of six photodiodes corresponding to one movement information signal out of four movement information signals outputted from the eight photodiode groups.

According to the present embodiment, the light-receiving part is provided with 24 photodiodes corresponding to three light transmission areas. Each of four movement information signals is obtained by adding output signals from six photodiodes. Thus, by balancedly arranging the 24 photodiodes corresponding to the light transmission areas and by subdiving each photodiode, factors such as difference, distortion and variance of the movement information signals obtained from the light-receiving part are suppressed and the resolution of the optical encoder is improved with the result that accurate movement information is obtained.

In one embodiment of the present invention, a number of the light transmission areas facing the light-receiving part is two, a number of the independent movement information signals is four, and the light-receiving part comprises eight photodiodes;

when the moving direction of the moving body is considered as a longitudinal direction and an arrangement pitch in the light transmission area is considered as one pitch, the eight photodiodes are arranged along the longitudinal direction, having a length equal to a quarter of the pitch respectively;

the light-receiving part comprises two photodiode groups each of which is composed of the four photodiodes, and the four photodiodes in each of the photodiode groups arranged at a ¼ of the pitch;

in two adjacent photodiode groups, a photodiode in one photodiode group closest to the other photodiode group and a photodiode in the other photodiode group closet to the one photodiode group are adjoined at a half of the pitch;

four photodiodes in each of the photodiode groups respectively output output signals corresponding to four independent different movement information signals, and output one movement information signal by adding output signals of two photodiodes corresponding to one movement information signal out of four movement information signals outputted from the two photodiode groups.

According to the present embodiment, the light-receiving part is provided with eight photodiodes corresponding to two light transmitting areas. Each of four movement information signals is obtained by adding output signals from two photodiodes. Thus, by balancedly arranging the eight photodiodes corresponding to the light transmission areas and by subdiving each photodiode, factors such as difference, distortion and variance of the movement information signals obtained from the light-receiving part are suppressed and the resolution of the optical encoder is improved with the result that accurate movement information is obtained.

In one embodiment of the present invention, four photodiodes of the two photodiode groups provided for each of the light-receiving parts are composed of a first photodiode for outputting an output signal corresponding to a first movement information signal, a second photodiode for outputting an output signal corresponding to a second movement information signal, a third photodiode for outputting an output signal corresponding to a third movement information signal and a fourth photodiode for outputting an output signal corresponding to a fourth movement information signal; and

in each of the two photodiode groups of one light-receiving part out of two adjacent light-receiving parts, the first photodiode, the second photodiode, the third photodiode and the fourth photodiode are arranged along the moving direction in order, and in each of the two photodiode groups of the other light-receiving part out of two adjacent light-receiving parts, the third photodiode, the fourth photodiode, the first photodiode and the second photodiode are arranged along the moving direction in order.

According to the present embodiment, since the arrangement order of photodiodes corresponding to movement information signals is changed in the two adjacent light-receiving parts, the light quantity distribution variance to the photodiodes for obtaining each movement information signal is suppressed with the result that dispersion among movement information signals is suppressed.

In one embodiment of the present invention, the moving body is of disk shape wherein light transmission areas of sectorial shape and non-light transmission areas of sectorial shape are circumferentially and alternately formed, and the moving direction is circumferential;

a profile of the photodiodes provided for the light-receiving part is made sectorial shape so as to be matched with the light transmission areas of sectorial shape.

According to the present embodiment, the optical encoder is provided with the light-receiving part having photodiodes of sectorial shape, facing light transmission areas of sectorial shape, which are provided for the moving body of disk shape moving circumferentially. As a result, the movement information signals of the moving body are effectively obtained.

In one embodiment of the present invention, additional photodiodes for detecting information other than movement information of the moving body are arranged between the photodiodes provided for the light-receiving part.

According to the present embodiment, information other than the movement information is obtained using signals outputted from additional photodiodes.

In one embodiment of the present invention, the additional photodiodes for detecting information other than movement information of the moving body are arranged between the photodiodes provided for the light-receiving part, and movement information is obtained by adding output signals of the additional photodiodes to output signals outputted from the photodiodes provided for the light-receiving part.

According to the present embodiment, the additional photodiodes provided for the optical encoder make it possible to correct the movement information using the output signals outputted from the additional photodiodes.

In one embodiment of the present invention, a plurality of photodiodes provided for the light-receiving part are formed on a semiconductor chip; and

cross under resistors under wiring for electrically connecting the plurality of the photodiodes are provided which are intersected with the wiring, and the cross under resistors are made by impurity diffusion in the semiconductor chip.

According to the present embodiment, the optical encoder is provided with a cross under resistor made by impurity diffusion, which prevents the wiring from electrically connecting with photodiodes not intended to be electrically connected, and desired photodiodes can be electrically connected with each other via the wiring.

In one embodiment of the present invention, a device includes the above optical encoder. Thus, the movement information signals which accurately represent the movement information of the moving body are obtained.

According to the optical encoder of the present invention, the light-receiving part is provided with photodiodes equal in number to the common multiplier of a number of light transmission areas facing the light-receiving part and a number of the independent movement information signals. The plurality of the output terminals of the photodiodes are connected so that the plurality of the movement information signals are respectively obtained by adding the output signals of the plurality of the photodiodes out of the photodiodes equal in number to the common multiplier. Therefore, by arranging balancedly the common multiplier number of photodiodes corresponding to the light transmission areas and by subdiving each photodiode, a light-receiving area of each photodiode is made smaller, as compared with the case in which the light-receiving part has the same number of photodiodes as the number of movement information signals. As a result, factors such as difference, distortion and variance of the movement information signals obtained from the light-receiving part are suppressed and the resolution of the optical encoder is improved with the result that accurate movement information is obtained.

Accordingly, as shown in this present invention, by subdividing a photodiode as a photodetector, the balance among each of the movement information signals is made better by means of arranging a plurality of photodiodes corresponding to a plurality of movement information signals in various locations. Thus, this good balance advantageously reduces variance of each optical encoder product. As shown in the present invention, by subdividing a photodiode as a photodetector, the resolution of the optical encoder is advantageously improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention will be described in further detail by way of preferred embodiments with reference to the accompanying drawings.

First Embodiment

FIG. 1shows a first embodiment of the optical encoder according to the present invention.

The optical encoder of the first embodiment includes a moving body101, a light-emitting part100and a light-receiving part102shown in region B ofFIG. 1. The light-emitting part100and the light-receiving part102are arranged so as to face each other across the moving body101. By way of an example, the light-emitting part100is composed of components such as a light-emitting diode.

The moving body101is provided with slits105, which are formed with a prescribed pitch P as a plurality of light transmission areas. The moving body101moves, relative to the light-emitting part100and the light-receiving part102, along the direction in which the plurality of the slits105are arranged. Lights emitted from the light-emitting part are transmitted through the slits105of the moving body101toward the light-receiving part102, but are blocked off by parts103which are arranged between the slits105as non-light transmission areas. The moving body101moves along a moving direction Z shown inFIG. 1.

In the first embodiment, an optical encoder is provided with the light-receiving part102shown in region B ofFIG. 1instead of the light-receiving part104shown in region A ofFIG. 1as a comparative example.

First, the comparative example is described. The light-receiving part104of the comparative example is composed of (n) photodiodes106with a light-receiving surface having a length equal to one-half of the pitch P. The photodiodes106are arranged along the moving direction Z at intervals of one-fourth of the pitch P ((n) represents a positive integer). The above mentioned length denotes a size of the light-receiving surface in the moving direction Z. By way of example, the light-receiving part104is formed on one semiconductor chip. In the light-receiving part104, an output signal is independently taken from each of the photodiodes106according to a light quantity received from the light-emitting part through the moving body101. Namely, the light-receiving part104obtains (n) independent output signals, which are movement information signals, from (n) photodiodes106facing the (m) slits105((m) represents a positive integer).

On the other hand, the light-receiving part102provided for the optical encoder of the present embodiment, as shown in region B ofFIG. 1, is composed of (k) photodiodes108arranged along the moving direction ((k) represents a common multiplier of the (n) and the (m)). By way of example, the light-receiving part102is formed on one semiconductor chip. The light-receiving part102faces the (m) slits105. Namely, the light-receiving part102is provided with (k)/(n) times as many photodiodes108as the photodiodes provided for the light-receiving part104of the comparative example. The output terminals of the (k) photodiodes108are connected to one another so as to obtain (n) independent output signals, which are movement information signals, from the light-receiving part102.

The connections among the output terminals is now described. In the above example in which the following values are assigned: n=4, m=3, k=12, the light-receiving part102corresponds to a light-receiving part102A, which is boxed with a dashed line inFIG. 1. The light-receiving part102A is composed of12photodiodes108. Among the12photodiodes108, output terminals of four photodiodes10811,10812,10813and10814are commonly connected, and output terminals of two photodiodes10821and10822are commonly connected. Also, output terminals of four photodiodes10831,10832,10833and10834are commonly connected, and output terminals of two photodiodes10841and10842are commonly connected.

In the light-receiving part102A, a first movement information signal is obtained by adding the output signals from the output terminals of the four photodiodes10811to10814, and a second movement information signal is obtained by adding the output signals from the output terminals of the two photodiodes10821and10822. Also, a third movement information signal is obtained by adding the output signals from the output terminals of the four photodiodes10831to10834, and a fourth movement information signal is obtained by adding the output signals from the output terminals of the two photodiodes10841and10842.

As shown in region B ofFIG. 1, the photodiodes10811to10814have a light-receiving surface with a length equal to one-eighth of the pitch P, and the photodiodes10821and10822have a light-receiving surface with a length equal to one-fourth of the pitch P. Also, the photodiodes10831to10834have a light-receiving surface with a length equal to one-eighth of the pitch P, and the photodiodes10841and10842have a light-receiving surface with a length equal to one-fourth of the pitch P. The above mentioned length denotes a size of the light-receiving surface in the moving direction Z of the moving body101.

According to the first embodiment, the light-receiving part102is composed of (k) photodiodes108((k) represented a common multiplier of (n) and (m)), so as to obtain (n) independent movement information signals from the light-receiving part102which faces (m) slits105of the moving body1, when the moving body1moves along the moving direction Z. The output terminals of the (k) photodiodes108is connected so that the light-receiving part102outputs (n) independent movement information signals.

Namely, according to the optical encoder of the first embodiment, (n) photodiodes106of the light-receiving part104in the comparative example shown in region A ofFIG. 1are divided into (k) photodiodes so that (n) independent movement information signals are obtained from (k) output signals of the (k) photodiodes108. By increasing the number of photodiodes (n) to (k) for the same number (m) of slits, dispersion among (n) independent movement information signals obtained from the light-receiving part102can be further reduced, as compared with dispersion among the (n) independent movement information signals obtained from the light-receiving part104.

Distance between each of the photodiodes108is made smaller by increasing the number of the photodiodes108(n) to (k) for the same number (m) of slits. Since a light-receiving area of each of the photodiodes108is made smaller, difference in light quantity is more sensitively detected.

Though the light-receiving part102is composed of (k: common multiplier of (n) and (m)) photodiodes108in the first embodiment, the light-receiving part102may be composed of the photodiodes108of a number which is larger than (n) but not (k).

When the light-receiving part is composed of the photodiodes108of (k), which is a common multiplier of (m) the number of slits and (n) the number of the movement information signal independently obtained, each of the photodiodes10811to10814and10831to10834can conform to the same shape, and each of the photodiodes10841and10842and the photodiodes10821and10822can conform to the same shape, for example the light-receiving part102A shown in the area boxed with the dashed line inFIG. 1. Accordingly, the sum of light-receiving areas of the four photodiodes10811to10814, the sum of light-receiving areas of the two photodiodes10821and10822, the sum of light-receiving areas of the four photodiodes10831to10834, and the sum of light-receiving areas of the two photodiodes10841and10842are all made equal. As a result, the signal balance among the first to the fourth independent signals is advantageously maintained.

In the present embodiment, the sizes (in the lengthwise direction and in the orthogonal direction) of each of the photodiodes108are made equal. As a result, when the normal direction of the light-receiving surface is in parallel with an optical axis of the light-emitting part, the light-receiving surface is in parallel with openings of the slits105, and the light quantity distributed from the light-emitting part to each of the slits105corresponding to each of the photodiodes108is approximately uniform, then the balance among (n) movement information signals obtained from the light-receiving part102is maintained.

Also, the optical encoder may be provided with the light-receiving part110shown in region C ofFIG. 1instead of the light-receiving part102shown in region B ofFIG. 1. The light-receiving part110is provided with (k) photodiodes111, which are obtained by each of the photodiodes106provided for the light-receiving part104shown in region A being equally divided into (x) ((k) represents a common multiplier of (n): the number of movement information signals and (m): the number of slits, and (x) represents (k)/(n)). Accordingly, the length of the light-receiving surface each of the photodiodes111is one-(x)th of the length of the light-receiving surface of the photodiodes106. The output terminals of each of the photodiodes106are connected so that the light-receiving part110having the (k) photodiodes111outputs (n) independent movement information signals.

In an example in which the following values are assigned: (m)=3, (n)=4, (k)=12, the light-receiving part110corresponds to a light-receiving part110A and (x) the equal division number is 3, so that the light-receiving part110A is provided with 12 photodiodes111which are obtained by each of the four photodiodes106being equally divided into three. Accordingly, the length of the light-receiving surface of the photodiodes111is one-third of the length of the light-receiving surface of the photodiodes106. InFIG. 1, output terminals of three photodiodes11111,11112and11113are commonly connected, and output terminals of three photodiodes11141,11142and11143are commonly connected. Also, output terminals of three photodiodes11131,11132and11133are commonly connected, and output terminals of three photodiodes11121,11122and11123are commonly connected. The light-receiving part110outputs four independent movement information signals through the connections.

In the light-receiving part110, the balance is maintained among all signals outputted from the output terminals of the photodiodes111.

FIG. 11Ashows a signal waveform Ach which is obtained by operationally comparing between movement information signals A+ and A− corresponding to the first and the third movement information signals out of the first to the fourth independent movement information signals outputted from the light-receiving part104of comparative example shown in region A ofFIG. 1and amplifying, and a signal waveform Bch which is obtained by operationally comparing between movement information signals B+ and B− corresponding to the second and the fourth movement information signals and amplifying. A phase difference between the signal waveforms Ach and Bch shown inFIG. 11Ais 105.2 degrees, which is shifted approximately 15 degrees from the ideal phase difference of 90 degrees, and offset between channels is also large.

In contrast,FIG. 11Bshows a signal waveform Ach which is obtained by operationally comparing between movement information signals A+ and A− corresponding to the first and the third movement information signals out of the first to the fourth independent movement information signals outputted from the light-receiving part110and amplifying, and a signal waveform Bch which is obtained by operationally comparing between movement information signals B+ and B− corresponding to the second and the fourth movement information signals and amplifying. A phase difference between the signal waveforms Ach and Bch inFIG. 11Bis 93.2 degrees, which is shifted closer to the ideal phase difference of 90 degrees, and offset between channels is made smaller than the comparative example. Note that each of the numbers 1, 2, 3 and 4 written in the frame representing photodiodes inFIG. 1, represents each of the photodiodes corresponding to the first, the second, the third and the fourth movement information signals respectively.

In the first embodiment, a plurality of the light-receiving parts102or110may be arranged along the column direction (the moving direction of the moving body101) and along the row direction (in a direction orthogonal to the moving direction) so as to improve photosensitivity. One example in this case will be described in the following second embodiment.

Second Embodiment

Referring now toFIG. 2, there is shown a second embodiment of the optical encoder according to the present invention.

The optical encoder of the second embodiment includes a moving body121which is moving along a moving direction Z, a light-emitting part120and a light-receiving part122shown in region B ofFIG. 2. The light-emitting part120and the light-receiving part122are arranged so as to face each other across the moving body121. By way of an example, the light-emitting part120is composed of components such as a light-emitting diode.

The moving body121,is provided with a plurality of slits125which are formed with a prescribed pitch P. The slits125function as light transmission areas. The moving body121moves relative to the light-emitting part120and the light receiving part122, along a direction Z in which the plurality of slits125are arranged. Lights emitted from the light-emitting part are transmitted through the slits125of the moving body121toward the light-receiving part122, but are blocked off by parts123between the slits125as non-light transmission areas. The parts123function as non-light transmission areas.

In the second embodiment, the optical encoder is provided with the light-receiving part122shown in region B ofFIG. 2instead of a light-receiving part124shown in region A ofFIG. 2as a comparative example. The light-receiving part122is provided with a first light-receiving part127and a second light-receiving part128.

First, the comparative example is described. The light-receiving part124as the comparative example is provided with eight photodiodes12611,12621,12631,12641,12612,12622,12632and12642. The eight photodiodes126are arranged along the moving direction Z at piches of three-fourths of the pitch P. Each of the photodiodes126has a light-receiving surface with a length equal to one-half of the pitch P. The length here denotes a size of the light-receiving surface in the moving direction Z. By way of example, the light-receiving part124is formed on one semiconductor chip. In the light-receiving part124, output terminals of the photodiodes12611and12612are connected, and a first movement information signal A+ is outputted by adding the output signals from the photodiodes12611and12612. Output terminals of the photodiodes12621and12622are connected, and a second movement information signal B+ is outputted by adding the output signals from the photodiodes12621and12622. Output terminals of the photodiodes12631and12632are connected, and a third movement information signal A− is outputted by adding the output signals of the photodiodes12631and12632. Output terminals of the photodiodes12641and12642are connected, and a fourth movement information signal B− is outputted by adding the output signals of the photodiodes12641and12642.

On the other hand, the light-receiving part122of the second embodiment is provided with the first light-receiving part127and the second light-receiving part128as shown in region B ofFIG. 2.

The first light-receiving part127is provided with 12 photodiodes130, whose number is three times as many as four movement information signals to be taken out independently. Each of the photodiodes130has a length equal to one-sixth of the pitch P. Namely, each of the photodiodes130has a length equal to one-third of the length of the photodiodes126. The first light-receiving part127is also provided with three photodiode groups127a,127band127c.

The photodiode group127ais provided with four photodiodes13011,13021,13031and13041. The four photodiodes13011to13041are arranged along the moving direction at the pitch being a quarter of the pitch P. The photodiode group127bis provided with four photodiodes13012,13022,13032and13042. The four photodiodes13012to13042are arranged along the moving direction at the pitch being a quarter of the pitch P. The photodiode group127cis provided with four photodiodes13013,13023,13033and13043. The four photodiodes13013to13043are arranged along the moving direction at the pitch being a quarter of the pitch P. The photodiodes13041and13012are arranged at the pitch being 5/12 of the pitch P, and the photodiodes13042and13013are at the pitch being 5/12 of the pitch P.

An output terminal of the photodiode13011of the photodiode group127a,an output terminal of the photodiode13012of the photodiode group127band an output terminal of the photodiode13013of the photodiode group127care connected. Output terminals of the photodiodes13021,13022and13023are connected. Output terminals of the photodiodes13031,13032and13033are connected. Output terminals of the photodiodes13041,13042and13043are connected.

Thus, in the first light-receiving part127, a first movement information signal generated by adding the output signals of the three photodiodes13011to13013and a second movement information signal generated by adding the output signals of the three photodiodes13021to13023are obtained. A third movement information signal generated by adding the output signals of the three photodiodes13031to13033and a fourth movement information signal generated by adding the output signals of the three photodiodes13041to13043are also obtained.

The second light-receiving part128is provided with 12 photodiodes131, whose number is three times as many as four movement information signals to be taken out independently. Each of the photodiodes131has a length equal to one-sixth of the pitch P. Accordingly each of the photodiodes131has a length equal to one-third of the length of the photodiodes126. The second light-receiving part128is also provided with three photodiode groups128a,128band128c.

The photodiode group128ais provided with four photodiodes13031,13041,13011and13021. The four photodiodes13031to13021are arranged along the moving direction at the pitch being a quarter of the pitch P. The photodiode group128bis provided with four photodiodes13032,13042,13012and13022. The four photodiodes13032to13022are arranged along the moving direction at the pitch being a quarter of the pitch P. The photodiode group128cis provided with four photodiodes13033,13043,13013and13023. The four photodiodes13033to13023are arranged along the moving direction at the pitch being a quarter of the pitch P. The photodiodes13021and13032are arranged at the pitch being 5/12 of the pitch P, and the photodiodes13022and13033are arranged at the pitch being 5/12 of the pitch P.

An output terminal of the photodiode13111of the photodiode group128a,an output terminal of the photodiode13112of the photodiode group128band an output terminal of the photodiode13113of the photodiode group128care connected. Output terminals of the photodiodes13121,13122and13123are connected. Output terminals of the photodiodes13131,13132and13033are connected. Output terminals of the photodiodes13141,13142and13143are also connected.

Thus, in the second light-receiving part128, a first movement information signal A+ which is added by the output signals of the three photodiodes13111to13013and a second movement information signal B− which is added by the output signals of the three photodiodes13121to13123are obtained. A third movement information signal A− which is added by the output signals of the three photodiodes13131to13133and a fourth movement information signal B+ which is added by the output signals of the three photodiodes13141to13143are also obtained.

Wiring is connected so that the first movement information signal A+ in the first light-receiving part127and the first movement information signal A+ in the second light-receiving part128are added. A first movement information signal A+ of the light-receiving part122is outputted by adding the two first movement information signals A+. In a similar process, a second movement information signals B− of the light-receiving part122is outputted by adding the second movement information signal B− in the first light-receiving part127and the second movement information signal B− in the second light-receiving part128are added. A third movement information signal A− of the light-receiving part122is outputted by adding the third movement information signal A− in the first light-receiving part127and the third movement information signal A− in the second light-receiving part128. A fourth movement information signal B+ of the light-receiving part122is outputted by adding the fourth movement information signal B+ in the first light-receiving part127and the fourth movement information signal B+ in the second light-receiving part128.

Referring now toFIG. 8, signal waveforms of the four movement information signals A+, A−, B+ and B− are illustrated which are outputted from the light-receiving part124in the comparative example when the moving body121moves along the moving direction Z.FIG. 8Ashows the moving body121.FIG. 8Bshows signal waveforms of the movement information signals A+ and A−.FIG. 8Cshows signal waveforms of the movement information signals B+ and B−. Although the phases of the movement information signal A+ and the movement information signal A− should be inverted to each other precisely at 180°, the phases of the movement information signal A+ and the movement information signal A− are not inverted precisely at 180°, with the result that phase shift is generated as shown inFIG. 8B. Although the movement information signals B+ and B− should be shifted relative to the movement information signal A+ at 90° and 270° respectively, phase shifts from optimum phases are generated as shown inFIG. 8C. The phase shifts are generated due to a large dispersion among signals outputted from each of the photodiodes126. The amplitudes among the movement information signals are also fluctuated due to the above dispersion, with the result that offset of each movement information signal is generated. Since the resolution of the movement information obtained by each of the photodiodes126is low, a signal waveform of each movement information signal is deformed.

In contrast, the light-receiving part122of the second embodiment is provided with photodiodes130and131into which the photodiode126in the light-receiving part124in the comparative example are subdivided. In the light-receiving part122, the phase difference between a signal waveform of the movement information signal A+ and a signal waveform of the movement information signal A− is precisely 180° as shown inFIG. 9B. The movement information signal B+ is made into phase difference precisely at 90° to the movement information signal A+, and the movement information signal B− is made into phase difference precisely at 270° to the movement information signal A+ as shown inFIG. 9C. In the light-receiving part122, fluctuation in amplitude and offset among the movement information signals practically disappeared. In addition, a trapezoidal wave is obtained as a signal waveform of each movement information signal, with the result that a highly exact signal processing is conducted. Therefore, highly exact movement information is obtained.

In the second embodiment, the arrangement orders of photodiodes corresponding each of the movement information signals (A+, B−, A− and B+) are varied between the first light-receiving part127and the second light-receiving part128as shown in region B ofFIG. 2. Specifically, in each of the photodiode groups127ato127cof the first light-receiving part127, a photodiode corresponding to the first movement information signal A+, a photodiode corresponding to the second movement information signal B−, a photodiode corresponding to the third movement information signal A− and a photodiode corresponding to the fourth movement information signal B+ are arranged in order. In each of the photodiode groups128ato128cof the second light-receiving part128, a photodiode corresponding to the third movement information signal A−, a photodiode corresponding to the fourth movement information signal B+, a photodiode corresponding to the first movement information signal A+ and a photodiode corresponding to the second movement information signal B− are arranged in order. The arrangement orders of photodiodes corresponding each of the movement information signals (A+, B−, A− and B+) are thus varied between the first light-receiving part127and the second light-receiving part128, so that the light quantity variance distributed to each photodiodes is suppressed with the result that dispersions of light quantity balance or the like are suppressed.

A third light-receiving part which has the same constitution as the first light-receiving part127may be arranged on the right neighbor of the second light-receiving part128, and a fourth light-receiving part which has the same constitution as the second light-receiving part128may be further arranged on the right neighbor of the third light-receiving part. In a similar manner, a prescribed number of light-receiving parts which have the same constitutions as the first light-receiving part127and the second light-receiving part128may be alternately arranged.

Third Embodiment

Referring now toFIG. 3, there is shown a third embodiment of the optical encoder according to the present invention. In the third embodiment, the optical encoder is provided with a light-emitting part150, a light-receiving part152shown in region B ofFIG. 3and a moving body151which moves along a moving direction Z relative to the light-emitting part150and the light-receiving part152. The light-emitting part150and the light-receiving part152are arranged so as to face each other across the moving body151. By way of an example, the light-emitting part150is composed of components such as a light-emitting diode.

The moving body151is provided with a plurality of slits155which are formed with a prescribed pitch P. The slits155function as light transmission areas. The moving body151moves along the direction Z in which the plurality of the slits155are arranged. Lights emitted from the light-emitting part are transmitted through the slits155of the moving body151toward the light-receiving part152, but the lights are blocked off by parts153between the slits155. The parts153function as non-light transmission areas. The moving body151has the same constitution as the moving body101shown inFIG. 1.

In the third embodiment, the optical encoder is provided with the light-receiving part152shown in region B ofFIG. 3instead of a light-receiving part154shown in region B ofFIG. 3as a comparative example. The light-receiving part154as the comparative example is provided with photodiodes106which are the first to the fourth photodiodes from the left in the light-receiving part104shown in region A ofFIG. 1.

As shown in region B ofFIG. 3, the light-receiving part152provided for the optical encoder of the present embodiment outputs corresponding to three slits155four independent movement signals, namely, a first movement information signal A+, a second movement information signal B+, a third movement information signal A− and a fourth movement information signal B−. The light-receiving part152is provided with24photodiodes160, equal in number to the common multiplier (k) of (m=3) the number of the slits and (n=4) the number of the movement information signals.

Namely, the length of the photodiodes160of the light-receiving part152in the moving direction Z is one-sixth of the length of the photodiodes106, and the width of the photodiodes160is equal to the width of the photodiodes106. The light-receiving part152is composed of eight photodiode groups152ato152hwhich are arranged in the longitudinal direction (the moving direction Z) and each of the photodiode groups152ato152his respectively composed of three photodiodes which are arranged in the longitudinal direction.

InFIG. 3, the first photodiode group152afrom the left is composed of three photodiodes16031,16021and16011, which are arranged at the pitch being 1/12 of the pitch P and adjoined each other with no gap. The second photodiode group152bis composed of three photodiodes16022,16012and16041, which are arranged at the pitch being 1/12 of the pitch P and adjoined each other with no gap. The third photodiode group152cis composed of three photodiodes16042,16032and16023, which are arranged at the pitch being 1/12 of the pitch P and adjoined each other with no gap.

The fourth photodiode group152dis composed of three photodiodes16033,16043and16013, which are arranged at the pitch being 1/12 of the pitch P and adjoined each other with no gap. The fifth photodiode group152eis composed of three photodiodes16034,16024and16014, which are arranged at the pitch being 1/12 of the pitch P and adjoined each other with no gap.

The sixth photodiode group152fis composed of three photodiodes16044,16035, and16025, which are arranged at the pitch being 1/12 of the pitch P and adjoined each other with no gap. The seventh photodiode group152gfrom the left is composed of three photodiodes16026,16015and16045, which are arranged at the pitch being 1/12 of the pitch P and adjoined each other with no gap. The eighth photodiode group152hfrom the left is composed of three photodiodes16016,16046and16036, which are arranged at the pitch being 1/12 of the pitch P and adjoined each other with no gap.

In the light-receiving parts152, the pitch between the photodiode16011of the first photodiode group152aand the photodiode16022of the second photodiode group152bis made equal to one-sixth of the pitch P. The pitch between the photodiode16041of the second photodiode group152band the photodiode16042of the third photodiode group152cis made equal to a quarter of the pitch P.

Similarly, the pitch between the photodiode16023of the third photodiode group152cand the photodiode16033of the fourth photodiode group152dis made equal to one-sixth of the pitch P. The pitch between the photodiode16013of the fourth photodiode group152dand the photodiode16034of the fifth photodiode group152eis made equal to a quarter of the pitch P.

The pitch between the photodiode16014of the fifth photodiode group152eand the photodiode16044of the sixth photodiode group152fis made equal to one-sixth of the pitch P. The pitch between the photodiode16025of the sixth photodiode group152fand the photodiode16026of the seventh photodiode group152gis made equal to a quarter of the pitch P. The pitch between the photodiode16045of the seventh photodiode group152gand the photodiode16016of the eighth photodiode group152his made equal to one-sixth of the pitch P.

Six output terminals of the photodiodes16011to16016are connected so as to output the first movement information signal A+. Six output terminals of the photodiodes16021to16026are connected so as to output the second movement information signal B+. Six output terminals of the photodiodes16031to16036are connected so as to output the third movement information signal A−. Six output terminals of the photodiodes16041to16046are connected so as to output the fourth movement information signal B−.

Thus, the light-receiving part152of the third embodiment is provided with24photodiodes160, which are obtained by each of the four photodiodes106of the light-receiving part154shown in region A being equally divided into six. Dispersion among the four independent output signals A+, B+, A− and B− obtained from the light-receiving part152is reduced, as compared with dispersion among the four independent output signals A+, B+, A− and B− obtained from the light-receiving part154by having subdivided photodiodes160and increasing the number of photodiodes (n=4) to (k=24) to be arranged for the same number (m=3) of slits.

Distance between each of the photodiodes160is consequently made smaller by increasing the number of the photodiodes160from four to 24 to be arranged for the same number (m=3) of slits. Since the light-receiving area of each of the photodiodes160is made smaller, difference in light quantity is sensitively detected.

According the third embodiment, in each of the photodiode groups152ato152h,three photodiodes160are adjoined each other with no gap so that there is no place for a separation part, which may cause photoelectric current between adjacent photodiodes. On the other hand, distance between each of the photodiodes is made smaller as compared with the second embodiment, so that dispersion among the four movement information signals is further made smaller and the balance among amplitudes and phases or the like of the four movement information signals is maintained.

In order to provide a separation part between each photodiode, as shown in region C ofFIG. 1, photodiodes are equally divided into the least common multiple of (n) and (m) ((n) is the number of the movement information signals independently obtained and (m) is the number of the slits).

Fourth Embodiment

Referring now toFIG. 4, there is shown a fourth embodiment of the optical encoder according to the present invention.

In the fourth embodiment, the optical encoder is provided with a light-emitting part170, a light-receiving part172shown in region B ofFIG. 4and a moving body170which moves along a moving direction Z relative to the light-emitting part171and the light-receiving part172. The light-emitting part and the light-receiving part172are arranged so as to face each other across the moving body171. By way of an example, the light-emitting part170is composed of components such as a light-emitting diode.

The moving body171is provided with a plurality of slits175which are formed with a prescribed pitch P. The slits175function as light transmission areas. The moving body171moves along the direction Z in which the plurality of slits175are arranged. Lights emitted from the light-emitting part are transmitted through the slits175of the moving body171toward the light-receiving part172, but the lights are blocked off by parts173between the slits175. The parts173function as non-light transmission areas. The moving body171has the same constitution as the moving body101shown inFIG. 1.

In the fourth embodiment, the optical encoder is provided with the light-receiving part172shown in region B ofFIG. 4instead of a light-receiving part174shown in region A ofFIG. 4as a comparative example. The light-receiving part174as the comparative example is provided with photodiodes106which are the first to the fourth photodiodes from the left in the light-receiving part104shown in region A ofFIG. 1.

As shown in region B ofFIG. 4, the light-receiving part172in the fourth embodiment is provided with a first light-receiving part173and a second light-receiving part174which are arranged along the longitudinal direction (the moving direction Z).

The first light-receiving part173and the second light-receiving part174, each of which is corresponding to two slits175, output four independent movement signals, namely, a first movement information signal A+, a second movement information signal B+, a third movement information signal A− and a fourth movement information signal B−. The light-receiving part173is provided with eight photodiodes180equal in number to the common multiplier (k) of (m=2) the number of the slits and (n=4) the number of the movement information signals. Similarly, the second light-receiving part174is provided with eight photodiodes181.

The length of each of the photodiodes180and181is equal to a quarter of P and a half of the photodiode106. The width of each of the photodiodes180and181is equal to the width of the photodiodes106. Namely, each of the photodiodes180and181is corresponding to one-half of the photodiode106.

The first light-receiving part173is composed of photodiode groups173aand173bwhich are arranged along the longitudinal direction (the moving direction Z) The photodiode group173ais composed of photodiodes18011,18041,18031and18021which are arranged along the longitudinal direction (the moving direction Z). The photodiode group173bis composed of photodiodes18012,18042,18032and18022which are arranged along the longitudinal direction (the moving direction Z).

In the photodiode group173a,four photodiodes18011to18021are arranged at the pitch being a quarter of the pitch P. In the photodiode group173b,four photodiodes18012to18022are arranged at the pitch being a quarter of the pitch P.

The photodiode18021of the photodiode group173aand the photodiode18012of the photodiode group173bare arranged at the pitch being a half of the pitch P.

In the first light-receiving part173, output terminals of the photodiodes18011and18012are connected so as to output a first movement information signal A+, and output terminals of the photodiodes18021and18022are connected so as to output a second movement information signal B+. Output terminals of the photodiodes18031and18032are connected so as to output a third movement information signal A−, and output terminals of the photodiodes18041and18042are connected so as to output a fourth movement information signal B+.

The second light-receiving part174is composed of photodiode groups174aand174bwhich are arranged along the longitudinal direction (the moving direction Z) The photodiode group174ais composed of photodiodes18131,18121,18111and18141which are arranged along the longitudinal direction (the moving direction Z). The photodiode group174bis composed of photodiodes18132,18122,18112and18142which are arranged along the longitudinal direction (the moving direction Z).

In the photodiode group174a,four photodiodes18031to18041are arranged at the pitch being a quarter of the pitch P. In the photodiode group174b,four photodiodes18032to18042are arranged at the pitch being a quarter of the pitch P.

The photodiode18041of the photodiode group174aand the photodiode18032of the photodiode group174bare arranged at the pitch being a half of the pitch P.

In the second light-receiving part174, output terminals of the photodiodes18111and18112are connected so as to output a first movement information signal A+, and output terminals of the photodiodes18121and18122are connected so as to output a second movement information signal B+. Output terminals of the photodiodes18131and18132are connected so as to output a third movement information signal A−, and output terminals of the photodiodes18141and18142are connected so as to output a fourth movement information signal B+.

According to the fourth embodiment, dispersion among the four independent output signals A+, B+, A− and B− which are outputted from the first light-receiving part173and the second light-receiving part174shown in region A, is reduced by providing each of subdivided photodiodes180and181in the light-receiving part172shown in region B as compared with each of the photodiodes106of the light-receiving part174. In the present embodiment, distance between each of the photodiodes is consequently made smaller and a light-receiving area of each of the photodiodes is also made smaller, so that difference in light quantity is sensitively detected.

In the present embodiment, each of the photodiodes180in the first light-receiving part173are arranged corresponding each of the movement information signals (A+, B−, A− and B+) and each of the photodiodes181in the second light-receiving part174are arranged corresponding each of the movement information signals (A−, B+, A+ and B−). The arrangement orders of photodiodes corresponding each of the movement information signals are thus varied between the first light-receiving part173and the second light-receiving part174, so that the light quantity variance distributed to each photodiodes is suppressed with the result that dispersions of light quantity balance or the like are suppressed.

As shown inFIG. 4, a third light-receiving part which has the same constitution as the first light-receiving part173may be arranged on the right neighbor of the second light-receiving part174, and a fourth light-receiving part which has the same constitution as the second light-receiving part174may be further arranged on the right neighbor of the third light-receiving part. In a similar manner, a prescribed number of light-receiving parts which have the same constitutions as the first light-receiving part and the second light-receiving part may be alternately arranged.

According the fourth embodiment, in each of the photodiode groups173a,173b,174aand174b,four photodiodes180and181are adjoined each other with no gap so that there is no place for a separation part, which may cause photoelectric current between adjacent photodiodes. On the other hand, distance between each of the photodiodes is made smaller as compared with the above two embodiments, so that dispersion among the four movement information signals is further made smaller and the balance among amplitudes and phases of the four movement information signals or the like is maintained.

The optical encoder is provided with a greater number of subdivided photodiodes as compared with the comparative example, as shown in the first to fourth embodiments, in which (m), the number of the slits, provided for the moving body is effectively chosen based on a balance among factors such as a quantity of lights received from the light source of the light-emitting part. The number of the slits is also effectively subdivided corresponding to (n), the number of the movement information signals. The slits are effectively arranged appropriately based on the optical characteristics and properties of the photodiodes.

The profile of the slits of the moving body is preferably matched with the profile of the photodiodes in order to obtain movement information of the moving body. When the moving body is of disk shape and the slits are of sectorial shape, the photodiodes are preferably of sectorial shape.

As shown in region B ofFIG. 5, the light-receiving part127shown in region B ofFIG. 2may be provided with dummy photodiodes (non-activated photodiodes) in remaining parts D1to D11between each of the photodiodes130, regarding a semiconductor chip on which each of the photodiodes130is formed. In this case, interference due to signals of each of the photodiodes130sneaking into another signal is prevented by absorbing electrons generated by photoelectric conversion in each of the photodiodes130using the dummy photodiodes D1to D11. When the dummy photodiodes are electrically grounded, the signals are further prevented from sneaking into another signal. These dummy photodiodes may be employed for the light-receiving part110shown in region C ofFIG. 1and the light-receiving part152shown in region B ofFIG. 3.

It would be further effective if photodiodes formed in remaining parts D1to D11shown inFIG. 5are utilized not only as dummy photodiodes but also for detecting information other than movement information of the moving body including slit positions of the moving body, light quantity distribution, parallel beams, distance between a slit and a photodiode.

For example, if it is difficult to subdivide photodiodes in the forming process of photodiodes in the light-receiving part of the optical encoder of the first to the fourth embodiment, a part of the photodiodes can be advantageously used as the dummy photodiodes. Photodiodes are separated by a metal film for blocking off lights and P-type impurity diffusion. Lights are prevented from sneaking using the above two method. Other effective methods to separate photodiodes include trench separation using a polycrystalline silicon film and oxide film separation.

To form the photodiodes, a method using an epitaxial film and impurity diffusion and a method using a semiconductor substrate and an epitaxial film are preferably employed.

In the case of the photodiodes formed using a semiconductor substrate and an epitaxial film, more photocurrent is obtained by shielding the photodiodes using impurity diffusion. Reflection of lights is suppressed and more photocurrent is obtained by forming an antireflection film on the photodiodes.

Cross under resistors R1to R12, as shown inFIG. 6, may be formed on a semiconductor chip on which each of the subdevided photodiodes130of the light-receiving part127shown in region B ofFIG. 5is formed. The cross under resistors R1to R12are formed by diffusing impurities in crosshatched parts in extended areas E1to E12from each of the photodiodes13011to13043in the widthwise direction shown inFIG. 6.

A non-diffusion part of the extended areas E1and a non-diffusion part of the extended areas E5are electrically connected in a connecting part L1, and a non-diffusion part of the extended areas E5and a non-diffusion part of the extended areas E9are electrically connected in a connecting part L5. As a result, the first movement information signal A+ is outputted from the non-diffusion parts in each of the extended areas E1, E5and E9, which is the sum of output signals from the three photodiodes13011,13012and13013.

A non-diffusion part of the extended areas E2and a non-diffusion part of the extended areas E6are electrically connected in a connecting part L2, and a non-diffusion part of the extended areas E6and a non-diffusion part of the extended areas E10are electrically connected in a connecting part L6. As a result, the second movement information signal B− is outputted from the non-diffusion parts in each of the extended areas E2, E6and E10, which is the sum of output signals from the three photodiodes13021,13022and13023.

A non-diffusion part of the extended areas E3and a non-diffusion part of the extended areas E7are electrically connected in a connecting part L3, and a non-diffusion part of the extended areas E7and a non-diffusion part of the extended areas E11are electrically connected in a connecting part L7. As a result, the third movement information signal A− is outputted from the non-diffusion parts in each of the extended areas E3, E7and E11, which is the sum of output signals from the three photodiodes13031,13032and13033.

A non-diffusion part of the extended areas E4and a non-diffusion part of the extended areas E8are electrically connected in a connecting part L4, and a non-diffusion part of the extended areas E8and a non-diffusion part of the extended areas E12are electrically connected in a connecting part L8. As a result, the third movement information signal B+ is outputted from the non-diffusion parts in each of the extended areas E4, E8and E12, which is the sum of output signals from the three photodiodes13041,13042and13043.

Thus, the constitution shown inFIG. 6allows the first to the fourth independent movement information signals being the sum of the three output signals to be taken from various locations with the result the light-receiving part127is easily connected to a circuit of the subsequent stages.

In each of the above embodiments, the balance among light quantities which contribute to the movement information signals to be obtained independently is maintained by arranging the photodiodes provided for the light-receiving part symmetrically with respect to the light source provided for the light-receiving part. The light source of the light-receiving part contains a collimating lens with the result that lights are condensed and parallel beams are emitted, which is useful for obtaining accurate movement information. The optical encoder of each of the above embodiments is suitable for uses such as printing apparatuses and a light sensor for factory automation equipment.