JP2012013654A - Absolute encoder and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and inexpensive absolute encoder with a detection accuracy that varies depending on a measurement position.SOLUTION: An absolute encoder that detects an absolute position of a measurement object includes: a scale unit that is configured to be movable with the measurement object and that includes a first track having first slits and a second track having second slits; first detection means that detects a first signal obtained from the first slits; second detection means that detects a second signal obtained from the second slits; and operation means that performs vernier operation using the first signal and the second signal. An interval of the second slits varies depending on a position in a movement direction of the scale unit.

Description

  The present invention relates to an absolute encoder that detects an absolute position of an object to be measured.

  Conventionally, as an apparatus for measuring the movement distance of an object, an absolute encoder capable of measuring an absolute position is known in addition to an incremental encoder that measures a relative movement distance. For example, Patent Document 1 discloses a configuration of a scale unit used in an absolute encoder. The scale portion is provided with two tracks on which reflection patterns having different arrangement periods are formed. In this absolute encoder, a position detection method called a vernier that obtains a predetermined periodic signal by relatively driving the scale unit and the sensor unit unit and calculating a phase difference between a plurality of periodic signals having two different periods. Is used. Then, absolute position information is obtained using this periodic signal.

Japanese Patent Publication No. 1-47052

  However, in the absolute encoder disclosed in Patent Document 1, the displacement amount of the vernier phase is constant without depending on the position of the scale portion. On the other hand, there are systems that require different detection schemes depending on the location. However, when trying to increase the absolute position detection accuracy at a predetermined measurement position, it is necessary to improve the accuracy of the absolute encoder as a whole, which has been a factor in increasing the size and cost of the absolute encoder.

  In order to improve the detection accuracy of the absolute position, it is conceivable to change the displacement amount of the vernier phase with respect to the position change by increasing the number of periods of the signal obtained by the vernier calculation means in the entire scale length. However, in this case, it is necessary to improve the accuracy of the signal (upper signal) for synchronizing with the signal obtained by the vernier calculation means.

  Therefore, the present invention provides a small and inexpensive absolute encoder having different detection accuracy depending on the measurement position.

  An absolute encoder as one aspect of the present invention is an absolute encoder that detects an absolute position of an object to be measured, and is configured to be movable together with the object to be measured, and includes a first track and a second slit having a first slit. A scale section having a second track, first detection means for detecting a first signal obtained from the first slit, and second detection means for detecting a second signal obtained from the second slit. Calculating means for performing vernier calculation using the first signal and the second signal, and the interval between the second slits differs according to the position of the scale portion in the moving direction.

  Other objects and features of the present invention are illustrated in the following examples.

  According to the present invention, it is possible to provide a small and inexpensive absolute encoder having different detection accuracy depending on the measurement position.

It is a perspective view which shows the structure of the absolute encoder in 1st Embodiment. It is sectional drawing of the absolute encoder in 1st Embodiment. It is a top view of the scale part in a 1st embodiment. It is a top view of the main components of the detection head in a 1st embodiment. It is a block diagram of the signal processing circuit part in 1st Embodiment. It is a figure which shows the processing block and processing flow of signal processing in 1st Embodiment. It is explanatory drawing about the correction method of the signal in 1st Embodiment. It is explanatory drawing about the synchronization guarantee of the absolute position information detection in 1st Embodiment. It is a top view of the scale part in 2nd Embodiment. It is a top view of the main components of the detection head in a 2nd embodiment. It is a figure which shows the processing block and processing flow of signal processing in 2nd Embodiment. It is explanatory drawing about the synchronization guarantee of the absolute position information detection in 2nd Embodiment. It is a top view of the scale part in 3rd Embodiment. It is a figure which shows the processing block and processing flow of signal processing in 3rd Embodiment. It is explanatory drawing about the synchronization guarantee of the absolute position information detection in 3rd Embodiment. It is sectional drawing of the imaging device in 4th Embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same members are denoted by the same reference numerals, and redundant description is omitted.
(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a perspective view showing a configuration of an absolute encoder 100 according to this embodiment, and FIG. 2 is a cross-sectional view of the absolute encoder 100 as viewed from the X-axis direction. The absolute encoder 100 detects the absolute position of the object to be measured. The scale unit 2 having a two-track pattern having a different length and a different number of slits is fixed to a moving object to be measured, and is configured to be movable together with the object to be measured in the X-axis direction that is the lattice arrangement direction. The sensor unit unit 7 is disposed to face the scale unit 2. The sensor unit section 7 includes a light source 1 composed of an LED chip, semiconductor elements 3, 8 composed of a photo IC chip incorporating two light receiving sections 9, 10 having a photodiode array, and a signal processing circuit section, and mounting them. And the printed circuit board 4 and the like. The light source 1 and the semiconductor elements 3 and 8 are sealed with a resin 5, and the resin 5 is covered with a transparent glass substrate 6. In the present embodiment, it is preferable to use the same semiconductor element as the two semiconductor elements 3 and 8 in order to share parts and reduce costs. Therefore, in the present embodiment, the semiconductor elements 3 and 8 are described as being configured using the same semiconductor element, but the present invention is not limited to this, and different semiconductor elements may be used.

  Next, an absolute position detection algorithm in this embodiment will be described. FIG. 3 is a plan view of the scale portion in the present embodiment, FIG. 3A is an overall configuration diagram of the scale portion, and FIG. 3B is an enlarged view of a part thereof. In FIG. 3, a reflective slit pattern is shown as an example. The scale part 41 is constituted by a glass substrate, and two tracks are formed on the glass substrate by patterning the chromium reflecting film. As a substrate constituting the scale portion 41, other materials such as silicon can be used besides glass. Moreover, you may use things other than a flat material like a thin film. The reflective film may be formed using a material other than chromium.

  The scale unit 41 includes two tracks, a first track 42 and a second track 43. The scale unit 41 is divided into at least two regions (region 1 and region 2) according to the position in the movement direction of the scale unit 41 (position in the X-axis direction). In the first track 42, slits 44 (first slits) that are reflection patterns are formed at intervals P1 in both the region 1 and the region 2. In the second track 43, slits 45 (second slits) are formed at the interval P2 in the region 1, and slits 46 (second slits) are formed at the interval P3 in the region 2. In this embodiment, as described above, the area of the scale unit 41 is divided into two areas (area 1 and area 2), and the relationship between the intervals is P2> P3> P1. In the present embodiment, the scale portion 41 has eight differences in the number of slits between the first track 42 and the second track 43. As described above, the interval between the slits 45 and 46 (second slits) differs depending on the position of the scale unit 2 in the moving direction (position in the X-axis direction). More specifically, the second slits are slits arranged at the first interval (interval P2) in the first region (region 1), and the second interval (interval P3) in the second region (region 2). ). On the other hand, the interval between the slits 44 (first slits) is equal in the moving direction of the scale unit 2.

  The light emitted from the light source 1 is applied to the scale portion 41 on which a two-track reflection pattern (slit) is formed. The light irradiated to the first track 42 in which the slit 44 is formed and the second track 43 in which the slits 45 and 46 are formed are reflected, respectively, and the light receiving unit 9 (first sensor) and the light receiving unit 10 (second sensor). Is incident on. The light receiving unit 9 is a first detection unit that detects a signal (first signal) obtained from the slit 44 (first track 42). The light receiving unit 10 is a second detection unit that detects a signal (second signal) obtained from the slits 45 and 46 (second track 43). Based on the amount of light received by the light receiving unit 9 or the amplitude of the signal obtained from the light receiving unit 9, the reflected light from the first track 42 incident on the light receiving unit 9 is subjected to APC (auto power control) to receive light. The amount of light incident on the unit 9 or the signal amplitude of the light receiving unit 9 is kept constant. With such a configuration, it is possible to make it less susceptible to changes over time such as fluctuations in the amount of light from the light source.

  FIG. 4 is a plan view of the main components of the detection head in the present embodiment. As shown in FIG. 4, semiconductor elements 3 and 8 are arranged in the vicinity of the light source 1. The semiconductor element 3 includes a light receiving region 24 and a signal processing circuit unit 25 disposed on the side close to the light source 1. The semiconductor element 8 includes a light receiving region 26 and a signal processing circuit unit 27 disposed on the side close to the light source 1. The signal processing circuit units 25 and 27 are calculation means for performing vernier calculation using the first signal and the second signal. In addition, you may comprise the high-order control apparatus (not shown) of the signal processing circuit parts 25 and 27 as a calculating means which performs a vernier calculation.

  In the light receiving region 24, 16 photodiodes 24a, 24b, 24c, 24d,..., 24m, 24n, 24o, 24p are arranged at equal intervals in the horizontal direction. Similarly, 16 photodiodes 26a, 26b, 26c, 26d,..., 26m, 26n, 26o, and 26p are arranged at equal intervals in the light receiving region 26 in the horizontal direction. The photodiodes 24a, 24e, 24i, and 24m (photodiodes 26a, 26e, 26i, and 26m) are electrically connected, and this set is referred to as a phase. Further, a set of photodiodes 24b, 24f, 24j, and 24n (photodiodes 26b, 26f, 26j, and 26n) is defined as a b-phase. Hereinafter, similarly, it is set as c phase and d phase. When receiving light, each of the a-phase, b-phase, c-phase, and d-phase photodiode groups outputs a photocurrent corresponding to the amount of light. As the scale portion 2 moves in the X direction, the a-phase to d-phase photodiode group varies with a phase relationship of 90 degrees for the b-phase, 180 degrees for the c-phase, and 270 degrees for the d-phase. Current is output. In each of the signal processing circuit units 25 and 27, the output current is converted into a voltage value by the current-voltage converter, and then the differential components of the a phase and the c phase and the b phase and the d phase are respectively converted by the differential amplifier. A differential component is obtained, and A and B phase displacement output signals having a 90 ° phase shift are output.

  FIG. 5 is a configuration diagram of the signal processing circuit unit 25. A light emitting circuit 31 of the light source 1 (light emitting element) and an analog signal processing unit 32 are included. Based on the A and B phase analog signals from the analog signal processing unit 32, a position calculation unit 33 is provided that calculates the amount of movement of the scale unit 2 to obtain the position of the measurement object (measurement object). The first stage amplifiers 34, 35, 36, and 37 are I / V amplifiers for current-voltage conversion of the photocurrent generated in each of the a-phase, b-phase, c-phase, and d-phase photodiode groups, and the potential of Vf1 is changed. As a reference, potentials V1, V2, V3, and V4 are generated. From the a-phase and c-phase photodiode groups, an A-phase signal (VA) having Vf2 as a bias potential is obtained by a differential output amplifier 38 that obtains the difference between the outputs V1 and V3. Similarly, the outputs V2 and V4 are differentially amplified by the differential output amplifier 39 from the b-phase and d-phase photodiode groups to obtain a B-phase signal (VB). The signal processing circuit unit 27 has a similar configuration.

  FIG. 6 is a diagram showing a processing block and a processing flow of signal processing in the present embodiment. FIG. 7 is an explanatory diagram of a signal correction method according to this embodiment. FIG. 8 is an explanatory diagram for guaranteeing the synchronization of absolute position information detection in the present embodiment. Hereinafter, a signal processing method and a processing flow of absolute position information detection in the present embodiment will be described with reference to FIGS. 3 and 6 to 8.

  The A and B phase signals obtained from the first track 42 and the second track 43 may have different signal offsets and signal amplitudes as shown in FIG. If such a signal is used in an absolute position information detection algorithm as it is, it causes an error in the detected position, and thus signal correction 61 is required. Therefore, first, signal offset correction and signal amplitude correction (correction 61) for the A and B phases of the first track 42 and the second track 43 will be described.

  Hereinafter, a light receiving unit having the same configuration is used as the light receiving unit 9 and the light receiving unit 10, and the pitch of the four photodiodes in the light receiving unit (for example, the interval between 24a to 24d) is twice the pitch P1 of the first track 42. Will be described. The A-phase and B-phase signals obtained from the first track 42 are expressed by the following equations (1) and (2), respectively.

A phase signal: a1 × COSθ + s1 (1)
B phase signal: a2 × SINθ + s2 (2)
Here, a1 and s1 are the amplitude and offset of the A phase signal, a2 and s2 are the amplitude and offset of the B phase signal, respectively, and θ is the phase of the signal. The maximum value of the A-phase signal is a1 + s1, the minimum value is a1-s1, the signal amplitude is a1, and the average value is s1. Similarly, the maximum value of the B phase signal is a2 + s2, the minimum value is a2-s2, the signal amplitude is a2, and the average value is s2. When these values are used to correct the A-phase and B-phase signals represented by the equations (1) and (2), they are represented by the following equations (3) and (4), respectively.

A phase signal: {(a1 × COSθ + s1) −s1} × a2
= A1 × a2 × COSθ (3)
B phase signal: {(a2 × SINθ + s2) −s2} × a1
= A1 × a2 × SINθ (4)
As a result, the offsets of the A phase and B phase signals are removed, and signals 62 and 63 having the same signal amplitude are obtained (FIG. 7B). Based on the A-phase and B-phase output signals thus obtained, an arctangent value 64 is calculated.

  Next, signal correction of the second track 43 will be described. As shown in FIG. 3, the interval P1 (period) of the first track 42 and the interval P2 of the second track 43 in the region 1 are configured to be slightly different from each other, and from the phase difference between the interval P1 and the interval P2, The signal obtained by the vernier calculation means can be acquired. For example, if the interval P1 is 100 μm and the interval P2 is 120 μm, the period of the signal obtained by the vernier calculation means in the region 1 is 600 μm which is the least common multiple thereof. Further, the interval P1 between the first tracks 42 and the interval P3 between the second tracks 43 in the region 2 are also slightly different, and the signal obtained by the vernier calculating means is obtained from the phase difference between the intervals P1 and P3. can do. For example, if the interval P1 is 100 μm and the interval P3 is 110 μm, the period of the signal obtained by the vernier calculation means in the region 2 is 1100 μm.

Since the intervals P2 and P3 of the second track 43 are different from the interval P1 of the first track 42, the interval between the four photodiodes in the light receiving unit 10 (for example, the interval of 26a to 26d) is the same as that of the second track 43. It is not twice the intervals P2 and P3. For this reason, the A phase and B phase signals obtained from the second track 43 have a phase relationship shifted from 90 degrees in both the region 1 and the region 2.
Hereinafter, first, signal correction of the second track 43 in the region 1 will be described.

  The A-phase and B-phase signals obtained from the second track 43 are expressed by the following equations (5) and (6), respectively.

A phase signal: b1 × COSθ + t1 (5)
B phase signal: b2 × SIN (θ + α) + t2 (6)
Here, b1 and t1 are the amplitude and offset of the A phase signal, b2 and t2 are respectively the amplitude and offset of the B phase signal, θ is the phase of the signal, and α is the amount of phase shift. First, as in the case of the first track 42, when signal offset and amplitude correction processing is performed, the A-phase and B-phase signals are represented by the following equations (7) and (8), respectively. The

A phase signal: {(b1 × COSθ + t1) −t1} × b2
= B1 × b2 × COSθ (7)
B phase signal: {(b2 × SIN (θ + α) + t2) −t2} × b1
= B1 × b2 × SIN (θ + α) (8)
At this time, the offset of the A phase and B phase signals is removed, and a signal having the same signal amplitude is obtained (FIG. 7B).

  Next, processing for setting the phase difference between the A phase and the B phase to 90 degrees will be described using equations (7) and (8). The difference between the expressions (7) and (8) is expressed as the following expression (9).

b1 × b2 × (SIN (θ + α) −COSθ)
= B1 × b2 × 2 × SIN {(α−90) / 2} × COS {θ + (α + 90) / 2} (9)
Further, the sum of the expressions (7) and (8) is expressed as the following expression (10).

b1 × b2 × (SIN (θ + α) + COSθ)
= B1 × b2 × 2 × COS {(α−90) / 2} × SIN {θ + (α + 90) / 2} (10)
Thus, the phase difference between the equations (9) and (10) is 90 degrees (FIG. 7C).

  Here, since the amplitudes of the equations (9) and (10) are different, the amplitude is corrected next. Multiplying equation (9) by COS {(α−90) / 2}, which is a part of the amplitude of equation (10), and SIN {(α−90), which is a part of the amplitude of equation (9), by equation (10). 90) / 2}, the following equations (11) and (12) are obtained.

b1 × b2 × 2 × SIN {(α−90) / 2} × COS {(α−90) / 2} × COS {θ + (α + 90) / 2} (11)
b1 × b2 × 2 × SIN {(α−90) / 2} × COS {(α−90) / 2} × SIN {θ + (α + 90) / 2} (12)
As a result, the amplitude is corrected (FIG. 7 (d)). In this way, the offsets of the A-phase and B-phase signals are removed, the signal amplitudes are the same, and signals 72 and 73 that have been subjected to the signal amplitude correction after the 90-degree phase difference correction can be obtained. Up to this point, the correction 71 of the signal of the second track 43 in the region 1 has been described, but the correction of the signal of the second track 43 in the region 2 is performed in the same manner.

  The arctangent value 74 is calculated from the A-phase and B-phase output signals obtained by performing the above correction, as in the case of the first track. The difference between the arctan value 64 obtained from the A-phase and B-phase output signals of the first track 42 and the arctan value 74 obtained from the A-phase and B-phase output signals of the second track 43 is calculated. Thus, a signal 75 (middle signal) obtained by the vernier calculation means is obtained.

  FIG. 8 shows a case where the number difference between the first track 42 and the second track 43 is eight in the entire length of the scale portion. The horizontal axis represents the position of the scale portion, and the vertical axis represents the phase difference obtained by calculating the arctan of the signal obtained by the vernier calculation means obtained from the first track 42 and the second track 43, and is displayed folded by ± π rad.

  As shown in FIG. 3B, the pattern of the second track 43 is different in the area 1 and the area 2. For this reason, regarding the signal obtained by the vernier calculation means, the displacement amount of the vernier phase with respect to the relative position change between the sensor unit section 7 and the scale section 2 is different in each region. In the configuration shown in FIG. 3B, the displacement amount of the vernier phase with respect to the position change is larger in the region 1 than in the region 2. For this reason, when interpolation processing is performed with the same phase difference resolution in both regions, that is, when the position detection accuracy is viewed with the same phase difference accuracy, the region 1 can be detected with higher accuracy than the region 2.

  As shown in FIG. 3B, the interval P2 between the slits 45 in the region 1 in the second track 43 and the interval P3 between the slits 46 in the region 2 are the slits 47 ( It is switched before and after the third slit). As shown in FIG. 8, the signal obtained by the vernier calculation means (calculation means) also switches from + πrad to −πrad at the position of the slit 47 for switching between the areas 1 and 2. In other words, the slit 47 is arranged at the boundary between the region 1 and the region 2, and the displacement amount of the vernier phase calculated by the calculating means is different at the position of the slit 47. The width of the slit 45 in the region 1 in the second track 43 is, for example, P2 / 2 which is 1/2 of the interval P2 between the slits 45, and the width of the slit 46 in the region 2 is P3 / 2. Here, it is preferable that the width of the slit 47 for switching between the region 1 and the region 2 is set to P2 / 2 in accordance with the region 1 that enables highly accurate position detection. In this way, the signal 75 (intermediate signal) obtained by the vernier computing means having eight cycles over the entire length of the scale portion can be obtained with an accuracy according to the required accuracy due to the difference in measurement position.

  In the present embodiment, the area is divided into two, the relationship between the slits is P2> P3> P1, and the difference in the number of slits between the first track 42 and the second track 43 is eight. The case where a scale is used has been described. However, the present embodiment is not limited to this, and the number of regions may be three or more. When the number of areas is 3 or more, there is a switching pattern for each area switching. Moreover, the structure which satisfy | fills P2 <P3 <P1 may be sufficient as the relationship of the space | interval of each slit. Further, the difference in the number of slits between the first track 42 and the second track 43 is not limited to eight, and any difference between two or more can be applied.

  Next, the upper signal in the present embodiment will be described. The upper signal in the present embodiment obtains an output value based on the scale position as shown in FIG. 8 using the upper signal acquisition sensor (upper signal acquisition 81). Here, as a kind of sensor for higher order signal acquisition, for example, a brush integrally attached to an object (object to be measured) for position detection is slid on a substrate on which a resistance pattern is printed. There is a configured volume encoder. As the upper signal acquisition sensor, another sensor capable of detecting the position, such as a potentiometer, may be used. The upper signal may be any signal as long as an output value based on the scale position can be obtained. However, from the viewpoint of making the synchronization accuracy with the signal obtained by the vernier calculation means uniform, as shown in FIG. 8, the relationship obtained by the vernier calculation means is proportional to the displacement amount of the vernier phase with respect to the position change. It is preferable to make such a signal. The proportionality constant of this relationship is preferably constant without depending on the position of the scale portion. Absolute position detection (absolute position synthesis and acquisition 83 of absolute position information) is performed by synchronizing the upper signal 82 obtained in this way with the signal obtained by the vernier calculation means.

  In this embodiment, a reflection type absolute encoder is used, but a transmission type absolute encoder can also be used.

As described above, according to this embodiment, it is possible to provide a small and inexpensive absolute encoder having different detection accuracy depending on the measurement position. In addition, by performing auto power control based on the amount of light received by the first sensor or the amplitude of the signal, it is possible to provide a high-accuracy absolute encoder that suppresses the influence of changes over time such as fluctuations in the amount of light from the light source. .
(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. FIG. 9 is a plan view of a scale portion used in the absolute encoder in this embodiment, FIG. 9A is an overall configuration diagram of the scale portion, and FIG. 9B is an enlarged view of a part thereof. FIG. 10 is a plan view of the main components of the detection head in this embodiment. FIG. 11 is a diagram showing a processing block and a processing flow of signal processing in the present embodiment. FIG. 12 is a diagram for explaining synchronization guarantee for absolute position information detection in the present embodiment.

  In the present embodiment, the scale unit 41a is configured by three tracks, and the sensor unit unit is also configured by a light receiving region 28 that receives reflected light from the corresponding three track scale and a signal processing circuit unit 29 thereof. A semiconductor element 11 is further provided. In the present embodiment, the signal 75 (intermediate signal) obtained from the first track 42 and the second track 43 is obtained by the same method as in the first embodiment. Further, the upper signal is acquired using the first track 42 and the third track 48. The first track 42 and the third track 48 are configured so that the difference in the number of slits is one. Similar to the first embodiment, the scale portion 41a is divided into at least two regions according to the position of the scale portion 41a in the moving direction. In the first track 42, slits 44 (reflection patterns) are formed at the interval P1. In the third track 48, the slits 49 in the region 1 are formed at the interval P4, and the slits 50 in the region 2 are formed at the interval P5.

  Hereinafter, a method for acquiring a higher order signal, which is a part different from the first embodiment, will be described. In the present embodiment, the area of the scale portion is divided into two, the relationship between the intervals of the respective slits is P4> P5> P1, and the difference in the number of slits of the first track 42 and the third track 48 is 1. It is a book. As shown in FIG. 9B, the scale unit of the present embodiment is configured such that the slit (pattern) interval is switched before and after the pattern 51 for switching between the region 1 and the region 2. The interval P1 (period) of the first track 42 and the interval P4 of the third track 48 in the region 1 are configured to be slightly different, and a signal obtained by the vernier calculating means is acquired from the phase difference between the interval P1 and the interval P4. be able to. The interval P1 between the first tracks 42 and the interval P5 between the third tracks 48 in the region 2 are also slightly different, and the signal obtained by the vernier computing means is obtained from the phase difference between the intervals P1 and P5. Can do.

  The interval P4 between the slits 49 in the third track 48 and the interval P5 between the slits 50 are different from the interval P1 between the slits 44 in the first track 42. For this reason, the interval between the four photodiodes existing in the light receiving region 28 of the semiconductor element 11 (for example, the interval between 28a to 28d and 28m to 28p) is not twice the interval P4 and P5 in the third track. For this reason, the A-phase and B-phase signals obtained from the third track 48 have a phase relationship shifted from 90 degrees in both the regions 1 and 2.

  Therefore, in the present embodiment, the signal obtained from the third track 48 is also corrected by the same method as the signal correction of the second track 43 in the first embodiment. By performing the correction process 91 for the offset and amplitude of the signal and the 90-degree phase difference, the offsets of the A-phase and B-phase signals are removed, the signal amplitude becomes the same, and the signal 92 and the signal 93 have the phase difference of 90 degrees. Is obtained. Based on the A-phase and B-phase output signals obtained by performing the above correction, the arctan value 94 is calculated as in the case of the second track in the first embodiment. Then, by calculating the difference between the arctan value 64 obtained from the A-phase and B-phase output signals of the first track and the arctan value 94 obtained from the A-phase and B-phase output signals of the third track, A signal 95 (upper signal) obtained by the vernier calculation means is obtained.

  Note that, based on the same concept as in the first embodiment, the upper signal is preferably a signal that is proportional to the amount of displacement of the vernier phase (middle signal) with respect to the position change, as shown in FIG. . By synchronizing the respective signals based on the signal 95 obtained by the vernier calculation means obtained in this way and the signal 75 obtained by the same method as in the first embodiment (absolute position synthesis), The absolute position information 96 of the scale part is calculated.

As described above, according to the absolute encoder of the present embodiment, it is possible to acquire the upper signal using the same semiconductor element as that used for acquiring the intermediate signal without using a dedicated sensor for acquiring the upper signal. .
(Third embodiment)
A third embodiment of the present invention will be described with reference to FIGS. FIG. 13 is a plan view of a scale portion used in the absolute encoder in the present embodiment, FIG. 13 (a) is an overall configuration diagram of the scale portion, and FIG. 13 (b) is a partially enlarged view thereof. FIG. 14 is a diagram showing a processing block and a processing flow of signal processing in the present embodiment. The configuration of the detection head is the same as that in the first embodiment. FIG. 15 is an explanatory diagram for guaranteeing the synchronization of absolute position information detection in the present embodiment.

  The signal 75 (intermediate signal) obtained from the first track and the second track is obtained by the same method as in the first embodiment. In the present embodiment, the upper signal is acquired using the second track 143. The second track 143 of the scale unit 141 includes a pattern that is missing at equal intervals in the width direction of the scale unit 141. The reflection area of the reflection part is configured to be modulated by the position of the scale part 141 in the moving direction. Note that the period of the omission does not have to be equal intervals, but is more preferably equal intervals in consideration of the uniformity of light reaching the photodiode. Further, when the distance from the light source to the scale portion is equal to the distance from the scale portion to the photodiode, it is preferable that the missing period is 1 / 2n of the width of the photodiode. Here, n is an integer.

The scale unit 141 is divided into at least two regions depending on the position of the scale unit 141 in the moving direction. In the first track 142, slits 144 (reflection patterns) are formed at the interval P1. The slits 145 in the region 1 in the second track 143 are formed at the interval P2, and the slits 146 in the region 2 are formed at the interval P3. Hereinafter, a method for acquiring the upper signal 102, which is a different part from the first embodiment, will be described. In this embodiment, the area of the scale portion 141 is divided into two, and the relationship between the slits is P2>P3> P1, and the difference in the number of slits between the first track 142 and the second track 143 is Eight. As shown in FIG. 13B, the scale unit 141 is configured so that the pattern interval is switched before and after the pattern 147 for switching between the region 1 and the region 2.
As shown in FIG. 14, the upper signal 102 performs calculation 101 of the root mean square of each value as the signal amplitude of the A phase signal and the B phase signal obtained from the second track 143 of the scale unit 141. Thus, the following equation (13) is obtained.

Here, the offsets of the A-phase and B-phase signals are removed, the signal amplitudes are the same, and the signals 72 and 73 that have been subjected to the signal amplitude correction after the 90-degree phase difference correction are the same as in the first embodiment. It is obtained by the method. Since the value of Expression (13) varies depending on the position of the scale portion, position information can be obtained based on the value obtained by Expression (13). The upper signal 102 is obtained by calculating the amplitude value using the equation (13) regardless of the signal acquisition position relationship between the sensor position and the track position. That is, the signal amplitude in the second track 143 can be calculated regardless of the phase states of the A-phase signal and the B-phase signal.

  As in the first embodiment, as shown in FIG. 15, the upper signal is preferably a signal that has a proportional relationship with the displacement amount of the vernier phase (middle signal) with respect to the position change. By synchronizing the respective signals based on the upper signal 102 obtained in this way and the signal 75 (middle signal) obtained by the same method as in the first embodiment (absolute position synthesis), The absolute position information 103 of the scale unit 141 can be calculated. In the present embodiment, the reflection pattern of the second track 143 in the scale portion 141 has a configuration in which the reflection area changes depending on the position. However, the present embodiment is not limited to this, and the same effect can be obtained even when a film whose reflectance changes according to the position is used. At this time, it is possible to change the reflectance by changing the density of the reflection film or changing the material of the reflection film.

As described above, according to the present embodiment, the absolute position information is acquired without providing the absolute information acquisition sensor, and therefore a small and low-cost absolute encoder can be provided. Further, the reflection pattern of the scale portion is configured by a pattern missing at equal intervals in the width (Y) direction of the scale portion or a uniform pattern in the width (Y) direction of the scale portion. For this reason, even if the relative position between the sensor unit 7 and the scale unit 2 fluctuates in the Y direction, the amount of light incident on the light receiving unit becomes substantially uniform, and an inexpensive light source such as an LED can be used without a lens. it can.
(Embodiment 4)
Next, a fourth embodiment of the present invention will be described with reference to FIG. The present embodiment relates to an imaging apparatus in which the absolute encoder of each of the above embodiments is mounted on a lens barrel. FIG. 16 is a cross-sectional view of the imaging apparatus 200 in the present embodiment. Reference numeral 201 denotes a lens group, 202 denotes a driving lens, 203 denotes a detection head of an absolute encoder for detecting displacement of the driving lens 202, 204 denotes a CPU, and 205 denotes an image sensor. The lens group 201, the driving lens 202, the CPU 204, and the imaging element 205 constitute an imaging unit.

  The drive lens 202 constituting the lens group 201 is, for example, an autofocus lens, and is movable in the optical axis direction. The drive lens 202 may be any other lens as long as it is driven, such as a zoom adjustment lens. In the present embodiment, the scale portion of the absolute encoder is held by an actuator that drives the drive lens 202 (not shown) and is movable relative to the detection head 203 of the absolute encoder. A signal corresponding to the displacement of the drive lens 202 obtained from the detection head 203 of the absolute encoder is output to the CPU 204. The CPU 204 generates a driving signal for moving the driving lens 202 to a desired position, and the driving lens 202 is driven based on the signal.

  In general, the driving lens has different optical sensitivity to displacement depending on its position. For this reason, the absolute encoder is set so that the second slit intervals (intervals P2, P3) differ according to the optical sensitivity to the displacement of the driving lens so that the displacement amount of the vernier phase with respect to this displacement increases. Is preferred.

  For example, when the drive lens is a zoom adjustment lens, it is generally designed such that the optical sensitivity to the lens position change is higher when the zoom adjustment lens is disposed on the telephoto side than on the close side. There are many cases. At this time, the absolute encoder has an interval between the second slits so that the displacement amount of the vernier phase with respect to the lens displacement increases on the telephoto side of the zoom adjustment lens and the displacement amount of the vernier phase with respect to the lens displacement decreases on the closest side. Is preferably different.

  With reference to FIG. 16 and FIG. 8, an example of a method for incorporating the absolute encoder into the imaging apparatus 200 will be described. In the absolute encoder and the imaging apparatus 200 on which the absolute encoder is mounted, there are often errors from design values when the absolute encoder is mounted on the imaging apparatus, such as individual differences due to manufacturing errors or assembling errors. If there is an error from the design value, it becomes an error of the signal obtained by the vernier calculation means, that is, a phase error, and the initial phase of the signal is shifted as shown in FIG. 8, so it is necessary to recognize this phase shift. is there.

  Therefore, in the present embodiment, when the absolute encoder is incorporated into the imaging apparatus 200, an apparatus that can detect the reference phase, such as a master encoder, by relatively driving the detection head 203 and the scale is used. A phase shift amount is calculated. That is, the absolute encoder is preferably configured to correct the actual measurement value using the phase shift amount detected when the absolute encoder is incorporated in the imaging apparatus. By correcting the absolute information obtained from the design value using the phase shift amount obtained from the above, imaging capable of absolute position detection with reduced effects of individual differences due to manufacturing errors and the incorporation error of absolute encoders, etc. An apparatus is provided. In addition, the absolute encoder of each embodiment can be applied to various apparatuses other than the imaging apparatus. For example, the present invention can be applied to detect the displacement of a stage of an exposure apparatus, a robot arm, or the like.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

2 Scale unit 3 Semiconductor element 9 Light receiving unit 24 Light receiving region 25 Signal processing circuit unit 100 Absolute encoder

Claims (8)

An absolute encoder that detects the absolute position of the object to be measured,
A scale unit comprising a first track having a first slit and a second track having a second slit configured to be movable together with the object to be measured;
First detection means for detecting a first signal obtained from the first slit;
Second detection means for detecting a second signal obtained from the second slit;
Computing means for performing vernier computation using the first signal and the second signal;
The absolute encoder is characterized in that the interval between the second slits differs according to the position of the scale portion in the moving direction.   The absolute encoder according to claim 1, wherein an interval between the first slits is equal in the moving direction of the scale portion. The second slit includes a slit arranged at a first interval in a first region, and a slit arranged at a second interval in a second region,
A third slit is disposed at the boundary between the first region and the second region,
3. The absolute encoder according to claim 1, wherein the displacement amount of the vernier phase calculated by the calculating means is different at the position of the third slit. 4. The displacement amount of the vernier phase is proportional to the displacement amount of the upper signal relative to the displacement of the scale portion,
4. The absolute encoder according to claim 3, wherein the proportional constant of the relationship is constant without depending on the position of the scale portion. An imaging means having a lens movable in the optical axis direction;
An imaging apparatus comprising: the absolute encoder according to claim 1 for detecting displacement of the lens.   6. The absolute encoder according to claim 5, wherein the distance between the second slits is varied in accordance with the optical sensitivity to the displacement of the lens so that the displacement amount of the vernier phase with respect to the displacement is increased. The imaging device described.   In the absolute encoder, the displacement amount of the vernier phase with respect to the displacement of the lens increases on the telephoto side of the lens, and the displacement amount of the vernier phase with respect to the displacement of the lens decreases on the near side of the lens. The imaging apparatus according to claim 5, wherein the interval between the two slits is different.   The imaging apparatus according to claim 5, wherein the absolute encoder corrects an actual measurement value using a phase shift amount detected when the absolute encoder is incorporated in the imaging apparatus.