Position converter

Abstract

The present invention aims to provide a position transducer capable of suppressing deterioration of linearity. [Solution] The position converter according to the present invention is characterized by comprising: a light source arranged opposite to the rotation axis; a reflective element arranged at one end of the rotation axis and reflecting light emitted from the light source; a first light-receiving element arranged around the light source and receiving the reflected light reflected by the reflective element and outputting a first electrical signal corresponding to the received reflected light; a second light-receiving element arranged adjacent to the first light-receiving element in the rotational direction of the rotation axis, receiving the reflected light and outputting a second electrical signal corresponding to the received reflected light; and a reflective member arranged around the first light-receiving element and the second light-receiving element and re-reflecting the reflected light.

Description

[Technical Field]

[0001] The present invention relates to a position transducer. [Background Art]

[0002] Conventionally, position transducers mounted on motors that drive optical components such as mirrors for scanning laser light have been known. For example, Patent Document 1 discloses a position transducer having a detector including a rotation-limited motor, a diffused light absorber, an LED die, a case, a printed circuit board, a butterfly-shaped reflector, and a photodiode. The position transducer described in Citation 1 includes a signal processing circuit that converts a photocurrent generated by a photodiode corresponding to the rotation angle of the rotation-limited motor into a voltage signal. The position transducer described in Citation 1 includes an Automatic Gain Control (AGC) circuit that performs temperature compensation and linearity compensation for temperature changes that cannot be fully compensated by the optical system. Since the position transducer described in Citation 1 includes the AGC circuit, high-precision position conversion output can be obtained. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Laid-Open No. 2014-102244 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] In the position transducer described in Citation 1, when the rotation angle of the reflector is increased, the light received by the photodiode tends to decrease. Therefore, linearity, which indicates the degree of matching between the angle command to the motor and the actual motor angle, deteriorates as the rotation angle of the reflector is increased. Such deterioration in linearity may not be fully compensated even by the AGC circuit.

[0005] The present invention aims to provide a position transducer capable of suppressing deterioration of linearity. [Means for solving the problem]

[0006] The position converter according to the present invention is characterized by comprising: a light source arranged opposite to the rotation axis; a reflective element arranged at one end of the rotation axis and reflecting light emitted from the light source; a first light-receiving element arranged around the light source and receiving the reflected light reflected by the reflective element and outputting a first electrical signal corresponding to the received reflected light; a second light-receiving element arranged adjacent to the first light-receiving element in the rotational direction of the rotation axis, receiving the reflected light and outputting a second electrical signal corresponding to the received reflected light; and a reflective member arranged around the first and second light-receiving elements and re-reflecting the reflected light.

[0007] Furthermore, in the position converter according to the present invention, it is preferable that the reflective member includes a first reflective member positioned near the end of the first light-receiving element opposite to the end adjacent to the second light-receiving element, and a second reflective member positioned near the end of the second light-receiving element opposite to the end adjacent to the first light-receiving element.

[0008] Furthermore, in the position converter according to the present invention, it is preferable that the first reflective member is a first electrode electrically connected to the first light-receiving element, and the second reflective member is a second electrode electrically connected to the second light-receiving element.

[0009] Furthermore, the position converter according to the present invention further comprises a third light-receiving element arranged together with a first light-receiving element to sandwich a light source, which receives reflected light and outputs a third electrical signal corresponding to the received reflected light; a fourth light-receiving element arranged together with a second light-receiving element to sandwich a light source and adjacent to the third light-receiving element in the rotational direction, which receives reflected light and outputs a fourth electrical signal corresponding to the received reflected light; and preferably the reflective member further comprises a third reflective member arranged near the end of the third light-receiving element opposite to the end adjacent to the fourth light-receiving element; and a fourth reflective member arranged near the end of the fourth light-receiving element opposite to the end adjacent to the third light-receiving element.

[0010] Furthermore, in the position converter according to the present invention, it is preferable that the third reflective member is a third electrode electrically connected to the third photodetector, and the fourth reflective member is a fourth electrode electrically connected to the fourth photodetector. [Effects of the Invention]

[0011] According to the present invention, the position transducer can suppress the deterioration of linearity. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic block diagram of a galvanoscanner G having a position transducer 50 according to Embodiment 1. [Figure 2] This is a longitudinal cross-sectional view of the position transducer 50. [Figure 3] This is a longitudinal cross-sectional view of the position converter 50 when the reflector 55 is rotated 90 degrees relative to Figure 2. [Figure 4] This is a perspective view showing the position converter 50 partially cut away. [Figure 5] This is a plan view of reflector 55. [Figure 6] This is a plan view of a printed circuit board 54 having a detector 56 and the like in a position converter 50. [Figure 7] This is a circuit diagram of the signal processing circuit 70 of the position converter 50. [Figure 8] This diagram shows the positional relationship between photodiodes 561-564 and butterfly-shaped images 550a, 550b, and 550c. [Figure 9] (a) is a plan view showing the arrangement of LED dies 52a, 52b and electrodes (reflective members) 57 mounted on the printed circuit board 54, and (b) is a plan view schematically showing the arrangement when photodiodes 561 to 564 are also arranged. [Figure 10] This is a plan view of the printed circuit board 54 in the comparative example position converter 50'. [Figure 11] This graph shows an example of the relationship between the amount of light received by the photodiode and linearity in the position converter 50'. [Figure 12] It is a graph showing an example of the difference in the amount of received light of photodiodes between an example and a comparative example. MODE FOR CARRYING OUT THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to the embodiments, and extends to the invention described in the claims and equivalents thereof.

[0014] (Embodiment 1) FIG. 1 is a schematic block diagram of a galvano scanner G having a position converter 50 according to Embodiment 1, FIG. 2 is a vertical cross-sectional view of the position converter 50, FIG. 3 is a vertical cross-sectional view of the position converter 50 when a reflector 55 is rotated 90 degrees with respect to FIG. 2, and FIG. 4 is a perspective view showing the position converter 50 with a part thereof cut away. Note that, in FIG. 4, the bearing 12 and the like are not illustrated.

[0015] The galvano scanner G includes a motor 10, an optical element 30, a position converter 50, and the like. The motor 10, the optical element 30, and the position converter 50 are structurally connected via the motor 10. The position converter 50 is electrically connected to a signal processing circuit 70 included in a control device 100 via a connector 54a.

[0016] The galvano scanner G sets the optical element 30 to a desired angle under the control of the control device 100. The galvano scanner G outputs a detection signal Sd indicating the angle detected by the position converter 50 to the control device 100, and receives a setting signal Ss for setting the optical element 30 to a desired angle input from the control device 100. Within an angular range in which an upper limit and a lower limit are defined with a reference position as a center, the galvano scanner G reflects a laser beam incident from a laser light source in different directions according to the rotation angle of the mirror, for example, by causing a mirror, which is an example of the optical element 30, to slightly rotate at high speed.

[0017] The motor 10 includes a rotating shaft 11, a bearing 12, and a rotor 13, and rotates the rotating shaft 11 in response to a setting signal Ss. The motor 10 does not continuously rotate the rotating shaft 11 in one direction, but rather rotates (moves) the rotating shaft 11 alternately clockwise and counterclockwise (forward and reverse directions) within the aforementioned angular range. Since the angle of rotation of the motor 10 is limited, it can also be called a rotation-limited motor.

[0018] The rotating shaft 11 is fixed to the rotor 13 and rotates in accordance with the rotation of the rotor 13. The rotating shaft 11 is located at the end of the rotor 13 and is supported by a bearing 12. A reflector mounting portion 11a is formed protruding from the tip of the rotating shaft 11. A reflector 55, which will be described later, is attached to the reflector mounting portion 11a.

[0019] Two bearings 12 are arranged to sandwich the rotor 13 and rotatably support the rotating shaft 11. The rotor 13 is made up of, for example, a cylindrical permanent magnet. A cylindrical coil 10a is arranged around the rotor 13 to which a setting signal Ss is input. The coil 10a is positioned at a predetermined distance from the outer surface of the rotor 13 and is fixed to the housing (stator) of the motor 10. In other words, the motor 10 is configured as a brushless motor. However, the motor 10 may also be configured as a brushed motor.

[0020] The optical element 30 is an element that reflects light such as laser light incident from the outside, and is fixed to the tip of the rotation shaft 11. The optical element 30 rotates when the rotation shaft 11 rotates by a desired angle in response to a setting signal Ss input from the control device 100. For example, if the angle corresponding to the detection signal Sd output from the position transducer 50 is 9°, and the higher-level control device (not shown) instructs to rotate the optical element 30 by 10°, the control device 100 outputs a setting signal Ss indicating that the optical element 30 should be rotated by 1°. When the setting signal Ss indicating that the optical element 30 should be rotated by 1° is input to the motor 10, the motor 10 rotates the rotation shaft 11 by 1°. The optical element 30, which is fixed to the rotation shaft 11, rotates by 1° in response to the 1° rotation of the rotation shaft 11.

[0021] The position converter 50 includes a diffuse light absorber 51, an LED die 52, a case 53, a printed circuit board 54, a reflector 55, a detector 56, and an electrode 57. The position converter 50 is a reflective optical position converter that detects the rotation angle of the motor 10 by detecting light emitted from the LED die 52 and reflected by the reflector 55 with the detector 56.

[0022] The diffuse light absorber 51 is a fixed member that does not rotate by the motor 10. The diffuse light absorber 51 has a trapezoidal shape 51a, a through hole 51b formed in the center of the trapezoidal shape 51a, and a disc-shaped part 51c formed on the outer circumference of the trapezoidal shape 51a. The diffuse light absorber 51 is attached to the lower end of the motor 10 in Figures 2 to 4 so that the rotation shaft 11 passes through the through hole 51b, and is positioned at a predetermined distance from the reflector 55. A diffuse light absorbing member is arranged on the surface of the diffuse light absorber 51.

[0023] A diffuse light absorbing member is a black material with a surface treatment, and its surface has a three-dimensional and complex microstructure, such as bumps and grooves with a pitch and height that match the wavelength of light. The diffuse light absorbing member confines and absorbs the light by repeatedly reflecting the incident light L onto its surface with this microstructure (stray light effect). Surface treatment is performed by methods such as vapor deposition, plating, inorganic baking paint, or electrostatic flocking.

[0024] The diffuse light absorbing member is positioned on the surface of the case 53 in addition to the surface of the diffuse light absorber 51. That is, the internal space formed by the diffuse light absorber 51 and the case 53 is surrounded by the diffuse light absorbing member. The diffuse light absorbing member absorbs the light emitted from the LED die 52 that does not hit the reflector 55.

[0025] The LED die 52 is an example of a light source and, as shown in Figures 2-4, is positioned on the printed circuit board 54 at a location corresponding to the center of the rotation axis 11. That is, the LED die 52 is positioned opposite the rotation axis 11. The LED die 52 is mounted directly on the printed circuit board 54 without packaging (chip-on-board). The position converter 50 has two LED dies 52a and 52b, which are collectively referred to as the LED die 52. The number of LED dies 52 can be one or three or more.

[0026] The LED die 52 is a diffuse light source from which light is emitted from a single point, and the emitted light is released with a predetermined spread. In Figures 2 and 3, the light emitted from the LED die 52 is indicated by arrows. In the position converter 50, for example, aluminum gallium arsenide (AlGaAs) with a peak wavelength of 870 nm is used as the LED die 52.

[0027] Case 53 is a cylindrical fixed member that does not rotate by the motor 10. A diffuse light absorber 51 is incorporated into case 53. A printed circuit board 54 is mounted over the bottom of case 53 in Figures 2-4.

[0028] The printed circuit board 54 is a circuit board that electrically connects the electronic components that realize the position transducer 50. In one example, a connector 54a having 10 pins is attached to the printed circuit board 54. Each pin (not shown) of the connector 54a is fixed to each land of the wiring pattern (not shown) formed on the printed circuit board 54 by soldering or the like, and is electrically connected to the terminals of the LED die 52 and the detector 56. The terminals of the LED die 52 are electrically connected to the land on the printed circuit board 54 via wires (not shown). The terminals of the detector 56 are formed on the corners of the photodiodes 561 to 564 (see Figure 6), which will be described later, and are electrically connected to the land on the printed circuit board 54 via wires W.

[0029] Figure 5 is a plan view of the reflector 55. The reflector 55 is an example of a reflective element, positioned at one end of the rotating shaft 11, and reflects light emitted from the LED die 52. The reflector 55 has a mounting hole 55a in its central part for attachment to the reflector mounting portion 11a of the rotating shaft 11 by fitting, and also has two butterfly-shaped flat reflective surfaces 55b and 55c that protrude radially from its central part. The number of reflective surfaces corresponds to the number of pairs of photodiodes, which will be described later.

[0030] The reflector 55 has reflective surfaces 55b and 55c, which are reflective regions, but it does not have non-reflective regions. Light emitted from the LED die 52 that strikes the reflective surfaces 55b and 55c of the reflector 55 is reflected towards the detector 56. A diffuse light absorber 51 (diffuse light absorbing member) is positioned behind the reflector 55 as seen from the LED die 52, so the light emitted from the LED die 52 that passes through regions other than the reflective surfaces 55b and 55c and goes to the back side of the reflector 55 is absorbed by the diffuse light absorber 51.

[0031] The reflector 55 is manufactured by processing a metal plate, which has been mirror-finished by cold rolling or the like, into a butterfly shape by etching or wire cutting. The reflectivity of the reflector 55 may be further improved by depositing aluminum, silver, gold, or the like onto the reflective surfaces 55b and 55c to create a metallic coating. The reflector 55 rotates in the forward and reverse directions within the aforementioned angular range when driven by the motor 10, together with the rotation shaft 11.

[0032] Figure 6 is a plan view of the printed circuit board 54 of the position converter 50, which includes a detector 56, etc. The detector 56 is composed of four photodiodes 561 to 564.

[0033] The four photodiodes 561-564 are made of silicon wafers with a sensitivity wavelength of 800-900 nm and each has a partially annular photosensitive region A1, B1, A2, and B2. Photodiodes 561, 562, 563, and 564 are examples of the first, second, third, and fourth photodetectors, respectively.

[0034] The photodiodes 561 to 564 are each quadrangular in plan view and are arranged on the printed circuit board 54 with 360-degree / 4 (=90-degree) rotational symmetry. The photodiodes 561 to 564 are mounted directly on the printed circuit board 54 without packaging (chip-on-board). The photodiodes 561 to 564 are arranged so that photodiodes 561 and 563 face each other, and photodiodes 562 and 564 also face each other, with the LED die 52 located in the center in between. In other words, the second light-receiving element 562 is positioned adjacent to the first light-receiving element 561 in the direction of rotation of the rotation axis 11. The third light-receiving element 563 is positioned so as to sandwich the LED die 52 together with the first light-receiving element 561. The fourth light-receiving element 564 is positioned so as to sandwich the LED die 52 together with the second light-receiving element 562 and is positioned adjacent to the third light-receiving element 563 in the direction of rotation of the rotation axis 11. In other words, the light-receiving elements 561 to 564 are arranged around the LED die 52.

[0035] Each of the photodiodes 561 to 564 receives the reflected light reflected by the reflector 55 and outputs an electrical signal corresponding to the received reflected light. In other words, the first light-receiving element 561, the second light-receiving element 562, the third light-receiving element 563, and the fourth light-receiving element 564 output the first electrical signal, the second electrical signal, the third electrical signal, and the fourth electrical signal, respectively.

[0036] The photosensitive areas A1, B1, A2, and B2 are each partially circular in shape with a central angle of approximately 60 degrees when viewed from above. The photosensitive areas A1, B1, A2, and B2 are arranged on the printed circuit board 54 with rotational symmetry of 360 degrees / 4 (=90 degrees). In other words, the photosensitive areas A1, B1, A2, and B2 are arranged on the circumference of a circle centered at a position directly below the axis of rotation 11 on the printed circuit board 54.

[0037] The detector 56 has two pairs of photodiodes: one pair of adjacent photodiodes 561 and 562, and the other pair of photodiodes 563 and 564. In the signal processing circuit 70, photodiodes 561 and 563 are connected in parallel, and photodiodes 562 and 564 are connected in parallel.

[0038] Figure 7 is a circuit diagram of the signal processing circuit 70 of the position converter 50. The signal processing circuit 70 converts the photocurrent from photodiodes 561-564, which corresponds to the rotation angle of the motor 10, into a voltage signal.

[0039] The photocurrent Ia, output from photodiodes 561 and 563, is input to the current-voltage conversion unit 71a. The photocurrent Ib, output from photodiodes 562 and 564, is input to the current-voltage conversion unit 71b. The output voltage Va of the current-voltage conversion unit 71a and the output voltage Vb of the current-voltage conversion unit 71b are input to the subtractor 72, where subtraction is performed. The position converter output Vo, processed by the signal processing circuit 70, is Vo = (Ia - Ib)Vref / (Ia + Ib), where Vref is the reference voltage. The position converter output Vo is further processed by the control device 100, which generates the setting signal Ss.

[0040] The signal processing circuit 70 includes an AGC circuit 78a that performs temperature compensation and linearity compensation for temperature changes that cannot be fully compensated by the optical system, in order to obtain a highly accurate position conversion output. The output voltage Va of the current-voltage conversion unit 71a and the output voltage Vb of the current-voltage conversion unit 71b are led to the AGC circuit 78a and added by the adder 73. This added output is compared with a reference voltage Vref by the comparator 74. The output of the comparator 74 is integrated by the integrator circuit 75 and amplified by the current amplifier 76a. As a result, the current If is supplied to the LED die 52 via the resistor 77.

[0041] Figures 8(a) to 8(c) show the positional relationship between photodiodes 561 to 564 and butterfly-shaped images 550a, 550b, and 550c. The images projected onto photodiodes 561 to 564 from the butterfly-shaped reflector 55 move according to the rotation angle of the motor 10, as shown in images 550a, 550b, and 550c in Figures 8(a) to 8(c). Note that, to avoid making the diagrams cluttered, the electrode 57 is omitted from Figures 8(a) to 8(c).

[0042] In Figures 8(a) to 8(c), the sum of the areas of photosensitive regions A1 and A2 of photodiodes 561 and 563 is denoted as Sa, and the photosensitive region of photodiodes 561 and 563 is referred to as the "Sa region." Similarly, the sum of the areas of photosensitive regions B1 and B2 of photodiodes 562 and 564 is denoted as Sb, and the photosensitive region of photodiodes 562 and 564 is referred to as the "Sb region." Figures 8(a) to 8(c) show the cases where the Sa region is larger than the Sb region, where the Sa region and Sb region are the same size, and where the Sa region is smaller than the Sb region, respectively.

[0043] For example, if the butterfly-shaped images are images 550a, 550b, and 550c, and their rotation angles are positive, 0, and negative respectively, then in the case of Figure 8(a), the area difference is Sa-Sb>0, so corresponding to a positive rotation angle, the output voltage of the position transducer 50 is Va-Vb>0. Also, in the case of Figure 8(b), the area difference is Sa-Sb=0, so corresponding to a rotation angle of 0, the output voltage of the position transducer 50 is Va-Vb=0. In the case of Figure 8(c), the area difference is Sa-Sb<0, so corresponding to a negative rotation angle, the output voltage of the position transducer 50 is Va-Vb<0.

[0044] Figure 9(a) is a plan view showing the arrangement of the LED die 52 and electrodes (reflective members) 57 mounted on the printed circuit board 54, and (b) is a schematic plan view showing the arrangement when photodiodes 561 to 564 are also arranged. In Figure 9, the electrodes 57 are shaded to clarify their arrangement. In Figure 9(b), the photodiodes 561 to 564 and the photosensitive areas A1, B1, A2, and B2 are shown with dotted lines to clarify each arrangement.

[0045] Electrode 57 is composed of four electrodes 571 to 574 and is electrically connected to photodiodes 561 to 564. Each electrode 571 to 574 is made of a metal such as gold foil, and in one example, is electrically connected to the anode of each photodiode 561 to 564. In this case, electrode 57 becomes the anode electrode. Each electrode 571 to 574 may also be electrically connected to the cathode of each photodiode 561 to 564. That is, electrode 57 may become the cathode electrode.

[0046] Each electrode 571 to 574 has mounting portions 571p to 574p on which each photodiode 561 to 564 is placed, and exposed portions 571e to 574e on which the photodiodes 561 to 564 are not placed.

[0047] Each mounting portion 571p to 574p is electrically connected to each photodiode 561 to 564, for example, by a conductive adhesive. The exposed portions 571e to 574e are integrally formed with each mounting portion 571p to 574p and are electrically connected to each photodiode 561 to 564.

[0048] Electrodes 571-574 are arranged around the photodiodes 561-564 and also act as reflective members that re-reflect the reflected light reflected by the reflector 55. That is, since each electrode 571-574 is made of metal, the exposed portions 571e-574e of electrodes 571-574 are emitted from the LED die 52 and are able to re-reflect the reflected light reflected by the reflector 55.

[0049] The exposed portion 571e of the first electrode 571 is positioned near the opposite end of the photosensitive region A1 to the end adjacent to the photosensitive region B1. The exposed portion 572e of the second electrode 572 is positioned near the opposite end of the photosensitive region B1 to the end adjacent to the photosensitive region A1. The exposed portion 573e of the third electrode 573 is positioned near the opposite end of the photosensitive region A2 to the end adjacent to the photosensitive region B2. The exposed portion 574e of the fourth electrode 574 is positioned near the opposite end of the photosensitive region B2 to the end adjacent to the photosensitive region A2. In other words, the first reflective member 571 (571e) is positioned near the opposite end of the first light-receiving element 561 to the end adjacent to the second light-receiving element 562. The second reflective member 572 (572e) is positioned near the opposite end of the second light-receiving element 562 to the end adjacent to the first light-receiving element 561. Furthermore, the third reflective member 573 (573e) is positioned near the end of the third light-receiving element 563 opposite to the end adjacent to the fourth light-receiving element 564. Similarly, the fourth reflective member 574 (574e) is positioned near the end of the fourth light-receiving element 564 opposite to the end adjacent to the third light-receiving element 563. The term "nearby" can also be described as a relatively close position.

[0050] Electrodes 571 to 574 are each adjacent to other adjacent electrodes and are arranged on the printed circuit board 54 so as to surround the entire circumference of the LED die 52, forming an annular shape overall. However, there is a small gap between adjacent electrodes 571 to 574 to prevent short circuits, and this gap is, for example, 0.5 mm or less. Note that the width of the gap is not limited to this.

[0051] Figure 10 is a plan view of the printed circuit board 54 in the comparative example position transducer 50'. The position transducer 50' differs from the position transducer 50 only in that the electrodes 571 to 574 having exposed portions 571e to 574e are not arranged around the photodiodes 561 to 564; otherwise, it has the same configuration as the position transducer 50.

[0052] As mentioned above, the position converter 50' does not have electrodes 57 with exposed portions 571e to 574e. Therefore, when reflected light is incident on the two regions 54b on the left and right in Figure 10, which face each other across the LED die 52, the position converter 50' cannot re-reflect the reflected light, and the amount of light received decreases accordingly. In the position converter 50', the AGC circuit 78a operates to compensate for this, but since the photocurrent value in a photodiode can be on the order of microamperes, there may be cases where the AGC circuit 78a cannot fully compensate for it.

[0053] Figure 11 is a graph showing an example of the relationship between the amount of light received by the photodiode and linearity in the position converter 50'. In Figure 11, the horizontal axis represents the rotation angle (swing angle) of the reflector 55 (unit: ° (deg)), and the vertical axis shows the amount of light received by the photodiode (unit: watts (W)) on the left and the linearity (unit: percent (%)) on the right. As shown in Figure 11, the amount of light received decreases as the rotation angle of the reflector 55 increases. Furthermore, linearity deteriorates with decreasing light received, even with linearity compensation by the AGC circuit 78a.

[0054] As shown in Figure 6, in the position converter 50, electrodes 57, which are also reflective members, are positioned in the regions corresponding to the two regions 54b in Figure 10. Therefore, when the rotation angle of the reflector 55 is increased, the electrodes 57 are able to re-reflect the reflected light that was reflected by the reflector 55 but not directly incident on the photosensitive regions A1, B1, A2, and B2. The re-reflected light diffuses in various directions and is either directly incident on the photosensitive regions A1, B1, A2, and B2, or is reflected again by the reflector 55 and incident on the photosensitive regions A1, B1, A2, and B2.

[0055] As described above, the position transducer 50 has a reflective member 57 positioned around the photodiodes 561 and 562 that re-reflects the reflected light reflected by the reflector 55. The reflective member 57 enables the re-reflection of reflected light that was not directly incident on the photodiodes 561 and 562. This allows the position transducer 50 to suppress deterioration of linearity.

[0056] Preferably, the reflective member 57 includes a first reflective member 571 positioned near the end of the photodiode 561 opposite to the end adjacent to the photodiode 562, and a second reflective member 572 positioned near the end of the photodiode 562 opposite to the end adjacent to the photodiode 561. When the rotation angle of the reflector 55 is increased, the photosensitive regions A1 and B1 of the photodiodes 561 and 562 may not receive all of the reflected light reflected by the reflector 55. By positioning the reflective members 571 and 572 as described above, they re-reflect the reflected light that was not received by the photosensitive regions A1 and B1 when the rotation angle of the reflector 55 is increased, and cause it to enter the photosensitive regions A1 and B1. This makes it possible for the position converter 50 to suppress deterioration of linearity even when the rotation angle of the reflector 55 is increased.

[0057] Preferably, the first reflective member 571 is a first electrode 571 electrically connected to the photodiode 561, and the second reflective member 572 is a second electrode 572 electrically connected to the photodiode 562. This allows the position converter 50 to re-reflect reflected light and to simplify the wiring pattern of the printed circuit board 54 by forming the reflective members using electrodes necessary to constitute the detector 56. Furthermore, even when using photodiodes 561 and 562 that have a larger external shape than those shown in Figure 6, the position converter 50 can mount the photodiodes on the printed circuit board 54 without changing the wiring pattern (electrodes) of the printed circuit board 54. In other words, it can contribute to the sharing of the printed circuit board 54 for multiple types of photodiodes with different external sizes.

[0058] Preferably, the position converter 50 further includes a photodiode 563 arranged to sandwich the LED die 52 together with the photodiode 561, and a photodiode 564 arranged to sandwich the LED die 52 together with the photodiode 562 and adjacent to the photodiode 563 in the rotational direction of the rotation axis 11. The reflective member 57 further includes a third reflective member 573 arranged near the end of the photodiode 563 opposite to the end adjacent to the photodiode 564, and a fourth reflective member 574 arranged near the end of the photodiode 564 opposite to the end adjacent to the photodiode 563. This allows the position converter 50 to enjoy various advantages (such as stabilization of the output signal) of having two pairs of photodiodes while suppressing deterioration of linearity even when the rotation angle of the reflector 55 is increased.

[0059] Preferably, the third reflective member 573 is a third electrode 573 electrically connected to the photodiode 563, and the fourth reflective member 574 is a fourth electrode 574 electrically connected to the photodiode 564. This allows the position converter 50 to re-reflect reflected light and enjoy various advantages (such as stabilization of the output signal) that come with having two pairs of photodiodes, while also simplifying the wiring pattern on the printed circuit board 54.

[0060] Preferably, the photodiodes 561 to 564 are arranged on a circumference centered directly below the rotation axis 11, and the reflective member 57 is arranged on the printed circuit board 54 so as to surround the entire circumference of the LED die 52 and form an annular shape overall. This allows the position converter 50 to position the reflective member 57 at positions corresponding to the photodiodes 561 to 564 arranged on the circumference, thereby more effectively suppressing deterioration of linearity compared to cases where the reflective member 57 is not arranged as described above.

[0061] Preferably, electrodes 571 to 574 have mounting portions 571p to 574p on which photodiodes 561 to 564 are placed, and exposed portions 571e to 574e on which the photodiodes 561 to 564 are not placed. This allows the position converter 50 to easily form reflective members on electrodes 571 to 574 that re-reflect reflected light. More preferably, the mounting portions 571p to 574p of electrodes 571 to 574 are electrically conductive and bonded to photodiodes 561 to 564 using a conductive adhesive. This allows the position converter 50 to easily electrically connect and bond the photodiodes and electrodes, enabling simplification of the wiring pattern on the printed circuit board 54.

[0062] (modified version) The position transducer may, for example, have three or more reflective surfaces in the reflector and consist of twice the number of reflective surfaces as the number of photodiodes, i.e., the same number of pairs of photodiodes as the number of reflective surfaces. Alternatively, the position transducer may have one semicircular reflective surface in the reflector and consist of two (one pair) photodiodes as detectors. However, if the reflector has one semicircular reflective surface and consists of two photodiodes as detectors, correction may not be effective when the reflective surface is eccentric, and the shape of each chip may become complex in order to secure the mounting area of ​​the LED die within the region surrounded by the two photodiodes. Considering this, it is more preferable for the position transducer to have two reflective surfaces in the reflector and four photodiodes.

[0063] The LED die and diode may be fixed to a substrate without wiring patterns, rather than being mounted on a printed circuit board. The light source is not limited to LEDs, but may be other light-emitting devices. The light source is not limited to diffuse light sources, but may be parallel light sources that emit substantially non-diffusive parallel light.

[0064] The reflective member and electrodes do not have to be integrated. That is, the reflective member may be made of a material other than the anode or cathode electrode of the photodiode. Furthermore, the reflective member may be any material that reflects light, such as a glass or silicone material with a metal coating on its surface, or a resin reflective tape (reflective sheet).

[0065] In the embodiment described above, the position converter 50 was used in the galvanoscanner G. However, the position converter 50 may be used in devices other than the galvanoscanner G.

[0066] (Examples) Figure 12 is a graph showing an example of the difference in the amount of light received by the photodiode between the example and the comparative example. In Figure 12, the horizontal axis represents the rotation angle (swing angle) of the reflector 55 (unit: ° (deg)), and the vertical axis represents the amount of light received by the photodiode (unit: watts (W)).

[0067] The graph in the embodiment is based on a simulation assuming position transducer 50, while the graph in the comparative example is based on a simulation assuming position transducer 50'. In this simulation, all conditions are the same except for whether or not exposed portions 571e to 574e of the electrodes 57 are formed on each position transducer.

[0068] As shown in Figure 12, the position transducer 50 received a relatively larger amount of light than the position transducer 50' as the rotation angle of the reflector 55 increased. The graph in Figure 12 shows that the position transducer 50 can increase the amount of light received by the exposed portions 571e to 574e of the electrode 57, which is also a reflective member, and that deterioration of linearity can be suppressed.

[0069] Furthermore, regarding the nonlinearity (percentage of angular error) of a rotation limiting motor, which is generally expressed by the formula "100 × (|Δθ1| + |Δθ2|) / θ" (Δθ1: angular error in the forward rotation direction, Δθ2: angular error in the reverse rotation direction, θ: operating angle range), according to the results of verification conducted by the applicant of this application, the rotation limiting motor using the position transducer 50' had a nonlinearity of 0.088% (average value of 20 prototypes) when the operating angle was ±10°, while the rotation limiting motor using the position transducer 50 had a nonlinearity of 0.037% (average value of 20 prototypes) when the operating angle was ±10°. In other words, the nonlinearity of the position transducer 50 was relatively lower than that of the position transducer 50' (in other words, the linearity was improved). This also demonstrates that the position transducer 50 can suppress the deterioration of linearity.

[0070] Those skilled in the art will understand that various changes, substitutions, and modifications can be made without departing the scope of the present invention. For example, the embodiments and modifications described above may be combined as appropriate within the scope of the invention. [Explanation of Symbols]

[0071] G Galvanoscanner 10 motors 11 Rotation axis 50, 50' Position Transmitter 52 LED die (light source) 54 Printed circuit boards 54a connector 55. Reflector (Reflective element) 56 detectors 561-564 Photodiode (light-receiving element) A1, A2, B1, B2 photosensitive area 57 Electrodes (reflective material) 70 Signal Processing Circuits 78a AGC circuit

Claims

1. A light source positioned opposite the axis of rotation, A reflective element is positioned at one end of the rotating shaft and reflects light emitted from the light source, A first light-receiving element is arranged around the light source, receives reflected light reflected by the reflecting element, and outputs a first electrical signal corresponding to the received reflected light. A second light-receiving element is positioned adjacent to the first light-receiving element in the rotational direction of the rotation axis, receives the reflected light, and outputs a second electrical signal corresponding to the received reflected light. A reflective member is arranged around the first and second light-receiving elements and re-reflects the reflected light, A position converter characterized by having

2. The reflective member is A first reflective member is positioned near the end of the first light-receiving element opposite to the end adjacent to the second light-receiving element, A second reflective member is positioned near the end of the second light-receiving element opposite to the end adjacent to the first light-receiving element, A position converter according to claim 1, having the following features.

3. The first reflective member is a first electrode electrically connected to the first light-receiving element, The position converter according to claim 2, wherein the second reflective member is a second electrode electrically connected to the second light-receiving element.

4. A third light-receiving element is positioned together with the first light-receiving element so as to sandwich the light source, and receives the reflected light and outputs a third electrical signal corresponding to the received reflected light. The system further includes a fourth light-receiving element which is positioned together with the second light-receiving element to sandwich the light source and adjacent to the third light-receiving element in the rotational direction, and which receives the reflected light and outputs a fourth electrical signal corresponding to the received reflected light, The reflective member is A third reflective member is positioned near the end of the third light-receiving element opposite to the end adjacent to the fourth light-receiving element, A fourth reflective member is positioned near the end of the fourth light-receiving element opposite to the end adjacent to the third light-receiving element, A position converter according to any one of claims 1 to 3, further comprising the above.

5. The third reflective member is a third electrode electrically connected to the third light-receiving element, The position converter according to claim 4, wherein the fourth reflective member is a fourth electrode electrically connected to the fourth light-receiving element.

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