Code plate of optical rotary encoder

Abstract: A code plate of a light-transmission type rotary encoder, said code plate comprising: a non-transparent disk; and light-transmitting apertures formed with a same width and at a same radius from the center of rotation of said non-transparent disk, wherein said light-transmitting apertures are in the form of a plurality of light-transmitting grooves and one or more light-transmitting holes, said light-transmitting grooves being cut out so as to be recessed inward from the outer peripheral edge of said non-transparent disk, and said one or more light-transmitting holes being formed between adjacent light-transmitting grooves.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a code plate of a light transmission type rotary encoder. 2. Description of the Related Art In a known conventional technique, control operations, such as controlling operations of the suspension damping force, controlling operations of the automatic transmission shift position, and steering control operations of the rear wheel of a four-wheel vehicle, are performed by detecting the steering angle, steering speed, and steering direction of a steering wheel mounted to a shaft as a result of rotation of a code plate by means of the steering shaft. In this technique, an optical rotary encoder comprising a combination of a photointerrupter and the code plate disposed around the steering shaft is used. As shown in Fig. 6, a commonly used code plate has fine rectangular or elliptical light detection patterns (or A, B phase detection patterns) 2 and arcuate light detection patterns (or Z phase detection patterns) 3. The A, B phase detection patterns 2 are used to detect the angle of rotation, direction of rotation, and rotational speed of a rotary substrate 1, which is a non-transparent disk formed from a plastic plate, metallic plate, or the like. The light detection patterns 3 are used to detect the origin and the number of rotations of the rotary substrate 1. However, in such a conventional code plate, the axial line in the longitudinal direction of the A, B phase detection patterns and the sides of the leading edge and the trailing edge of the Z phase detection patterns 3 are both oriented radially from the rotational center O of the rotary substrate 1. In this document, light detection pattern is a general term used to cover light-transmitting apertures in a light transmission type rotary encoder and light reflection portions in a light reflection type rotary encoder. As shown in Fig. 6 illustrating a portion of the code plate, a predetermined number of light-transmitting holes 2, forming the light detection patterns, are formed with the same width and at a constant pitch in the outer periphery of the non-transparent disk 1 formed from, for example, a plastic sheet or a metallic plate. Ordinarily, as shown in Fig. 10, light-transmitting holes 2, forming the light detection patterns, are formed in the non-transparent disk 1 by interposing the non-transparent disk 1 between a punch 44 and a dice 46. The punch 44 is provided with a predetermined number of light-transmitting hole opening pins 43 which can move into and out of the dice 46. The dice 46 has pin receiving holes 45 formed so as to oppose the light-transmitting hole opening pins 43. Then, the light-transmitting hole opening pins 43 move into and beyond the dice 46 to form the light-transmitting holes 2 forming the light detection patterns. Optical rotary encoders used, for example, to detect the steering angle of a vehicle steering wheel are required to perform angle detection with high precision and resolution in order to perform control operations with high responsivity. In addition, in such optical rotary encoders, a first photointerrupter 4 for Z phase detection and a second photointerrupter 5 for A,B phase detection must often be disposed on the left and right in nonalignment relationship due to the limited space available, as shown in Fig. 7. Although in Fig. 7, the second photointerrupter 5 for A, B phase detection is set on a vertical line X-X which is perpendicular to the surface of a printed board (not shown) having the photointerrupter 5 mounted thereon and which passes through the rotational center O of the rotary substrate 1, while the first photointerrupter 4 for Z phase detection is disposed along a side of the photointerrupter 5, the photointerrupter 4 for Z phase detection can be set on the vertical line X-X passing through the rotational center O of the rotary substrate 1, while the second photointerrupter 5 for A, B phase detection can be placed along a side of the photointerrupter 4. In the photointerrupters 4 and 5, the light-emitting device and the light-receiving device are combined in a predetermined arrangement such that light from the light-emitting device impinges upon the light-receiving device by passing through the code plate. The light-transmission type rotary encoder used has the light-emitting device 6 disposed in opposing relationship with the light-receiving device 7 on the same axis. As is clear from Fig. 8, in the case of a light transmission type rotary encoder, the light-emitting device 6 and the light-receiving device 7 are disposed on the front and back sides of the rotary substrate 1, with an optical axis Z-Z being oriented perpendicular to a line Y-Y defining the surface of the rotary substrate 1. Although not shown, in the case of a reflection type rotary encoder, the light-emitting device and the light-receiving device are set at locations where total refection occurs through the reflecting surfaces of the rotary substrate 1. The light-receiving device 7 has at least two light-receiving surfaces 7a and 7b formed in the horizontal direction, so as to be disposed toward the left and right in Fig. 7 Pulse signals (A phase signal and B phase signal) which are 90 degrees out of phase can be detected from the first light-receiving surface 7a and the second light-receiving surface 7b, respectively. In such an encoder, a light-receiving device with four light-receiving surfaces 7a, 7b, 7a', and 7b' is used to allow high-precision signal detection by the so-called differential output. The sides of each of the light-receiving surfaces 7a and 7b are formed parallel to the vertical line X-X passing through the rotational center O of the rotary substrate 1. Terminals 20 of the photointerrupter 5 are set parallel to the vertical line X-X. Taking as an example the light-transmission type rotary encoder in which the first photointerrupter 4 for Z phase detection is set on the vertical line X-X passing through the rotational center O of the rotary substrate 1 and the second photointerrupter 5 for A, B phase detection is disposed along a side of the first photointerrupter 4, a spot S is formed by light emitted from the light-emitting device 6, passing through the A, B phase detection patterns 2, and impinging upon the set surfaces of the light-receiving device 7. The shape of the spot S changes in accordance with the angle of rotation of the rotary substrate 1, as indicated by cross-hatching in Figs. 9A to 9D. Fig. 9 shows the shape formed when the A, B phase detection patterns 2 with a two-degree pitch exactly matches the set positions of the light-emitting device 6 and the light-receiving device 7 (defined as the initial position). Fig. 9B shows the shapes formed when the rotary substrate 1 has been rotated 0.5 degrees counterclockwise from the initial position. Fig. 9C shows the shapes formed when the rotary substrate 1 has been rotated 1.0 degree counterclockwise from the initial position. Fig. 9D shows the shapes formed when the rotary substrate 1 has been rotated 1.5 degrees counterclockwise from the initial position. As is clear from the Figs. 9A to 9C, in the optical rotary encoder of the present embodiment, the two light-receiving surfaces 7a and 7b are arranged in the horizontal direction, while the shape of the spot S formed by the light impinging upon the light-receiving surfaces is tilted in correspondence with tilting angle  of the A, B phase detection patterns 2, causing the light spot 2 to cross the light-receiving surfaces 7a and 7b obliquely as the code plate rotates. Therefore, when the encoder is constructed to output the A phase and B phase signals with a phase difference of 90 degrees as the untilted light spot on the two light-receiving surfaces 7a and 7b moves, the phase difference of the A phase signal and the B phase signal is not 90 degrees, as illustrated in Fig. 9E, and, in addition, the duty ratio between the A phase and B phase is not 50%. For this reason, limitations are placed on how the A, B phase detection second photointerrupter 5 can be arranged, thus making it difficult to design the optical rotor encoder and tending to create errors in the rotational angle detection, which may seriously affect the accuracy of the various control operations. This problem becomes more noticeable, the smaller the pitch of the plurality of light detection patterns is made to increase resolution. The same problem occurs when detecting a signal by the so-called differential output where the A, B phase detection device used is one having four light-receiving surfaces 7a, 7b, 7a', and 7b', so that the light-receiving surface 7a' is connected to the light-receiving surface 7a so as to generate opposite phases and the light-receiving surface 7b' is connected to the light-receiving surface 7b so as to generate opposite phases. Such a problem can be overcome by changing the forms and arrangement of the light-receiving surfaces 7a and 7b and using the light-receiving device 7 which outputs an A phase signal and a B phase signal which are out of phase by 90 degrees with respect to the tilted light spot S. However, this is far from being a practical solution, since developing and producing a special-purpose light-receiving device 7 in accordance with the type of encoder results in expensive rotary encoders. In the first photointerrupter 4 for Z phase detection set on the vertical line X-X passing through the rotational center O of the rotary substrate 1, the above-described problem does not arise even when the sides of the leading edge and the trailing edge of the Z phase detection patterns 3 are formed radially from the rotational center O of the rotary substrate 1, since the light spot crosses the light-receiving surfaces of the light-receiving device, while being kept perpendicular thereto. US-A-4 670 750 discloses a code plate, wherein a disk comprises a plurality of grooves, which are recessed inwardly from the peripheral edge of the disk. Since said grooves extend radially, the distance between adjacent grooves becomes smaller as the grooves approach the center of the disk. Therefore, the grooves must have a certain minimum angular distance. SUMMARY OF THE INVENTION Accordingly, the object of the present invention is to provide an optical rotary encoder which detects rotation with high resolution and precision, wherein the photointerrupters can be mounted with more freedom and inexpensively. In recent years, the light transmission type rotary encoder used, for example, to detect the steering angle of a vehicle steering wheel is required provide high resolution detection in order to perform various control operations with high responsivity. For this reason, it is necessary to form more light-transmitting holes 2 with a smaller pitch and more accurately in the code plate of such a light transmission type rotary encoder. Since the width between adjacent light-transmitting holes becomes narrower, as the number of light-transmitting holes 2 increases and the pitch between the light-transmitting holes 2 becomes smaller, during formation of the light-transmitting holes 2 it becomes difficult to properly press a portion of the non-transparent disk 1 between the punch 44 and the dice 46 with the required force (see Fig. 10). This prevents very accurate formation of the light-transmitting holes 2, and tends to cause deformation of the light-transmitting holes 2 and the portion therearound. When such problems occur, the output signals of the photointerrupters generated are pulse signals which are not in phase, which may seriously affect the responsivity of the various control operations. In addition, when a larger number of light-transmitting holes 2 need to be formed, a larger number of expensive light-transmitting hole opening pins 43 are required, the die structure becomes complicated, and maintenance costs for repairing broken pins 43 are increased. This results in higher die production costs and thus high rotary encoder production costs. To achieve the above-described objects, according to the present invention, in the code plate of the light transmission type rotary encoder which has light-transmitting apertures having the same width and formed at the same radius from the rotational center of a non-transparent disk, the light-transmitting apertures are in the form of a plurality of light-transmitting grooves cut out so as to be recessed inward from the outer peripheral edge of the non-transparent disk and one or more light-transmitting holes formed between adjacent grooves. When the light-transmitting apertures to be formed in the code plate are in the form of a plurality of light-transmitting grooves cut out so as to be recessed inward from the outer peripheral edge of the non-transparent disk and one or more light-transmitting holes formed between adjacent light-transmitting grooves, a method is used to form either the light-transmitting holes or the light-transmitting grooves first, followed by formation of either the light-transmitting holes or the light-transmitting grooves which have not been formed yet. Such a method allows a larger area of the non-transparent disk to be held by the punch and the dice during formation of the light-transmitting holes and the light-transmitting grooves, so that the non-transparent disk is held more securely, making it possible to achieve more accurate formation of the light-transmitting holes and the light-transmitting grooves. Using the production method in which the light-transmitting holes first, followed by formation of the light-transmitting grooves, results in less frequent deformation of the light-transparent disk, when the light-transmitting holes are being punched out, since the light-transmitting holes are punched out at a large pitch, whereby the light-transmitting holes can be formed more accurately. When the light-transmitting grooves are being cut out, the light-transmitting grooves can be cut out with a much smaller force than is required for punching the light-transmitting holes, thus permitting the light-transmitting grooves to be formed within a narrow space with more accuracy, after the light-transmitting holes have been punched out. When the light-transmitting apertures to be formed in the code plate are in the form of light-transmitting grooves and light-transmitting holes, the number of expensive light-transmitting hole opening pins are reduce in correspondence with the number of light-transmitting grooves, and the die construction can be simplified, resulting in large reductions in die production costs, and reduced maintenance costs for repairing broken light-transmitting hole opening pins. Therefore, it is possible to considerably reduce the overall production costs of the rotary encoder. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of a code plate of Embodiment 1 in accordance with the present invention. Fig. 2 is a view showing in detail portion B of Fig. 1. Figs. 3A to 3C are views illustrating the manufacturing processes of the code plate of Embodiment 1 in accordance with the present invention. Fig. 4 is a plan view showing the main portion of a code plate of Embodiment 2 in accordance with the present invention. Fig. 5 is a plan view showing the main portion of a code plate of Embodiment 3 in accordance with the present invention. Fig. 6 is a front view of the main portion of a conventional code plate. Fig. 7 is a front view of the mounting position of the photointerrupter (s) of the conventional code plate. Fig. 8 is a main sectional view of the construction of and arrangement of the component parts of the photointerrupter. Figs. 9A to 9E are views illustrating the disadvantages of the conventional code plate. Fig. 10 is a main sectional view illustrating the method of producing the conventional code plate. DESCRIPTION OF THE PREFERRED EMBOMIMENTS A description will now be given of Embodiment 1 of a code plate of a light transmission type rotary encoder in accordance with the present invention, with reference to Figs. 1 to 3. Fig. 1 is a plan view of an embodiment of a code plate. Fig. 2 is a view showing in detail portion B of Fig. 1. Figs. 3a to 3C are plan views illustrating the method of producing the code plate of the embodiment and effects obtained from the production method. Embodiment 1 As shown in Fig. 1, the code plate of the present embodiment comprises a non-transparent disk 30, composed of a non-transparent plastic plate, metallic plate, or the like, which contains a center hole 31, a mounting-and-positioning hole 32a, mounting holes 32b, a positioning hole 33, a Z phase signal detection hole 34, light-transmitting holes 35, and light-transmitting grooves 36. The center hole is a hole for passing through a drive ahaft 37 (such as a steering shaft) of the non-transparent disk 30, and is formed in the center of the non-transparent plate 30. The mounting-and-positioning hole 32a, the mounting holes 32b, and the positioning hole 33 are holes for mounting the non-transparent plate 30 to a rotor 38 mounted to the drive shaft 37 in a predetermined positional relationship. They are formed around the center hole 31. The rotor 38 is provided with protrusions (not shown) formed into shapes in correspondence with the shapes of the mounting-and-positioning hole 32a and the positioning hole 33. These holes 32a and 33 receive their respective protrusions to thereby mount the non-transparent disk 30 to the rotor 38 in a predetermined orientation and positional relationship. This causes the non-transparent disk 30 to be secured to the rotor 38 by screws which are passed through the mounting holes 32b. In this case, the non-transparent disk 30 and the rotor 38 can be directly secured together with screws, or can be indirectly secured together by interposing of the non-transparent disk 30 between the clamper (not shown) and the disk 30, with the clamper having screw through holes at locations in correspondence with the holes of the disk 30. The Z phase signal detection signal is a through hole used for detecting the reference position of the drive shaft 37 and the number of rotations from the reference position, and is formed at a constant radius (R 1 in the embodiment) from the rotational center O of the non-transparent disk 30. The light-transmitting holes 35 and the light-transmitting grooves 36 are apertures used for detecting the angle of rotation, direction of rotation, and the rotational speed of the drive shaft 37, and are formed with the same width w and at a constant pitch p at the outermost periphery of the non-transparent disk 30, as shown in Fig. 2. The light-transmitting holes 35, being slots, are formed radially and slightly inward from the outer peripheral edge of the non-transparent plate 30. On the other hand, the light-transmitting grooves 36 are long grooves cut out so as to extend inwardly from the outer peripheral edge of the non-transparent disk 30, and are formed radially between adjacent light-transmitting holes 35. The inner edges of each of the light-transmitting holes 35 and the light-transmitting grooves 36 are formed at a constant radius (R 2 , where R 1 < R 2 ) measured from the rotational center O of the non-transparent disk 30, so that setting a photointerrupter 39 at the center of the light-transmitting holes 35, or at a radius R 3 from the rotational center O of the transparent disk 30, allows the signals from the light-transmitting holes 35 and those from the light-transmitting grooves 36 to be detected at the same level. A description will now be given of the method of producing the code plate of the present embodiment. A non-transparent plastic plate, metallic plate, or the like is punched to produce the non-transparent disk 30 provided with the center hole 31, the mounting-and-positioning hole 32, the mounting holes 32b, the positioning hole 33, and the Z phase signal detection hole 34. The non-transparent disk is interposed between the punch and the dice. The punch is provided with a predetermined number of light-transmitting hole opening pins and a light-transmitting groove forming cutter. The light-transmitting hole opening pins are moved into and beyond the dice to form the light-transmitting holes 35. In this case, the portion where the light-transmitting grooves 36 are to be formed and the portion therearound, which are indicated by slanted lines in Fig. 3B, can be held between the punch and the dice, so that during formation of the light-transmitting holes 35, the non-transparent disk is held more securely, resulting in more accurate formation of the light-transmitting holes 35. The light-transmitting groove forming cutter is then driven to form the light-transmitting grooves 36 in the outer periphery of the non-transparent disk 30 with the light-transmitting holes 35. In this case, the portion around the light-transmitting holes 35, indicated by slanted lines in Fig. 3C, can be held between the punch and the dice, so that in this case too during formation of the light-transmitting grooves 36, the non-transparent plate 30 can be held more securely. In addition, since the force required to cut out the light-transmitting grooves is considerably less than the force required to punch out the light-transmitting holes, the light-transmitting grooves 36 can be formed more accurately in a narrow space, after the light-transmitting holes have been punched out. According to the method of producing the code plate of the present embodiment, the light-transmitting holes 35 and the light-transmitting grooves 36 can be formed more accurately, since the non-transparent disk 30 can be held more securely by the dice and the punch. In addition, it is possible to reduce die production costs and thus rotary encoder production costs, since the number of expensive light-transmitting hole opening pins can be reduced by an amount corresponding to the number of light-transmitting grooves 36. Embodiment 2 Although in Embodiment 1, one light-transmitting hole 30 was formed for every light-transmitting groove 36 in the outer periphery of the non-transparent disk 30, the gist of the present invention is not limited thereto, so that as in Embodiment 2 illustrated in Fig. 4 a plurality of light-transmitting holes 35 can be formed for every light-transmitting groove 36. Although in the embodiment of Fig. 4, two light-transmitting holes 35 are formed for every light-transmitting groove 36, it is obvious that three or more light-transmitting holes 35 can be formed for every light-transmitting groove 36. Embodiment 3 Although in Embodiment 1, the light-transmitting holes 35 and the light-transmitting grooves 36 were formed radially, the gist of the present invention is not limited thereto, so that as in Embodiment 3 shown in Fig. 5, the light-transmitting holes 35 and the light-transmitting grooves 36 can be tilted at a constant angle from the radial line X-X extending from the rotational center O of the non-transparent plate 30. Although in Embodiment 1, the light-transmitting grooves 36 were formed after the light-transmitting holes 35, the grooves 36 may be formed before the light-transmitting holes 35. Although in Embodiment 1, the center hole 31, the mounting-and-positioning hole 32, the mounting holes 32b, the positioning hole 33, the Z phase signal detection hole 34 were formed in the non-transparent disk plate, in addition to the light-transmitting holes 35 and the light-transmitting grooves 36, not all of these holes need to be formed, so that only those required may be formed, as required. In addition, the arrangement of the holes 31 to 34 is not limited to that of Embodiment 1, so that they may be appropriately arranged, as required. According to the present invention, in order to form light-transmitting apertures in the code plate, a plurality of light-transmitting grooves recessed inward from the outer peripheral edge of the non-transparent disk are formed, and one or more light-transmitting holes are formed between the light-transmitting grooves. Accordingly, when the light-transmitting apertures are produced so that either the light-transmitting holes or the light-transmitting grooves are formed first, followed by formation of either the light-transmitting holes or the light-transmitting grooves which have not been formed yet, the light-transmitting holes and the light-transmitting grooves can be formed accurately. Therefore, it is possible to produce a more reliable light-transmission type rotary encoder with a high resolution and having light-transmitting apertures disposed at a narrow pitch, as a result of which various control operations with high responsivity can be achieved using the rotary encoder. Forming a plurality of light-transmitting grooves and light-transmitting holes, as light-transmitting apertures to be formed in the code plate, can reduce the number of expensive light-transmitting hole opening pins in correspondence with the number of light-transmitting grooves and can simplify the die construction to thereby reduce die production costs. In addition, maintenance costs for repairing broken light-transmitting hole opening pins can be reduced, resulting in reduced overall production costs of the light-transmission type rotary encoder.

Claims: A code plate of a light transmission type rotary encoder, said code plate comprising: a non-transparent disk (30) and light transmitting apertures (35, 36) formed with a same width (w) and at the same radius (R 3 ) from the center of rotation (O) of said non-transparent disk (30), wherein said light transmitting apertures (35, 36) are in the form of a plurality of light-transmitting grooves (36) being cut out so as to be recessed inward from the outer peripheral edge of said non-transparent disk (30), and one or more light transmitting holes (35) being formed between adjacent light-transmitting grooves (36).

Inventors: SANO TADASHI, SANO, TADASHI
Applicants: ALPS ELECTRIC CO LTD, ALPS ELECTRIC CO., LTD.
Application year: 1997
Main classification: G01D5
IPC codes: G01D5