JP2005127378A - Bearing with absolute encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bearing with an absolute encoder capable of detecting an absolute angle, and obtaining an original point signal with high accuracy without providing a detected part separately from that for detecting the absolute angle. <P>SOLUTION: This bearing with absolute encoder has a rolling bearing part 1 comprising a rotary side race ring 2, a stationary side race ring 3, and a rolling element 4. A detected part 7 with its magnetic characteristic periodically changed in a circumferential direction is attached to the rotary side race ring 2. A magnetic detecting part 8 opposed to the detected part 7, and a magnetic detecting circuit 9 processing output signals of the magnetic detecting part 8 and outputting them to the outside are attached to the stationary side race ring 3. The magnetic characteristic of the detected part 7 against the magnetic detecting part 8 is obtained by change with one rotation of the rotary side race ring 2 as one period, and is designed to steeply rise or fall in a sinusoidal wave form near a zero crossing point. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bearing with an absolute encoder that has an absolute angle detection function and is used for various devices such as robot joints.

  Focusing on the advantage of being compact and easy to assemble, there is one in which a rotation sensor is built in a rolling bearing. An example is shown in FIG. The rolling bearing 51 in FIG. 1 includes a rolling element 54 held by a retainer 55 between an inner ring 52 that is a rotating side raceway and an outer ring 53 that is a fixed side raceway. An annular magnetic encoder 56 is fixed to 52. A magnetic sensor 57 made of, for example, a Hall element is fixed to the outer ring 53 so as to face the magnetic encoder 56. The magnetic encoder 56 is made of, for example, a rubber magnet and has N poles and S poles alternately magnetized in the circumferential direction. The magnetic sensor 57 is resin-molded in a state inserted in the resin case 58, and is fixed to the outer ring 53 by fitting the resin case 58 to the outer ring 53 via the metal case 59.

  With this configuration, as the inner ring 52 rotates, the magnetic sensor 57 detects the magnetic pole change of the magnetic encoder 56 as shown in FIG. 7, and the detected signal is an incremental rotation pulse signal as shown in FIG. Become. The number of rotations of the inner ring 52 can be known from this signal.

  However, with such a configuration, although an incremental rotation pulse signal can be obtained, the absolute rotation angle cannot be known. In this case, in order to know the absolute rotation angle, the number of pulses must be counted after performing an initialization operation when the power is turned on.

  As a solution to such a problem, as shown in FIG. 9, a magnetic characteristic of a radial type detected portion 61 provided in an inner ring is changed, for example, in a sinusoidal shape with one rotation of the inner ring as one cycle. (Japanese Patent Application No. 2003-101396). The magnetic detection unit 60 that detects the magnetic change of the detected unit 61 includes two magnetic sensors 60A and 60B that are arranged with a predetermined interval (here, a phase difference of 90 degrees) in the circumferential direction. . According to this configuration, since the magnetic characteristic of the detected portion 61 is changed with one rotation as one cycle, an absolute angle can be easily output. Further, in this case, a rectangular signal of one cycle per rotation can be obtained as an origin signal by subjecting the differential output of the two magnetic sensors 60A and 60B to rectangular processing (comparing). Alternatively, a rectangular signal can be obtained by comparing the sine wave output of one of the two magnetic sensors 60A and 60B with the center voltage of the output amplitude, and this can be used as the origin signal.

  However, in the case of the above configuration, a highly accurate origin signal cannot be obtained due to variations in threshold values of the magnetic sensors 60A and 60B and the influence of demagnetization of the detected portion 61 due to temperature. For this reason, when repeated origin detection accuracy is strictly required, it is necessary to provide an origin detection target part and a magnetic detection part separately from the absolute angle detection to generate an origin signal.

  An object of the present invention is to provide a bearing with an absolute encoder that can detect an absolute angle and can obtain a highly accurate origin signal without providing a detected part separate from that for detecting an absolute angle. It is.

A bearing with an absolute encoder according to the present invention includes a rolling bearing portion including a rotating side race ring, a fixed side race ring, and a rolling element, and a covered bearing that is attached to the rotary side race ring and whose magnetic characteristics are periodically changed in the circumferential direction. A detection unit, a magnetic detection unit mounted on the fixed-side raceway facing the detected unit, and a magnetic detection unit that supplies power to the magnetic detection unit, processes an output signal of the magnetic detection unit, and outputs the processed signal to the outside A bearing with an absolute encoder, wherein the magnetic characteristic of the detected portion with respect to the magnetic detection portion is changed with one rotation of the rotation side raceway as one cycle,
The magnetic characteristic of the detected portion is characterized by a sine wave shape and a steep rising or falling edge near the zero cross than the sine wave. The magnetic detection circuit, for example, processes the output signal of the magnetic detection unit and outputs an absolute angle detection signal and an origin signal.
According to this configuration, the absolute angle can be detected because the magnetic characteristic of the detected portion with respect to the magnetic detection portion is changed with one rotation of the rotation-side raceway as one cycle. In addition, since the magnetic characteristics of the detected part are sinusoidal and rise or fall steeper than the sine wave near the zero cross, a highly accurate origin signal can be obtained using the output signal of the magnetic detection part. Can be generated. In this way, an absolute angle can be detected, and a highly accurate origin signal can be obtained without providing a detected part separate from that for absolute angle detection.
The magnetic detection circuit may output only the origin signal by processing the output signal of the magnetic detection unit, and may not have an absolute angle detection signal output function.

In the present invention, a plurality of magnetic sensors may be arranged as the magnetic detection unit, and one or more of the magnetic sensors may be origin signal generating means for generating an origin signal.
By arranging a plurality of magnetic sensors, the absolute angle can be easily detected by detecting the detected portion that changes with one rotation as one cycle. As the origin signal generating means, any one of a plurality of magnetic sensors used for detecting an absolute angle may be used, or another magnetic sensor may be used. If a magnetic sensor for detecting an absolute angle is used for origin detection, the number of magnetic sensors can be reduced and the configuration is simplified. If a dedicated magnetic sensor is used for origin detection, a magnetic sensor having characteristics suitable for origin detection can be used, and a more accurate origin signal can be obtained.

In the present invention, the magnetic sensor serving as the origin signal generating means may be a latch type or switch type Hall IC.
In the case of this configuration, the output of the magnetic sensor serving as the origin signal generation means can be used as a rectangular wave origin signal.

  In these inventions, the origin signal may be used for direction detection of the origin position return operation. For example, the direction of the home position return operation can be easily understood by incorporating the absolute encoder bearing of any one of the above configurations of the present invention into a portion where the operation rotation angle is limited, such as a robot arm. In the control means for rotating the movable part using the bearing with the absolute encoder of the present invention for the rotatable support of the movable part in which the operation rotation angle is limited, the movable part is set at the start of the operation after the power is turned on. The origin signal may be used to detect the rotation direction when returning to the origin position.

  The bearing with an absolute encoder according to the present invention includes a rolling bearing portion including a rotating side race ring, a fixed side race ring, and a rolling element, and a covered bearing that is attached to the rotary side race ring and whose magnetic characteristics are periodically changed in the circumferential direction. A detection unit, a magnetic detection unit mounted on the fixed-side raceway facing the detected unit, and a magnetic detection unit that supplies power to the magnetic detection unit, processes an output signal of the magnetic detection unit, and outputs the processed signal to the outside A magnetic circuit board having an absolute encoder, wherein the magnetic characteristic of the detected part with respect to the magnetic detecting part is changed with one rotation of the rotation-side raceway as one cycle. It is wavy and has a sharper rise or fall than the sine wave near the zero cross, so that it can detect absolute angles and provide a part to be detected that is separate from absolute angle detection. Ku, it is possible to obtain a high-precision origin signal.

  A first embodiment of the present invention will be described with reference to FIGS. This bearing with an absolute encoder includes a rolling bearing portion 1 having a rotating side race ring 2 and a fixed side race ring 3 that are rotatable with respect to each other via a rolling element 4, and a detected portion provided at one end portion of the rotating side race ring 2. 7, a magnetic detection unit 8 attached to one end portion of the fixed-side track ring 3 so as to face the detected portion 7, and a magnetic detection circuit 9. The magnetic detection circuit 9 is an electronic component mounted on a circuit board, but may be composed of a single chip. The rolling bearing portion 1 is formed of a deep groove ball bearing, and an inner ring thereof serves as a rotating side race and an outer ring serves as a fixed side race. The raceway surfaces 2 a and 3 a of the rolling element 4 are formed on the outer diameter surface of the rotation side raceway ring 2 and the inner diameter surface of the fixed side raceway ring 2, and the rolling element 4 is held by a cage 5. The annular space between the rotation-side raceway 2 and the fixed-side raceway 3 is sealed with a seal member 6 at the end opposite to the installation side of the detected portion 7 and the magnetic detection portion 8.

  The detected portion 7 is a radial type, and is an annular component in which the magnetic characteristics with respect to the magnetic detecting portion 8 are changed in the circumferential direction. This magnetic characteristic changes with one rotation of the rotation-side race 2 as one cycle. Specifically, it comprises an annular back metal 12 and a magnetic generating member 13 provided on the outer peripheral side thereof and magnetized with magnetic poles N and S that change in the circumferential direction. The magnetization distribution is sinusoidal with one rotation as one cycle. In particular, here, the magnetic characteristics rise or fall sharper than the sine wave A in the vicinity of the magnetic flux 0, that is, near the zero cross, as shown by the sine wave waveforms B, C, and D shown by broken lines in FIG. It is trying to become. Note that this sinusoidal magnetization distribution has a steep rise or rise as described above than a sine wave having the same area surrounded by a half period of the curve indicating the waveform and the coordinate axis of the zero value. It is trying to become. The detected portion 7 is fixed to the rotating side race 2 through a back metal 12. The magnetism generating member 13 is a rubber magnet, for example, and is vulcanized and bonded to the back metal 12. The magnetism generating member 13 may be formed of a plastic magnet or a sintered magnet. In this case, the back metal 12 is not necessarily provided.

  In FIG. 1, the magnetic detection unit 8 includes two magnetic sensors 8A and 8B that generate an output signal corresponding to the magnetic flux density. These two magnetic sensors 8A and 8B are arranged with a predetermined interval (here, a phase difference of 90 °) in the circumferential direction as shown in FIG. Both of these magnetic sensors 8A and 8B are composed of analog sensors. These magnetic sensors 8A and 8B are mounted on the circuit board of the magnetic detection circuit 9 as shown in FIG. 5A, and are inserted into the resin case 10 together with the circuit board of the magnetic detection circuit 9 and then resin-molded. By fixing the resin case 10 to the fixed-side raceway 3 via the metal case 11, the magnetic sensors 8A and 8B and the magnetic detection circuit 9 are attached to the fixed-side raceway 3. The magnetic detection circuit 9 is a circuit for processing the power supply to the magnetic detection unit 8 and the output signal of the magnetic detection unit 8 and outputting the processed signal to the outside. The magnetic detection circuit 9 generates an absolute angle output and an origin position output as shown below as processing of the output signal. The magnetic detection circuit 9 may be provided outside.

According to the bearing with an encoder having this configuration, the detected portion 7 has a sinusoidal magnetization distribution with one rotation as one cycle, and the two magnetic sensors 8A and 8B are provided with a phase difference of 90 °. Quadrant discrimination is possible from the outputs of the magnetic sensors 8A and 8B, and the absolute rotation angle of the rotating side race 2 can be known. In addition, since the magnetic characteristics of the detected portion 7 are steeply rising or falling in the vicinity of the zero cross, the variation in threshold values of the magnetic sensors 8A and 8B and the influence on the demagnetization of the magnet due to temperature are affected. The origin signal can be generated with high accuracy by using the outputs of the magnetic sensors 8A and 8B. Therefore, it can be used in applications that require repeated origin accuracy.
In this case, the origin signal is generated by taking a difference between the outputs of the two magnetic sensors 8A and 8B and performing a rectangular process (comparing) to output a rectangular signal of one rotation and one cycle as an origin signal. Alternatively, the output of one of the magnetic sensors 8A (8B) may be compared with the center voltage of the output amplitude of the sine wave to output a rectangular signal as an origin signal.

  Incidentally, if the magnetic characteristic of the detected portion 7 is such that the change in magnetic flux near the magnetic flux 0 is loose like the sine wave A shown by the solid line in FIG. The origin signal generated by the origin detection processing does not have good origin detection accuracy repeatedly. As in waveforms B, C, and D in this embodiment, when steep rises or falls near the zero cross, even if the absolute angle detection accuracy is somewhat reduced, repeated origin accuracy is required. Suitable for the intended use.

Further, in this embodiment, apart from the two magnetic sensors 8A and 8B, as shown by a chain line in FIG. 1B, the detected portion 7 and the magnetic sensor 8A and 8B are not in phase with each other. A third magnetic sensor 8C may be provided at a predetermined position on the concentric circumference, and this magnetic sensor 8C may be used as the origin signal generating means. In this case, the magnetic sensor 8C is a one-side magnetic field operation type (ie, switch type) or alternating magnetic field operation type (ie, latch type) digital output sensor. For example, a Hall IC is used as the magnetic sensor 8C as the digital output sensor.
FIG. 3 shows an origin signal generated when the magnetic sensor 8C is an alternating magnetic field operation type digital output sensor. As can be seen from the figure, an origin signal is obtained. Therefore, in this case, the absolute angle can be obtained from the outputs of the two magnetic sensors 8A and 8B having a sine wave shape, and the origin signal can be obtained from the output of the third magnetic sensor 8C having a rectangular wave shape.

Note that only one of the two magnetic sensors 8A and 8B is provided, and an absolute value is obtained from the sinusoidal waveform of the magnetic sensor 8A or the magnetic sensor 8B and the rectangular wave output from the third magnetic sensor 8C. An angle detection signal may be generated. In this case, both the absolute position and the origin signal can be obtained with two signals.
Further, in the bearing with the absolute encoder according to the first embodiment, the magnetic detection circuit 9 does not have a means for calculating the absolute angle, and only generates the output of the origin position as the processing of the output signal. good. In that case, only one of the magnetic sensors 8A to 8C may be provided.

  4A and 4B are a plan view and a cross-sectional view of a robot arm device incorporating a bearing with an absolute encoder according to any of the above embodiments. The robot arm device 15 includes a first arm portion 16 fixed to the outer ring 3 of the absolute encoder bearing 14 and a second arm portion 17 fixed to the inner ring 2 of the encoder bearing 14. In this case, the movable rotation angle of both arm parts 16 and 17 is limited to mechanical interference. For example, when the second arm portion 17 is operated by an actuator (not shown) or the like as indicated by a broken line in FIG. 4A, the absolute position of the second arm portion 17 can be determined by the bearing 14 when the power is turned on. When obtaining the position accuracy, it is necessary to perform origin position return (initialization) using a highly accurate origin detection function provided in the bearing 14. In this origin position return operation, in order to avoid mechanical interference, it is necessary to rotate the second arm portion 17 in the return operation, that is, in the direction in which the origin is located. In this case, a means for knowing in which direction the second arm portion 17 operates with respect to the origin position is necessary.

  In this embodiment, a method for detecting the rotation direction for returning to the origin position using only the origin signal will be described. In FIG. 4A, the encoder bearing 14 is set to detect the origin at the origin position a of the second arm portion 17. Thus, when the second arm unit 17 is operated, for example, an origin signal obtained by the magnetic sensor 8C of FIG. 1B or an origin signal obtained by processing one of the detection signals of the magnetic sensors 8A and 8B. 5 and the position of the second arm portion 17 is as shown in FIG. That is, for example, in FIG. 4A, when the second arm portion 17 is at the position b, the origin signal is at a high level, and it can be seen from this that the operation direction in which the origin can be detected is counterclockwise. Further, in FIG. 4A, when the second arm portion 17 is at the position c, the origin signal is at a low level, which indicates that the operation direction in which the origin can be detected is clockwise.

  In this embodiment, the direction of the origin may be detected from the detected value of the absolute position. However, according to the means using the origin signal shown in FIGS. 4 and 5, the origin position return can be performed without detecting the absolute angle. The direction of rotation can be detected. Therefore, the magnetic detection circuit may be one in which an arithmetic circuit for calculating an absolute angle is omitted.

(A) is sectional drawing of the bearing with an absolute encoder concerning one Embodiment of this invention, (B) is the II sectional view taken on the line in (A). It is the magnetization distribution of the to-be-detected part in the same bearing. It is a wave form diagram of the origin signal generated from the magnetism detection part in the bearing. (A) is a top view of the robot arm which mounts the same bearing, (B) is the IV-IV sectional view taken on the line in (A). It is explanatory drawing which shows the relationship between the position of the 2nd arm part of a robot arm apparatus, and an origin signal. It is sectional drawing of a prior art example. It is explanatory drawing which shows the relationship between the magnetic sensor and magnetic encoder in the prior art example. It is a wave form diagram of a detection signal of the magnetic sensor. It is explanatory drawing which shows the relationship between the to-be-detected part and the magnetic detection part in the proposal example of a bearing with an absolute encoder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rolling bearing part 2 ... Rotation side race ring 3 ... Fixed side race ring 4 ... Rolling body 7 ... Detected part 8 ... Magnetic detection part 8A-8C ... Magnetic sensor 9 ... Magnetic detection circuit

Claims (4)

A rolling bearing unit composed of a rotating side race ring, a fixed side race ring, and a rolling element, a detected portion that is attached to the rotating side race ring and whose magnetic characteristics are periodically changed in the circumferential direction, and the detected portion A magnetic detection unit opposed to the fixed-side raceway; and a magnetic detection circuit that supplies power to the magnetic detection unit, processes an output signal of the magnetic detection unit, and outputs the processed signal to the outside. A magnetic encoder bearing having an absolute encoder in which the magnetic characteristic of the magnetic detection unit is changed with one rotation of the rotation-side raceway as one cycle,
A bearing with an absolute encoder, characterized in that the magnetic characteristics of the detected portion are sinusoidal and rise or fall sharper than the sine wave in the vicinity of the zero cross.   The bearing according to claim 1, wherein a plurality of magnetic sensors are arranged as the magnetic detection unit, and one or more of the magnetic sensors are used as origin signal generation means for generating an origin signal.   3. The bearing according to claim 2, wherein the magnetic sensor serving as the origin signal generating means is a latch type or switch type Hall IC. The bearing according to any one of claims 1 to 3, wherein the origin signal is used for direction detection of the origin position return operation.

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