Position detecting device

At a time that a position detecting device is initiated, an arithmetic processing unit calculates the absolute position of a rotating shaft at the time of initiation, on the basis of first to third analog signals corresponding to first to third angles of rotation, which are detected respectively by first to third rotational angle detectors. During rotation of the rotating shaft, a current position counter detects a current absolute position of the rotating shaft by counting a number of pulses of forward rotation pulses or reverse rotation pulses, corresponding to the first angle of rotation detected by the first rotational angle detector, taking as a standard a total number of pulses corresponding to the absolute position of the rotating shaft at the time of initiation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Applications No. 2016-126346 filed on Jun. 27, 2016 and No. 2017-110919 filed on Jun. 5, 2017, the contents all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a position detecting device which, in the event that a speed reducing mechanism is connected to a rotating shaft of a rotating body, is adapted to detect an absolute position of the rotating shaft based on an angle of rotation of the rotating shaft and an angle of rotation of an output shaft of the speed reducing mechanism.

Description of the Related Art

Heretofore, a position detecting device for detecting an absolute position of a rotating shaft of a rotating body has been installed on an electric actuator or the like equipped with a rotating body such as a motor or the like. This type of position detecting device is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2013-164316, Japanese Laid-Open Patent Publication No. 2012-145380, Japanese Laid-Open Patent Publication No. 2007-078459, Japanese Laid-Open Patent Publication No. 2002-513923 (PCT), Japanese Laid-Open Patent Publication No. 64-023107, and Japanese Laid-Open Patent Publication No. 2003-161641.

In Japanese Laid-Open Patent Publication No. 2013-164316, Japanese Laid-Open Patent Publication No. 2012-145380, and Japanese Laid-Open Patent Publication No. 2007-078459, there are disclosed multi-rotational-angle detection type position detecting devices in which a planetary gear is used in a speed reducing mechanism connected to a rotating shaft of a rotating body. In Japanese Laid-Open Patent Publication No. 2002-513923 (PCT) and Japanese Laid-Open Patent Publication No. 64-023107, there are disclosed position detecting devices in which a code recording medium is attached to a rotating shaft of a rotating body, together with attaching a multi-rotational angle detector attached to an output shaft of a speed reducing mechanism connected to the rotating shaft. In Japanese Laid-Open Patent Publication No. 2003-161641, there is disclosed a position detecting device in which data of a detected angle of rotation of a rotating shaft is converted into an absolute position, after having converted orthogonal coordinates into polar coordinates.

SUMMARY OF THE INVENTION

However, with the position detecting devices of Japanese Laid-Open Patent Publication No. 2013-164316, Japanese Laid-Open Patent Publication No. 2012-145380, and Japanese Laid-Open Patent Publication No. 2007-078459, magnets are attached to the shafts of a plurality of driven gears, and a plurality of sets of rotational angle detectors are attached at positions relative thereto. Therefore, in such position detecting devices, there is a disadvantage in that the size in the radial direction of the rotating shaft becomes greater.

Further, in the position detecting devices of Japanese Laid-Open Patent Publication No. 2002-513923 (PCT) and Japanese Laid-Open Patent Publication No. 64-023107, the code recording medium attached to the rotating shaft serves as an absolute position disc on which a specialized scannable code is deposited by vapor deposition or the like. Therefore, high accuracy is required, and such position detection devices tend to be high in cost.

Further, with the position detecting device of Japanese Laid-Open Patent Publication No. 2003-161641, in order to enable the absolute position to be output in real time, a high speed arithmetic processing unit is required.

The present invention has been devised with a view to solving the aforementioned problems, and has the object of providing a position detecting device, which is both small in size and low in cost, and is capable of carrying out arithmetic processing to calculate an absolute position using a low speed arithmetic processing device.

The present invention relates to a position detecting device in which a speed reducing mechanism is connected to a rotating shaft of a rotating body, and which is configured to detect an absolute position of the rotating shaft, on a basis of an angle of rotation of the rotating shaft and an angle of rotation of an output shaft of the speed reducing mechanism.

In addition, in order to accomplish the aforementioned object, the position detecting device according to the present invention includes first to third rotational angle detectors, an arithmetic processing unit, and a current position detecting unit.

The first rotational angle detector is configured to detect a first angle of rotation in a pitch interval of a gear attached substantially coaxially to the rotating shaft. The second rotational angle detector is configured to detect a second angle of rotation lying within one rotation of the rotating shaft. The third rotational angle detector is configured to detect a third angle of rotation lying within one rotation of the output shaft and corresponding to multiple rotations of the rotating shaft.

The arithmetic processing unit is configured to calculate an absolute position of the rotating shaft at a time of initiation of the position detecting device, on a basis of the first to third angles of rotation detected respectively by the first to third rotational angle detectors at the time of initiation. The current position detecting unit is configured to detect a current absolute position of the rotating shaft during rotation of the rotating shaft upon driving of the rotating body, on a basis of the first angle of rotation detected by the first rotational angle detector, and the absolute position of the rotating shaft at the time of initiation.

In accordance with the above configuration, the gear, the speed reducing mechanism, and the output shaft are disposed along the axial direction of the rotating shaft, and the first to third rotational angle detectors are arranged around the rotating shaft and the output shaft. Consequently, in the position detecting device, the size in the radial direction of the rotating shaft can be reduced.

Further, the first rotational angle detector detects the first angle of rotation in a pitch interval of the gear attached to the rotating shaft. Therefore, there is no need to provide a code recording medium on which a specialized code is carried, as disclosed in Japanese Laid-Open Patent Publication No. 2002-513923 (PCT) and Japanese Laid-Open Patent Publication No. 64-023107. Accordingly, the position detecting device can be produced at a reduced cost.

Furthermore, only at the time of initiation, and on the basis of the first to third angles of rotation, the arithmetic processing unit calculates the absolute position of the rotating shaft, which is in a stopped state at the time of initiation. As a result, during rotation of the rotating shaft, the current position detecting unit is capable of determining in a pseudo manner the current absolute position of the rotating shaft, from the first angle of rotation detected by the first rotational angle detector, taking as a standard the absolute position of the rotating shaft at the time of initiation.

More specifically, the position detecting device functions as an absolute type rotary encoder only at the time of initiation, and thereafter, functions as an incremental type rotary encoder. Stated otherwise, at the time of initiation, the absolute position of the rotating shaft in a stopped state is detected, and thereafter, during rotation of the rotating shaft, the first angle of rotation corresponding to the amount of movement of the rotating shaft with respect to the absolute position thereof at the time of initiation is detected. In addition, the position of the first angle of rotation with respect to the absolute position at the time of initiation may be determined as the current absolute position of the rotating shaft. As a result, calculating the absolute position in real time as in Japanese Laid-Open Patent Publication No. 2003-161641 is rendered unnecessary, and thus, it is possible to use a low speed and low cost arithmetic processing unit (CPU).

Further, in a conventional incremental rotary encoder, whenever the power supply is turned on and off, it is necessary to perform a magnetic pole detection operation and an origin point return operation. In contrast thereto, with the present invention, since the absolute position of the rotating shaft in the stopped state is detected at the time of initiation, the respective operations described above are unnecessary. As a result, if the position detecting device is installed in an electric actuator, it becomes possible to shorten the tact time.

In the foregoing manner, according to the present invention, it is possible to realize a smaller scale and a reduction in cost of the position detecting device, together with carrying out arithmetic processing to calculate an absolute position using a low speed arithmetic processing device.

In this instance, the first to third rotational angle detectors preferably are constituted in the manner described below.

Initially, the first rotational angle detector comprises a spur gear made up from a magnetic material and attached substantially coaxially with the rotating shaft, two first magnetic detecting elements disposed in facing relation to the spur gear, and with phases shifted mutually by 90°, in a case that an interval between tooth ends of the spur gear is defined as one cycle, and a first bias magnet. In this case, the first magnetic detecting elements are configured to output first analog signals, respectively, corresponding to the first angle of rotation, and whose phases are shifted mutually by 90°.

Accordingly, in the case that the magnetic field generated by the first bias magnet in a region including the respective first magnetic detecting elements undergoes a change due to rotation of the spur gear, each of the first magnetic detecting elements outputs the change in the magnetic field, respectively, as respective first analog signals. Since the respective first analog signals are signals that correspond to the first angle of rotation, the arithmetic processing unit is capable of highly accurately determining that the absolute position of the rotating shaft at the time of initiation corresponds to the position of a certain numbered tooth of the gear, based on the first analog signals, etc. Further, since a commercially available spur gear can be used, in comparison with the configurations of Japanese Laid-Open Patent Publication No. 2002-513923 (PCT) and Japanese Laid-Open Patent Publication No. 64-023107, a further reduction in cost of the position detecting device can be realized.

Next, the second rotational angle detector comprises a ring shaped second bias magnet attached substantially coaxially with the rotating shaft, and two second magnetic detecting elements disposed in facing relation to the second bias magnet, and with phases shifted mutually by 90°, in a case that one rotation of the rotating shaft is defined as one cycle. In this case, the second magnetic detecting elements are configured to output second analog signals, respectively, corresponding to the second angle of rotation, and whose phases are shifted mutually by 90°.

Accordingly, in the case that the magnetic field generated by the second bias magnet in a region including the respective second magnetic detecting elements undergoes a change, each of the second magnetic detecting elements outputs the change in the magnetic field, respectively, as respective second analog signals. Since the respective second analog signals are signals that correspond to the second angle of rotation, the arithmetic processing unit is capable of easily determining that the absolute position of the rotating shaft at the time of initiation corresponds to a certain angle within one rotation of the rotating shaft, based on the second analog signals, etc.

Further, the third rotational angle detector comprises a ring shaped third bias magnet attached substantially coaxially with the output shaft, and two third magnetic detecting elements disposed in facing relation to the third bias magnet, and with phases shifted mutually by 90°, in a case that one rotation of the output shaft is defined as one cycle. In accordance with this feature, the third magnetic detecting elements are configured to output third analog signals, respectively, corresponding to the third angle of rotation, and whose phases are shifted mutually by 90°.

Accordingly, in the case that the magnetic field generated by the third bias magnet in a region including the respective third magnetic detecting elements undergoes a change, each of the third magnetic detecting elements outputs the change in the magnetic field, respectively, as respective third analog signals. In this case, the speed reducing mechanism decelerates the rotational speed of the rotating body at a predetermined speed reduction ratio, and rotates the output shaft. Therefore, on the basis of the respective third analog signals, the arithmetic processing unit is capable of easily determining that the absolute position of the rotating shaft at the time of initiation corresponds to a certain angle within multiple rotations of the rotating shaft.

The position detecting device may further comprise an interpolator configured to convert the respective first analog signals output respectively by each of the first magnetic detecting elements into two-phase first pulse signals. In this case, the arithmetic processing unit is configured to calculate the absolute position of the rotating shaft at the time of initiation, based on each of the first to third analog signals output respectively by the first to third rotational angle detectors, and output a second pulse signal corresponding to the calculated absolute position.

Consequently, the current position detecting unit is capable of easily detecting the current absolute position of the rotating shaft on a basis of the first pulse signals output from the interpolator, and the second pulse signal output from the arithmetic processing unit. Further, regardless of the forward or reverse rotation of the rotating shaft, it is possible to ignore the influence of any backlash in the speed reducing mechanism.

In this case, the arithmetic processing unit may be configured to transmit the second pulse signal to the current position detecting unit as a serial signal including a number of pulses corresponding to the absolute position of the rotating shaft at the time of initiation. In accordance with this feature, a relatively low speed arithmetic processing unit can be used as the arithmetic processing unit, and by transmitting the serial signal to the current position detecting unit by way of serial communications, it is possible to further reduce the cost of the position detecting device.

The position detecting device may further include a multiplication circuit configured to generate a multiplied pulse signal obtained by multiplying each of the first pulse signals, and output the multiplied pulse signal to the current position detecting unit. In this case, the current position detecting unit may be a current position counter, which is configured to preset a number of pulses corresponding to the serial signal at the time of initiation, and during rotation of the rotating shaft, configured to count the number of pulses corresponding to the multiplied pulse signal from the preset number of pulses, thereby detecting the current absolute position of the rotating shaft.

In accordance with this feature, the current position counter, using the preset number of pulses as a reference, counts the number of pulses corresponding to the multiplied pulse signal, and therefore, is capable of easily and highly efficiently determining the current absolute position of the rotating shaft. Further, by supplying the multiplied pulse signal from the multiplication circuit to the current position counter, the resolution of the current absolute position of the rotating shaft in the current position counter is improved, and the absolute position can be obtained with high accuracy.

In this case, the multiplication circuit may be configured to determine a forward rotation or a reverse rotation of the rotating shaft by comparing the respective first pulse signals, and generate the multiplied pulse signal of the determined forward rotation or reverse rotation. Consequently, the current position counter is capable of accurately determining the current absolute position of the rotating shaft.

The position detecting device may further include a rotating body drive control unit configured to rotate the rotating shaft by driving the rotating body, in an event that the number of pulses corresponding to the serial signal is preset in the current position counter. Owing thereto, the rotating body can be operated after such presetting, and the absolute position of the rotating shaft during rotation of the rotating shaft can reliably be acquired.

Further, in the position detecting device according to the present invention, the above-mentioned configuration (also referred to as the basic configuration) can be exchanged with the following configurations.

That is, in order to accomplish the aforementioned object, the position detecting device according to the present invention, as another first configuration, includes a first rotational angle detector, a second rotational angle detector, an arithmetic processing unit, and a current position detecting unit.

The first rotational angle detector is configured to detect a first angle of rotation lying within one rotation of the rotating shaft. The second rotational angle detector is configured to detect a second angle of rotation lying within one rotation of the output shaft and corresponding to multiple rotations of the rotating shaft. The arithmetic processing unit is configured to calculate the absolute position of the rotating shaft at a time of initiation of the position detecting device, on a basis of the first angle of rotation and the second angle of rotation detected respectively by the first rotational angle detector and the second rotational angle detector at the time of initiation. The current position detecting unit is configured to detect a current absolute position of the rotating shaft during rotation of the rotating shaft upon driving of the rotating body, on a basis of the first angle of rotation detected by the first rotational angle detector, and the absolute position of the rotating shaft at the time of initiation.

In this case, the first rotational angle detector comprises a cylindrical bias magnet which is substantially coaxially attached to the rotating shaft, and a magnetic detecting element which is arranged in facing relation to the bias magnet. The magnetic detecting element is configured to output to the arithmetic processing unit a serial signal corresponding to the first angle of rotation, and further output to the current position detecting unit two-phase pulse signals which correspond to the first angle of rotation and whose phases are shifted mutually by 90°.

In this first configuration, the magnetic detecting element has both functions of outputting the serial signal to the arithmetic processing unit and of outputting the two-phase pulse signals to the current position detecting unit as interpolation processing. Further, the arithmetic processing unit calculates the absolute position of the rotating shaft at the time of initiation, on the basis of the serial signal, and the second angle of rotation detected by the second rotational angle detector. Therefore, according to the first configuration, the position detecting device can be produced at a reduced cost since the number of parts of the position detecting device is reduced, and computation load in the arithmetic processing unit is reduced. Further, since the cylindrical bias magnet is adopted, the detection accuracy of the first angle of rotation can be improved.

In the first configuration as well, the following advantageous effects can be achieved, in a manner similar to the case of the position detecting device having the basic configuration described above.

That is, the speed reducing mechanism and the output shaft are disposed along the axial direction of the rotating shaft, and the first rotational angle detector and the second rotational angle detector are arranged around the rotating shaft and the output shaft. Consequently, the size in the radial direction of the rotating shaft can be reduced.

Further, only at the time of initiation, and on the basis of the first angle of rotation and the second angle of rotation, the arithmetic processing unit calculates the absolute position of the rotating shaft, which is in a stopped state at the time of initiation. As a result, during rotation of the rotating shaft, the current position detecting unit is capable of determining in a pseudo manner and easily the current absolute position of the rotating shaft, from the two-phase pulse signals, taking as a standard the absolute position of the rotating shaft at the time of initiation. Furthermore, regardless of the forward or reverse rotation of the rotating shaft, it is possible to ignore the influence of any backlash in the speed reducing mechanism.

More specifically, the position detecting device functions as an absolute type rotary encoder only at the time of initiation, and thereafter, functions as an incremental type rotary encoder. As a result, calculating the absolute position in real time is rendered unnecessary, and thus, it is possible to use a low speed and low cost CPU. If such a position detecting device is installed in an electric actuator or the like, it becomes possible to shorten the tact time.

Consequently, according to the first configuration, it is possible to realize a smaller scale and a reduction in cost of the position detecting device, together with carrying out arithmetic processing to calculate an absolute position using a low speed arithmetic processing device.

The position detecting device may include a rotation transmission mechanism configured to transmit a rotational force of the rotating shaft to an input shaft of the speed reducing mechanism, and the rotating shaft, the input shaft, and the output shaft may be arranged substantially coaxially. Though the position detecting device becomes slightly large in the radial direction due to the rotation transmission mechanism, the number of parts of the position detecting device is reduced because the first rotational angle detector having the interpolation function is used. Thus, it is possible to realize a reduction in cost of the entire device. As the rotation transmission mechanism, various types of rotation transmission mechanisms such as another speed reducing mechanism having the speed reducing ratio of 1 or rotation transmission means using belts can be preferably adopted.

That is, in order to accomplish the aforementioned object, the position detecting device according to the present invention, as another second configuration, includes first to third rotational angle detectors, a first speed reducing mechanism, a second speed reducing mechanism, an arithmetic processing unit, and a current position detecting unit.

The first rotational angle detector is configured to detect a first angle of rotation lying within one rotation of the rotating shaft. The first speed reducing mechanism is configured to decelerate and output a rotational speed of the rotating shaft. The second speed reducing mechanism includes an input shaft connected to the first speed reducing mechanism, and is configured to further decelerate the rotational speed of the rotating shaft which has been decelerated by the first speed reducing mechanism and to output the further decelerated rotational speed to the output shaft. The second rotational angle detector is configured to detect a second angle of rotation lying within one rotation of the input shaft and corresponding to multiple rotations of the rotating shaft. The third rotational angle detector is configured to detect a third angle of rotation lying within one rotation of the output shaft and corresponding to the multiple rotations of the rotating shaft.

The arithmetic processing unit is configured to calculate an absolute position of the rotating shaft at a time of initiation of the position detecting device, on a basis of the first to third angles of rotation detected respectively by the first to third rotational angle detectors at the time of initiation. The current position detecting unit is configured to detect a current absolute position of the rotating shaft during rotation of the rotating shaft upon driving of the rotating body, on a basis of the first angle of rotation detected by the first rotational angle detector, and the absolute position of the rotating shaft at the time of initiation.

In this case, the first rotational angle detector includes a cylindrical bias magnet which is substantially coaxially attached to the rotating shaft, and a magnetic detecting element which is arranged in facing relation to the bias magnet. The magnetic detecting element is configured to output to the arithmetic processing unit a serial signal corresponding to the first angle of rotation, and further output to the current position detecting unit two-phase pulse signals which correspond to the first angle of rotation and whose phases are shifted mutually by 90°.

In this second configuration, compared with the above-mentioned position detecting device equipped with the first and second rotational angle detectors, the position detecting device is equipped with three rotational angle detectors (first to third rotational angle detectors), and two speed reducing mechanisms (first speed reducing mechanism and second speed reducing mechanism). Thus, compared with the first configuration, the number of parts is large, and computation load in the arithmetic processing unit is large, resulting in high cost.

However, the second rotational angle detector and the third rotational angle detector respectively detects the second angle of rotation and the third angle of rotation corresponding to multiple rotations of the rotating shaft, and the arithmetic processing unit is capable of calculating the absolute position of the rotating shaft at the time of initiation with high precision, using the detected second and third angles of rotation, etc. As a result, compared with conventional position detecting devices, the absolute position can be calculated with high precision and the cost can be reduced. Further, since the cylindrical bias magnet is adopted, the detection accuracy of the first angle of rotation can be improved.

In the second configuration as well, because of the first to third rotational angle detectors, the advantageous effects can be achieved in a manner similar to the position detecting device having the basic configuration described above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of a position detecting device according to the present invention will be described in detail below with reference to the accompanying drawings.

Configuration of the Present Embodiment

FIG. 1is a block diagram of a position detecting device10according to a present embodiment.

The position detecting device10includes a rotational angle detecting mechanism16that detects an angle of rotation of a rotating shaft14of a rotating body12such as a motor or the like, and a controller18that controls driving of the rotating body12.

A speed reducing mechanism20is connected to the rotating shaft14. The speed reducing mechanism20decelerates the rotational speed of the rotating shaft14by 1/N, and causes an output shaft22to rotate at such a decelerated speed. N is a speed reduction ratio of the speed reducing mechanism20.

The rotational angle detecting mechanism16comprises first to third rotational angle detectors24to28, an arithmetic processing unit30, and an interpolator32.

As shown inFIGS. 1 to 3, the first rotational angle detector24is an angle detector for a spur gear, made up from a spur gear34which is attached substantially coaxially with the rotating shaft14, two first magnetic detecting elements36a,36bdisposed in facing relation to the spur gear34, and a first bias magnet38disposed behind the first magnetic detecting elements36a,36b(on an outer side in the radial direction of the spur gear34).

For the spur gear34, a commercially available spur gear can be used which is capable of being attached to the rotating shaft14. In the case that an interval (pitch interval) between tooth ends of the spur gear34is defined as one cycle (360°), the two first magnetic detecting elements36a,36bare arranged in facing relation to the spur gear34in a state with the phases thereof being shifted mutually by 90° in the circumferential direction of the spur gear34. The first bias magnet38is arranged in a state with the N-pole thereof on a radial inner side and the S-pole thereof on a radial outer side of the spur gear34, on the rear side of the respective first magnetic detecting elements36a,36b.

In addition, with the first rotational angle detector24, when a magnetic field is generated by the first bias magnet38in a region including the respective first magnetic detecting elements36a,36b, the magnetic field undergoes a change when the spur gear34which is a magnetic body rotates accompanying a rotating operation of the rotating shaft14. Each of the first magnetic detecting elements36a,36bdetects the change in the magnetic field as a voltage change, and outputs the detected voltage as a first analog signal.

FIG. 4Ais a waveform diagram of first analog signals (output voltage waveforms) output from the first magnetic detecting elements36a,36b. InFIG. 4A, the A-phase indicates a first analog signal (sine wave signal) output from one first magnetic detecting element36a, and the B-phase indicates a first analog signal (cosine wave signal) output from the other first magnetic detecting element36b. Further, it should be noted that, inFIG. 4A, the horizontal axis shows the angle of rotation of the spur gear34as time elapses.

As noted previously, since the two first magnetic detecting elements36a,36bare arranged in a state of being shifted 90° in phase, a phase difference of 90° occurs between the A-phase and the B-phase. Further, in the A-phase and the B-phase, the angle of rotation of 360° corresponds to one cycle between the tooth ends of the spur gear34. In other words, the one cycle corresponds to an electrical angle of 360°. Consequently, in the case that the interval between tooth ends of the spur gear34is defined as one cycle, the first rotational angle detector24detects an arbitrary position (first angle of rotation) of the spur gear34within one cycle, and outputs the arbitrary position as a first analog signal to the arithmetic processing unit30and the interpolator32.

The interpolator32is an analog voltage comparison type of phase interpolation circuit in which a resistor network is used. Concerning the respective first analog signals shown inFIG. 4A, by performing interpolation over a predetermined number of divisions S, the first analog signals are converted into two-phase first pulse signals shown inFIG. 4Bwith a phase difference of 90°, which are output to the controller18. In comparison with the transmission of second pulse signals, which will be described later, from the arithmetic processing unit30to the controller18by way of serial communications, transmission of the two-phase first pulse signals from the interpolator32to the controller18takes place at a higher transmission speed.

As shown inFIGS. 1 and 2, the second rotational angle detector26is a one-rotation rotational angle detector, made up from a ring shaped second bias magnet40attached substantially coaxially with the rotating shaft14, and two second magnetic detecting elements42a,42barranged in facing relation to the second bias magnet40.

The second bias magnet40is mounted on the rotating shaft14at a location between the spur gear34and the speed reducing mechanism20. In this case, within the ring shaped second bias magnet40, one semicircular portion thereof is allocated to the N-pole, whereas the other semicircular portion thereof is allocated to the S-pole. The two second magnetic detecting elements42a,42bare Hall elements which, in the case that one rotation of the rotating shaft14and the second bias magnet40is defined as one cycle (360°), are arranged in facing relation to the second bias magnet40in a state with the phases thereof being shifted mutually by 90° in the circumferential direction of the rotating shaft14and the second bias magnet40.

In addition, with the second rotational angle detector26, when a magnetic field is generated by the second bias magnet40in a region including the respective second magnetic detecting elements42a,42b, the magnetic field undergoes a change when the second bias magnet40rotates accompanying a rotating operation of the rotating shaft14. Each of the second magnetic detecting elements42a,42bdetects the change in the magnetic field as a voltage change, and outputs the detected voltage as a second analog signal.

FIG. 5Ais a waveform diagram of second analog signals output from second magnetic detecting elements42a,42b. InFIG. 5A, the letter “A” indicates a second analog signal (cosine wave signal) output from one second magnetic detecting element42a, and the letter “B” indicates a second analog signal (sine wave signal) output from the other second magnetic detecting element42b. Further, inFIG. 5A, the horizontal axis represents the angle of rotation of the rotating shaft14and the second bias magnet40as time elapses.

FIG. 5Bshows a change in the angle of rotation lying within one rotation of the rotating shaft14and the second bias magnet40. In this instance, rotation in a counterclockwise direction with respect to 0° (in a case where the B-phase lags with respect to the A-phase) is defined as a forward rotation, whereas rotation in a clockwise direction (in a case where the A-phase lags with respect to the B phase) is defined as a reverse rotation.

As noted previously, since the two second magnetic detecting elements42a,42bare arranged in a state of being shifted 90° in phase, a phase difference of 90° occurs between the A and B waveforms. Further, in the A and B waveforms, 360° corresponds to one cycle of the rotating shaft14and the second bias magnet40. In other words, the one cycle corresponds to an electrical angle of 360°. Consequently, in the case that one rotation of the rotating shaft14and the second bias magnet40is defined as one cycle, the second rotational angle detector26detects an arbitrary position (second angle of rotation) of the rotating shaft14and the second bias magnet40within one cycle, and outputs the arbitrary position as a second analog signal to the arithmetic processing unit30.

As shown inFIGS. 1 and 2, the third rotational angle detector28is a multi-rotation rotational angle detector, made up from a ring shaped third bias magnet44attached substantially coaxially with the output shaft22, and two third magnetic detecting elements46c,46darranged in facing relation to the third bias magnet44. Within the ring shaped third bias magnet44, one semicircular portion thereof is allocated to the N-pole, whereas the other semicircular portion thereof is allocated to the S-pole. The two third magnetic detecting elements46c,46dare Hall elements which, in the case that one rotation of the output shaft22is defined as one cycle (360°), are arranged in facing relation to the third bias magnet44in a state with the phases thereof being shifted mutually by 90° in the circumferential direction of the output shaft22and the third bias magnet44.

In addition, with the third rotational angle detector28, when a magnetic field is generated by the third bias magnet44in a region including the respective third magnetic detecting elements46c,46d, the magnetic field undergoes a change when the third bias magnet44rotates accompanying a rotating operation of the output shaft22. Each of the third magnetic detecting elements46c,46ddetects the change in the magnetic field as a voltage change, and outputs the detected voltage as a third analog signal.

Accordingly, as shown inFIG. 5A, the waveforms of the third analog signals output from the third magnetic detecting elements46c,46dare waveforms having similar characteristics as those of the second analog signals. Moreover, inFIG. 5A, the letter “C” indicates a third analog signal (cosine wave signal) output from one third magnetic detecting element46c, and the letter “D” indicates a third analog signal (sine wave signal) output from the other third magnetic detecting element46d. Further, since the two third magnetic detecting elements46c,46dare arranged in a state of being shifted 90° in phase, a phase difference of 90° occurs between the C and D waveforms. Furthermore, in the C and D waveforms, an electrical angle of 360° corresponds to one cycle of the output shaft22and the third bias magnet44.

However, the speed reducing mechanism20decelerates the rotational speed of the rotating shaft14by 1/N, and causes the output shaft22to be rotated at such a decelerated speed. Consequently, in the case that one rotation of the output shaft22and the third bias magnet44is defined as one cycle, the third rotational angle detector28detects an arbitrary position (third angle of rotation) of the output shaft22and the third bias magnet44corresponding to multiple rotations of the rotating shaft14, and outputs the arbitrary position as a third analog signal to the arithmetic processing unit30. Therefore, the maximum amount of rotation of the rotating shaft14corresponds to an amount within one rotation of the output shaft22.

The arithmetic processing unit30is constituted by a comparatively low speed and small scale arithmetic processing device (CPU). The arithmetic processing unit30calculates the absolute position of the rotating shaft14in a stopped state at a time of initiation, on the basis of the first to third analog signals from the first to third rotational angle detectors24to28, at the time of initiation of the position detecting device10. In addition, in the case that a request is made from the controller18to transfer the absolute position, the arithmetic processing unit30transfers to the controller18by way of serial communications a serial signal corresponding to the absolute position.

Processing that takes place in the arithmetic processing unit30will now be described in detail. Initially, the arithmetic processing unit30converts the output voltages of the first to third analog signals from rectangular coordinates into polar coordinates.

In this case, concerning the first analog signal, a distance between the tooth ends of the spur gear34defines one cycle (360°), and the one cycle is divided into S individual segments. Further, concerning the second analog signal, one rotation of the rotating shaft14and the second bias magnet40defines one cycle (360°), and the one cycle is divided into T individual segments. Concerning the third analog signal, one rotation of the output shaft22defines one cycle (360°), and the one cycle is divided into N individual segments. Furthermore, the maximum amount of rotation of the rotating shaft14is made to correspond to an amount within one rotation of the output shaft22. Moreover, concerning the conversion process (division process) from rectangular coordinates to polar coordinates, a known type of interpolation method may be applied, as disclosed for example in Japanese Laid-Open Patent Publication No. 2002-513923 (PCT).

In this instance, if the position of the spur gear34is designated by P1 (first angle of rotation), the division number at the spur gear34is designated by S, the position of the second bias magnet40is designated by P2 (second angle of rotation), the division number at the second bias magnet40is designated by T, the position of the third bias magnet44is designated by P3 (third angle of rotation), and the division number at the third bias magnet44is designated by N, then the amount of rotation TA of the rotating shaft14can be expressed by the following equation (1).
TA=(P1÷T)+INT(P2×T÷360)×(360÷T)+(P3×N)  (1)

The term INT(P2×T÷360) implies rounding off of the decimal places of the calculation result of P2×T÷360 to place it in the form of an integer. Further, the division number T is the number of teeth T of the spur gear34, and the division number N is the speed reduction ratio N.

In addition, in the case that the absolute position is transferred by way of serial communications from the arithmetic processing unit30to the controller18, assuming that the number of pulses when the rotating shaft14is rotated one time is represented by PP, then the number of pulses (total number of pulses) TP corresponding to the amount of rotation TA is given by the following equation (2).
TP=TA÷(360÷PP)  (2)

Accordingly, when the calculation result of the total number of pulses TP is rounded to an integer by truncating the decimal portion, the following equation (3) is obtained.
TP=INT(TA×PP÷360)  (3)

Using equations (1) and (3), the arithmetic processing unit30calculates the total number of pulses TP corresponding to the absolute position of the rotating shaft14in a stopped state at the time of initiation, and following calculation thereof, transfers to the controller18a serial signal (second pulse signal) corresponding to the calculated total number of pulses TP.

In this instance, for example, in the case that T=25, N=150, P1=55°, P2=175°, P3=156°, PP=200, and S=8, then TA=23575° and TP=13097.

The controller18includes a serial communications unit50, a multiplication circuit52, a current position counter (current position detecting unit)54, and a rotating body drive control unit56.

The serial communications unit50carries out serial communications with the arithmetic processing unit30. For example, a transfer request for the total number of pulses TP is transmitted with respect to the arithmetic processing unit30, and a serial signal responsive to the transfer request (a second pulse signal of the total number of pulses TP) is received.

The multiplication circuit52multiplies the first pulse signals received from the interpolator32, and following multiplication thereof, outputs the first pulse signals (multiplied pulse signal) to the current position counter54. In this case, as shown inFIGS. 6 and 7, for example, by examining the voltage level of the B-phase at a time when the A-phase is rising, the multiplication circuit52distinguishes between forward rotation or reverse rotation of (the rotating shaft14corresponding to) the two-phase first pulse signals, and generates a multiplied pulse signal of the forward rotation or reverse rotation thus determined.

In the case ofFIG. 6, since the voltage level of the B-phase is of a low level (L level) at times when the A-phase is rising, the multiplication circuit52distinguishes the two-phase first pulse signals as being indicative of forward rotation, and generates a multiplied pulse signal (forward rotation pulse signal) multiplied four times with forward rotation. In the case ofFIG. 7, since the voltage level of the B-phase is of a high level (H level) at times when the A-phase is rising, the multiplication circuit52distinguishes the two-phase first pulse signals as being indicative of reverse rotation, and generates a multiplied pulse signal (reverse rotation pulse signal) multiplied four times with reverse rotation.

FIGS. 6 and 7illustrate one example in which the multiplication circuit52is capable of generating from the two-phase first pulse signals a multiplied pulse signal multiplied one time (×1), two times (×2), or four times (×4). Further, the multiplication circuit52is capable of changing from a multiplied pulse signal having a high scaling factor to a multiplied pulse signal having a low scaling factor (multiplied four times multiplied two times multiplied one time).

At the time of initiation of the position detecting device10, the current position counter54presets the number of total pulses TP acquired by the serial communications unit50. Further, during rotation of the rotating shaft14, the multiplied pulse signal from the multiplication circuit52is input to the current position counter54. Thus, the current position counter54, using the preset total number of pulses TP as a reference, counts the number of pulses corresponding to the multiplied pulse signal, whereby the current absolute position of the rotating shaft14is detected in a pseudo manner.

In the event that the total number of pulses TP is preset in the current position counter54, and by supplying a rotating body operation signal to the rotating body12, the rotating body drive control unit56drives the rotating body12and causes the rotating shaft14to rotate.

Operations of the Present Embodiment

Next, operations of the position detecting device10according to the present embodiment will be described with reference to the sequence diagrams shown inFIGS. 8 and 9. In the description of such operations, as necessary, explanations may also be made while referring toFIGS. 1 through 7.

First, in step S1, the operator turns on the power supply of the controller18of the position detecting device10. Consequently, in step S2, the controller18starts supplying power with respect to the rotational angle detecting mechanism16. As a result, in step S3, the rotational angle detecting mechanism16receives the supply of power from the controller18and is started. In this case, the rotational angle detecting mechanism16activates only the first to third rotational angle detectors24to28and the arithmetic processing unit30.

In the following step S4, the first to third rotational angle detectors24to28detect the first to third angles of rotation at the current time (at the time of initiation of the position detecting device10), and output to the arithmetic processing unit30first to third analog signals corresponding to the first to third angles of rotation.

Next, in step S5, the arithmetic processing unit30calculates the total number of pulses TP corresponding to the absolute position of the rotating shaft14, which is in a stopped state at the time of initiation of the position detecting device10, from the above-described equations (1) and (3), and based on the input first to third analog signals. In step S6, the arithmetic processing unit30converts the total number of pulses TP into a serial signal (second pulse signal).

In the following step S7, the arithmetic processing unit30confirms whether or not a transfer request for the serial signal has been issued from the controller18. If there is no such transfer request, the routine returns to step S4, and the processes of steps S4to S7are executed again. Accordingly, until a notification of the transfer request from the controller18is received, the rotational angle detecting mechanism16sequentially executes the detection process for the absolute position of the rotating shaft14in the stopped state.

On the other hand, in step S8, if the serial communications unit50of the controller18carries out a transfer request for the serial signal with respect to the arithmetic processing unit30, then the arithmetic processing unit30receives the notification of the transfer request (step S7: YES), and initiates transmission of the serial signal to the serial communications unit50(step S9). The arithmetic processing unit30continues the transmission process of the serial signal until a notification of completion of reception of the serial signal is received from the serial communications unit50(step S9, step S10: NO).

When reception of the serial signal is initiated, in step S11, the serial communications unit50carries out a judgment process as to whether or not reception of the serial signal has ended. If reception of the serial signal is not yet completed (step S11: NO), step S8is executed again, and the transfer request for the serial signal is carried out with respect to the arithmetic processing unit30.

On the other hand, if reception of the serial signal has ended (step S11: YES), the serial communications unit50outputs the serial signal to the current position counter54, and in step S12, the current position counter54presets the total number of pulses TP corresponding to the input serial signal.

In step S13, the serial communications unit50, upon confirming that the total number of pulses TP has been preset, transmits a notification of completion of reception to the arithmetic processing unit30. When the notification of completion of reception is received, the arithmetic processing unit30determines that transmission of the serial signal has ended (step S10: YES), and transitions into an operating mode for driving rotation of the rotating body12(step S14ofFIG. 9). In the operating mode, the rotational angle detecting mechanism16operates only the first rotational angle detector24and the interpolator32.

In step S15, upon confirming that the total number of pulses TP has been preset, the rotating body drive control unit56supplies to the rotating body12a rotating body operating signal for driving rotation of the rotating body12. The rotating body12is driven based on the supply of the rotating body operating signal, whereupon the rotating shaft14is rotated (step S16).

In step S17, the first magnetic detecting elements36a,36bof the first rotational angle detector24output first analog signals, respectively, to the interpolator32, corresponding to the first angle of rotation of the rotating shaft14during rotation thereof. The first angle of rotation is an angle of rotation indicative of an amount of movement (amount of rotation) of the rotating shaft14with respect to the absolute position of the rotating shaft14in the stopped state, and the respective first analog signals are analog signals corresponding to such an amount of movement. The interpolator32converts the respective first analog signals into the two-phase first pulse signals, and outputs each of the converted first pulse signals to the multiplication circuit52of the controller18.

Next, in step S18, the rotational angle detecting mechanism16determines whether or not the supply of power from the controller18has been stopped. If the supply of power is not stopped (step S18: NO), the processes of steps S16to S18are executed again. More specifically, until the supply of power from the controller18is stopped (step S18: YES), the rotational angle detecting mechanism16repeatedly executes the detection operation of the first angle of rotation, and the output operation of the two-phase first pulse signals.

On the other hand, in step S19, if the respective first pulse signals have been input to the multiplication circuit52, the multiplication circuit52compares the two-phase first pulse signals, and determines whether the two-phase first pulse signals are indicative of forward rotation or reverse rotation. On the basis of such a determination result, the multiplication circuit52generates either a forward rotation multiplied pulse signal (forward rotation pulses) or a reverse rotation multiplied pulse signal (reverse rotation pulses) in which the first pulse signals are multiplied, and the generated forward rotation pulses or reverse rotation pulses are output to the current position counter54.

The current position counter54, using the preset total number of pulses TP as a reference, counts the number of pulses of the forward rotation pulses or the reverse rotation pulses from the total number of pulses TP. More specifically, the current position counter54detects in a pseudo manner the current absolute position corresponding to the angle of rotation (amount of movement, amount of rotation) of the rotating shaft14during rotation thereof, taking as an origin point the absolute position of the rotating shaft14in a stopped state at the time of initiation, which corresponds to the total number of pulses TP.

Next, in step S20, the controller18confirms whether or not the power supply of the controller18should be turned off. If the power supply is not to be turned OFF (step S20: NO), the controller18executes the processes of steps S15, S19, and S20again. More specifically, in the position detecting device10, the process of detecting the absolute position of the rotating shaft14is executed sequentially until the power supply of the controller18is turned off.

In step S20, if the operator turns off the power supply of the controller18(step S20: YES), the respective components inside the controller18are stopped (step S21), together with stopping the supply of power to the rotational angle detecting mechanism16(step S18: YES). As a result, the respective components inside the rotational angle detecting mechanism16also are stopped (step S22).

Effects of the Present Embodiment

As has been described above, in accordance with the position detecting device10according to the present embodiment, the spur gear34, the speed reducing mechanism20, and the output shaft22are disposed along the axial direction of the rotating shaft14, and by arranging the first to third rotational angle detectors24to28around the rotating shaft14and the output shaft22, the size in the radial direction of the rotating shaft14in the position detecting device10can be reduced.

Further, the first rotational angle detector24detects the first angle of rotation in a pitch interval of the spur gear34attached to the rotating shaft14. Therefore, there is no need to provide a code recording medium on which a specialized code is carried, as disclosed in Japanese Laid-Open Patent Publication No. 2002-513923 (PCT) and Japanese Laid-Open Patent Publication No. 64-023107. Accordingly, the position detecting device10can be produced at a reduced cost.

Furthermore, the arithmetic processing unit30calculates the absolute position of the rotating shaft14in a stopped state at a time of initiation, on the basis of the first to third angles of rotation, only at the time of initiation of the position detecting device10. As a result, during rotation of the rotating shaft14, the current position counter54is capable of determining in a pseudo manner the current absolute position of the rotating shaft14, from the first angle of rotation detected by the first rotational angle detector24, taking as a standard the absolute position of the rotating shaft14in the stopped state at the time of initiation.

More specifically, the position detecting device10functions as an absolute type rotary encoder only at the time of initiation, and thereafter, functions as an incremental type rotary encoder. Stated otherwise, with the position detecting device10, at the time of initiation, the absolute position of the rotating shaft14in a stopped state is detected, and thereafter, during rotation of the rotating shaft14, the first angle of rotation corresponding to the amount of movement (rotation amount) of the rotating shaft14with respect to the absolute position thereof at the time of initiation is detected. In addition, the position of the first angle of rotation with respect to the absolute position at the time of initiation is determined as the current absolute position of the rotating shaft14. As a result, calculating the absolute position in real time as in Japanese Laid-Open Patent Publication No. 2003-161641 is rendered unnecessary, and thus, it is possible to use a low speed and low cost arithmetic processing unit (CPU) as the arithmetic processing unit30.

Further, in a conventional incremental rotary encoder, whenever the power supply is turned on and off, it is necessary to perform a magnetic pole detection operation and an origin point return operation. In contrast thereto, with the position detecting device10, since the absolute position of the rotating shaft14at the time of initiation can be detected, the aforementioned operations are unnecessary. As a result, if the position detecting device10is installed in an electric actuator or the like, it becomes possible to shorten the tact time.

In the foregoing manner, in accordance with the position detecting device10according to the present embodiment, it is possible to realize a smaller scale and a reduction in cost of the position detecting device10, together with carrying out arithmetic processing to calculate an absolute position using a low speed arithmetic processing device.

Further, in the first rotational angle detector24, in the case that the magnetic field generated by the first bias magnet38in a region including the respective first magnetic detecting elements36a,36bundergoes a change due to rotation of the spur gear34, each of the first magnetic detecting elements36a,36boutputs the change in the magnetic field, respectively, as respective first analog signals. The respective first analog signals are signals corresponding to the first angle of rotation. Therefore, on the basis of the respective first analog signals, the arithmetic processing unit30is capable of determining with high precision that the absolute position of the rotating shaft14at the time of initiation corresponds to the position of a certain numbered tooth of the spur gear34. Further, since a commercially available spur gear34can be used, in comparison with the configurations of Japanese Laid-Open Patent Publication No. 2002-513923 (PCT) and Japanese Laid-Open Patent Publication No. 64-023107, a further reduction in cost of the position detecting device10can be realized.

Furthermore, in the second rotational angle detector26, in the case that the magnetic field generated by rotation of the second bias magnet40in a region including the respective second magnetic detecting elements42a,42bundergoes a change, each of the second magnetic detecting elements42a,42boutputs the change in the magnetic field, respectively, as respective second analog signals. The respective second analog signals are signals corresponding to the second angle of rotation. Therefore, on the basis of the respective second analog signals, the arithmetic processing unit30is capable of easily determining that the absolute position of the rotating shaft14at the time of initiation corresponds to a certain angle within one rotation of the rotating shaft14.

Further, in the third rotational angle detector28, in the case that the magnetic field generated by rotation of the third bias magnet44in a region including the respective third magnetic detecting elements46c,46dundergoes a change, each of the third magnetic detecting elements46c,46doutputs the change in the magnetic field, respectively, as respective third analog signals. In this case, since the speed reducing mechanism20rotates the output shaft22by decelerating the rotational speed of the rotating body12at the predetermined reduction ratio N, on the basis of the respective third analog signals, the arithmetic processing unit30is capable of easily determining that the absolute position of the rotating shaft14at the time of initiation corresponds to a certain angle within multiple rotations of the rotating shaft14.

Moreover, since the rotating shaft14penetrates through the second bias magnet40whereas the output shaft22penetrates through the third bias magnet44, there is a possibility that the detection accuracy of the second angle of rotation and the third angle of rotation in the second rotational angle detector26and the third rotational angle detector28may be lowered. However, according to the position detecting device10, the first angle of rotation is detected with high precision by the first rotational angle detector24using the spur gear34. As a result, since lowering of the detection accuracy of the second angle of rotation and the third angle of rotation is compensated for by the high detection accuracy of the first angle of rotation, any influence thereof on the process of calculating the absolute position in the arithmetic processing unit30can be suppressed.

Further, the interpolator32converts the respective first analog signals into the two-phase first pulse signals, and the arithmetic processing unit30calculates the absolute position of the rotating shaft14at the time of initiation on the basis of the respective first to third analog signals, and outputs the second pulse signal corresponding to the calculated absolute position. Consequently, the current position counter54is capable of easily detecting the current absolute position of the rotating shaft14on the basis of the respective first pulse signals output from the interpolator32, and the second pulse signals output from the arithmetic processing unit30. Further, regardless of the forward or reverse rotation of the rotating shaft14, it is possible to ignore the influence of any backlash in the speed reducing mechanism20.

The backlash of the speed reducing mechanism20preferably resides within an angular range of 360°/(2× N). Further, as discussed above, correction of any backlash can be handled in accordance with software processing performed by the interpolator32and the current position counter54. In the present embodiment, by providing a mechanism such as a spiral spring, which applies torque in a fixed direction with respect to the output shaft22of the speed reducing mechanism20, corrective processing by software can be rendered unnecessary.

Further, in the position detecting device10, because the arithmetic processing unit30transmits the second pulse signals, in the form of a serial signal representative of the total number of pulses TP corresponding to the absolute position of the rotating shaft14at the time of initiation, to the current position counter54via the serial communications unit50, it is possible to further reduce the cost of the position detecting device10.

Furthermore, at the time of initiation of the position detecting device10, the current position counter54presets the number of total pulses TP. Further, during rotation of the rotating shaft14, the multiplication circuit52produces the multiplied pulse signal on the basis of the first pulse signals. Thus, the current position counter54, using the preset total number of pulses TP as a reference, counts the number of pulses corresponding to the multiplied pulse signal, whereby the current absolute position of the rotating shaft14is detected. As a result, the current absolute position of the rotating shaft14can be determined easily and highly efficiently. Further, by supplying the multiplied pulse signal from the multiplication circuit52to the current position counter54, the resolution of the current absolute position of the rotating shaft14in the current position counter54is improved, and the absolute position can be obtained with high accuracy.

Further, the multiplication circuit52determines a forward rotation or a reverse rotation of the rotating shaft14by comparing the two-phase first pulse signals, and generates a multiplied pulse signal of the determined forward rotation or reverse rotation. Therefore, the current position counter54is capable of accurately determining the current absolute position of the rotating shaft14.

Furthermore, in the event that the total number of pulses TP is preset in the current position counter54, the rotating body drive control unit56drives the rotating body12and causes the rotating shaft14to rotate, and therefore, the absolute position of the rotating shaft14during rotation thereof can be acquired reliably.

Modified Examples of the Present Embodiment

Next, modified examples (a position detecting device10A according to the first modified example and a position detecting device10B according to the second modified example) of the position detecting device10according to the present embodiment will be described with reference toFIGS. 10 through 14. Regarding position detecting devices10A,10B, constituent elements thereof that are the same as those of the position detecting device10described with reference toFIGS. 1 through 9are denoted by the same reference characters, and detailed description of such features is omitted.

First Modified Example

First, the position detecting device10A according to the first modified example as the first configuration will be described with reference toFIGS. 10 through 12B.

The position detecting device10A is different from the position detecting device10shown inFIGS. 1 through 9as the basic configuration in that the rotational angle detecting mechanism16includes a first speed reducing mechanism60, a second speed reducing mechanism62, a first rotational angle detector64, and a second rotational angle detector66.

The first speed reducing mechanism60is a rotation transmission mechanism which is capable of decelerating the rotational speed of the rotating shaft14of the rotating body12and transmitting the decelerated rotational speed to an input shaft68of second speed reducing mechanism62which also serves as the output shaft of the first speed reducing mechanism60. In the first modified example, it should be noted that the speed reducing ratio of the first speed reducing mechanism60is 1 (one), so that the rotational speed (rotational force) of the rotating shaft14is output to the input shaft68as it is.

The first speed reducing mechanism60is equipped with a first speed reducing unit60awhich is provided on a side of the rotating shaft14, an intermediate shaft60bwhich extends substantially in parallel to the rotating shaft14, the input shaft68, and the output shaft22, and one end of which is connected to the first speed reducing unit60a, and a second speed reducing unit60cwhich is provided on a side of the input shaft68and connected to the other end of the intermediate shaft60b.

The first speed reducing unit60ais made up from a first gear70aon an input side which is substantially coaxially attached to the rotating shaft14, and a second gear72aon an output side which is substantially coaxially attached to one end side of the intermediate shaft60band which engages with the first gear70a. The second speed reducing unit60cis made up from a third gear70bon an input side which is substantially coaxially attached to the other end of the intermediate shaft60b, and a fourth gear72bon an output side which is substantially coaxially attached to the input shaft68and which engages with the third gear70b. As described above, since the speed reducing ratio of the first speed reducing mechanism60is 1, each of the speed reducing ratios n of the first speed reducing unit60aand the second speed reducing unit60cis set such that n=1.

The second speed reducing mechanism62has substantially the same configuration as the speed reducing mechanism20of the position detecting device10. The second speed reducing mechanism62is equipped with the input shaft68which is substantially coaxially arranged with the rotating shaft14, and to which the rotational force of the rotating shaft14is transmitted through the first speed reducing mechanism60, and the output shaft22which is substantially coaxially arranged with the rotating shaft14and the input shaft68, and which rotates at a rotational speed decelerated from the rotational speed of the input shaft68by the speed reducing ratio N.

Therefore, in the first modified example, the entire speed reducing ratio of the first speed reducing mechanism60and the second speed reducing mechanism62is N (=1×N).

The first rotational angle detector64is made up from a cylindrical bias magnet74which is substantially coaxially attached to a front end side of the rotating shaft14, and a magnetic detecting element76which is arranged in facing relation to the center of the bias magnet74. In the bias magnet74, one semicircular portion thereof is allocated to the N-pole, whereas the other semicircular portion thereof is allocated to the S-pole. Thus, the first rotational angle detector64is a one-rotation rotational angle detector for detecting a first angle of rotation lying within one rotation of the rotating shaft14. The magnetic detecting element76outputs by way of serial communications to the arithmetic processing unit30a serial signal (a signal of the rotational angle data shown inFIG. 12B) corresponding to the first angle of rotation. Also, the magnetic detecting element76outputs to the multiplication circuit52two-phase digital pulse signals (A-phase and B-phase first pulse signals shown inFIG. 12A), which correspond to the first angle of rotation and whose phases are shifted mutually by 90°.

Stated otherwise, according to the first modified embodiment, the magnetic detecting element76has both functions of outputting the serial signal to the arithmetic processing unit30and of outputting two-phase first pulse signals to the multiplication circuit52as interpolation processing. That is, the position detecting device10A according to the first modified embodiment exchanges the first rotational angle detector24and the second rotational angle detector26in the position detecting device10with the first rotational angle detector64.FIG. 12Bshows a case in which, during a predetermined time period (serial transmission period), the magnetic detecting element76sends a serial signal to the arithmetic processing unit30. The second rotational angle detector66has a configuration similar to the third rotational angle detector28(seeFIGS. 1 and 2) of the position detecting device10. The second rotational angle detector66detects by the third magnetic detecting elements46c,46dthe second angle of rotation lying within one rotation of the output shaft22corresponding to the multiple rotations of the rotating shaft14, and outputs analogue signals (similar to the third analogue signal) to the arithmetic processing unit30, which correspond to the detected second angle of rotation.

The arithmetic processing unit30performs sampling of the serial signal from the magnetic detecting element76at predetermined sampling intervals shown inFIG. 12B. Further, the arithmetic processing unit30converts output voltages of the analog signals from the third magnetic detecting elements46c,46dfrom rectangular coordinates into polar coordinates. Then, the arithmetic processing unit30calculates the absolute position of the rotating shaft14at the time of initiation, based on the serial signal which is obtained by sampling and the output voltages converted into polar coordinates.

In this case, the arithmetic processing unit30calculates the amount of rotation TA of the rotating shaft14based on the following equation (4).
TA=P1+(P3×N)  (4)

In the first modified example, since the spur gear34is not used, it should be noted that P1 in the equation (4) represents an angle (first angle of rotation) of the rotating shaft14.

Further, in the first modified example, the total number of pulses TP is calculated by the following equation (5).
TP=INT(TA×PP÷360)  (5)

The position detecting device10A according to the first modified example can also operate according to the sequence diagrams shown inFIGS. 8 and 9. In this case, the position detecting device10A operates similarly to the position detecting device10, except that, as to steps S4, S5, and S17, the two-phase first pulse signals are directly output from the magnetic detecting element76to the multiplication circuit52, the serial signal is output from the magnetic detecting element76to the arithmetic processing unit30, the analog signals are output from the third magnetic detecting elements46c,46dto the arithmetic processing unit30, and the total number of pulses TP is calculated by the arithmetic processing unit30based on the equations (4) and (5). Accordingly, the description of detailed operation will be omitted.

As described above, in the position detecting device10A according to the first modified example, the magnetic detecting element76of the first rotational angle detector64has both functions of outputting the serial signal to the arithmetic processing unit30and of outputting two-phase first pulse signals to the multiplication circuit52of the controller18as interpolation processing. Further, the arithmetic processing unit30calculates the absolute position of the rotating shaft14at the time of initiation, on the basis of the serial signal, and the second angle of rotation detected by (the third magnetic detecting elements46c,46dof) the second rotational angle detector66. Therefore, in the first modified example, the position detecting device10A can be produced at a reduced cost since the number of parts of the position detecting device10A is reduced, and computation load in the arithmetic processing unit30is reduced. Further, since the cylindrical bias magnet74is adopted, the reduction in magnetic flux density is suppressed in comparison with a ring magnet, and the detection accuracy of the first angle of rotation can be improved.

Further, in the position detecting device10A according to the first modified example as well, the following advantages can be obtained in a similar manner to the case of the position detecting device10.

That is, the second speed reducing mechanism62and the output shaft22are disposed along the axial direction of the rotating shaft14, and by arranging the first rotational angle detector64and the second rotational angle detector66around the rotating shaft14and the output shaft22, the size in the radial direction of the rotating shaft14can be reduced.

Furthermore, the arithmetic processing unit30calculates the absolute position of the rotating shaft14in a stopped state at a time of initiation, on the basis of the first and second angles of rotation, only at the time of initiation. As a result, during rotation of the rotating shaft14, (the current position counter54of) the controller18is capable of determining in a pseudo manner and easily the current absolute position of the rotating shaft14, from the two-phase first pulse signals, taking as a standard the absolute position of the rotating shaft14at the time of initiation.

More specifically, the position detecting device10A functions as an absolute type rotary encoder only at the time of initiation, and thereafter, functions as an incremental type rotary encoder. Thus, calculating the absolute position in real time is rendered unnecessary, and thus, it is possible to use a low speed and low cost CPU.

As a result, if such a position detecting device10A is installed in an electric actuator or the like, it becomes possible to shorten the tact time.

Thus, in accordance with the first modified example as well, it is possible to realize a smaller scale and a reduction in cost of the position detecting device10A, together with carrying out arithmetic processing to calculate an absolute position using a low speed arithmetic processing device.

Furthermore, in accordance with the first modified example as well, regardless of the forward or reverse rotation of the rotating shaft14, it is possible to ignore the influence of any backlash in the first speed reducing mechanism60and the second speed reducing mechanism62. The backlash of the first speed reducing mechanism60preferably resides within an angular range of 360°/(4× n× n). In the first modified example, n=1. Thus, it is preferable that the backlash resides within an angular range of 90°.

The position detecting device10A further includes the first speed reducing mechanism60which transmits the rotational force of the rotating shaft14to the input shaft68of the second speed reducing mechanism62, wherein the rotating shaft14, the input shaft68, and the output shaft22are arranged substantially coaxially. Though the position detecting device10A becomes slightly large in the radial direction due to the first speed reducing mechanism60, the number of parts of the position detecting device10A is reduced because the first rotational angle detector64having the interpolation function is used. Thus, it is possible to realize a reduction in cost of the entire device. In the description above, a case is described in which the first speed reducing mechanism60having the speed reducing ratio of 1 is used. Alternatively, instead of the first speed reducing mechanism60, various types of rotation transmission mechanisms such as rotation transmission means using belts can be preferably adopted.

Second Modified Example

Next, the position detecting device10B according to the second modified example as the second configuration will be described with reference toFIGS. 13 and 14.

The position detecting device10B is different from the configuration of the position detecting device10A according to the first modified example (seeFIGS. 10 and 11) in that the rotational angle detecting mechanism16includes first to third rotational angle detector64,78,80and that each of the speed reducing ratios n of the first speed reducing unit60aand the second speed reducing unit60cof the first speed reducing mechanism60is more than 1. Thus, the entire speed reducing ratio of the first speed reducing mechanism60and the second speed reducing mechanism62becomes n×n×N (first speed reducing unit60a: n; second speed reducing unit60c: n; second speed reducing mechanism62: N). As a result, the rotational speed of the output shaft22becomes a rotational speed which is decelerated from the rotational speed of the rotating shaft14by (1/n)×(1/n)×(1/N).

The second rotational angle detector78has a configuration substantially similar to the second rotational angle detector26(seeFIGS. 1 and 2) of the position detecting device10. It should be noted, however, that the second rotational angle detector78is provided for the input shaft68instead of the rotating shaft14. That is, in the second modified example, the first speed reducing mechanism60having a speed reducing ratio n×n is provided between the rotating shaft14and the input shaft68. Therefore, the second magnetic detecting elements42a,42bof the second rotational angle detector78can detect a second angle of rotation lying within one rotation of the input shaft68and corresponding to multiple rotations of the rotating shaft14.

The third rotational angle detector80has a configuration similar to the second rotational angle detector66(seeFIGS. 10 and 11) of the position detecting device10A. The third magnetic detecting elements46c,46dof the third rotational angle detector80can detect a third angle of rotation lying within one rotation of the output shaft22and corresponding to multiple rotations of the rotating shaft14.

The arithmetic processing unit30performs sampling of the serial signal from the magnetic detecting element76at predetermined sampling intervals shown inFIG. 12B. Further, the arithmetic processing unit30converts output voltages of the respective analog signals (similar to the second analog signal) corresponding to the second angle of rotation from the second magnetic detecting elements42a,42b, and the analog signals (similar to the third analog signal) corresponding to the third angle of rotation from the third magnetic detecting elements46c,46d, from rectangular coordinates into polar coordinates. Then, the arithmetic processing unit30calculates the absolute position of the rotating shaft14at the time of initiation, based on the serial signal which is obtained by sampling and the output voltages converted into polar coordinates.

In this case, the arithmetic processing unit30calculates the amount of rotation TA of the rotating shaft14based on the following equation (6).
TA=P1+(P2×n×n)+(P3×N×n×n)  (6)

In the second modified example, since the spur gear34is not used, and since the second rotational angle detector78is arranged for the input shaft68, it should be noted that in the equation (6), P1 represents an angle (first angle of rotation) of the rotating shaft14and P2 represents an angle (second angle of rotation) of the input shaft68. Further, in the second modified example, the total number of pulses TP is calculated by the equation (5) described above.

In a similar manner to the case of the position detecting device10A, the position detecting device10B according to the second modified example can also operate according to the sequence diagrams shown inFIGS. 8 and 9. In this case as well, the position detecting device10B operates similarly to the position detecting device10, except that, as to steps S4, S5, and S17, the two-phase first pulse signals are directly output from the magnetic detecting element76to the multiplication circuit52, the serial signal is output from the magnetic detecting element76to the arithmetic processing unit30, the analog signals are output from the second magnetic detecting elements42a,42band the third magnetic detecting elements46c,46dto the arithmetic processing unit30, and the total number of pulses TP is calculated by the arithmetic processing unit30based on the equations (5) and (6). Accordingly, the description of detailed operation will be omitted.

As described above, compared with the position detecting device10A according to the first modified example, the position detecting device10B according to the second modified example is equipped with three rotational angle detectors (first to third rotational angle detectors64,78,80), and two speed reducing mechanisms (first speed reducing mechanism60and second speed reducing mechanism62) having speed reducing ratios n, N, each of which is more than 1. Thus, compared with the position detecting device10A, the number of parts is large, and computation load in the arithmetic processing unit30is large, resulting in high cost.

In the second modified example, however, the second rotational angle detector78and the third rotational angle detector80respectively detects the second angle of rotation and the third angle of rotation corresponding to multiple rotations of the rotating shaft14, and the arithmetic processing unit30is capable of calculating the absolute position of the rotating shaft14at the time of initiation with high precision, using the detected second and third angles of rotation, etc. As a result, compared with conventional position detecting devices, the absolute position can be calculated with high precision and the cost can be reduced. Further, in the second modified example as well, since the cylindrical bias magnet74is adopted, the reduction in magnetic flux density is suppressed in comparison with a ring magnet, and the detection accuracy of the first angle of rotation can be improved.

Furthermore, since the position detecting device10B according to the second modified example is also equipped with the first to third rotational angle detectors64,78,80, advantageous effects similar to the position detecting device10can be obtained.

The present invention is not limited to the embodiment described above, and it goes without saying that various modified or additional configurations could be adopted therein without departing from the essence and gist of the present invention as set forth in the appended claims.