Position detection device

A processor of a position detection device intermittently performs an acquisition process during a measurement period to acquire a detection signal induced in a detection coil depending on the position of an object by driving an excitation coil. The processor configured to monitor whether or not the processor is executing the acquisition process without driving the excitation coil during a monitoring period set before the measurement period of the processor, and the processor is configured to execute a predetermined process when the processor is executing the acquisition process.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. § 371 of International Application No. PCT/JP2015/000833, filed on Feb. 23, 2015, which in turn claims the benefit of Japanese Application No. 2014-035589, filed on Feb. 26, 2014, Japanese Application No. 2014-257745, filed Dec. 19, 2014 and Japanese Application No. 2014-257746, filed Dec. 19, 2014, the disclosures of which are incorporated by reference herein.

TECHNICAL FIELD

The present invention generally relates to position detection devices, and specifically relates to a position detection device including a plurality of detectors.

BACKGROUND ART

An electromagnetic induction-type displacement sensor (position detection device) has been provided which includes two detection circuits (detectors) so that even when a fault occurs on one of the detectors, displacement of an object is detectable by the other of the detectors. Such a position detection device has been disclosed in, for example, Document 1 (JP 2005-265463 A). The position detection device includes two detectors each including a coil drive unit, two drive coils (excitation coils) each connected to the coil drive unit, and two detection coils each connected to the detector. The position detection device further includes an electromagnetic coupling member displaceable relatively to the excitation coils and the detection coils. The coil drive units include oscillation circuits each connected to a corresponding one of the excitation coils and timers each configured to output an oscillation inhibiting signal to the oscillation circuit of the other of the coil drive units.

In this position detection device, while one of the coil drive units drives the excitation coil, drive of the other of the excitation coils is interrupted by the oscillation inhibiting signal of the timer of the one coil drive unit, thereby allowing the two detectors to detect the displacement of the electromagnetic coupling member in a time sharing manner.

However, the conventional example described above does not consider a circumstance in which drive periods of the excitation coils overlap each other on activation of the detectors. Therefore, in the conventional example described above, when the drive periods of the excitation coils overlap each other on activation of the detectors, for example, detection processes by the detectors may be simultaneously performed, which may lead to mutual magnetic interference.

SUMMARY OF INVENTION

In view of the foregoing, it is an object of the present invention to provide a position detection device capable of reducing the possibility that drive periods of excitation coils overlap each other on activation of detectors.

A position detection device according to an aspect of the present invention includes a first detector and a second detector. The first detector includes a first excitation coil, a first detection coil, and a first processor. The second detector includes a second excitation coil, a second detection coil, and a second processor. The first excitation coil is magnetically coupled to the first detection coil and the second detection coil. The second excitation coil is magnetically coupled to the first detection coil and the second detection coil. The first processor is configured to intermittently execute a first acquisition process during a measurement period of the first processor to drive the first excitation coil and to acquire a first detection signal induced in the first detection coil depending on a position of an object by driving the first excitation coil. The second processor is configured to intermittently execute a second acquisition process during a measurement period of the second processor to drive the second excitation coil and to acquire a second detection signal induced in the second detection coil depending on a position of the object by driving the second excitation coil. The second processor is configured to monitor whether or not the first processor is executing the first acquisition process without driving the second excitation coil during a monitoring period set before the measurement period of the second processor, and the second processor is configured to execute a predetermined process when the first processor is executing the first acquisition process.

DESCRIPTION OF EMBODIMENTS

First Embodiment

As illustrated inFIG. 1, a position detection device according to a first embodiment of the present invention includes a detector2(here, first detector) and a detector3(here, second detector). The detector2includes a (first) excitation coil21, a (first) detection coil22, and a (first) processor23. The detector3includes a (second) excitation coil31, a (second) detection coil32, and a (second) processor33. The excitation coil21is magnetically coupled to the detection coil22and the detection coil32. The excitation coil31is magnetically coupled to the detection coil22and the detection coil32.

The processor23is configured to intermittently execute a (first) acquisition process during a measurement period of the processor23. The (first) acquisition process is a process of driving the excitation coil21and acquiring a (first) detection signal Y1(seeFIG. 2) induced in the detection coil22depending on the position of an object100by the driving the excitation coil21. The processor33is configured to intermittently execute a (second) acquisition process during a measurement period of the processor33. The (second) acquisition process is a process of driving the excitation coil31and acquiring a (second) detection signal Y2(seeFIG. 2) induced in the detection coil32depending on the position of the object100by the driving the excitation coil31.

The processor33is configured to monitor whether or not the processor23is executing the acquisition process without driving the excitation coil31during a monitoring period set before the measurement period of the processor33, and the processor33is configured to execute a predetermined process when the processor23is executing the acquisition process.

The position detection device1according to the first embodiment of the present invention will be described in detail below. Note that the following configurations described below are mere examples of the present invention. The present invention is not limited to the following embodiments. Even in configurations other than those illustrated in the embodiments, various modifications may be made depending on design, etc., without departing from the technical idea of the present invention.

First, a basic configuration of the position detection device1of the present embodiment will be described. As illustrated inFIG. 1, the position detection device1of the present embodiment includes the detector2and the detector3each configured to detect the position of the object100. In the position detection device1of the present embodiment, the object100represents a metal piece which moves simultaneously with a brake pedal of a vehicle. Therefore, the position detection device1of the present embodiment can be used to detect the pedal travel of a brake by detecting the position of the metal piece. Of course, this example does not intend to limit the application of the position detection device1. Other applications are possible as long as the position detection device1is used to detect the position of the object100.

The detector2includes the excitation coil21, the detection coil22, the processor23, and an amplifier24. The detector3includes the excitation coil31, the detection coil32, the processor33, and the amplifier34. The detectors2and3are mounted to, for example, one substrate. The excitation coil21, the detection coil22, the excitation coil31, and the detection coil32are arranged in the same area of the substrate. Therefore, the excitation coil21is magnetically coupled to the detection coils22and32. The excitation coil31is magnetically coupled to the detection coils22and32. Of course, this example does not intend to limit the arrangement of the excitation coils21and31and the detection coils22and32. Any arrangement is possible as long as the excitation coils21and31and the detection coils22and32are magnetically coupled to one another.

InFIG. 1, each of the excitation coil21, the detection coil22, the excitation coil31, and the detection coil32includes a single coil but may include a combination of a plurality of coils.

The processor23is connected to an Electronic Control Unit (ECU)4via electric cables41to43. The processor33is connected to the ECU4via electric cables44to46. The electric cable41(electric cable44) is a power supply line configured to supply an operating voltage to the processor23(processor33). The electric cable42(electric cable45) is a signal line used for communication between the processor23(processor33) and the ECU4. Here, a communication system between the processor23(processor33) and the ECU4may be either an analog communication system or a digital communication system. When the communication system is digital, bidirectional communication is possible between the processor23(processor33) and the ECU4via the electric cable42(electric cable45). The electric cable43(electric cable46) is a grounding conductor used to connect ground of the processor23(processor33) to ground of the ECU4.

The processor23(processor33) includes, for example, a microcontroller. Of course, the processor23(processor33) does not include the microcontroller but may include hardware such as a Field-Programmable Gate Array (FPGA) and a dedicated Integrated Circuit (IC) other than the microcontroller. The processor23(processor33) may include the amplifier24(amplifier34) which is integrated into a microcontroller or into hardware other than the microcontroller and which will be described later. The processor23(processor33) may include a microcontroller and other hardware in combination.

In the position detection device1of the present embodiment, the processor23(33) is configured to differently operate during a measurement period for actually detecting the position of the object100and during a monitoring period set before the measurement period. First, the operation of the processor23(processor33) during the measurement period will be described.

The processor23(processor33) is configured to intermittently execute a position detecting process of detecting the position of the object100. In the position detection device1of the present embodiment, the position detecting process includes an acquisition process and an arithmetic process. In the acquisition process, the processor23(processor33) gives a drive signal X1(drive signal X2) having a predetermined frequency and having a predetermined wave number of square waves to the excitation coil21(excitation coil31), thereby driving the excitation coil21(excitation coil31) (seeFIG. 2). While in the position detection device1of the present embodiment, the processor23(processor33) gives the drive signal X1(drive signal X2) to drive the excitation coil21(excitation coil31), other configurations may be possible. For example, a resonance capacitor may be connected in parallel with the excitation coil21(excitation coil31) to form a resonance circuit, and the processor23(processor33) may perform positive feedback on the resonance circuit to cause oscillation, thereby driving the excitation coil21(excitation coil31). That is, the processor23(processor33) may be configured to drive the excitation coil21(excitation coil31).

In the acquisition process, the processor23(processor33) acquires a detection signal Y1(detection signal Y2) induced in the detection coil22(detection coil32) by driving the excitation coil21(excitation coil31) (seeFIG. 2). In order to acquire the detection signal Y1(detection signal Y2), for example, a built-in timer or an Analog to Digital Converter (ADC) is used. In the position detection device1of the present embodiment, the detection signal Y1(detection signal Y2) induced in the detection coil22(detection coil32) is amplified by the amplifier24(amplifier34), and is then input to the processor23(processor33).

Here, the object100is magnetically coupled to the excitation coil21(excitation coil31), and an induced current flows through the object100when the excitation coil21(excitation coil31) is driven. Since the induced current changes depending on the position of the object100, the detection signal Y1(detection signal Y2) also changes depending on the position of the object100. Therefore, the processor23(processor33) executes an arithmetic process to compute the position of the object100based on the acquired detection signal Y1(detection signal Y2). Note that the acquisition process and the arithmetic process take, for example, 1 ms.

That is, when the detector2is assumed to be a first detector, the processor23(first processor) is configured to intermittently execute the (first) acquisition process during the measurement period. In the (first) acquisition process, the processor23gives the drive signal X1to the excitation coil21(first excitation coil) to drive the excitation coil21. The processor23acquires the detection signal Y1(first detection signal) induced in the detection coil22(first detection coil) depending on the position of the object100by driving the excitation coil21. When the detector3is assumed to be a second detector, the processor33(second processor) is configured to intermittently execute the (second) acquisition process during a measurement period. In the (second) acquisition process, the processor33gives the drive signal X2to the excitation coil31(second excitation coil) to drive the excitation coil31. The processor33acquires the detection signal Y2(second detection signal) induced in the detection coil32(second detection coil) depending on the position of the object100by driving the excitation coil31.

The processor23(processor33) is configured to, in a state where the processor23(processor33) is not executing the acquisition process (hereinafter referred to as a “standby state”), determine a timing to execute the acquisition process, and the processor23(processor33) is configured to execute the acquisition process at the determined timing. For example, it is assumed that the processor23of the detector2is executing the acquisition process and the processor33of the detector3is in the standby state. In this case, a detection signal Y3is induced in the detection coil32by driving the excitation coil21(seeFIG. 2). The processor33determines a timing to execute the acquisition process based on the detection signal Y3. Then, the processor33executes the acquisition process at the determined timing.

Similarly, it is assumed that the processor33of the detector3is executing the acquisition process, and the processor23of the detector2is in the standby state. In this case, a detection signal Y4is induced in the detection coil22by driving the excitation coil31(seeFIG. 2). The processor23determines a timing to execute the acquisition process based on the detection signal Y4. Then, the processor23executes the acquisition process at the determined timing.

That is, when the detector2is assumed to be a first detector and the detector3is assumed to be a second detector, the processes described above will be explained as follows. The processor23(first processor) executes the (first) acquisition process such that the time period of the (first) acquisition process is separated from the time period of the (second) acquisition process. More specifically, the processor23(first processor) executes the (first) acquisition process at a timing based on the detection signal Y4(fourth detection signal) induced in the detection coil22(first detection coil) by driving the excitation coil31(second excitation coil). The processor33(second processor) executes the (second) acquisition process such that the time period of the (first) acquisition process is separated from the time period of the (second) acquisition process. More specifically, the processor33(second processor) executes the (second) acquisition process at a timing based on the detection signal Y3(third detection signal) induced in the detection coil32(second detection coil) by driving the excitation coil21(first excitation coil).

As illustrated inFIG. 3, in the position detection device1of the present embodiment, the processor33determines the timing based on a definite time period T12having elapsed since the end of the induction of the detection signal Y3. That is, a time period during which the detector2is executing the acquisition process is a time period during which the excitation coil21is receiving the drive signal X1, and during this time period, the detection signal Y3is induced in the detection coil32. Therefore, the processor33determines that the acquisition process by the detector2has ended at the end of the induction of the detection signal Y3, and executes the acquisition process after the lapse of the definite time period T12. Similarly, the processor23determines the timing based on the definite time period T12having elapsed since the end of the induction of the detection signal Y4.

That is, when the detector2is assumed to be a first detector and the detector3is assumed to be a second detector, the processes described above will be explained as follows. The processor33(second processor) is configured to determine the timing based on the definite time period T12having elapsed since the end of the induction of the detection signal Y3(third detection signal). Similarly, the processor23(first processor) is configured to determine a timing based on the definite time period T12having elapsed since the end of the induction of the detection signal Y4(fourth detection signal). Note that the length of the definite time period T12of the processor23and the length of the definite time period T12of the processor33may be equal to or different from each other.

To realize the processes described above, for example, the detection signal Y3(detection signal Y4) may be regularly read by an ADC. With this configuration, it is possible to determine that inducing the detection signal Y3(detection signal Y4) has ended when the level of a read signal is continuously lower than a predetermined threshold. Alternatively, to realize the processes described above, for example, a free running counter may be used, and the counter may be reset by considering switching the detection signal Y3(detection signal Y4) from a low level to a high level as a trigger. With this configuration, it is possible to determine that inducing the detection signal Y3(detection signal Y4) has ended when the counter overflows or reaches a predetermined count value.

Here, the time period during which the processor23(processor33) executes the acquisition process is a time period during which the excitation coil21(excitation coil31) is receiving the drive signal X1(drive signal X2) (seeFIG. 3). A time required for the acquisition process is preset. The detection signal Y3(detection signal Y4) is induced in the detection coil32(detection coil22) when the excitation coil21(excitation coil31) operates. That is, a timing at which the acquisition process ends can be detected by detecting a timing at which the detection signal Y3(detection signal Y4) is induced in the detection coil32(detection coil22).

Therefore, as illustrated inFIG. 3, the processor33(second processor) may be configured to determine the timing based on the definite time period T11having elapsed since the start of inducing the detection signal Y3(third detection signal). Similarly, the processor23(first processor) may be configured to determine the timing based on the definite time period T11having elapsed since the start of inducing the detection signal Y4(fourth detection signal). Note that the length of the definite time period T11of the processor23and the length of the definite time period T11of the processor33may be equal to or different from each other.

Moreover, since the time required for the acquisition process is preset, the wave number of the drive signal X1(drive signal X2) is also preset. That is, when the wave number of the detection signal Y3(detection signal Y4) is counted, a timing at which the acquisition process ends can be detected based on the wave number having reached the preset number.

Thus, the processor33(second processor) may have the function of counting the wave number of the detection signal Y3(third detection signal). In this case, the processor33may be configured to determine the timing based on the wave number having reached the preset number. Similarly, the processor23(first processor) may have the function of counting the wave number of the detection signal Y4(fourth detection signal). In this case, the processor23may be configured to determine the timing based on the wave number having reached the preset number. Note that the function of counting the wave number of the detection signal Y3(detection signal Y4) can be realized by conventionally known simple hardware or software.

The timing at which the acquisition process ends can also be detected by detecting the amplitude of the detection signal Y3(detection signal Y4) having decreased below a predetermined threshold. Thus, the processor33(second processor) may have the function of measuring the amplitude of the detection signal Y3(third detection signal). In this case, the processor33may be configured to determine the timing based on the amplitude having decreased below the predetermined threshold. Similarly, the processor23(first processor) may have the function of measuring the amplitude of the detection signal Y4(fourth detection signal). In this case, the processor23may be configured to determine the timing based on the amplitude having decreased below the predetermined threshold. Note that the function of measuring the amplitude of the detection signal Y3(detection signal Y4) can be realized by conventionally known simple hardware such as a rectifier circuit, an ADC, etc. or software.

In the position detection device1of the present embodiment, the resonance capacitor is connected in parallel with the detection coil22(detection coil32) so as not to detect high-frequency noise. With this configuration, the influence of resonance of the detection coil22(detection coil32) and the resonance capacitor may cause free vibration (reverberation) to remain in the detection signals Y1to Y4. Therefore, the processor23(processor33) preferably determines that the acquisition process has ended at a time point at which the reverberation in the detection signal is sufficiently reduced. It is optional whether or not the resonance capacitor is used.

A configuration may also be possible in which the processor23(processor33) executing the acquisition process gives an end signal notifying the end of the acquisition process to the excitation coil21(excitation coil31). Inducing the end signal in the detection coil22(detection coil32) allows the processor23(processor33) in the standby state to detect a timing at which the acquisition process ends. Examples of the end signal may include signals including specific bit sequences or having frequencies different from that of the drive signal X1(drive signal X2).

That is, the processor23(first processor) may have the function of giving an end signal notifying the end of the (first) acquisition process to the excitation coil21(first excitation coil). The processor33(second processor) may be configured to determine the timing based on the end signal having been induced in the detection coil32(second detection coil) and having been detected. Similarly, the processor33(second processor) may have the function of giving the end signal notifying the end of the (second) acquisition process to the excitation coil31(second excitation coil). The processor23(first processor) may be configured to determine the timing based on the end signal having been induced in the detection coil22(first detection coil) and having been detected.

That is, as illustrated inFIG. 5, the position detection device1of the present embodiment is configured to alternately execute the acquisition process by the processor23of the detector2and the acquisition process by the processor33of the detector3. That is, the detector2transitions to the standby state when the acquisition process ends, stands by until the acquisition process by the detector3ends, and then executes the acquisition process again. Similarly, the detector3transitions to the standby state when the acquisition process ends, stands by until the acquisition process by the detector2ends, and then executes the acquisition process again. Therefore, in the position detection device1of the present embodiment, the detector2and the detector3alternately execute the acquisition process, thereby preventing mutual magnetic interference.

Moreover, in the position detection device1of the present embodiment, the processor23(processor33) executes a process of determining whether or not the detector2(detector3) is normal at the time of the execution of the acquisition process. That is, when the detection signal Y1(detection signal Y2) is not induced in the detection coil22(detection coil32), the processor23(processor33) determines that at least one of the excitation coil21and the detection coil22is at fault. Then, when the processor23(processor33) determines the fault, the processor23(processor33) outputs a fault signal to the ECU4and stops operation of the processor23(processor33).

That is, when the detector2is assumed to be a first detector and the detector3is assumed to be a second detector, the processes described above will be explained as follows. The processor23(first processor) is configured to stop operation of the processor23(first processor) when the detection signal Y1(first detection signal) is not detected in the (first) acquisition process. Similarly, the processor33(second processor) is configured to stop operation of the processor33(second processor) when the detection signal Y2(second detection signal) is not detected in the (second) acquisition process.

With this configuration, the acquisition process is not executed by a faulty detector2(detector3), and therefore, the acquisition process can be executed by a normal detector2(detector3). Therefore, with this configuration, it is possible to reduce the possibility of unfavorable mutual interference due to the faulty detector2(detector3). Note that it is optional whether or not this configuration is adopted.

Moreover, in the position detection device1of the present embodiment, the processor23(processor33) executes, in the standby state, a process of determining whether or not the detector2(detector3) which is presumably executing the acquisition process is normal. That is, when the processor23(processor33) ends the acquisition process, the processor23(processor33) measures the standby time T2by using a built-in timer (seeFIG. 4). When the detection signal Y4(detection signal Y3) is not induced in the detection coil22(detection coil32) within the standby time T2, the processor23(processor33) determines that the detector3(detector2) which is presumably executing the acquisition process is at fault. When the processor23(the processor33) determines the fault, the processor23(processor33) executes the acquisition process after the standby time T2has elapsed. Thereafter, the processor23(processor33) repeats the acquisition process each time when the standby time12elapses.

That is, when the detector2is assumed to be a first detector and the detector3is assumed to be a second detector, the processes described above will be explained as follows. The processor33(second processor) has a function of measuring the (second) standby time12after the (second) acquisition process has ended. In this case, the processor33is configured to execute the (second) acquisition process when the detection signal Y3(third detection signal) is not detected within the standby time T2. Similarly, the processor23(first processor) has a function of measuring the (first) standby time T2after the (first) acquisition process has ended. In this case, the processor23is configured to execute the (first) acquisition process when the detection signal Y4(fourth detection signal) is not detected within the standby time T2.

With this configuration, even when any fault occurs on the detector2(detector3) executing the acquisition process, the detector2(detector3) in the standby state can continue executing the acquisition process. Therefore, with this configuration, it is possible to avoid a situation where the detector2(detector3) in the standby state remains in that state. Note that it is optional whether or not this configuration is adopted.

In the configuration described above, when the processor23(processor33) determines the fault, the processor23(processor33) may be switched to a mode different from a normal mode to repeat the acquisition process. For example, when the processor23(processor33) determines the fault, the processor23(processor33) may be switched to a mode for shortening the standby time T2. In this case, it is possible to shorten an interval at which the normal processor23(processor33) executes the acquisition process.

That is, the processor23(first processor) may be configured to be switched to a mode different from the normal mode to execute the (first) acquisition process when the detection signal Y4(fourth detection signal) is not detected within the (first) standby time T2. Similarly, the processor33(second processor) may be configured to be switched to a mode different from the normal mode to execute the (second) acquisition process when the detection signal Y3(third detection signal) is not detected within the (second) standby time T2.

The processor23(processor33) performs an output process of outputting a position signal corresponding to a computation result to the ECU4via the electric cable42(electric cable45) by using, for example, a built-in Digital to Analog Converter (DAC). The processor23(processor33) may be configured to output a position signal to the ECU4by a Pulse Width Modulation (PWM) method. Alternatively, the processor23(processor33) may be configured to output the position signal to the ECU4by a wireless signal by use of a radio wave as a medium. With this configuration, the processor23(processor33) and the ECU4each require a wireless module. The processor23(processor33) may execute the arithmetic process and the output process described above concurrently with the acquisition process or may execute the arithmetic process and the output process in the standby state.

The ECU4has a function of activating the detector2and the detector3by supplying an operating voltage to the detector2(detector3) via the electric cable41(electric cable44) by considering an operation, for example, starting the engine of a vehicle as a trigger. In the position detection device1of the present embodiment, the ECU4activates the detector2and the detector3at the same timing. Note that “the same” is an expression including “the same time” or “substantially the same time.” Moreover, the ECU4regularly (for example, every 3 ms) reads the position signal output from the detector2(detector3) via the electric cable42(electric cable45). This allows the ECU4to recognize the position of the object100. The ECU4executes various processes depending on the position of the object100. The position signal is output to the ECU4in the form of a direct-current voltage at 0.5 V to 4.5 V varying in accordance with, for example, the position of the object100. Of course, the range does not intend to limit the range of the voltage of the position signal. The ECU4may acquire the position signal from at least one of the detector2and the detector3.

Furthermore, the ECU4can recognize whether or not the detector2(detector3) includes a fault from the fault signal output from the detector2(detector3) via the electric cable42(electric cable45). The fault signal is output to the ECU4, for example, in the form of a direct-current voltage lower than or equal to 0.2 V or higher than or equal to 4.8 V. Of course, these voltages do not intend to limit the voltage of the fault signal.

While in the position detection device1of the present embodiment, the processor23(processor33) executes the arithmetic process based on the acquired detection signal Y1(detection signal Y2), other configurations may be possible. For example, the processor23(processor33) may be configured to output the acquired detection signal Y1(detection signal Y2) to the ECU4without executing the arithmetic process. With this configuration, the ECU4may compute the position of the object100based on the detection signal Y1(detection signal Y2).

An example of the operation of the position detection device1of the present embodiment during the measurement period will be specifically described below with reference to the drawings. In the following description, it is assumed that on activation of the detectors, the detector2is a first detector and the detector3is a second detector. Of course, on the activation, the detector3may be the first detector and the detector2may be the second detector. As illustrated inFIG. 6, first, when the ECU4activates the detectors2and3, the processor23and the processor33are initialized respectively in the detector2and the detector3. Then, the monitoring periods start. In the detectors2and3, the measurement periods are started after the monitoring periods have ended (S1). Since the detector2is the first detector (S2), the processor23executes the acquisition process before the processor33(S3).

That is, the processor23(first processor) is configured to executes the (first) acquisition process on the activation before the processor33(second processor) executes the (second) acquisition process. With this configuration, it is possible to avoid simultaneous execution of the acquisition processes by the detector2and the detector3on the activation. To realize this configuration, the detector2and the detector3each previously store information representing which of the first detector and the second detector either the detector2or the detector3is on the activation. The information may be stored in, for example, a built-in memory of the processor23(processor33) or may be included in a program executed on the activation.

At this time, the processor23executes a process of determining whether or not the detector2is normal (S4). When the processor23determines that the detector2is at fault, the processor23outputs a fault signal to the ECU4(S5) and stops operation of the processor23(S6). When the processor23determines that the detector2is normal, the processor23transitions to the standby state (S7). When the processor23transitions to the standby state, the processor23executes a process similar to the processor33described below.

On the other hand, since the detector3is the second detector (S2), the processor33transitions to the standby state on the activation (S7). The processor33determines, in the standby state, a timing to execute the acquisition process based on the detection signal Y3induced in the detection coil32by driving the excitation coil21.

At this time, the processor33executes a process of determining whether or not the detector2which is presumably executing the acquisition process is normal (S8). When the processor33determines that the detector2is normal, the processor33executes the acquisition process (S3) in a manner similar to the processor23described above. When the processor33determines that the detector2is at fault, the processor33thereafter repeats the acquisition process (S9). At this time, the processor33may be switched to a mode different from the normal mode to repeat the acquisition process.

As described above, in the position detection device1of the present embodiment, the processor33(second processor) intermittently executes the (second) acquisition process during the measurement period such that the time period of the (first) acquisition process is separated from the time period of the (second) acquisition process. The (second) acquisition process is determined at a timing based on the detection signal Y3(third detection signal) induced in the (second) detection coil32by driving the (first) excitation coil21. That is, in the position detection device1of the present embodiment, the processor33magnetically detects a timing at which the (first) acquisition process ends. Therefore, the position detection device1of the present embodiment does not electrically detect a timing at which the acquisition process ends. Therefore, the position detection device1of the present embodiment can prevent the detectors2and3from being magnetically interfering with each other even when a fault occurs on one of the detectors and the fault electrically influences the remaining detector.

While in the position detection device1of the present embodiment, the power supply line (electric cable41) and the grounding conductor (electric cable43) are connected to the detector2and the power supply line (electric cable44) and the grounding conductor (electric cable46) are connected to the detector3, one power supply line and one grounding conductor may be shared. With this configuration, the detector2and the detector3are not electrically independent of each other. However, as described above, this configuration can also prevent the detectors2and3from being magnetically interfering with each other even when a fault occurs on one of the detectors and the fault electrically influences the remaining detector.

<Possibility of Mutual Interference on Activation>

Now, in the position detection device1of the present embodiment, the ECU4generally activates the detector2and the detector3at the same timing. Therefore, in the position detection device1of the present embodiment, one detector2(detector3) executes the acquisition process on activation of the detector whereas the remaining detector3(detector2) transitions to the standby state on the activation. However, in the position detection device1of the present embodiment, it is possible, although very rare, that the detector2and the detector3are activated at different timings due to, for example, an abnormality in the ECU4. In this case, in the position detection device1of the present embodiment, it is possible that the detector2and the detector3execute the acquisition processes (that is, time periods during which the excitation coils21and31operate overlap each other) on activation of the detectors2and3if later described monitoring periods are not provided. As in this case, when the time periods during which the excitation coils21and31operate overlap each other, the position detecting process by the detector2and the position detecting process by the detector3are performed at the same time, which may result in mutual magnetic interference.

To solve the problem described above, when the detector2is assumed to be a first detector and the detector3is assumed to be a second detector, the processor23(first processor) in the position detection device1of the present embodiment is configured such that the monitoring period is started before the measurement period. Similarly, the processor33(second processor) is configured such that the monitoring period is started before the measurement period. In particular, as illustrated inFIG. 7, in the position detection device1of the present embodiment, the processor23(processor33) is configured such that the monitoring period is started after initialization when the detector2(detector3) is activated. Time required for the initialization is, for example, 10 ms. Moreover, the length of the monitoring period is a predetermined constant length, which is for example, 3 ms. Note that the length of the monitoring period may be variable.

The (first) processor23monitors whether or not the (second) processor33is executing the (second) acquisition process without driving the (first) excitation coil21during the monitoring period. The (first) processor23is configured to execute a predetermined process when the (first) processor23determines that the (second) processor33is executing the (second) acquisition process. Although detailed description will be given later, the predetermined process here is a process to avoid the occurrence of mutual magnetic interference due to simultaneously performed acquisition processes by the detectors2and3.

Here, the (first) processor23monitors whether or not a signal (detection signal Y4) is induced in the (first) detection coil22. The (first) processor23is configured to determine that the (second) processor33is executing the (second) acquisition process when the signal (detection signal Y4) is induced in the (first) detection coil22. The (first) processor23is configured to transition to the measurement period at the end of the monitoring period when the signal (detection signal Y4) is not induced in the (first) detection coil22during the monitoring period.

Similarly, the (second) processor33monitors whether or not the (first) processor23is executing the (first) acquisition process without driving the (second) excitation coil31during the monitoring period. The (second) processor33is configured to execute the predetermined process when the (second) processor33determines that the (first) processor23is executing the (first) acquisition process.

Here, the (second) processor33monitors whether or not a signal (detection signal Y3) is induced in the (second) detection coil32. The (second) processor33is configured to determine that the (first) processor23is executing the (first) acquisition process when the signal (detection signal Y3) is induced in the (second) detection coil32during the monitoring period. The (second) processor33is configured to transition to the measurement period at the end of the monitoring period when the signal (detection signal Y3) is not induced in the (second) detection coil32during the monitoring period.

An example of the operation of the position detection device1of the present embodiment including the monitoring period will be described below. The term “activation” in the following description includes activation by supplying the processor23(processor33) with the operating voltage from the ECU4and a restart by resetting the processor23(processor33) at the occurrence of any abnormality. Alternatively or additionally, the term “activation” includes a restart of the processor23(processor33) at the time of recovery from the momentary power failure or the momentary voltage drop. The operation of the processor23(processor33) during the measurement period may be an operation of intermittently executing the acquisition process, and is not limited to the operation described in <Measurement Period>.

First, with reference toFIG. 7, a case where the detector2and the detector3are activated at the same timing will be described. In this case, the monitoring period of the processor23substantially coincides with the monitoring period of the processor33. Therefore, since the detection signal Y4is not induced in the detection coil22during the monitoring period, the processor23executes the acquisition process at the end of the monitoring period and transitions to the measurement period. Since the detection signal Y3is not induced in the detection coil32during the monitoring period, the processor33transitions to the standby state at the end of the monitoring period and transitions to the measurement period. Thereafter, the processor23and the processor33intermittently execute the acquisition processes such that the time periods during which the acquisition processes are executed do not overlap each other.

Next, with reference toFIG. 8A, a case where the activation of the detector3lags the activation of the detector2will be described. In this case, since the detection signal Y4is not induced in the detection coil22during the monitoring period, the processor23executes the acquisition process at the end of the monitoring period and transitions to the measurement period. The monitoring period of the processor33overlaps a time period during which the processor23executes the acquisition process. Therefore, during the monitoring period of the processor33, the detection signal Y3is induced in the detection coil32. Therefore, the processor33executes the predetermined process at the end of the monitoring period.

Next, with reference toFIG. 8B, a case where the activation of the detector2lags the activation of the detector3will be described. In this case, since the detection signal Y3is not induced in the detection coil32during the monitoring period, the processor33transitions to the standby state at the end of the monitoring period and transitions to the measurement period. The monitoring period of the processor23overlaps a time period during which the processor33executes the acquisition process. Therefore, during the monitoring period of the processor23, the detection signal Y4is induced in the detection coil22. Therefore, the processor23executes the predetermined process at the end of the monitoring period.

As described above, in the position detection device1of the present embodiment, when the detector2is assumed to be a first detector and the detector3is assumed to be a second detector, the processor33(second processor) has the following configuration. That is, the (second) processor33is configured to monitor whether or not the (first) processor23is executing the (first) acquisition process during the monitoring period set before the measurement period, and the (second) processor33is configured to execute a predetermined process when the (first) processor23is executing the (first) acquisition process.

Therefore, the (second) detector3can execute the predetermined process based on the result of the determination of whether or not the (first) detector2is executing the (first) acquisition process during the monitoring period. Therefore, the position detection device1of the present embodiment can reduce the possibility that the first acquisition process and the second acquisition process are simultaneously executed on activation of the detectors2and3, that is, the possibility that time periods during which the excitation coils21and31operate overlap each other.

Here, the predetermined process may be a process of allowing transition to the measurement period based on a signal induced during the monitoring period. In other words, the predetermined process, when executed by the processor33(second processor), may be a process of adjusting a starting time point of the measurement period of the (second) processor33so as not to overlap the (first) acquisition process. Similarly, the predetermined process, when executed by the processor23(first processor), may be a process of adjusting a starting time point of the measurement period of the (first) processor33so as not to overlap the (second) acquisition process. For example, there may be a case where inducing the detection signal Y4(detection signal Y3) in the detection coil22(detection coil32) is started from the starting time point of the monitoring period, and the inducing the detection signal Y4(detection signal Y3) ends before the monitoring period ends. In this case, the processor23(processor33) starts the acquisition process at a timing based on the end of the detection signal Y4(detection signal Y3).

Moreover, for example, there may be a case where inducing the detection signal Y4(detection signal Y3) in the detection coil22(detection coil32) is started during the monitoring period, and the inducing the detection signal Y4(detection signal Y3) does not end by the time the monitoring period ends. In this case, the processor23(processor33) starts the acquisition process at a timing based on the starting time point of the inducing the detection signal Y4(detection signal Y3).

Furthermore, for example, there may be a case where inducing the detection signal Y4(detection signal Y3) in the detection coil22(detection coil32) is started during the monitoring period, and the inducing the detection signal Y4(detection signal Y3) ends before the monitoring period ends. In this case, the processor23(processor33) starts the acquisition process at a timing based on one of the starting time point and the end of the inducing the detection signal Y4(detection signal Y3).

In any of the above-described cases, the detectors2and3can transition to the measurement periods while avoiding mutual magnetic interference.

The predetermined process, when executed by the processor33(second processor), may be a process of stopping the operation of the processor33. Similarly, the predetermined process, when executed by the processor23(first processor), may be a process of stopping the operation of the processor23. In this case, the acquisition process is not executed by a detector2(detector3) which presumably includes any fault, and therefore, the acquisition process can be executed by the normal detector2(detector3). Therefore, in this case, it is possible to reduce the possibility of unfavorable mutual interference due to the detector2(detector3) which presumably includes any fault.

Moreover, as illustrated in, for example,FIGS. 7, 8A, and 8B, the processor23(first processor) in the position detection device1of the present embodiment is configured as follows. The (first) processor23monitors whether or not the (second) processor33is executing the (second) acquisition process without driving the (first) excitation coil21during the monitoring period of the (first) processor23. The (first) processor23is configured to execute the (first) acquisition process at the end of the monitoring period when the (second) processor33is not executing the (second) acquisition process. That is, the processor23(first processor) is configured to execute the (first) acquisition process at the end of the monitoring period before the processor33(second processor) executes the (second) acquisition process.

With this configuration, it is possible to avoid simultaneous execution of the acquisition processes by the detector2and the detector3at the end of the monitoring period. Note that it is optional whether or not this configuration is adopted.

<Possibility of Mutual Interference During Measurement Period>

Here, in the position detection device1of the present embodiment, it is possible, although very rare, that the detector2and the detector3execute the acquisition processes almost at the same timing during the measurement periods. With reference toFIG. 9, an example of the operation in such a case will be described below. The processor23of the detector2transitions to the standby state when the acquisition process ends. Here, since the detector2and the detector3execute the acquisition processes almost at the same timing, the detection signal Y4is not induced in the detection coil22during a period after the end of the acquisition process until the standby time T2elapses. Therefore, the processor23executes the acquisition process again after the standby time T2has elapsed. The processor33of the detector3also transitions to the standby state when the acquisition process ends. Here, the detection signal Y3is not induced in the detection coil32during a period from the end of the acquisition process until the standby time T2elapses. Therefore, the processor33also executes the acquisition process again after the standby time T2has elapsed.

Therefore, the detector2and the detector3repeatedly execute the acquisition processes almost at the same timing. Here, even when timings at which the detector2and the detector3execute the acquisition processes coincide with each other, the cycles or the phases of signals output from the excitation coil21and the excitation coil31respectively driven by the detector2and detector3do not completely match each other, and therefore, magnetic mutual interference occurs. Thus, the detector2and the detector3may continue outputting position signals involving errors.

Now, a first variation and a second variation which solve the above-described problem during the measurement period will be described below.

As illustrated inFIG. 10A, in a position detection device1of the first variation, a standby time T22of a detector3is set to be longer than a standby time T21of a detector2. That is, when the detector2is assumed to be a first detector and the detector3is assumed to be a second detector, the length of the (first) standby time T21set by a processor23(first processor) and the length of the (second) standby time T22set by a processor33(second processor) are different from each other.

With reference theFIG. 10B, an example of the operation of the position detection device1of the first variation will be described below, wherein the detector2and the detector3execute acquisition processes almost at the same timing. The processor23of the detector2transitions to the standby state when the acquisition process ends. Here, since the detector2and the detector3execute the acquisition processes almost at the same timing, the detection signal Y4is not induced in the detection coil22during a period after the end of the acquisition process until the standby time T21elapses. Therefore, the processor23executes the acquisition process again after the standby time T21has elapsed.

The processor33of the detector3also transitions to the standby state when the acquisition process ends. Here, the processor23executes the acquisition process during a period after the end of the acquisition process until the standby time T22elapses. Therefore, since a detection signal Y3is induced in a detection coil32within the standby time T22, the processor33determines a timing to execute the acquisition process based on the detection signal Y3. Then, the processor33executes the acquisition process at the determined timing. Thereafter, the detector2and the detector3alternately execute the acquisition process.

As described above, the position detection device1of the first variation can resume the acquisition process in a normal mode even when the detector2and the detector3executes the acquisition processes almost at the same timing.

As illustrated inFIG. 11A, a processor23(processor33) of a detector2(detector3) in a position detection device1of a second variation has a function of measuring a determination time T3when the acquisition process ends. The processor23(processor33) determines that the detector2(detector3) is at fault when a detection signal Y4(detection signal Y3) is induced in a detection coil22(detection coil32) within the determination time T3. When the processor23(processor33) determines the fault, the processor23(processor33) outputs a fault signal to an ECU4and stops operation of the processor23(processor33). Moreover, as illustrated inFIG. 11A, in the position detection device1of the second variation, a time period during which the processor33executes the acquisition process is longer than a time period during which the processor23executes the acquisition process.

That is, when the detector2is assumed to be a first detector and the detector3is assumed to be a second detector, the processor33(second processor) has a function of measuring the determination time T3when the (second) acquisition process ends. The processor33is configured to stop operation of the processor33when the detection signal Y3(third detection signal) is detected within the determination time T3. Similarly, the processor23(first processor) has a function of measuring the determination time T3when the (first) acquisition process ends. The processor23is configured to stop operation of the processor23when the detection signal Y4(fourth detection signal) is detected within the determination time T3. The length of the time period during which the (first) acquisition process is executed and the length of the time period during which the (second) acquisition process is executed are preferably different from each other.

With reference toFIG. 11B, an example of the operation of the position detection device1of the second variation will be described below, wherein the detector2and the detector3execute acquisition processes almost at the same timing. The processor23of the detector2measures the determination time T3when the acquisition process ends. Here, the time period during which the processor33of the detector3executes the acquisition process is longer than the time period during which the processor23executes the acquisition process. Therefore, the detection signal Y4is induced in the detection coil22within the determination time T3. Thus, the processor23determines the fault, and stops operation of the processor23.

The processor33of the detector3also measures the determination time T3when the acquisition process ends. Here, the processor23has stopped operation of the processor23, and therefore, the detection signal Y3is not induced in the detection coil32within the determination time T3. Therefore, the processor33executes the acquisition process again after the standby time T2has elapsed. Thereafter, the processor33executes the acquisition process every standby time T2.

As described above, when the detector2and the detector3execute the acquisition processes almost at the same timing, the position detection device1of the second variation determines that mutual interference exists, and the processor23(processor33) of one detector2(detector3) stops operation of the processor23(processor33). Therefore, the position detection device1of the second variation avoids a state in which mutual magnetic interference occurs, and can continue the acquisition process by using the remaining detector2(detector3).

Second Embodiment

While in the position detection device1of the first embodiment, the processor23(processor33) monitors whether or not the detection signal Y4(detection signal Y3) is induced in the detection coil22(detection coil32) during the monitoring period, other configurations may be possible. A position detection device1according to a second embodiment of the present invention will be described below with reference to the drawings. The description of elements of the position detection device1of the present embodiment which are shown in the position detection device1of the first embodiment is accordingly omitted.

As illustrated inFIG. 12, the position detection device1of the present embodiment includes a (first) processor23and a (second) processor33which are electrically connected to each other via one communication line5. The (first) processor23and the (second) processor33can perform bidirectional communication via the one communication line5.

Specifically, the processor23(processor33) includes a signal generation unit configured to generate a signal flowing through the communication line5. The signal generation unit includes a series circuit of a pull-up resister and a switch and is electrically connected between a power supply and circuit ground of the processor23(processor33). A first connection point of the pull-up resister and the switch of the processor23and a second connection point of the pull-up resister and the switch of the processor33are electrically connected to each other via the communication line5. In a case where the communication line5is not connected, a voltage between the first connection point and the circuit ground is hereinafter referred to as a “first output voltage V1,” and a voltage between the second connection point and the circuit ground is hereinafter referred to as a “second output voltage V2.”

The processor23(processor33) is configured to turn on the switch while executing the acquisition process and to turn off the switch while not executing the acquisition process. Therefore, the first output voltage V1is at a low (L) level while the processor23is executing the acquisition process, and the first output voltage V1is at a high (H) level while the processor23is not executing the acquisition process. Similarly, the second output voltage V2is at the L level while the processor33is executing the acquisition process, and the second output voltage V2is at the H level while the processor33is executing the acquisition process.

Here, the first connection point and the second connection point are electrically connected to each other via the communication line5in practice. Therefore, the potential of the communication line5is a logical conjunction of the first output voltage V1and the second output voltage V2. That is, the (first) processor23is configured to change the first output voltage V1(to change the signal flowing through the communication line5) while executing the (first) acquisition process. Similarly, the (second) processor33is configured to change the second output voltage V2(to change the signal flowing through the communication line5) while executing the (second) acquisition process. One processor23(processor33) monitors the potential of the communication line5, thereby determining whether or not the remaining processor33(processor23) is executing the acquisition process.

An example of the operation of the position detection device1of the present embodiment including the monitoring period will be described below. First, with reference toFIG. 13, a case where a detector2and a detector3are activated at the same timing will be described. In this case, the monitoring period of the processor23substantially coincides with the monitoring period of the processor33. Therefore, during the monitoring period of the processor23(processor33), the first output voltage V1and the second output voltage V2remain at the H level and do not change. That is, during the monitoring period of the processor23(processor33), the potential of the communication line5does not change.

Therefore, since the potential of the communication line5does not change (the signal flowing through the communication line5does not change) during the monitoring period, the processor23executes the acquisition process at the end of the monitoring period and transitions to the measurement period. Since the potential of the communication line5does not change (the signal flowing through the communication line5does not change) during the monitoring period, the processor33transitions to the standby state at the end of the monitoring period and then transitions to the measurement period. Thereafter, the processor23and the processor33intermittently execute the acquisition processes such that the time periods during which the acquisition processes are executed do not overlap each other.

Next, with reference toFIG. 14, a case where the activation of the detector3lags the activation of the detector2will be described. In this case, since the potential of the communication line5does not change (the signal flowing through the communication line5does not change) during the monitoring period, the processor23executes the acquisition process at the end of the monitoring period and transitions to the measurement period. The monitoring period of the processor33overlaps a time period during which the processor23executes the acquisition process. Therefore, during the monitoring period of the processor33, the first output voltage V1changes from the H level to the L level. That is, during the monitoring period of the processor33, the potential of the communication line5changes (the signal flowing through the communication line5changes). Therefore, the processor33determines that the processor23is executing the acquisition process during the monitoring period, and the processor33executes the predetermined process at the end of the monitoring period.

As described above, in the position detection device1of the present embodiment, the (first) processor23and the (second) processor33are electrically connected to each other via the communication line5. The (second) processor33is configured to determine that the (first) processor23is executing the (first) acquisition process when a change is caused in the signal flowing through the communication line5during the monitoring period. Also with this configuration, the (second) detector3can execute the predetermined process based on the result of the determination of whether or not the (first) detector2is executing the (first) acquisition process during the monitoring period.

In the position detection device1of the present embodiment, the (first) processor23and the (second) processor33may be capable of communicating with each other. For example, the (first) processor23and the (second) processor33may be electrically connected with each other via two communication lines5. With this configuration, unidirectional communication from the (first) processor23to the (second) processor33and unidirectional communication from the (second) processor33to the (first) processor23can be performed by using the two communication lines5. In the processor23(processor33), the communication line5may be electrically connected to circuit ground via a pull-down resistor. With this configuration, the switch may be electrically connected between the power supply and the communication line5.

Third Embodiment

A position detection device1according to a third embodiment of the present invention will be described below with reference to the drawings. The description of elements of the position detection device1of the present embodiment which are shown in the position detection device1of the first embodiment is accordingly omitted.

<Possibility of Mutual Interference During Measurement Period>

It is possible, although very rare, that due to, for example, a temporal abnormality of a processor23(processor33), a time period during which the processor23executes the acquisition process and a time period during which the processor33executes the acquisition process partly overlap each other. The time period during which the processor23(processor33) executes the acquisition process is hereinafter referred to as an “execution time period DP1.” That is, as an example illustrated inFIG. 15A, an event occurs in which the execution time period DP1of the processor23and the execution time period DP1of the processor33partly overlap each other. This event may also occur when, for example, noise is induced in the detection coil22(detection coil32) and the processor23(processor33) erroneously determines the induction of the noise as acquisition of a detection signal Y4(detection signal Y3), which results in deviation in timing at which the acquisition process is started. When the event described above occurs, any measures have to be taken. Otherwise, the detectors2and3would continue magnetically interfering with each other and would continue outputting position signals including errors.

To solve the problem described above, when the detector2is assumed to be a first detector and the detector3is assumed to be a second detector, the processor23(first processor) in the position detection device1of the present embodiment has the following configuration. That is, the (first) processor23is configured to monitor whether or not a change is caused in a signal (detection signal Y1) induced in a (first) detection coil22while executing the (first) acquisition process. The (first) processor23is configured to execute a predetermined process when the change is caused in the signal (detection signal Y1). While detailed description will be given later, the predetermined process here is a process to prevent the detectors2and3from continuing magnetically interfering with each other.

Similarly, the (second) processor33is configured to monitor whether or not a change is caused in a signal (detection signal Y2) induced in a (second) detection coil32while executing the (second) acquisition process. The (second) processor33is configured to execute the predetermined process when the change is caused in the signal (detection signal Y2).

In the position detection device1of the present embodiment, the processor23(processor33) has the following configuration to monitor whether or not a change is caused in the detection signal Y1(detection signal Y2). That is, the processor23(processor33) is configured to sample the detection signal Y1(detection signal Y2) at a frequency higher than the frequency of a drive signal X1(drive signal X2) to obtain data, and to compute the phase and the amplitude of the detection signal Y1(detection signal Y2) from the obtained data. With this configuration, the processor23(processor33) obtains data of the phase and the amplitude of the detection signal Y1(detection signal Y2) in real time, thereby monitoring changes in the phase and the amplitude of the detection signal Y1(detection signal Y2). A sampling frequency is preferably set such that one half of the sampling frequency (i.e., Nyquist frequency) is higher than or equal to the frequency of the drive signal X1(drive signal X2).

An example of the operation of the position detection device1of the present embodiment will be described below. When the detectors2and3do not magnetically interfere with each other, no change is caused in the detection signal Y1(detection signal Y2). In this case, the processor23(processor33) determines that time periods during which excitation coils21and31operate do not overlap each other, and the processor23(processor33) executes the acquisition process as usual. As previously described, in the position detection device1of the present embodiment, the processors23and33execute the acquisition processes such that time periods during which the acquisition processes are performed are separated from each other.

On the other hand, when the detectors2and3magnetically interfere with each other, one or both of the phase and the amplitude of the detection signal Y1(detection signal Y2) change with a time point of the occurrence of mutual interference as a border. For example, as an example illustrated inFIG. 15B, when the mutual interference occurs after time t0, the phase and the amplitude of the detection signal Y1(detection signal Y2) change with the time t0as a border. In this case, the processor23(processor33) determines that time periods during which the excitation coils21and31operate overlap each other, and the processor23(processor33) executes the predetermined process.

That is, when the detector2is assumed to be a first detector and the detector3is assumed to be a second detector, the processor33(second processor) in the position detection device1of the present embodiment has the following configuration. That is, the (second) processor33is configured to monitor whether or not a change is caused in the signal (detection signal Y2) induced in the (second) detection coil32in the (second) acquisition process. Therefore, the (second) processor33can monitor whether or not the detectors2and3magnetically interfere with each other (i.e., whether or not time periods during which the excitation coils21and31operate overlap each other). The (second) processor33is configured to execute the predetermined process when a change is caused in the signal (detection signal Y2) (i.e., when the time periods during which the excitation coils21and31operate overlap each other). Therefore, the position detection device1of the present embodiment executes the predetermined process when the time periods during which the excitation coils21and31operate overlap each other, thereby preventing the detectors2and3from continuing magnetically interfering with each other.

Here, the predetermined process, when executed by the processor33(second processor), may be a process of executing the (second) acquisition process so as not to overlap the (first) acquisition process. Similarly, the predetermined process, when executed by the processor23(first processor), may be a process of executing the (first) acquisition process so as not to overlap the (second) acquisition process.

For example, when the detectors2and3magnetically interfere with each other, the (first) processor23may execute the (first) acquisition process based on a timing at which the mutual interference occurs (i.e., based on a timing at which a change is caused in the detection signal Y1) such that the (first) acquisition process does not overlap the (second) acquisition process. Similarly, when the detectors2and3magnetically interfere with each other, the (second) processor33may execute the (second) acquisition process based on a timing at which the mutual interference occurs (i.e., based on a timing at which a change is caused in the detection signal Y2) such that the (second) acquisition process does not overlap the (first) acquisition process.

Moreover, for example, when the detectors2and3magnetically interfere with each other, the (first) processor23may transition to the standby state and may execute the (first) acquisition process at a timing based on the detection signal Y4induced in the (first) detection coil22in the standby state. Similarly, when the detectors2and3magnetically interfere with each other, the (second) processor33may transition to the standby state and may execute the (second) acquisition process at a timing based on the detection signal Y3induced in the (second) detection coil32in the standby state.

Any of the configurations can prevent the detectors2and3from continuing magnetically interfering with each other.

The predetermined process, when executed by the processor33(second processor), may be a process of stopping the operation of the processor33. Similarly, the predetermined process, when executed by the processor23(first processor), may be a process of stopping the operation of the processor23. In this case, the acquisition process is not executed by the detector2(detector3) which presumably includes any abnormality, and therefore, the acquisition process can be executed by the normal detector2(detector3). Therefore, in this case, it is possible to reduce the possibility of unfavorable mutual interference due to the detector2(detector3) which presumably includes any abnormality.

The processor23(processor33) may have the following configuration in order to monitor whether or not a change is caused in the detection signal Y1(detection signal Y2). That is, the processor23(processor33) may be configured to acquire the detection signal Y1(detection signal Y2) during a sampling period different from a period represented by using a natural number M as M/2 times the period of the drive signal X1(drive signal X2). Here, the detection signal Y1(detection signal Y2) is a signal induced in the detection coil22(detection coil32). For example, the processor23(processor33) may be configured to sample the detection signal Y1(detection signal Y2) at a period of N+(1/L) times the period of the drive signal X1(drive signal X2), where N is an integer greater than or equal to 0, and L is an integer greater than or equal to 3.

As an example, here, it is assumed that the processor23(processor33) samples the detection signal Y1(detection signal Y2) at a period of 5/4 times the period of the drive signal X1(drive signal X2) (i.e., N=1, L=4). When the detectors2and3do not magnetically interfere with each other, the processor23(processor33) acquires data having the same voltage value (or signal value) every period of L times the sampling period.

On the other hand, when the detectors2and3magnetically interfere with each other, at least one of the phase and the amplitude of the detection signal Y1(detection signal Y2) changes. In this case, for example, as illustrated inFIG. 16, when the mutual interference occurs at the time t0, a change is caused in data acquired by the processor23(processor33) around the time t0. Specifically, data acquired at a time t1before the time t0is different from data acquired at times t2and t3after the time t0. The time period from the time t1to the time t2and the time period from the time t2to the time t3are each equal to L times the sampling period.

As described above, with this configuration, the processor23(processor33) monitors whether or not a change is caused in data in each period having a length equal to L times the sampling period, thereby monitoring whether or not a change is caused in the detection signal Y1(detection signal Y2). With this configuration, sampling can be performed at a period longer than the period of the drive signal X1(drive signal X2). Therefore, for example, a microcontroller having a low processing speed can be used as the processor23(processor33), thereby reducing manufacturing cost.

Fourth Embodiment

A position detection device1according to a fourth embodiment of the present invention will be described below with reference to the drawings. The description of elements of the position detection device1of the present embodiment which are shown in the position detection device1of the third embodiment is accordingly omitted.

As previously described in connection with the first embodiment, it is possible, although very rare, that when a detector2and a detector3are activated at different timings due to an abnormality in an ECU4, or the like, the detector2and the detector3execute the acquisition processes almost at the same timing. Also when a temporal abnormality occurs in a processor23(processor33) or when the processor23(processor33) erroneously determines noise as a detection signal Y4(detection signal Y3), the detectors2and3may execute the acquisition processes almost at the same timing. In the position detection device1of the third embodiment, when the execution time period DP1of the processor23and the execution time period DP1of the processor33overlap each other in large part as described above, time periods during which excitation coils21and31operate also overlap each other in large part. Therefore, a change is less likely to be caused in the detection signal Y1(detection signal Y2). Thus, in the above case, the position detection device1of the third embodiment may not be able to monitor whether or not the mutual interference occurs.

Therefore, to solve the problem described above, a processor23(first processor) and a processor33(second processor) in the position detection device1according to the present embodiment have the following configurations. That is, the (first) processor23is configured to drive a (first) excitation coil21a plurality of times in the (first) acquisition process. Similarly, the (second) processor33is configured to drive a (second) excitation coil31a plurality of times in the (second) acquisition process.

For example, as illustrated inFIG. 17A, it is assumed that the (first) processor23drives the (first) excitation coil21two times at a first interval IN1during an execution time period DP1. Similarly, it is assumed that the (second) processor33drives the (second) excitation coil31two times at second intervals IN2during the execution time period DP1. It is assumed that the length of the first interval IN1and the length of the second interval IN2are different from each other. In the following description, a time period during which the (first) processor23drives the (first) excitation coil21is referred to as a “first drive period DP11,” and a time period during which the (second) processor33drives the (second) excitation coil31is referred to as a “second drive period DP12.”

In this case, during the execution time period DP1, a first-time first drive period DP11and a first-time second drive period DP12overlap each other in large part. However, a second-time first drive period DP11and a second-time second drive period DP12partly overlap each other, and therefore, a change is caused in a detection signal Y1(detection signal Y2). Thus, the processor23(processor33) can monitor mutual magnetic interference even when the execution time periods DP1overlap each other in large part.

Alternatively, the processors23and33may be configured such that the number of times of driving the (first) excitation coil21and the number of times of driving the (second) excitation coil31are different from each other during the execution time period DP1. For example, as illustrated inFIG. 17B, it is assumed that the (first) processor23drives the (first) excitation coil21two times at the first interval IN1during the execution time period DP1, whereas it is assumed that the (second) processor33drives the (second) excitation coil31three times at the second intervals IN2during the execution time period DP1.

In this case, during the execution time period DP1, the first-time first drive period DP11partly overlaps the first-time second drive period DP12and the second-time second drive period DP12. The second-time first drive period DP11partly overlaps the second-time second drive period DP12and a third-time second drive period DP12. Therefore, since a change is caused in the detection signal Y1(detection signal Y2) during the execution time period DP1, the processor23(processor33) can monitor mutual magnetic interference.

Alternatively or additionally, the processors23and33may be configured such that the length of the first drive period DP11and the length of the second drive period DP12are different from each other during the execution time period DP1. For example, as illustrated inFIG. 18, it is assumed that during the execution time period DP1, the second drive period DP12is longer than the first drive period DP11. In this case, during the execution time period DP1, the first drive period DP11ends before the end of the second drive period DP12ends. Therefore, since a change is caused in a signal induced in the (first) detection coil22with the end of the first drive period DP11as a border, the (first) processor23can monitor mutual magnetic interference. Similarly, since a change is caused in the detection signal Y2with the end of the first drive period DP11as a border, the (second) processor33can monitor mutual magnetic interference.

In the above description, the detector2is assumed to be a first detector and the detector3is assumed to be a second detector, but a similar effect may be obtained also when the detector2is assumed to be a second detector and the detector3is assumed to be a first detector. That is, the position detection device1of each embodiment may include two detectors2and3, and one of the two detectors2and3may be configured as a first detector and the remaining one of the two detectors2and3may be configured as a second detector. That is, the detectors2and3have the same configuration and each serve as either a first detector or a second detector. Thus, even when a fault occurs on one of the detectors in the position detection device1of each embodiment, the remaining one of the detectors can execute the acquisition process.

While the position detection device1of each embodiment includes two detectors2and3, the embodiment does not intend to limit the number of detectors. That is, the position detection device1of each embodiment may include three or more detectors. In this case, the position detection device1may be configured such that the processors of the detectors execute the acquisition processes in turn, and time periods during which the detectors perform the acquisition processes do not overlap each other.

As described above, the position detection device1of the present embodiment includes the following first feature.

According to the first feature, the position detection device1includes the detector2(here, a first detector) and the detector3(here, a second detector). The detector2includes the (first) excitation coil21, the (first) detection coil22, and the (first) processor23. The detector3includes the (second) excitation coil31, the (second) detection coil32, and the (second) processor33. The (first) excitation coil21is magnetically coupled to the (first) detection coil22and to the (second) detection coil32. The (second) excitation coil31is magnetically coupled to the (first) detection coil22and to the (second) detection coil32.

The (first) processor23is configured to intermittently execute a (first) acquisition process during a measurement period of the (first) processor23. The (first) acquisition process is a process of driving the (first) excitation coil21and acquiring a (first) detection signal Y1induced in the (first) detection coil22depending on the position of an object100by the driving the (first) excitation coil21. The (second) processor33is configured to intermittently execute a (second) acquisition process during a measurement period of the (second) processor. The (second) acquisition process is a process of driving the (second) excitation coil31and acquiring a (second) detection signal Y2induced in the (second) detection coil32depending on the position of the object100by the driving the (second) excitation coil31.

The (second) processor33monitors whether or not the (first) processor23is executing the (first) acquisition process without driving the (second) excitation coil31during a monitoring period set before the measurement period of the (second) processor33. The (second) processor33is configured to execute the predetermined process when the (first) processor23is executing the (first) acquisition process.

Moreover, in addition to the first feature, the position detection device1of the present embodiment may include the following second feature.

According to the second feature, the (first) processor23and the (second) processor33are electrically connected to each other via the communication line5. The (second) processor33is configured to determine that the (first) processor23is executing the (first) acquisition process when a change is caused in a signal flowing through the communication line5during the monitoring period.

In addition to the first feature, the position detection device1of the present embodiment may include the following third feature.

According to the third feature, the (second) processor33is configured to determine that the (first) processor23is executing the (first) acquisition process when the signal (detection signal Y3) is induced in the (second) detection coil32during the monitoring period.

In addition to the third feature, the position detection device1of the present embodiment may include the following fourth feature.

According to the fourth feature, the (second) processor33executes the (second) acquisition process such that the time period of the (first) acquisition process is separated from the time period of the (second) acquisition process. More specifically, the (second) processor33is configured to execute the (second) acquisition process at a timing based on the (third) detection signal Y3induced in the (second) detection coil32by driving the (first) excitation coil21.

In addition to the fourth feature, the position detection device1of the present embodiment may include the following fifth feature.

According to the fifth feature, the (second) processor33has a function of measuring the amplitude of the (third) detection signal Y3. The (second) processor33is configured to determine a timing based on the amplitude having decreased below a predetermined threshold.

In addition to the fourth feature, the position detection device1of the present embodiment may include the following sixth feature.

According to the sixth feature, the (first) processor23has a function of giving an end signal notifying the end of the (first) acquisition process to the (first) excitation coil21. The (second) processor33is configured to determine a timing based on the end signal having been induced in the (second) detection coil32and having been detected.

In addition to the fourth feature, the position detection device1of the present embodiment may include the following seventh feature.

According to the seventh feature, the (first) processor23is configured to stop operation of the (first) processor when the (first) detection signal Y1is not detected in the (first) acquisition process.

In addition to the fourth feature, the position detection device1of the present embodiment may include the following eighth feature.

According to the eighth feature, the (second) processor33has a function of measuring the (second) standby time T2when the (second) acquisition process ends. The (second) processor33is configured to execute the (second) acquisition process when the (third) detection signal Y3is not detected within the (second) standby time T2.

In addition to the eighth feature, the position detection device1of the present embodiment may include the following ninth feature.

According to the ninth feature, the (first) processor23is configured to be switched to a mode different from the normal mode to execute the (first) acquisition process when the (fourth) detection signal Y4is not detected within the (first) standby time T2.

In addition to the eighth feature, the position detection device1of the present embodiment may include the following tenth feature.

According to the tenth feature, the (first) processor23has a function of measuring the (first) standby time T2when the (first) acquisition process ends. The (first) processor23is configured to execute the (first) acquisition process when the (first detection coil) is not detected by driving the (second) excitation coil31.

In addition to the eighth feature, the position detection device1of the present embodiment has the following eleventh feature.

According to the eleventh feature, the (second) processor33has a function of measuring the determination time T3when the (second) acquisition process ends. The (second) processor33is configured to stop operation of the (second) processor33when the (third) detection signal Y3is detected within the determination time T3.

In addition to the second feature, the position detection device1of the present embodiment may include the following twelfth feature.

According to the twelfth feature, the predetermined process is a process in which a starting time point of the measurement period of the (second) processor33is adjusted not to overlap the (first) acquisition process.

In addition to the second feature, the position detection device1of the present embodiment may include the following thirteenth feature.

According to the thirteenth feature, the predetermined process is a process of stopping the operation of the (second) processor33.

In addition to the second feature, the position detection device1of the present embodiment may further include the following fourteenth feature.

According to the fourteenth feature, the (second) processor33is configured to monitor whether or not a change is caused in the signal (detection signal Y2) induced in the (second) detection coil32while executing the (second) acquisition process. The (second) processor33is configured to execute the predetermined process when the change is caused in the signal (detection signal Y2).

In addition to the fourteenth feature, the position detection device1of the present embodiment may include the following fifteenth feature.

According to the fifteenth feature, the (first) processor23is configured to drive the (first) excitation coil21a plurality of times in the (first) acquisition process. The (second) processor33is configured to drive the (second) excitation coil31a plurality of times in the (second) acquisition process.

In addition to the fifteenth feature, the position detection device1of the present embodiment may include the following sixteenth feature.

According to the sixteenth feature, the (second) processor33drives the (second) excitation coil31by a drive signal X2having a predetermined frequency. The (second) processor33is configured to acquire the signal (detection signal Y2) induced in the (second) detection coil32at a sampling period different from a period represented by using a natural number M as M/2 times the period of the drive signal X2while executing the (second) acquisition process.

In addition to the sixteenth feature, the position detection device1of the present embodiment may include the following seventeenth feature.

According to the seventeenth feature, the predetermined process is a process of executing the (second) acquisition process not overlap the (first) acquisition process.

In addition to the sixteenth feature, the position detection device1of the present embodiment may include the following eighteenth feature.

According to the eighteenth feature, the predetermined process is a process of stopping the operation of the (second) processor33.

The (second) processor33of the position detection device1of the present embodiment monitors whether or not the (first) processor23is executing the (first) acquisition process during the monitoring period before the measurement period is started, so that the position detection device1can execute the predetermined process depending on the result of the determination. This provides the effect that the position detection device1of the present embodiment can reduce the possibility that the (first) acquisition process and the (second) acquisition process are simultaneously executed on activation of the detectors2and3, that is, the possibility that time periods during which the excitation coils21and31operate overlap each other.