JP5151426B2 - Positioning device - Google Patents

Description

  The present invention relates to a positioning device, and more particularly to a positioning device using a vibration type actuator.

  In Patent Document 1, a member magnetized to a movable member of a vibration type actuator that displaces the movable member by vibration of a piezoelectric element is provided, and a change in the magnetic field formed by the movable member is detected by a Hall element or the like. There is described a positioning device that calculates a position and controls a driving circuit that applies a driving voltage to a piezoelectric element so as to place a movable member at a set position.

  Patent Document 2 describes that a movable member can be moved in a pull-back direction or a feed-out direction by applying a rectangular wave having a duty ratio of 0.3 or 0.7 to a vibration type actuator. As described in Patent Document 2, when a rectangular wave voltage is generated by switching with a switching element, a large inrush current flows during switching, and electromagnetic noise is generated.

  In the positioning device of Patent Document 1, when the drive circuit generates electromagnetic noise, the electromagnetic noise is superimposed on the magnetic field intensity detected by the Hall element or the like, and an error occurs in position detection. Since the vibration type actuator uses a drive source having a capacitive load such as a piezoelectric element, the rush due to switching is compared to that using a drive source having an inductive load such as a DC motor or a stepping motor. There is a problem that the current increases and the positioning error due to electromagnetic noise increases.

  Patent Document 3 describes an invention in which noise is determined when a difference between position displacement output signals is large, and a motor is driven by correcting a detection position. However, it is difficult to detect minute noise. Therefore, accurate positioning cannot be guaranteed.

Japanese Patent Application Laid-Open No. H10-228561 describes an invention for controlling an actuator by performing filter processing and averaging processing for noise removal. However, when the switching frequency of the driving circuit is close to the sampling frequency for position detection, noise is continuously added to the sampled position displacement output signal, so that the noise component cannot be effectively removed.
JP 2006-292396 A JP 2001-21669 A JP 2005-230939 A JP 2003-131690 A

  In view of the above problems, an object of the present invention is to provide a positioning device that is not affected by switching noise of a drive circuit and has high positioning accuracy.

In order to solve the above-mentioned problems, a positioning device according to the present invention includes a vibration type actuator that generates vibration in response to a change in applied voltage and slides and displaces a movable member by the vibration, and a drive that changes in voltage by circuit switching. A drive circuit for applying a voltage to the vibration type actuator, a displacement output means for outputting a displacement value that changes in accordance with the displacement of the movable member, the displacement value is sampled, and the movable device is based on the sampled displacement value. Position detection means for outputting a position signal indicating the position of the member, and based on the position signal, the switching of the drive circuit is controlled so as to move the movable member to a set position, and the displacement value is sampled. A control device for controlling the position detecting means so that the timing is different from the switching of the driving circuit. Have a, the control unit, every predetermined driving period T, using the duty ratio D, so as to reciprocate transitions the potential of the driving voltage at the time 0 and the time D · T, the switching to the drive circuit It is assumed that the duty control is performed, and the position detection unit is caused to perform the sampling at a timing of (1-D) · T.

  According to this configuration, since the displacement value is sampled when there is no electromagnetic noise due to switching of the drive circuit, the position signal has no error from the position of the movable member, and the movable member can be accurately positioned.

Further , according to this configuration, the sampling timing is determined by the duty ratio of the drive circuit, so that control is easy. In general, in driving a vibration type actuator, the duty ratio D is set to about 0.3 or about 0.7 depending on the driving direction. For this reason, there is a margin of about 0.3T or about 0.4T from the timing of (1-D) · T to the next switching, and a time for sampling can be easily secured.

  In the positioning device of the present invention, the vibration type actuator may include a piezoelectric element that expands and contracts according to a driving voltage, and includes a driving member fixed to one end of the piezoelectric element. The movable member may be frictionally engaged.

  According to this configuration, high-accuracy positioning can be performed using the piezoelectric actuator.

  In the positioning device of the present invention, the displacement output means may include a magnetized magnetic field generating member attached to the movable member and a magnetic field detecting means for detecting the strength of the magnetic field formed by the magnetic field generating member. Good.

  According to this configuration, position detection by magnetism that is easily affected by electromagnetic noise can be detected with high accuracy.

  Since the positioning device of the present invention detects the position of the movable member at a timing different from the switching of the drive circuit, the accurate position can be detected and the positioning can be performed with high accuracy without being affected by the electromagnetic noise due to the switching.

Embodiments of the present invention will now be described with reference to the drawings.
FIG. 1 is a schematic diagram showing a configuration of a positioning device 1 according to one embodiment of the present invention. The positioning device 1 includes a piezoelectric actuator (vibration type actuator) 2 and a displacement output device (displacement output means) 3, and processes a drive circuit 4 of the piezoelectric actuator 2 and a displacement output signal (displacement value) of the displacement output device 3. And a control device 6 for controlling the drive circuit 4 so as to obtain an output of the position detection circuit (position detection means) 5 corresponding to the position indicated by the position command signal.

  The piezoelectric actuator 2 is fixed to the base member 7 and expands and contracts in the x direction indicated by the arrow by the drive voltage of the drive circuit 4, and is fixed to the piezoelectric element 8 and advances and retracts in the x direction by the expansion and contraction of the piezoelectric element 8. And a movable member 10 that is frictionally engaged with the drive member 9 and that can slide on the drive member 9.

  The displacement output device 3 includes a magnetic field generating member 11 attached to the movable member 10 and a magnetic field detecting means 12 fixed to the base member 7 so as to face the magnetic field generating member 11.

  FIG. 2 shows the configuration of the displacement output device 3 in detail. The magnetic field generating member 11 includes an N pole portion 13 whose surface facing the magnetic field detection means 12 is magnetized to N pole, an S pole portion 14 whose surface facing the magnetic field detection means 12 is magnetized to S pole, It is provided between the N pole part 13 and the S pole part 14, and is composed of a non-magnetized part 15 that is not magnetized in the N pole or the S pole. The N pole portion 13, the non-magnetized portion 15, and the S pole portion 14 are arranged in the x direction, which is the movable direction of the movable member 10. The magnetic field detection means 12 includes two Hall elements 16a and 16b arranged in the x direction.

  FIG. 3 shows a circuit configuration of the positioning device 1. The drive circuit 4 includes four transistors 17, 18, 19, and 20 that are switching elements driven by control signals C 1, C 2, C 3, and C 4 output from the control device 6. The transistor 17 is made of a p-channel FET, and is turned on to connect the electrode 8a of the piezoelectric element 8 to the power source E (V). The transistor 18 is made of a p-channel FET, and is turned on to turn on the piezoelectric element 8. The electrode 8b is connected to the power source E (V). The transistor 19 is composed of an n-channel FET, and is turned on to ground the electrode 8a. The transistor 20 is composed of an n-channel FET, and is turned on to ground the electrode 8b. The drive circuit 4 applies a drive voltage of + E (V) to the piezoelectric element 8 when the transistor 17 and the transistor 20 are turned on, and −E to the piezoelectric element 8 when the transistor 18 and the transistor 19 are turned on. It is a full bridge circuit which applies the drive voltage of (V).

  The position detection circuit 5 includes amplifiers 21a and 21b that amplify the displacement output signals of the Hall elements 16a and 16b, and an arithmetic unit 23 that includes AD converters 22a and 22b that convert the amplified displacement output signals to digital. . When the trigger signal TS of the control device 6 is input, the arithmetic device 23 starts sampling by converting the displacement output signal into a digital value by the AD converters 22a and 22b.

  The arithmetic unit 23 calculates A> 0 from the output of the amplifier 21a (amplified displacement output signal of the Hall element 16a) A and the output of the amplifier 21b (amplified displacement output signal of the Hall element 16b) B, which are sampled after digital conversion. In the case of (A−B) / (A + B) +2, B <0, (A−B) / (A + B) −2, A ≦ 0 and B ≧ 0, (B + A) / (B−A And the calculation result is input to the control device 6 as a position signal PS indicating the position of the movable member 10.

  The control device 6 receives a position command signal SS indicating the position where the movable member 10 should be positioned, and determines the drive voltage that the drive circuit 4 should apply to the piezoelectric element 8 from the deviation between the position signal PS and the position command signal SS. The waveform is determined, and the switching of the transistors 17, 18, 19, and 20 of the drive circuit 4 is controlled.

  FIG. 4 shows a control device for moving the movable member 10 away from the piezoelectric element 8, that is, when the position of the movable member 10 indicated by the position signal PS is closer to the piezoelectric element 8 than the position indicated by the position command signal SS. 6 shows a timing chart of the control of the drive circuit 4 and the position detection circuit 5 and the operation of the piezoelectric actuator 2, and FIG. 5 shows the case where the movable member 10 is moved closer to the piezoelectric element 8, that is, the position signal PS shows. A timing chart of the control of the drive circuit 4 and the position detection circuit 5 by the control device 6 and the operation of the piezoelectric actuator 2 when the position of the movable member 10 is farther from the piezoelectric element 8 than the position indicated by the position command signal SS is shown.

  When the control signals C1 and C3 of the control device 6 are HI and C2 and C4 are LO, the transistors 17 and 20 are turned off, the transistors 18 and 19 are turned on, and the piezoelectric element 8 has a voltage of −E (V). Is applied. Here, when the control signals C2 and C4 are set to HI, the transistor 18 is turned off and the transistor 20 is turned on. Thereby, both electrodes 8a and 8b of the piezoelectric element 8 are grounded, and the voltage of the piezoelectric element 8 becomes 0 (V). Subsequently, when the control signals C1 and C3 are set to LO, the transistor 17 is turned on and the transistor 19 is turned off. As a result, a voltage of + E (V) is applied to the piezoelectric element 8. Similarly, when -E (V) is applied to the piezoelectric element 8, the drive voltage is applied after the electrodes 8a and 8b are once grounded.

  In this embodiment, the electrodes 8a and 8b are once grounded in this way, and then the polarity of the drive voltage applied to the piezoelectric element 8 is reversed. This is because the electrodes 8a and 8b are grounded together. When the charged electric charge is discharged to the ground and the power supply is connected in the reverse polarity, the amount of charge to be supplied by the power supply can be halved, and the power of the power supply can be saved. In the figure, the output voltage observed when the piezoelectric element 8 is removed and the output terminal of the drive circuit 4 is opened is shown in an easy-to-understand manner. The drive voltage is regarded as a rectangular wave drive that instantaneously transits between + E (V) and -E (V). Actually, the control signals C1, C3, C2, and C4 may be inverted signals of each other, and one end of the piezoelectric element 8 is always grounded, and the other end is connected to the power source, and the power circuit is connected to and disconnected from the rectangular circuit. The drive voltage may be applied.

  The control device 6 inputs to the drive circuit 4 control signals C1, C2, C3, and C4 that change the drive voltage applied to the piezoelectric actuator 2 periodically and repeatedly with the time T as one cycle. As shown in FIG. 4, when the drive circuit 4 drives (feeds out) the movable member 10 away from the piezoelectric element 8, + E (V) is applied to the piezoelectric element 8 by 0.3T and 0.7T. -E (V) is applied (duty ratio D = 0.3). Further, as shown in FIG. 5, when the drive circuit 4 drives (retracts) the movable member 10 so as to approach the piezoelectric element 8, + E (V) is applied to the piezoelectric element 8 by 0.7 T, and 0. -E (V) is applied only for 3T (duty ratio D = 0.7).

  Due to switching of the transistors 17, 18, 19, and 20, a charging current (or discharging current) flows through the piezoelectric element 8. Since the piezoelectric element 8 is a capacitive load, as shown in the figure, a large inrush current flows at the moment when the transistors 17, 18, 19, and 20 are turned on, and when the charge is saturated, no current flows. Further, due to the voltage drop due to the charging current, the waveform of the voltage that is actually applied to the piezoelectric element 8 is a slightly broken rectangular wave.

  Further, the dimensional displacement of the piezoelectric element 8 is further delayed from the change of the drive voltage due to its own elasticity and the like, and has a sawtooth period change as shown in the figure due to its frequency characteristics. When the piezoelectric element 8 is slowly dimensionally displaced (expanded), the drive member 9 moves slowly, and the movable member 10 moves together while being frictionally engaged with the drive member 9. When the piezo-electric element 8 is suddenly displaced in size, the driving member 9 moves steeply, and the movable member 10 is slidably displaced with respect to the driving member 9 so as to remain in place due to its own inertia.

  When the piezoelectric actuator 2 is driven, the charging current that flows when the transistors 17, 18, 19, and 20 are switched generates electromagnetic noise in proportion thereto. This electromagnetic noise is superimposed on the magnetic field formed by the magnetic field generating member 11 of the displacement output device 3, and a noise component is superimposed on the displacement output of the Hall elements 16a and 16b. In other words, when the transistors 17, 18, 19, and 20 of the drive circuit 4 are not switched, it indicates that no noise component is present on the displacement output signals of the Hall elements 16a and 16b. Therefore, the control device 6 inputs the trigger signal TS to the position detection circuit 5 at the timing when the state of the control signals C1, C2, C3, and C4 does not change, thereby outputting the displacement output of the Hall elements 16a and 16b without noise. The signal is converted into a digital signal by an AD converter and sampled.

  As described above, the positioning device 1 accurately determines the position of the movable member 10 of the piezoelectric actuator 2 by causing the position detection circuit 5 to sample the output of the displacement output device 3 by the control device 6 selecting a timing without noise. Can be detected. Accordingly, the positioning device 1 can accurately position the movable member 10 at the position specified by the position command signal SS.

  FIG. 6 shows a practical shape of the positioning device 1. In the positioning device 1, the movable member 10 is a ball frame that holds a lens 24 that is an optical element, and is movable along a suspension shaft 25 that is parallel to the drive member 9 fixed to the base member 7. The magnetic field generating member 11 is attached to a portion that engages with the suspension shaft 25 of the movable member 10. A piezoelectric element 8 and a magnetic field detection means 12 are fixed to the base member 7 so as to face the magnetic field generating member 11 through a fixing member 7 ′.

  The positioning device 1 configured in this way is small and lightweight, but the displacement output device 3 accurately detects the position of the lens 24 held by the movable member 10 in the direction of the suspension shaft 25, and the piezoelectric actuator 2 detects the lens. 24 can be positioned at the required position.

7 and 8 show alternative driving timings of FIGS. 4 and 5 for the positioning device 1 of the present invention. In the present plan, the control device 6 inputs the trigger signal TS to the position detection circuit 5 at the center of the driving cycle T, at a timing of 0.5T from the start of the cycle. For this reason, from the switching operation of the drive circuit 4 immediately before to the start of sampling of the displacement output signals of the Hall elements 16a and 16b, 0.2T is used for the extension drive (duty ratio D = 0.3), and the return drive is performed. In the case of (duty ratio D = 0.7), the time of 0.5T has elapsed and no charging current remains. Also, from the start of sampling of the displacement output signals of the Hall elements 16a and 16b to the next switching operation of the drive circuit 4, 0.5T is used for the extension drive (duty ratio D = 0.3), and the return drive is performed. In the case of (duty ratio D = 0.7), there is a time of 0.2T, and sampling can be completed before the charging current flows.

  The AD converters 21a and 21b of the position detection circuit 5 often require continuous input for about 1 to 2 μsec. When the driving cycle T of the driving circuit 4 is 10 μsec (driving frequency 100 kHz), for example, 2 μsec from the start of sampling of the displacement output signals of the Hall elements 16a and 16b to the next switching operation of the driving circuit 4 It is preferable that there is a margin above, and it is more preferable that the time be 3 μsec or more. If the sampling start timing is set at the center timing of the driving cycle T, there is a margin of 2 μsec for sampling in both the feed-out drive and the pull-back drive, and the influence of noise can be avoided.

9 and 10 show further alternatives of the drive timings of FIGS. 4 and 5 of the positioning device 1 of the present invention. In the present plan, when the duty ratio D of the switching of the drive circuit 4 is 0.3, the control device 6 causes the position detection circuit 5 to start sampling at a timing of 0.7 T from the start of the cycle, and the switching duty of the drive circuit 4 When the ratio D is 0.7, the trigger signal TS is input to the position detection circuit 5 at a timing of 0.3T from the start of the cycle. That is, the control device 6 causes the position detection circuit to start sampling at the timing (1-D) · T when the complement ratio of the duty ratio D of the driving cycle T has elapsed.

  Thus, at a general duty ratio of 0.3 / 0.7, sampling is started after at least 0.3T has elapsed since the switching of the drive circuit 4, and at least 0.3T from the start of sampling to the next switching. I can afford. When the driving cycle T is 10 μsec, it is possible to devote 3 μsec to AD conversion. As described above, when the sampling start timing is determined by the duty ratio D, the position of the movable member 11 can be detected at a timing free from noise even if the sampling speed of the AD converters 22a and 22b is low.

The schematic block diagram of the positioning device of embodiment of this invention. The block diagram of the displacement output device of the positioning device of FIG. The circuit diagram of the positioning device of FIG. The timing chart of the control operation at the time of the feeding operation of the positioning device of FIG. The timing chart of the control operation at the time of the pull-back operation | movement of the positioning device of FIG. The figure which shows the specific application example of the positioning device of FIG. FIG. 5 is an alternative timing chart of FIG. 4. FIG. 6 is an alternative timing chart of FIG. 5. FIG. FIG. 5 is a further alternative timing chart of FIG. 4. FIG. FIG. 6 is a timing chart of a further alternative of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Positioning device 2 ... Piezoelectric actuator (vibration type actuator)
3. Displacement output device (displacement output means)
DESCRIPTION OF SYMBOLS 4 ... Drive circuit 5 ... Position detection circuit 6 ... Control apparatus 8 ... Piezoelectric element 9 ... Drive member 10 ... Movable member 11 ... Magnetic field generation member 12 ... Magnetic field detection means

Claims (4)

A vibration type actuator that generates a vibration in response to a change in an applied voltage and slides and displaces the movable member by the vibration;
A drive circuit for applying a drive voltage that varies in voltage by switching of the circuit to the vibration actuator;
A displacement output means for outputting a displacement value that varies with the displacement of the movable member;
Position detecting means for sampling the displacement value and outputting a position signal indicating the position of the movable member based on the sampled displacement value;
Based on the position signal, the switching of the driving circuit is controlled so as to move the movable member to a set position, and the sampling of the displacement value is performed at a timing different from the switching of the driving circuit. have a control device for controlling the position detecting means,
The control device performs duty control for switching the drive circuit so that the potential of the drive voltage is reciprocally transitioned at time 0 and time D · T using a duty ratio D for each predetermined drive cycle T. Done
A positioning apparatus characterized by causing the position detection means to perform the sampling at a timing of (1-D) · T. The positioning device according to claim 1 , wherein the vibration type actuator includes a piezoelectric element that expands and contracts according to a driving voltage. The positioning apparatus according to claim 2 , wherein the vibration type actuator includes a driving member fixed to one end of the piezoelectric element, and the movable member is frictionally engaged with the driving member. The displacement output means, said movable member magnetized magnetic field generating member was attached to, claims 1 to 3, characterized in that it comprises a magnetic field detection means for detecting the field strength of the formation of the magnetic field generating member A positioning device according to any one of the above.

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