JP4992037B2 - DRIVE DEVICE, DRIVE DEVICE STATE DETECTION METHOD, AND DRIVE DEVICE CONTROL METHOD - Google Patents

Description

  The present invention relates to a friction drive type drive device using a piezoelectric element.

  Depending on the piezoelectric element, the axial vibration member is reciprocally displaced in the axial direction so that the displacement speed varies depending on the direction, and the friction engagement member that frictionally engages the vibration member is slid relative to the vibration member (friction engagement member). There is a known friction drive device that moves the vibration member and the vibration member.

  Such a friction drive type drive device requires a drive device that applies a periodically varying voltage to the piezoelectric element. In particular, a drive circuit that applies a voltage to the electrode of the piezoelectric element or grounds the semiconductor switching element is used.

  For example, Patent Document 1 discloses a drive circuit formed of a half bridge that includes a switch that connects one pole of a piezoelectric element to the power source and connects the other pole to a power source and a switching element that is grounded. Patent Document 2 discloses a full bridge circuit in which the polarity applied to the piezoelectric element is changed by connecting any one of the electromechanical conversion elements to a power source and grounding the other pole.

In such a drive device, there is a possibility that the drive speed at which the friction engagement member is slid and displaced changes due to a change in the characteristics of the piezoelectric element. In addition, when a failure such as a short circuit of the piezoelectric element occurs, an excessive current flows, and there is a risk of causing damage not only to the driving device but also to the power source and the like.
JP 2001-268951 A JP 2001-21669 A

  In view of the above problems, it is an object of the present invention to provide a drive device that can detect the state of a piezoelectric element, a drive device state detection method, and a drive device control method.

In addition, according to the present invention, a piezoelectric element that expands and contracts when a voltage is applied, a vibration member that is fixed at one end to the piezoelectric element, and that can reciprocate in the axial direction by expansion and contraction of the piezoelectric element, and the vibration member A friction engagement member that frictionally engages and reciprocally displaces with respect to the vibration member by a reciprocating displacement of the vibration member, a charge switching element that connects an electrode of the piezoelectric element to a power source at a predetermined drive cycle, and A method for detecting a state of a driving device having a driving circuit including a discharge switching element that grounds an electrode is detected in an electric circuit between the power source and the piezoelectric element or an electric circuit between the piezoelectric element and a grounding point. resistance disposed, said detecting a potential difference across the detection resistor with a predetermined timing during the driving cycle, determines the state of the piezoelectric element based on the potential difference detected, the predetermined timing A timing delayed from the operation of the charge switching element and the discharge switching element by a time constant of a circuit from the power source to the ground point via the piezoelectric element, and when the detected potential difference is larger than the predetermined range A method for determining that the piezoelectric element is short-circuited.

According to this method, it is possible to detect a current value when charging / discharging the piezoelectric element as a voltage drop in the detection resistor, and to detect a capacitance change of the piezoelectric element and an abnormality in a charging / discharging path by a change in the voltage drop waveform. it can. As a result, the drive voltage waveform can be adjusted according to the state change of the piezoelectric element to standardize the drive force and the drive speed, or the operation can be stopped by detecting the occurrence of a failure, thereby minimizing the failure.

Further, the control method of the driving device according to the present invention includes a piezoelectric element that expands and contracts when a voltage is applied, and a vibration member that has one end fixed to the piezoelectric element and is capable of reciprocating in the axial direction by the expansion and contraction of the piezoelectric element. Charge switching for frictionally engaging the vibration member and slidingly displacing the vibration member by reciprocating displacement of the vibration member and the electrode of the piezoelectric element connected to a power source at a predetermined drive cycle A drive device control method comprising: an element; and a drive circuit including a discharge switching element for grounding the electrode, wherein an electric path between the power source and the piezoelectric element, or between the piezoelectric element and a ground point A detection resistor is disposed in the electric circuit between the two, and a potential difference between both ends of the detection resistor is measured at a predetermined timing during the driving cycle, and a state of the piezoelectric element is determined based on the detected potential difference. Predetermined timing is a timing which is slightly delayed from the operation of the charge switching device and the discharge switching element, when the potential difference detected is increased, it is determined that the capacity of the piezoelectric element is increased, the When an increase in the capacitance of the piezoelectric element is detected, the driving cycle is lengthened.

When the piezoelectric element is short-circuited, the charge / discharge current is not attenuated, so the potential difference of the detection resistor is measured at a timing that is delayed by more than the time constant of the RC circuit consisting of the piezoelectric element and the detection resistor from the operation of the switching element. Is a short circuit of the piezoelectric element. The driving force and driving speed can be standardized by changing the duty ratio and the driving cycle according to the change in the capacitance of the piezoelectric element.

  According to the present invention, the operation of the driving device can be optimized by measuring the voltage drop due to the detection resistor and detecting the change in the capacitance of the piezoelectric element.

Embodiments of the present invention will now be described with reference to the drawings.
In FIG. 1, the structure of the drive device 1 of 1st Embodiment of this invention is shown. The driving device 1 includes a driving circuit 4 to which a DC power source 2 having a voltage Vp (V) and a control device 3 are connected, a piezoelectric element 5 to which an output of the driving circuit is applied to the electrodes 5a and 5b, and one end to the piezoelectric element 5. Is fixed to the shaft-like vibration member 6 and the friction engagement member 7 is engaged with the vibration member 6 by a frictional force.

  The piezoelectric element 5 expands and contracts in the axial direction of the vibration member 6 according to the voltage applied between the electrodes 5a and 5b. When the piezoelectric element 5 expands and contracts, the vibrating member 6 reciprocates (displaces) in the axial direction. When the vibration member 6 moves slowly, the friction engagement member 7 moves together with the vibration member 6 while being frictionally engaged. However, when the vibration member 6 moves steeply, the friction engagement member 7 stays in place due to its inertial force. As a result, the sliding displacement occurs with respect to the vibrating member 6.

  The drive circuit 4 includes four transistors 8, 9, 10, 11 that are turned on / off by control signals S 1, S 2, S 3, S 4 of the control device 3 and a protective resistor 12. The transistor 8 is a charge switching element composed of a p-channel FET that turns on to apply the voltage of the power supply 2 to the electrode 5a of the piezoelectric element 5 via the protective resistor 12, and the transistor 9 turns on the electrode 5a. Is a discharge switching element composed of an n-channel FET that grounds through a protective resistor 12. The transistor 10 is a charge switching element composed of a p-channel FET that turns on and applies the voltage of the power supply 2 to the electrode 5b. The transistor 11 is an n-channel FET that turns on and grounds the electrode 5b. This is a discharge switching element.

  The driving device 1 also includes a differentiator (potential difference detection means) 13 that derives a potential difference dV between the potentials V1 and V2 across the detection resistor 12 and inputs the potential difference dV to the control device 3. The control device 3 performs A / D conversion on the input potential difference dV, determines the state of the piezoelectric element 5 based on the potential difference dV (state determination unit), and optimizes the drive circuit 4 according to the state of the piezoelectric element 5. Control.

  The control device 3 outputs periodic rectangular wave-shaped control signals S1, S2, S3, and S4 that drive the transistors 8, 9, 10, and 11 respectively, but the control signal S1 and the control signal S2 have the same waveform, The control signal S3 and the control signal S4 are inverted outputs of the control signals S1 and S2. Thereby, the control device 3 controls the drive circuit 4 so that the transistor 8 and the transistor 11 are simultaneously turned on, and the transistor 9 and the transistor 10 are turned on when the transistors 8 and 11 are off. That is, the drive circuit 4 applies the voltage Vp (V) of the power source 2 to one of the electrodes 5 a and 5 b of the piezoelectric element 5 while grounding the other, and applies the electrodes 5 a and 5 b to which the voltage Vp (V) is applied. It is a full bridge circuit that switches alternately.

  Assuming that the drive period of the control signals S1, S2, S3, S4 is T (seconds), for example, the transistors 8 and 11 repeat 0.7T (seconds) on and 0.3T (seconds) off, 9 and 10 repeat 0.7T (second) off and 0.3T (second) on. Accordingly, + Vp (V) is repeatedly applied between the electrodes 5 a-5 b of the piezoelectric element 5 by 0.7 T (seconds) and -Vp (V) by 0.3 T (seconds). In this case, due to the mechanical delay of the piezoelectric element 5 and the vibration member 6, the moving speed of the vibration member 6 is different between the direction in which the vibration member 6 is pushed out to the piezoelectric element 5 and the direction in which the vibration member 6 is pulled back to the piezoelectric element 5. Is driven by sliding in one direction with respect to the vibration member 6.

  The ratio (duty ratio) of the time during which the transistors 8 and 11 are turned on is changed according to the speed at which the friction engagement member 7 is moved, and the control signals S1 and S2, the control signals S3 and S4, By switching the output time ratio, the direction in which the friction engagement member 7 slides can be reversed.

  FIG. 2 shows the control signals S1, S2, S3, S4 of the driving device 1, the voltage applied between the electrodes 5a-5b of the piezoelectric element 5, and the voltage drop (dV) in the detection resistor 12, that is, the detection resistor 12 The relationship with the potential difference (V1-V2) of both ends of is shown.

  The control signals S1, S2, S3, and S4 are rectangular waves, and the transistors 8 and 11 or the transistors 9 and 10 are simultaneously turned on to connect the power source 2 and the ground point via the piezoelectric element 5. However, because of the on-resistance of the transistors 8, 11 or 9, 10 and the internal resistance of the detection resistor 13 and the piezoelectric element, the charging current is limited and a voltage drop occurs in these resistors. The voltage appearing between the electrodes 5a-5b of the piezoelectric element 5 has a first-order lag waveform.

  A circuit related to charging / discharging of the piezoelectric element 5, that is, a circuit extending from the power source 2 of the driving device 1 to the ground point via the piezoelectric element 5 can be regarded as an RC circuit. For example, the detection resistance is 1 (Ω), the on-resistance of the transistors 8 and 10 made of p-channel FET is 0.7 (Ω), and the on-resistance of the transistors 9 and 11 made of n-channel FET is 0.3 (Ω) If the capacitance of the piezoelectric element 5 is (70 nF), the time constant τ of this RC circuit is about 0.14 (μ seconds).

The control device 3 of the driving device 1 calculates the potential difference (referred to as dV ₁ and dV ₂ respectively) at the detection resistor 12 after τμ seconds and 10τμ seconds after the operation (switching) of the transistors 8, 9, 10, 11. Measuring.

In the normal state in which the driving device 1 is in the initial state, the potential difference dV ₁ is about 37% of the maximum value that appears when the transistors 8, 9, 10, and 11 are operated, and the potential difference dV ₂ is substantially zero.

When the capacity of the piezoelectric element 5 is increased, the amount of electric charge necessary for charging the piezoelectric element 5 is increased, so that the current value is gradually decreased as compared with the normal time. For this reason, the potential difference dV ₂ when a sufficient amount of time has elapsed from the operation of the transistors 8, 9, 10, 11 does not change, but the potential difference dV at a timing slightly delayed from the operation of the transistors 8, 9, 10, 11. ₁ shows a larger value than in the normal state.

Thus, if the potential difference dV ₁ across the detection resistor 12 is measured at a timing slightly delayed from the operation of the transistors 8, 9, 10, 11, the capacitance of the piezoelectric element 5 increases or decreases depending on the magnitude of the potential difference dV _1. Can be determined.

The timing for measuring the potential difference dV ₁ is large immediately after the operation of the transistors 8, 9, 10, and 11, but it is easy to determine increase / decrease, but the measurement rate increases because the change rate of the potential difference is large. Conversely, if the operation of the transistors 8, 9, 10, and 11 is greatly delayed, the change rate of the potential difference is small and the measurement error is small. However, the measurement value is very small, so that comparison with the normal time becomes difficult.

Assuming that the driving device 1 is a complete RC circuit, the potential difference dV of the detection resistor 12 is about 90 times the maximum value at a time delayed by 0.1 times the time constant τ from the operation of the transistors 8, 9, 10, and 11. %, The rate of change will be moderate to some extent. When the operation of the transistors 8, 9, 10, and 11 is delayed by twice the time constant τ, the potential difference dV of the detection resistor 12 decreases to about 14% of the maximum value, and the measured value further decreases. The ratio to the normal time cannot be obtained accurately. Therefore, in order to determine the change in the capacitance of the piezoelectric element 5, the potential difference dV ₁ across the detection resistor 12 is set to 0.1 times or more and 2 times the time constant τ from the operation of the transistors 8, 9, 10, and 11. It is preferable to measure at a point delayed by the following.

When the piezoelectric element 5 is short-circuited, not only the potential difference dV ₁ but also the potential difference dV ₂ is increased. That is, in order to determine whether the piezoelectric element 5 is short-circuited, it is effective to measure the potential difference dV ₂ when it is sufficiently delayed from the operation of the transistors 8, 9, 10, and 11. When the operation is delayed by the time constant τ from the operation of the transistors 8, 9, 10, and 11, the potential difference dV of the detection resistor 12 decreases to about 37% of the maximum value, and the difference from the potential difference at the time of short-circuit can be easily detected. . That is, for determining whether the piezoelectric element 5 is short-circuited, it is preferable to measure the potential difference dV ₂ of the detection resistor 12 after a time constant τ or more from the operation of the transistors 8, 9, 10, and 11.

Further, when the piezoelectric element 5 or the drive circuit 4 is disconnected, the potential differences dV ₁ and dV ₂ are both zero. That is, the disconnection can be monitored by the potential difference dV ₁ measured slightly after the operation of the transistors 8, 9, 10, and 11.

  When a short circuit of the piezoelectric element 5 or a disconnection of the piezoelectric element 5 or the drive circuit 4 is detected, the control device 3 should not output the control signals S1, S2, S3, S4 in order to protect the power supply 2 and the like. . Further, a signal may be output to the outside in order to notify such an abnormality.

  In the present embodiment, the detection resistor 12 is provided in the electric circuit between the transistors 8 and 9 and the electrode 5a. However, the electric circuit between the transistors 10 and 11 and the electrode 5b (point A in the figure), the power source 2 And the detection resistor 12 may be arranged in the electric circuit between the transistors 8 and 10 (point B in the figure) or the electric circuit between the transistors 9 and 11 and the ground point (point C in the figure). .

  In the present embodiment, the potential difference dV of the detection resistor 12 is measured by the differentiator 13, but may be calculated by calculation inside the control device 3. If the integral value of the potential difference dV of the detection resistor 12 is measured, the sum of the current values, that is, the total amount of charges charged in the piezoelectric element 5 can be calculated, and the capacitance of the piezoelectric element 5 can be further increased. Accurate judgment can be made.

  Further, FIG. 3 shows a configuration of the driving apparatus 1 according to the second embodiment of the present invention. In the description of the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The drive circuit 4 of the present embodiment includes one transistor 8 that is a charge switching element and one transistor 9 that is a discharge switching element, and the electrode 5a of the piezoelectric element 5 is connected to the power supply 2 or the ground point, and the electrode A half bridge circuit 5b is always grounded.

  In this embodiment, the bipolar transistor 13 and the plurality of resistors 14, 15, 16, 17, and 18 are provided so that the transistor 8 can be switched with a small input current. However, the transistor 8 is turned on by the control signal S1, and the control is performed. The transistor 9 is still turned on by the signal S2.

  Also in this embodiment, a voltage drop due to the charging / discharging current of the piezoelectric element 5 occurs in the detection resistor 12, and by measuring this voltage drop, the state of the driving device 1 such as a capacitance change of the piezoelectric element 5 can be determined. The performance change of the drive device 1 can be compensated by changing the pattern of the control signals S1 and S2 according to the determination result.

  Also in this embodiment, the detection resistor 12 may be provided on the electric circuit (point D) between the transistors 8 and 9 and the electrode 5a, or on the electric circuit (point E) between the electrode 5b and the ground point.

  In this embodiment, if the piezoelectric element 5 is fixed to the housing of the lens unit and the lens is held on the friction engagement member 7, an element-fixing type lens moving mechanism is obtained. If the piezoelectric element 5 is fixed to the moving stage and the friction engagement member 7 is fixed to the housing, the vibration member 6 and the piezoelectric element 5 move relative to the friction engagement member 7 (the friction engagement member 7 is relatively Thus, a self-propelled stage moving mechanism that drives the moving stage by sliding relative to the vibration member 6 is obtained.

The circuit diagram of the drive device of a 1st embodiment of the present invention. The time chart which shows the relationship between a control signal and charging / discharging electric current in the drive device of FIG. The circuit diagram of the drive device of 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Drive apparatus 2 Power supply 3 Control apparatus (state determination means)
4 Drive Circuit 5 Piezoelectric Element 5a, 5b Electrode 6 Vibration Member 7 Friction Engagement Member 8 Transistor (Charge Switching Element)
9 Transistor (Discharge switching element)
10 Transistor (Charge switching element)
11 Transistor (Discharge switching element)
12 Detection resistor 13 Differentiator (potential difference detection means)

Claims (2)

A piezoelectric element that expands and contracts when a voltage is applied, a vibration member that is fixed at one end to the piezoelectric element, and that can reciprocally move in the axial direction by the expansion and contraction of the piezoelectric element, and frictionally engage with the vibration member, and the vibration A friction engagement member that slides and displaces with respect to the vibration member by a reciprocal displacement of the member; a charge switching element that connects an electrode of the piezoelectric element to a power source at a predetermined drive cycle; and a discharge switching element that grounds the electrode A state detection method for a drive device having a drive circuit comprising:
A detection resistor is disposed in an electric circuit between the power source and the piezoelectric element, or an electric circuit between the piezoelectric element and a ground point,
Measure the potential difference between both ends of the detection resistor at a predetermined timing during the driving cycle,
Determine the state of the piezoelectric element based on the detected potential difference ,
The predetermined timing is a timing delayed from the operation of the charge switching element and the discharge switching element by a time constant of a circuit from the power source to the ground point via the piezoelectric element,
When the detected potential difference is larger than the predetermined range, it is determined that the piezoelectric element is short-circuited . A piezoelectric element that expands and contracts when a voltage is applied, a vibration member that is fixed at one end to the piezoelectric element, and that can reciprocally move in the axial direction by the expansion and contraction of the piezoelectric element, and frictionally engage with the vibration member, and the vibration A friction engagement member that slides and displaces with respect to the vibration member by a reciprocal displacement of the member; a charge switching element that connects an electrode of the piezoelectric element to a power source at a predetermined drive cycle; and a discharge switching element that grounds the electrode A drive circuit control method comprising: a drive circuit comprising:
A detection resistor is disposed in an electric circuit between the power source and the piezoelectric element, or an electric circuit between the piezoelectric element and a ground point,
Measure the potential difference between both ends of the detection resistor at a predetermined timing during the driving cycle,
Determine the state of the piezoelectric element based on the detected potential difference,
The predetermined timing is a timing slightly delayed from the operation of the charge switching element and the discharge switching element,
When the detected potential difference increases, it is determined that the capacitance of the piezoelectric element has increased,
The drive device control method, wherein when the increase in the capacitance of the piezoelectric element is detected, the drive cycle is lengthened.

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