JP2017169273A - Method of controlling ultrasonic motor and surveying instrument for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of controlling an ultrasonic motor for reducing abrasion of a rotor and a surveying instrument equipped with the ultrasonic motor.SOLUTION: The method of controlling an ultrasonic motor is a control method of ultrasonic motors (5, 12) in which, by a piezoelectric element (42) caused to vibrate by driving signals (S1, S2) of AC voltages of two different phases, a traveling wave is generated in a stator metal (43) to cause the stator metal (43) and a rotor (46) to relatively rotate. An initial phase φ of drive signals (S, S) is changed each time the drive is started.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for controlling an ultrasonic motor provided on a rotating shaft of a surveying instrument and a surveying instrument therefor.

  A surveying instrument, for example, a total station, includes a telescope that collimates a measurement point, a rack that supports the telescope so as to be rotatable in a vertical direction, and a base that supports the rack so as to be rotatable in a horizontal direction. ing. The telescope is driven by a vertical rotation motor, and the rack is driven by a horizontal rotation motor. Patent Document 1 discloses a surveying instrument that employs an ultrasonic motor for the vertical rotation motor and the horizontal rotation motor.

FIG. 5 is a simplified configuration diagram of the ultrasonic motor. As shown in FIG. 5, the ultrasonic motor 5 includes a piezoelectric ceramic (piezoelectric element) 42 that generates vibration, a stator metal 43 that amplifies vibration, a rotor 46 that interferes with the stator metal 43, and a rotor 46. A wave washer (elastic body) 48 that presses the stator toward the stator metal 43 side is provided in a ring shape. A plurality of piezoelectric ceramics 42 are attached by changing the polarization direction alternately along the circumferential direction. The piezoelectric ceramic 42 (A phase) attached in the + polarization direction is compressed and expanded when a + voltage and a −voltage are applied. The piezoelectric ceramic 42 (phase B) applied in the polarization direction is compressed and expanded when a negative voltage and a positive voltage are applied. The A-phase and B-phase piezoelectric ceramics 42 are respectively supplied with an A-phase drive signal S ₁ and a B-phase drive signal S ₂ that are 90 degrees out of phase with the required drive frequency and amplitude, so that the stator metal 43 has a wave shape. , And the stator metal 43 and the rotor 46 are rotated relative to each other by friction caused by the pressure of the wave washer 48. The A-phase drive signal S ₁ and the B-phase drive signal S ₂ can be expressed by equations (1) and (2), respectively.
S ₁ (t) = α sin (2πft) (1)
S ₂ (t) = α cos (2πft) (2)
Where α is the amplitude of the drive signal, f is the drive frequency, and t is the time.

JP 2014-137299 A

Employing an ultrasonic motor for the rotating shaft of a surveying instrument has the advantages of higher turning performance, better quietness, and higher shaft holding power when no current is applied compared to an electric motor. On the other hand, some surveying instruments have an automatic collimation function. FIG. 6 is a measurement image diagram in automatic collimation. Reference numeral 1 denotes a surveying instrument. As shown in FIG. 6, in automatic collimation, measurement may be performed by repeatedly directing the surveying instrument 1 to a certain point T1 and a certain point T2. When such a measurement is performed, the ultrasonic motor 5 determines the waveform of the stator metal 43 based on the A-phase drive signal S ₁ and the B-phase drive signal S _2. ) Is the same each time, and there is a problem that the portion of the rotor 46 that faces the raised position is shaved and worn.

  In order to solve the above problems, an object of the present invention is to provide an ultrasonic motor control method for reducing the wear of a rotor and a surveying instrument therefor.

  In order to solve the above-described problem, a method for controlling an ultrasonic motor according to an aspect of the present invention is the method of generating a traveling wave in a stator metal by a piezoelectric element that vibrates by driving signals of two types of alternating voltages having different phases. And an ultrasonic motor for rotating the rotor relative to each other, wherein the initial phase φ of the drive signal is changed every time the drive is started.

  In the above aspect, it is also preferable that the initial phase φ is set at random every time driving is started.

In the above aspect, the initial phase φ is φ = 2π {(θ _R / λ) − (i / N)}, where θ _{R is} the rotational position of the rotor, λ is the wavelength of the traveling wave, and N is an integer greater than or equal to 2. , I = 0, 1, 2,..., N−1, and it is also preferable to increase i by 1 each time driving is started.

  In order to solve the above-described problems, a surveying instrument according to an aspect of the present invention includes a piezoelectric element that vibrates in accordance with drive signals of two types of alternating voltages having different phases, and a stator metal that generates a traveling wave in response to the vibration, in order from the base portion. A rotor that interferes with the stator metal, an ultrasonic motor that includes an elastic body that presses the rotor against the stator metal, and a controller that changes the initial phase φ of the drive signal applied to the piezoelectric element each time driving is started. It is characterized by having.

  ADVANTAGE OF THE INVENTION According to this invention, the control method of the ultrasonic motor which can reduce wear of a rotor, and the surveying instrument for it can be provided.

It is a schematic longitudinal cross-sectional view of the surveying instrument which concerns on this form. It is a cross-sectional perspective view of the part containing the ultrasonic motor of FIG. It is a block diagram of the surveying instrument concerning this form. It is an image figure which shows rotation of an ultrasonic motor. It is a simplified block diagram of an ultrasonic motor. It is a certain measurement image figure in automatic collimation.

  Next, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic longitudinal sectional view of a surveying instrument of the surveying instrument according to the present embodiment, and FIG. 2 is a sectional perspective view of a portion including the ultrasonic motor of FIG. The surveying instrument 1 includes a base part 4 provided on the leveling part 3, a rack part 7 that horizontally rotates on the base part 4 around the horizontal rotation axis 6, and a vertical rotation axis 11 around the rack part 7. And a telescope 9 that rotates vertically. The surveying instrument 1 has an automatic collimation function and an automatic tracking function, and the telescope 9 houses a distance measuring optical system and a tracking optical system (not shown). The configuration of the distance measuring optical system and the tracking optical system may be the same as the configuration of the prior art, and the description is omitted. In the surveying instrument 1, the distance measuring light and the tracking light are irradiated to the target by the cooperation of the horizontal rotation of the rack 7 and the vertical rotation of the telescope 9.

  An ultrasonic motor 5 for horizontal rotation is provided at the lower end portion of the horizontal rotation shaft 6, and a rotary encoder 21 for horizontal angle detection is provided at the upper end portion. An ultrasonic motor 12 for vertical rotation is provided at one end of the vertical rotation shaft 11, and a rotary encoder 22 for detecting a vertical angle is provided at the other end. The rotary encoders 21 and 22 are absolute encoders having a rotating disk, a slit, a light emitting diode, and an image sensor. In addition, an incremental encoder may be used.

  About the structure of the ultrasonic motors 5 and 12 in the surveying instrument 1, since the structure of a perpendicular direction and a horizontal direction is equivalent, it demonstrates using a structure of a horizontal direction. The ultrasonic motor 5 includes the base portion 39, the piezoelectric ceramic 42, the stator metal 43, the rotor 46, and the wave washer 48 described above. In this embodiment, the motor case 25 is fixed to the base portion 4, and the rotor 46 is a motor. Since it is fixed to the case 25, the stator metal 43 rotates, and the horizontal rotating shaft 6 rotates integrally with the stator metal 43 via the base portion 39.

  FIG. 3 is a block diagram of the surveying instrument according to the present embodiment. Since the vertical block diagram and the horizontal block diagram are the same, only the ultrasonic motor 5 for horizontal rotation and the rotary encoder 21 for horizontal angle detection are shown. The ultrasonic motor 12 for vertical rotation and the rotary encoder for vertical angle detection are shown. The description of 22 is omitted. The surveying instrument 1 includes a control unit 23, a rotary encoder 21, a distance measurement unit 61, a tracking unit 62, a clock signal oscillation unit 63, a drive circuit 73, and the ultrasonic motor 5.

  The control unit 23 is configured by a microcontroller in which a CPU, a ROM, a RAM, and the like are mounted on an integrated circuit. The control unit 23 can change software from an external personal computer (not shown).

  The distance measuring unit 61 is controlled by the control unit 23 to irradiate distance measuring light onto the target using the distance measuring optical system, and receive the reflected light to perform distance measurement. The tracking unit 62 is controlled by the control unit 23 to irradiate the target with tracking light using the tracking optical system and receive the reflected light, and performs tracking when the target moves.

The drive circuit 73 includes an FPGA (Field Programmable Gate Array) 731 and an analog circuit 732. The FPGA 731 can change the definition of the internal logic circuit by the control unit 23 or an external device (not shown). The FPGA 731 can generate a control signal with a variable driving frequency (frequency of the driving signal) and a variable amplitude, and can dynamically change the driving frequency and the amplitude. The analog circuit 732 is composed of a transformer or the like, and amplifies the control signal. The drive circuit 73 is controlled by the control unit 23 to output the control signal from the FPGA 731, amplifies the analog circuit 732, and outputs the A-phase drive signal S ₁ to the A-phase piezoelectric ceramic 42. and it outputs the B-phase driving signal _{S 2} to the piezoelectric ceramic 42. The drive circuit 73 may be another programmable logic device (PLD) such as an ASIC (Application Specific Integrated Circuit).

  The clock signal oscillating unit 63 outputs a clock signal to the control unit 23 and the drive circuit 73. The FPGA 731 controls the amplitude of the drive signal, the drive frequency, and the control cycle TM based on the clock signal. The control unit 23 controls the light emission cycle TR and the like of the rotary encoder 21 based on the clock signal.

In the present embodiment, the control unit 23, the A-phase driving signals S ₁ and B-phase driving signal S ₂ to be generated by the drive circuit 73 is set as follows.

(First embodiment)
Control unit 23, the A-phase driving signals _{S 1} and the B-phase driving signals _{S 2,} respectively formula (3) is set by equation (4).
S ₁ (t) = α sin (2πft + φ) (3)
S ₂ (t) = α cos (2πft + φ) (4)
Where α is the amplitude of the drive signal, f is the drive frequency, t is the time, and φ is the initial phase.

The control unit 23 randomly sets the initial phase φ in the equations (3) and (4) from numerical values ranging from 0 to 2π every time the ultrasonic motor 5 starts to be driven. Thus, the A-phase driving signals S ₁ and B-phase driving signal S ₂ is a phase that is different each time the drive start is set, the waveform of the stator metal 43 (raised position) is in each case different. Therefore, it is possible to prevent only a part of the rotor 46 from being scraped and worn.

(Second Embodiment)
Control unit 23, the A-phase driving signals _{S 1} and the B-phase driving signals _{S 2,} respectively formula (3) is set by equation (4). At this time, the traveling wave on the stator metal 43 can be expressed by Expression (5), and the traveling wave on the rotor 46 can be expressed by Expression (6).
W _S (t, θ) = A sin {2π (ft + θ / λ) + φ} (5)
W _R (t, θ) = A sin [2π {ft + (θ + θ _R ) / λ) + φ} (6)
Where A is the amplitude of the traveling wave, λ is the wavelength of the traveling wave, θ is the rotational position, and θ _R is the rotational position of the rotor.
The amplitude A and wavelength λ of the traveling wave are also shown in FIG. As shown in FIG. 4, the rotational position θ is an angle that represents the position of the traveling wave with respect to point A. Rotational position theta _R of the rotor 46, represents the rotation angle of the rotor 46 relative to the point A.

Considering this, it is considered to give a signal for gradually shifting the initial phase φ at an arbitrary rotational position on the rotor 46 at the start of driving (t = 0). For example, if an arbitrary rotational position is θ = 0, the traveling wave on the rotor 46 can be expressed by Expression (7).
W _R (0,0) = A sin {2π (θ _R / λ) + φ} (7)
Here, a function φ ′ for shifting the initial phase φ little by little can be expressed by Expression (8).

φ ′ = 2π (θ _R / λ) + φ = 2π (i / N) (8)
However, N is an integer equal to or greater than 2, i = 0, 1, 2,..., N−1. From Equation (8), the initial phase φ can be expressed as Equation (9).
φ = 2π {(θ _R / λ) − (i / N)} (9)
The rotational position θ _{R of the} rotor is obtained from the rotational angle of the rotary encoders 21 and 22. Since the wavelength λ of the traveling wave is the same as the circumferential length of the pair of positive and negative piezoelectric ceramics 42 in the ultrasonic motors 5 and 12, it is obtained from the design value of the motor.

The control unit 23 gives the initial phase φ of the A-phase drive signal S ₁ and the B-phase drive signal S ₂ of the ultrasonic motor 5 by the equation (9), and i is incremented by 1 from 0 to N−1 every time driving is started. increase. Thereby, the waveform (position which protrudes) of the stator metal 43 can be shifted equally every time. That is, since the position where the rotor 46 can be shaved is shifted evenly in the circumferential direction, the wear of the rotor 46 can be further delayed.

  The preferred embodiment has been described above. For example, if a deviation in the amount of wear of the rotor 46 can be detected, φ is set where there is little wear. If a deviation in the rotational torque can be detected, φ is set where the torque is large. It is also possible. In addition, modifications based on the knowledge of those skilled in the art are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Surveying instrument 5,12 Ultrasonic motor 23 Control part 39 Base part 42 Piezoelectric ceramic (piezoelectric element)
43 Stator metal 46 Rotor 48 Wave washer (elastic body)

Claims (4)

A method for controlling an ultrasonic motor in which a traveling wave is generated in a stator metal by a piezoelectric element that vibrates by driving signals of two types of alternating voltages having different phases, and the stator metal and the rotor are rotated relative to each other.
The method of controlling an ultrasonic motor, wherein the initial phase φ of the drive signal is changed every time driving is started.
The method for controlling an ultrasonic motor according to claim 1, wherein the initial phase φ is randomly set every time driving is started.
The initial phase φ is
φ = 2π {(θ _R / λ) − (i / N)}
Where θ _{R is} the rotational position of the rotor, λ is the wavelength of the traveling wave, N is an integer of 2 or more, and i = 0, 1, 2,..., N−1.
2. The method of controlling an ultrasonic motor according to claim 1, wherein i is incremented by 1 each time driving is started.
In order from the base part, a piezoelectric element that vibrates in response to drive signals of two types of alternating voltages having different phases, a stator metal that generates a traveling wave due to the vibration, a rotor that interferes with the stator metal, and presses the rotor against the stator metal An ultrasonic motor with an elastic body;
A surveying instrument comprising: a control unit that changes an initial phase φ of a driving signal applied to the piezoelectric element each time driving is started.

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