JP3495810B2 - Vibration wave motor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generates a progressive vibration wave on the surface of a vibrating body by applying a frequency voltage to an electro-mechanical energy conversion element such as an electrostrictive element or a piezoelectric element, and moves by the vibration wave. The present invention relates to a vibration wave motor device that drives a body.

[0002]

2. Description of the Related Art As a method of rotating a vibration wave motor at a desired speed, the actual rotation speed of the vibration wave motor is detected, and the frequency of a frequency voltage applied to the vibration wave motor is controlled based on the detection result. Well-known are speed control, phase control for detecting the vibration state of the vibration wave motor, and controlling the frequency of the frequency voltage applied to the vibration wave motor based on the detection result.

The speed control detects the rotation speed of the motor at a certain cycle, compares the obtained rotation speed with a desired rotation speed, and controls the frequency of the frequency voltage applied to the vibration wave motor based on the comparison result. To do. FIG. 8 shows the relationship between the frequency and the speed of the vibration wave motor, and has a characteristic that the rotation speed increases as the frequency decreases in the high frequency region. When the motor starts, the frequency is gradually decreased from the high frequency, and after the start, the motor rotation speed becomes the desired rotation speed.When the actual rotation speed is faster than the desired rotation speed, the frequency is set to the specified value. If the actual rotation speed is slower than the desired rotation speed, the frequency is lowered by a predetermined value.
By changing the cycle for detecting the rotation speed of the motor, control can be speeded up or slowed down according to the response speed of the motor. Regarding the width of increasing and decreasing the frequency, there are a uniform method and a method of changing the width according to the ratio of the actual rotation speed to the desired rotation speed.

As is apparent from FIG. 8, if the frequency is lowered too much, the rotation speed of the motor drops sharply. Therefore, in the speed control described above, if the desired rotation speed is set to a value higher than the maximum speed at which the motor can rotate, the desired rotation speed cannot be reached no matter how much the frequency is lowered after the motor is started, and finally The inconvenience arises in that the rotation speed of the motor drops sharply. for that reason,
As will be described below, it is common to perform phase control for controlling the frequency so that the rotation speed of the motor does not suddenly decrease.

The phase control detects the phase difference between the frequency voltage applied to the piezoelectric body arranged on the stator of the vibration wave motor and the frequency voltage obtained from the sensor piezoelectric body, and also obtains information on the obtained phase difference. It is a method to control the frequency. Figure 9
Shows the relationship between the frequency of the vibration wave motor and the speed and phase.
When the motor starts rotating and the speed gradually increases, the phase gradually approaches the resonance state. Then, when the phases are in a resonance state, the rotation speed of the motor reaches near the maximum speed. When the frequency is further reduced from the resonance state, the rotation speed rapidly decreases and the phase also deviates from the resonance state. Therefore, in order to prevent the phase from advancing from the resonance state to the direction of lower frequency, when the phase is detected and approaching the resonance state, control is performed to return the frequency to the higher side.

The speed control and the phase control described above are generally realized by using a microcomputer. In order to enable the phase detection in the phase control by the microcomputer, the speed control and the phase control are arranged on the stator of the vibration wave motor. The frequency voltage (hereinafter referred to as φA) applied to the piezoelectric body as the electrical-mechanical energy conversion element and the frequency voltage (hereinafter referred to as φS) obtained from the sensor piezoelectric body as the sensor mechanical-electrical energy conversion element are described below. It is necessary to shape the waveform into a voltage that can be input to the microcomputer.
FIG. 10 shows a conventional waveform shaping circuit, FIG. 11 shows a waveform of an input signal of the waveform shaping circuit of FIG. 10, and FIG. 12 shows a waveform of an output signal of the waveform shaping circuit of FIG. φA and φS are almost sine waves, φA is divided by the voltage dividing resistors 101 and 102, the DC component is cut by the capacitor 103, and biased by the bias resistors 104 and 105.
8 non-inverting input terminal. Here, the resistors 104 and 105 have the same resistance value, and the voltage waveform input to the non-inverting input terminal of the comparator 108 is a sine wave centered at 1/2 of the power supply voltage. A voltage obtained by dividing the power supply voltage by the resistors 106 and 107 is input to the inverting input terminal of the comparator 108. Here, the resistors 106 and 107 have the same resistance value, and a voltage half the power supply voltage is input to the inverting input terminal of the comparator 108. The comparator 108 compares the magnitude of the voltage input to its own non-inverting input terminal with the magnitude of the voltage input to the inverting input terminal, and outputs the power supply voltage when the voltage input to the non-inverting input terminal is higher, and outputs it to the inverting input terminal. When the input voltage is higher, 0V is output. Through the above circuit operation, the sine wave of φA is converted into a square wave. Further, φS is divided by the voltage dividing capacitor 109, the DC component is cut by the capacitor 110, biased by the bias resistors 111 and 112, and input to the non-inverting input terminal of the comparator 115. Resistor 111
And 112 have the same resistance value, and the voltage waveform input to the non-inverting input terminal of the comparator 115 is 1/100 of the power supply voltage.
It becomes a sine wave centered on 2. A voltage obtained by dividing the power supply voltage by the resistors 113 and 114 is input to the inverting input terminal of the comparator 115. Here, the resistors 113 and 114
Have the same resistance value, and a voltage half the power supply voltage is input to the inverting input terminal of the comparator 115. The comparator 115 compares the magnitude of the voltage input to its own non-inverting input terminal with the magnitude of the voltage input to the inverting input terminal, and outputs the power supply voltage if the voltage input to the non-inverting input terminal is greater and outputs it to the inverting input terminal. When the input voltage is higher, 0V is output. Through the above circuit operation, the φS sine wave is converted into a square wave. Square wave D obtained in this way
A and DS are input to a microcomputer (not shown) to detect the phase difference.

By the way, the conventional drive voltage of the vibration wave motor is applied by boosting the battery voltage by a DC / DC converter or the like to make it a constant voltage, and further boosting the voltage by a matching coil.

However, in recent years, the drive voltage of the vibration wave motor has been lowered, and the vibration wave motor which can be driven by the battery voltage has come to a stage where it can be put to practical use. As a means for lowering the voltage when driving such a vibration wave motor, instead of the ground terminal of the conventional vibration wave motor, the phase of the frequency voltage applied to the piezoelectric body arranged on the stator of the vibration wave motor is inverted. There is a driving method (floating driving) in which the voltage applied to the vibration wave motor is doubled by applying this voltage. FIG. 13 shows a block diagram of a drive circuit of a vibration wave motor driven by floating. In FIG. 13, reference numeral 116 is a frequency control circuit that controls the frequency of the frequency voltage applied to the vibration wave motor 126, and 117 is a frequency division circuit that divides the frequency signal of the frequency control circuit 116 to generate two signals having different phases. Phase shifters 118 and 119 are inverters for inverting the signals output from the frequency divider / phase shifter 117, 120, 121, 122, 123 are amplification circuits for amplifying frequency signals by the battery 127, 124, 125 are matching coils, and 126 is Vibration wave motor, 126a is rotor, 126b is stator, 126c is stator 12
6b is a piezoelectric body pressed against one surface of 6b. In this circuit, sine waves having different phases are applied to .phi.A and .phi.B, and square waves having inverted phases of .phi.A and .phi.B are applied to .phi.A 'and .phi.B'. As a result, since φA ′ and φB ′ are applied instead of the conventional ground terminal, the frequency voltage applied to the vibration wave motor 126 is double that of the conventional one.

[0009]

However, in the above-mentioned conventional example, since φA and φB swing with reference to φA ′ and φB ′, the square wave components of φA ′ and φB ′ are superposed on φA and φB. It doesn't become a clean sine wave as shown in. Similarly, the square wave component of φA ′ is also superimposed on the signal φS of the sensor electrode. When waveform shaping is performed by the waveform shaping circuit of FIG. 10 using such a signal, the comparator 108 erroneously compares the square wave component in the overlapping portion, and as shown in FIG. The descent appears multiple times. Therefore, if an attempt is made to detect a phase difference using DA and DS shown in FIG. 15, an erroneous phase difference is detected, which causes a problem that accurate phase control cannot be performed.

[0010]

It is a first object of the present invention to provide a vibration wave motor device capable of accurately detecting the driving frequency voltage or the state of the sensor electrode output even when the vibration wave motor is driven in a floating manner. .

A second object of the present invention is to provide an oscillating wave motor device which can accurately detect the phase even in the floating drive.

A third object of the present invention is to make it possible to configure the phase detection circuit by a circuit that operates with a low voltage power supply such as a microcomputer so that the frequency voltage used for phase detection is within a predetermined voltage range. A phase detection circuit for a vibration wave motor to which a damping circuit is added.

[0013]

In order to achieve the first object, the invention according to claim 1 is characterized in that the first and second frequency voltages applied to the screen of the driving energy conversion element are It is possible to obtain a signal that accurately represents the phase of the frequency voltage in which the influence of the floating drive is removed, as compared with the comparison means.

In order to achieve the second object, claim 2
In addition to the structure of claim 1, the described invention compares the voltages on both sides of the detection energy conversion element by the second comparison means, and based on the comparison result of the first and second comparison means, The phase comparison between the frequency voltage and the detected frequency voltage can be performed accurately.

The invention described in claim 3 provides an apparatus having the same structure as the object of claim 2 and showing a specific configuration thereof.

The invention described in claim 4 provides an apparatus which achieves the same object as the invention described in claim 2.

The invention described in claim 5 provides an apparatus having the same purpose as the invention described in claim 3.

The invention described in claim 6 is the same as the invention described in claim 4, and provides a specific configuration of the motor.

The invention described in claim 7 is the same as in claims 1 and 2, and further provides a specific structure of floating driving.

In order to achieve the third object, the invention according to claim 8 regulates each frequency voltage to a voltage within a predetermined voltage range through the attenuating means before inputting the frequency voltage to the comparing means. Thus, the present invention can be applied to a circuit that operates with a low voltage power supply. In order to achieve the first object, the present invention according to claim 9 compares the voltages on both sides of the detecting element so that an accurate monitor signal can be obtained from the comparison result.

[0021]

1 is a circuit diagram showing an embodiment of a vibration wave motor according to the present invention. In the figure, 1 is a frequency control circuit for controlling the frequency of the frequency voltage applied to the vibration wave motor 12, and outputs a square wave signal. 2 is a frequency divider / phaser that divides the square wave output from the frequency control circuit 1 and generates two signals having different phases (for example, 90 ° different), and 3 and 4 are the phases of the frequency divider / phaser 2. The inverters 5, 6, 7, 8 for inverting are amplification circuits, which are amplified by the battery 9. 10 and 11 are matching coils, 12
Is a vibration wave motor, 12a is a rotor, 12b is a stator, 12c is a piezoelectric body pressed against one surface of the stator 12b, and φA and φB are piezoelectric bodies arranged on one surface of the stator 12b of the vibration wave motor 12. Frequency voltage to give to
φA ′ and φB ′ are frequency voltages applied to the other surface of the piezoelectric body, φS is a frequency voltage obtained from the sensor piezoelectric body on the stator 12 b of the vibration wave motor 12, and 13 and 14 are φ.
A comparator for waveform shaping A and φS, and a phase difference detection circuit 15 for detecting the phase difference between the waveform shaped φA and φS.

Next, the vibration wave motor 12 will be described with reference to FIGS.

FIG. 2 is an explanatory view showing a disposition state of the piezoelectric body 12c arranged on one surface of the stator 12b. In addition, FIG. 3 is an explanatory view showing a disposition state of the other surface of the piezoelectric body 12c. A and B in FIG. 2 are a first electrode and a second electrode arranged on one surface of the piezoelectric body 12c in the illustrated phase and polarization relationship, respectively. Further, S is an electrode for a sensor arranged at a position shifted in phase from the second electrode B by 45 °. Further, A'and B'in FIG. 3 are a third electrode and a fourth electrode arranged on the other surface of the piezoelectric body 12c in the illustrated phase and polarization relationship, respectively. These piezoelectric bodies may be attached to the vibrating body individually.
Alternatively, they may be integrally formed by polarization treatment.

Returning to FIG. 1, the operation of the circuit of this embodiment will be described. The frequency control circuit 1 selects an optimum frequency for rotating the vibration wave motor 12 at a desired speed, and outputs a square wave of that frequency. The frequency divider / phaser 2 divides the square wave output from the frequency control circuit 1 and outputs two square waves having 90 ° different phases. The square wave output from the frequency divider / phase shifter 2 is input to the amplifier circuits 5 and 7, and a signal whose phase is inverted by the inverters 3 and 4 is generated to be input to the amplifier circuits 6 and 8 in increments of 90 °. The four signals having different phases are amplified by the battery 9. Amplifier 5, 7
The signals (φA, φB) amplified by are further boosted by the matching coils 10 and 11, and are transmitted to the first of the vibration wave motor 12.
And the signals (φA ′, φB ′) amplified by the amplifiers 6 and 8 are directly applied to the third and fourth electrodes A ′ and B ′ of the vibration wave motor 12. It φ
Waveforms of A, φB, φA ′, and φB ′ are shown in FIG. As can be seen from FIG. 4, since φA and φB fluctuate with respect to φA ′ and φB ′, a square wave component of φA ′ and φB ′ is superimposed on the sine wave. Further, the frequency voltage (φS) obtained from the piezoelectric body for a sensor also has a waveform in which a square wave component (φA ′) is superimposed on a sine wave. Comparator 1
3 removes the square wave component superimposed on φA by comparing φA and φA ′, and the comparator 14 causes φS and φA ′.
The square wave component superimposed on φS is removed by comparing FIG. 5 shows the waveforms of the outputs DA and DS of the comparators 13 and 14. The waveforms DA and DS shown in FIG. 5 are input to the phase difference detection circuit 15, the vibration state of the vibration wave motor 12 is detected by detecting the phase difference between DA and DS, and the detection result is sent to the frequency control circuit 1. The frequency is controlled by feedback, and the phase is controlled so that the vibration wave motor does not suddenly stop rotating.

Although the phase difference of the frequency voltage applied to the vibration wave motor 12 is shifted by 90 ° in this embodiment, the present invention can be applied even if the phase difference is other than 90 °. .

In the present embodiment, the battery 9 is used as the power source of the driving means, but the present invention uses a method other than the battery as the power source, for example, a method in which a high voltage power source is stepped down by a DC / DC converter and used. It is applicable even if there is.

Further, in the present embodiment, the shape of the vibration wave motor is described as a ring shape, but the present invention can be applied to other shapes.

FIG. 6 is a drawing showing a second embodiment of the present invention. In FIG. 6, the same components as those in the first embodiment are designated by the same reference numerals, and only different components will be described. . In FIG. 6, reference numerals 16, 17, and 18 denote resistors and diodes for clipping the φA voltage within a predetermined voltage range, 19 is a capacitor for dividing the φS voltage, and 20 is a DC component of the voltage divided by the capacitor 19. Capacitors for cutting 21, 21 and 22 are capacitors 20, which are resistors for applying a bias voltage to the cut voltage of the DC component, 2
Reference numerals 3 and 24 denote diodes for clipping the voltage applied with the bias voltage by the resistors 21 and 22 within a predetermined voltage range, and 2
Reference numerals 5, 26 and 27 are resistors and diodes for clipping the voltage of φA 'within a predetermined voltage range. Further, the comparators 28 and 29 and the phase difference detection circuit 30 are assumed to operate with a low voltage power supply (for example, 5V).

Next, the operation of the circuit of this embodiment will be described.
φA is converted into a voltage that can be input to the comparator 28 by the resistor 16 and the diodes 17 and 18, and is input to the non-inverting input terminal of the comparator 28. φS is divided by the capacitor 19, the direct current component is cut by the capacitor 20, bias voltage is applied by the resistors 21 and 22, and converted into a voltage that can be input to the comparator 29 by the diodes 23 and 24, and the non-inversion of the comparator 29 is performed. It is input to the input terminal. Here, the resistors 21 and 22 have the same resistance value, and the voltage input to the comparator 29 fluctuates around 1/2 of the power supply voltage. φA ′ is converted into a voltage that can be input to the comparators 28 and 29 by the resistor 25 and the diodes 263 and 27, and is input to the inverting input terminals of the comparators 28 and 29. The comparator 28 has φA and φA ′.
The square wave component superimposed on φA is removed by comparing
Waveform D of sine wave frequency of φA converted to square wave
Output A. The comparator 29 removes the square wave component superimposed on φS by comparing φS and φA ′, and outputs DS in which the frequency of the sine wave component of φS is converted into a square wave. FIG. 7 shows the waveforms of the outputs DA and DS of the comparators 28 and 29. The waveforms DA and DS shown in FIG. 7 are input to the phase difference detection circuit 30, the vibration state of the vibration wave motor 12 is detected by detecting the phase difference between DA and DS, and the detection result is sent to the frequency control circuit 1. The frequency is controlled by feedback, and the phase is controlled so that the vibration wave motor does not suddenly stop rotating.

With the above configuration, the waveform used for shaping φA and φS used for phase detection falls within a predetermined voltage range, and the operating voltage of the waveform shaping circuit can be lowered. Further, the shaped waveform becomes a clean square wave as shown in FIG. 7, the phase difference detection circuit 30 can correctly detect the phase difference, and the phase control can be performed.

The present invention can be applied even if the means for attenuating the voltage used for waveform shaping within a predetermined voltage range is other than a resistor or a diode.

Further, the object to be driven in the present invention is directly driven by the traveling wave generated in the stator. Such as paper,
The stator (motor) main body may be configured to move with respect to the fixed body.

[0033]

As described above, according to the present invention of claim 1, it is possible to accurately form a signal representing the phase of the drive frequency voltage even in the case of floating driving.

According to the present invention as set forth in claims 2, 3, 4, 5, 6, and 7, it is possible to accurately perform control by detecting the phase difference even during floating driving.

Further, according to the present invention of claim 8, since the drive voltage and the detection voltage can be suppressed within a predetermined voltage, the present invention can be applied to a low voltage operating circuit of a microcomputer.

According to the present invention of claim 9, a monitor signal can be accurately obtained even in the case of floating driving.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a vibration wave motor device according to the present invention.

FIG. 2 is an explanatory diagram illustrating an arrangement state of the piezoelectric body illustrated in FIG.

FIG. 3 is an explanatory diagram illustrating a disposition state of the other surface of the piezoelectric body illustrated in FIG.

FIG. 4 is a diagram showing voltage waveforms applied to and generated in electrodes of a vibration wave motor.

FIG. 5 is a diagram showing voltage waveforms output by the comparators 13 and 14 in the first embodiment of the present invention.

FIG. 6 is a block diagram showing a second embodiment of the present invention.

FIG. 7 is a diagram showing voltage waveforms output by comparators 28 and 29 in the second embodiment of the present invention.

FIG. 8 is a diagram showing the relationship between the frequency and the rotation speed of the vibration wave motor.

FIG. 9 is a diagram showing the relationship between the frequency of the vibration wave motor, the rotation speed, and the phase.

FIG. 10 is a diagram showing a conventional waveform shaping circuit.

11 is a diagram showing voltage waveforms input to the waveform shaping circuit of FIG.

12 is a diagram showing voltage waveforms output from the waveform shaping circuit of FIG.

FIG. 13 is a block diagram showing a drive circuit of a vibration wave motor during floating drive.

FIG. 14 is a diagram showing voltage waveforms applied to and generated in a vibration wave motor during floating driving.

FIG. 15 is a diagram showing an output waveform when waveform shaping is performed using a conventional waveform shaping circuit during floating driving.

[Explanation of symbols]

1 Frequency control circuit Divide by 2, Phaser 12 Vibration wave motor 12c Piezoelectric body 13, 14, 28, 29 Comparator 15 Phase difference detection circuit 17, 18, 23, 24, 26, 27 Diode 21, 22 resistance 19, 20 condenser

Continuation of the front page (56) Reference JP-A-6-70561 (JP, A) JP-A-5-38172 (JP, A) JP-A-6-253558 (JP, A) JP-A-6-336764 (JP , A) JP 6-14565 (JP, A) JP 3-103081 (JP, A) JP 7-123744 (JP, A) JP 8-33363 (JP, A) Actual flat 2-125801 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02N 2/00 B06B 1/06

Claims (9)

(57) [Claims] 1. An elastic body, an electro-mechanical energy conversion means arranged on the elastic body, a first frequency voltage with respect to the conversion means, and a phase relationship inverted with respect to the phase of the first frequency voltage. In a vibration wave motor device that applies a voltage having a difference between the second frequency voltages to excite the elastic body to obtain a driving force, the first frequency voltage and the second frequency voltage are compared in magnitude. Is provided to remove the influence of the second frequency voltage on the first frequency voltage to obtain a square wave corresponding to the first frequency voltage. 2. An elastic body, a drive electro-mechanical energy conversion means arranged on the elastic body, and a first frequency voltage with respect to the conversion means and an inversion with respect to the phase of the first frequency voltage. In a vibration wave motor device that applies a voltage having a difference between the second frequency voltages having the above-described phase relationship to excite the elastic body to obtain a driving force, the vibration wave motor device is disposed on the elastic body and has the first or the first surface on one side. one frequency voltage of the second frequency voltage is applied
A vibration detecting electric-mechanical energy converting means, a first comparing means for comparing the magnitude of the first frequency voltage and a second frequency voltage, and the other of the vibration detecting electric-mechanical energy converting means. A second comparing means for comparing the magnitude of the detection output from the surface and the one of the frequency voltages, and detecting the deviation state from the resonance frequency based on the comparison output of the first and second comparing means. Characteristic vibration wave motor device. 3. The vibration wave motor device performs a phase comparison between a square wave as a comparison result from the first comparing means and a square wave as a comparison result from the second comparing means, and detects a resonance state. The vibration wave motor device according to claim 2, further comprising a phase comparison unit that detects a shift state of the vibration wave motor. 4. An elastic body, a first drive electro-mechanical energy conversion element arranged on the elastic body, and a first electrode for applying a first frequency voltage to one surface of the conversion element, A second electrode that applies a second frequency voltage whose phase relationship is inverted to the phase of the first frequency voltage on the other surface, and the second frequency voltage is applied to the one surface through the second electrode. An electro-mechanical energy conversion element for detection in which a monitor electrode is applied to the other surface and a frequency voltage of one of the first or second frequency voltage and the electro-mechanical energy conversion for detection from the monitor electrode In a vibration wave motor device including a phase detection unit that detects a phase relationship with an element output, a first comparison unit that compares the magnitudes of voltages at the first and second electrodes, and a voltage at the second electrode and the Electro-mechanical sensors for detection from monitor electrodes A vibration wave motor device comprising: a second comparison means for comparing the magnitudes of the energy conversion element outputs, and the result of comparison by the first and second comparison means is input to the phase detection means. 5. The phase detecting means performs a phase comparison between a square wave which is a comparison result of the first comparing means and a square wave which is a comparison result of the second comparing means, and a deviation state from a resonance state. The vibration wave motor device according to claim 4, which detects a vibration. 6. The vibration wave motor device includes a second drive electro-mechanical energy conversion element arranged on the elastic body, and a phase of the first frequency voltage applied to one surface of the conversion element. A third electrode for applying a third frequency voltage that is phase-shifted by a predetermined phase, and a fourth electrode for applying a fourth frequency voltage whose phase relationship is inverted to the phase of the third frequency voltage on the other surface. The vibration wave motor device according to claim 4 or 5. 7. The oscillatory wave according to claim 1, wherein the first frequency voltage is a substantially sinusoidal voltage, and the second frequency voltage is a square wave voltage. Motor device. 8. The first attenuating means for attenuating the first frequency voltage within a predetermined voltage range and then inputting it to the first comparing means, and the other one of the detecting electro-mechanical energy converting means. A second attenuating means for attenuating the detection output from the surface within a predetermined voltage range and then inputting it to the second comparing means; and after attenuating the second frequency voltage within the predetermined voltage range The vibration wave motor device according to any one of claims 2, 3, 4, 5, 6, and 7, further comprising third damping means for inputting to the first and second comparing means. 9. An elastic body, a drive electro-mechanical energy conversion element arranged on the elastic body, a first electrode for applying a first frequency voltage to one surface of the conversion element, and a second surface on the other surface. A second electrode that applies a second frequency voltage whose phase relationship is inverted with respect to the phase of the first frequency voltage, and the second frequency voltage is applied to one surface through the second electrode and the other. In terms of
In a vibration wave motor device provided with a detection electro-mechanical energy conversion element provided with a monitor electrode, the magnitude of the voltage of the second electrode and the detection electro-mechanical energy conversion element output from the monitor electrode is compared. A vibration wave motor device comprising a comparison means for outputting the comparison result as a monitor signal.