JP6144021B2 - Excavator and control method of excavator - Google Patents

Description

The present invention relates to a hydraulic excavator including a PWM oscillator that generates a PWM signal having a predetermined PWM (Pulse-Width Modulation) frequency, and a method for controlling the hydraulic excavator .

  2. Description of the Related Art Conventionally, a technique for forming a dither current superimposed on a basic current by alternately outputting two PWM signals having different duty ratios every predetermined time is known (see, for example, Patent Document 1).

JP-A-8-303628

  However, the dither current in the technique described in Patent Document 1 can be a factor of disturbance when changing the basic current. Specifically, when a dither current that acts to decrease the basic current is superimposed at a timing at which the basic current is increased to a desired level, the basic current may be delayed from reaching the desired level. . The probability that such a situation will occur becomes more prominent as the difference between the PWM frequency and the dither frequency lower than the PWM frequency is larger. As a result, the technique described in Patent Document 1 that employs a PWM frequency that is higher than the dither frequency may deteriorate the responsiveness of PWM control.

In view of the above-described points, an object of the present invention is to provide a hydraulic excavator including a PWM oscillator that improves the responsiveness of PWM control using a command signal including a dither signal, and a method for controlling the hydraulic excavator .

In order to achieve the above object, a method for controlling a hydraulic excavator including a PWM oscillator according to an embodiment of the present invention generates a PWM signal having a predetermined PWM frequency and a duty ratio corresponding to a command signal. the hydraulic excavator control method and a reference command signal acquisition step of acquiring a reference command signal, superimposing a dither generating the superimposed dither signal having a dither frequency to be set above the PWM frequency independently A signal generation step, and a command signal generation step of generating the command signal by superimposing the superposition dither signal on the reference command signal, and the strength of the superposition dither signal is a change in the reference command signal. are reduced in accordance with the level of the command signal between instantaneous said reference command signal has changed, Ri same der the level of the reference command signal, the reference The intensity of the superposition dither signal is restored in a continuous time after the change of the command signal, the current flowing through the solenoid valve is detected, the deviation between the detected current and the level of the command signal is calculated, and the calculated The solenoid valve is controlled based on the deviation.

Further, a hydraulic excavator including a PWM oscillator according to an embodiment of the present invention is a hydraulic excavator including a control device that generates a PWM signal having a predetermined PWM frequency and a duty ratio corresponding to a command signal. A superposition dither signal generation unit that generates a superposition dither signal having a dither frequency that is set independently of the PWM frequency, a reference command signal, and superimposing the superposition dither signal on the reference command signal A command signal generation unit that generates the command signal, and the superposition dither signal generation unit reduces the intensity of the superposition dither signal to be generated according to a change in the reference command signal, and the reference command level of the command signal between instantaneous signal changes, Ri same der the level of the reference command signal, continuing the superimposed dither signal in the time after the change of the reference command signal The intensity of the signal is restored, the current flowing through the solenoid valve is detected, the deviation between the detected current and the level of the command signal is calculated, and the solenoid valve is controlled based on the calculated deviation.

With the above-described means, the present invention can provide a hydraulic excavator provided with a PWM oscillator that improves the responsiveness of PWM control using a command signal including a dither signal, and a method for controlling the hydraulic excavator .

It is a block diagram which shows the structural example of the digital current amplifier which performs the control method of the PWM oscillator based on the Example of this invention. It is a figure which shows the time transition of various signals. It is a figure which shows the time transition of a command signal and an analog detection signal. It is a flowchart which shows the flow of a PWM signal generation process. It is a flowchart which shows the flow of the dither signal generation process for superimposition.

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

  FIG. 1 is a block diagram illustrating a configuration example of a digital current amplifier 1 that executes a control method of a PWM oscillator according to an embodiment of the present invention.

  The digital current amplifier 1 is a control device that controls the PWM oscillator 15, receives a reference command signal as an input, and outputs a PWM signal from the PWM oscillator 15. In this embodiment, the digital current amplifier 1 is a microcomputer including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like.

  The digital current amplifier 1 mainly includes a dither oscillator 10, an adder 11, a subtractor 12, an A / D converter 13, a PID controller 14, and a PWM oscillator 15. The PWM oscillator 15 may be installed outside the digital current amplifier 1 independently of the digital current amplifier 1.

  The “reference command signal” is a signal that the digital current amplifier 1 receives from the outside as an input. For example, the reference command signal includes a signal generated by a signal generation device (not shown) in response to an operator input, or a signal automatically generated by the signal generation device at a predetermined timing.

  The dither oscillator 10 is a functional element that adjusts the dither signal to generate a superposition dither signal. Specifically, the dither oscillator 10 functions as a superposition dither signal generator, and generates a superposition dither signal by multiplying a dither signal having a predetermined dither frequency and a predetermined amplitude by a dither setting signal.

  The “dither setting signal” is a signal that changes a value in accordance with a change in the reference command signal, and takes a value not less than zero and not more than 1, for example.

  In the present embodiment, the dither oscillator 10 continuously monitors the value of the reference command signal, sets the value of the dither setting signal to zero when the reference command signal increases or decreases at a predetermined change rate or more, and then sets the dither setting. The signal value is gradually returned to 1. The dither oscillating unit 10 maintains the value of the dither setting signal at 1 unless the reference command signal is increased or decreased at a predetermined change rate or higher.

  Then, the dither oscillator 10 multiplies the dither setting signal generated as described above and the dither signal to generate a superposition dither signal, and outputs the generated superposition dither signal to the adder 11.

  The adder 11 is a functional element that adds two input signals and outputs one signal. In the present embodiment, the adder 11 functions as a command signal generator, receives a reference command signal from the outside, and receives a dither signal for superimposition from the dither oscillator 10. The adding unit 11 adds the reference command signal and the superposition dither signal to generate a command signal, and outputs the generated command signal to the subtracting unit 12.

  The subtraction unit 12 is a functional element that outputs a deviation between two input signals. In this embodiment, the subtractor 12 receives a command signal from the adder 11 and a digital detection signal from the A / D converter 13. Then, the subtraction unit 12 outputs a deviation between the command signal and the digital detection signal to the PID control unit 14.

  The “digital detection signal” is a digital signal representing the current flowing through the control target of the digital current amplifier 1. A method for detecting the current flowing through the controlled object will be described later.

  The A / D converter 13 is a functional element that converts an analog signal into a digital signal. In the present embodiment, the A / D converter 13 converts the measured analog value of the current flowing through the control target of the digital current amplifier 1 into a digital value.

  In the present embodiment, the digital current amplifier 1 outputs a PWM signal to a high-side MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor) 22 to control the current flowing through the electromagnetic valve 20.

  The high side MOSFET 22 is disposed between the electromagnetic valve 20 and the voltage source 21. The electromagnetic valve 20 realizes a throttle opening (opening area) corresponding to a current flowing from the voltage source 21 via the high-side MOSFET 22. In the present embodiment, the solenoid valve 20 is a valve that moves a plunger as a movable portion with a solenoid, and is used to control the pressure or flow rate of hydraulic fluid flowing in a hydraulic circuit mounted on a construction machine such as a hydraulic excavator. .

  The current flowing through the electromagnetic valve 20 is detected as an analog detection signal in the form of a voltage value by the shunt resistor 23 and the voltage detector 24. The voltage detector 24 outputs an analog detection signal to the filter 25. The filter 25 is configured by, for example, a CR circuit, and removes noise from the analog detection signal, and outputs the noise-removed analog detection signal after removing the noise to the A / D conversion unit 13.

  The A / D conversion unit 13 receives the analog detection signal after noise removal from the filter 25, converts it into a digital detection signal as a current value, and outputs the converted digital detection signal to the subtraction unit 12.

  The PID control unit 14 is a functional element that performs feedback control (PID control) on the current flowing through the control target of the digital current amplifier 1. In the present embodiment, the PID control unit 14 receives a deviation from the subtraction unit 12, calculates a duty ratio that acts to cancel the deviation, and outputs the calculated duty ratio to the PWM oscillator 15.

  The PWM oscillator 15 is a functional element that generates a PWM signal having a predetermined PWM frequency, a predetermined amplitude, and a variable duty ratio. In this embodiment, the PWM oscillator 15 receives a duty ratio from the PID control unit 14 and outputs a PWM signal for realizing the received duty ratio to the high-side MOSFET 22. Note that the PWM frequency and the dither frequency are set independently of each other. In this embodiment, the PWM frequency is set to a value higher than the dither frequency. This is because the response of the digital current amplifier 1 depends on the switching frequency, that is, the PWM frequency, and the higher the PWM frequency, the higher the response.

  The high side MOSFET 22 performs switching by receiving the PWM signal from the PWM oscillator 15 and controls the current flowing through the electromagnetic valve 20.

  A current is supplied to the electromagnetic valve 20 so that the movable part slightly vibrates in order to prevent sticking of the movable part and to ensure responsiveness, that is, in order not to generate a stick-slip phenomenon (static friction). Specifically, the electromagnetic valve 20 slightly reciprocates the plunger according to the dither current included in the drive current supplied via the high-side MOSFET 22 separately from the case where the plunger is moved to adjust the throttle opening. Move.

  “Dither current” is a current corresponding to the superposition dither signal. The “drive current” is a current corresponding to the command signal obtained by superimposing the superposition dither signal on the reference command signal, and by summing the reference drive current and the dither current corresponding to the reference command signal. This is the current obtained. Note that the dither frequency and amplitude of the dither signal are determined based on the specifications of the electromagnetic valve 20, and in this embodiment, the dither signal value is determined to be zero when time averaged. Therefore, the value of the superposition dither signal generated based on the dither signal is similarly determined to be zero when time averaged.

  On the other hand, when the solenoid valve 20 moves the plunger to adjust the throttle opening, the solenoid valve 20 does not generate a slight vibration of the plunger due to a dither current. This is because if the slight vibration is generated, the movement of the plunger for adjusting the throttle opening may be delayed. Specifically, when the plunger is slightly vibrated in the direction opposite to the moving direction of the plunger at the moment when the plunger is moved to adjust the throttle opening, the plunger is prevented from reaching a desired position. It is.

  Next, the temporal transition of various signals when the electromagnetic valve 20 is controlled as described above will be described with reference to FIG. 2A and 2B are diagrams showing temporal transitions of various signals. FIG. 2A shows the temporal transition of the reference command signal, and FIG. 2B shows the temporal transition of the dither signal. FIG. 2C shows the temporal transition of the dither setting signal, and FIG. 2D and FIG. 2E each show the temporal transition of the superposition dither signal. In addition, each horizontal axis of FIG. 2 (A)-FIG.2 (E) is a time axis, and makes the scale common.

  As shown in FIG. 2A, the reference command signal initially changes at a level L1 corresponding to a predetermined throttle opening in the electromagnetic valve 20. Further, as shown in FIG. 2B, the dither signal is a pulse waveform signal having an amplitude D, that is, a peak value of ± D. Further, as shown in FIG. 2C, the dither setting signal changes with a value of 1 when there is no change in the reference command signal. Further, as shown in FIGS. 2D and 2E, the superposition dither signal follows the same transition as the dither signal in FIG. 2B when the value of the dither setting signal is 1.

  At time t1, as shown in FIG. 2A, when the reference command signal increases stepwise to level L2 corresponding to another predetermined throttle opening, as shown in FIG. 2C, the dither setting signal The value of becomes zero once. The dither setting signal then gradually increases to a value of 1. In the present embodiment, the dither setting signal that has once become zero returns to a value of 1 following a path represented by a predetermined function. However, the route until the dither setting signal once returned to zero is arbitrary, and may be a route represented by a linear line or a step-like route, for example. Moreover, the dither setting signal that has once become zero may maintain a zero value state for a predetermined time. The dither setting signal may be reduced to a predetermined lower limit value that is larger than zero and smaller than 1 instead of decreasing to zero. Further, the path until the dither setting signal once returned to zero and the predetermined lower limit value may be made different according to the magnitude of change of the reference command signal.

  When the value of the dither setting signal is less than 1, the superposition dither signal represented by the product of the dither signal and the dither setting signal has an absolute intensity as shown in FIGS. 2 (D) and 2 (E). The value is less than D. Note that the transition shown in FIG. 2D is a filtering process in which the value of the superposition dither signal is regarded as zero when the absolute value of the value represented by the product of the dither signal and the dither setting signal is less than the predetermined value TH1. It shows the transition when doing. Moreover, the transition shown in FIG. 2E indicates a transition when the above-described filter processing is not performed.

  In FIG. 2, two examples of generation of the superposition dither signal when the reference command signal is changed are shown, but the present invention is not limited to this. The value of the dither signal for superimposition is, for example, regardless of the magnitude of the value represented by the product of the dither signal and the dither setting signal until the predetermined time elapses after the dither setting signal value once becomes zero. , May be considered zero. Further, the method of generating the superposition dither signal may be varied according to the magnitude of the change in the reference command signal.

  Next, the relationship between the command signal and the analog detection signal will be described with reference to FIG. 3A and 3B are diagrams showing temporal transitions of the command signal and the analog detection signal. FIG. 3A shows temporal transition of the command signal, and FIG. 3B shows temporal transition of the analog detection signal. Indicates. The transition indicated by the broken line in the figure is a transition when the strength (magnitude) of the superposition dither signal is not adjusted even if the reference command signal changes, that is, the dither signal is directly adopted as the superposition dither signal. Shows the transition. Note that the horizontal axes in FIGS. 3A and 3B are time axes, and the scale is common.

  The transition of the broken line in FIG. 3A shows the case where the negative superposition dither signal is superimposed on the reference command signal at the moment when the reference command signal increases stepwise at time t1. In this case, the value of the analog detection signal cannot reach the level L2 until time t3 as indicated by the broken line in FIG. Specifically, the level L2 cannot be reached until a while after the value of the superposition dither signal changes to a positive value. This is because the value of the command signal is limited to a level less than the level L2 (a value lower than the level L2 by the amplitude D of the dither signal) at the moment when the reference command signal increases stepwise.

  On the other hand, the transition of the solid line in FIG. 3A shows a case where the superimposing dither signal having a value of zero is superimposed on the reference command signal at the moment when the reference command signal increases stepwise at time t1. In this case, as indicated by the solid line in FIG. 3B, the value of the analog detection signal reaches level L2 at time t2, which is a time earlier than time t3. This is because the value of the command signal becomes level L2 at the moment when the reference command signal increases stepwise.

  Thus, the transition indicated by the broken line in FIG. 3B is delayed in rising compared to the transition indicated by the solid line in FIG. 3B, and reaches the level L2 by the time DL. This is because adopting the dither signal as it is as the superposition dither signal when the reference command signal is changed extends the time until the throttle opening of the solenoid valve 20 is changed to the desired throttle opening. Means there is. This also shortens the time required to change the throttle opening of the solenoid valve 20 to the desired throttle opening by temporarily reducing the intensity of the superposition dither signal at the moment when the reference command signal changes. This means that responsiveness can be improved.

  In addition, the transition indicated by the broken line in FIG. 3B is longer in settling time than the transition indicated by the solid line in FIG. 3B, and it is slow to reach a stable vibration state centered on the level L2. This means that adopting the dither signal as it is as the superposition dither signal means that the superposition dither signal is accepted as a complete disturbance at the moment when the reference command signal changes. This is because the movable part has already moved in accordance with the change of the reference command signal, so that the fine vibration of the movable part for preventing sticking is no longer necessary. Further, this is because the intensity of the superposition dither signal is temporarily reduced at the moment when the reference command signal changes, so that the current flowing through the electromagnetic valve 20 reaches a stable vibration state centered on the level L2. It means that time can be shortened. That is, it means that the occurrence of overshoot and undershoot due to feedback control can be suppressed or prevented by limiting or eliminating the superposition dither signal as a disturbance.

  Note that the above-described improvement in response and shortening of the settling time become more significant as the gain of the PID control unit is higher.

  The above description with reference to FIGS. 2 and 3 relates to the case where the reference command signal increases in a stepped manner, but the same applies to the case where the reference command signal decreases in a stepped manner.

  Next, a process in which the digital current amplifier 1 generates and outputs a PWM signal (hereinafter referred to as “PWM signal generation process”) will be described with reference to FIG. FIG. 4 is a flowchart showing the flow of the PWM signal generation process. The digital current amplifier 1 repeatedly executes the PWM signal generation process at a predetermined cycle.

  First, the digital current amplifier 1 acquires a reference command signal as a current value from an external signal generation device (step S1: reference command signal acquisition step).

  Thereafter, the digital current amplifier 1 executes a superposition dither signal generation process to output a superposition dither signal as a current value from the dither oscillator 10 (step S2: superposition dither signal generation step). Details of the dither signal generation processing for superimposition will be described later.

  Thereafter, the digital current amplifier 1 adds the reference command signal and the superposition dither signal in the adding unit 11 to generate a command signal as a current value (step S3: command signal generation step).

  The digital current amplifier 1 receives an analog detection signal as a voltage value detected by the voltage detector 24 and noise-removed by the filter 25 by the A / D converter 13. The A / D conversion unit 13 generates a digital detection signal as a current value corresponding to the analog detection signal, and outputs the generated digital detection signal to the subtraction unit 12.

  Thereafter, the digital current amplifier 1 derives a deviation between the command signal and the digital detection signal in the subtraction unit 12 (step S4: deviation derivation step).

  Thereafter, the digital current amplifier 1 determines the duty ratio from the derived deviation in the PID control unit 14 (step S5: feedback control step), and outputs the determined duty ratio to the PWM oscillator 15.

  Thereafter, the digital current amplifier 1 causes the PWM oscillator 15 to generate a PWM signal having the determined duty ratio, a predetermined PWM frequency, and a predetermined amplitude (pulse intensity) (step S6: PWM signal generation step). Then, the PWM oscillator 15 outputs the generated PWM signal to the high side MOSFET 22.

  Next, the superposition dither signal generation processing will be described with reference to FIG. FIG. 5 is a flowchart showing the flow of the superposition dither signal generation process. The digital current amplifier 1 repeatedly executes the superposition dither signal generation process at a predetermined cycle. Note that the value of the dither setting signal is maintained at a value of 1 unless a change occurs in the reference command signal.

  First, the dither oscillator 10 of the digital current amplifier 1 acquires a reference command signal, calculates a change rate with respect to the previously acquired reference command signal, and compares the calculated change rate with a predetermined threshold value TH2 (step S11). ). Note that the dither oscillator 10 may compare the magnitude of change with a predetermined threshold instead of comparing the change rate with the threshold TH2.

  When the change rate of the reference command signal is equal to or higher than the threshold value TH2 (YES in step S11), the dither oscillator 10 sets the value of the dither setting signal to zero (step S12). The value of the dither setting signal is once set to zero, and then gradually increases to return to the value 1. Further, the path to be followed when the dither setting signal returns from the value zero to the value 1 is determined in advance.

  Thereafter, the dither oscillator 10 multiplies the dither setting signal and the dither signal to generate a superposition dither signal (step S13).

  On the other hand, if the change rate of the reference command signal is less than the threshold value TH2 (NO in step S11), the dither oscillator 10 executes step S13 while maintaining the value 1 without setting the value of the dither setting signal to zero. To do.

  Thereafter, the dither oscillator 10 outputs the generated superposition dither signal to the adder 11.

  Note that steps S11 and S12 constitute a dither setting signal generation step for generating a dither setting signal whose value changes in accordance with a change in the reference command signal.

  With the above configuration, the digital current amplifier 1 can improve the response by temporarily reducing the intensity of the superposition dither signal at the moment when the reference command signal fluctuates. This is because it is possible to prevent the strength of the command signal from becoming smaller than the strength of the reference command signal when the variation direction of the reference command signal and the variation direction of the superposition dither signal are in conflict. That is, the strength of the command signal obtained by superimposing the superposition dither signal on the reference command signal is smaller than the strength of the changed reference command signal corresponding to the desired current value, and the actual current value becomes the desired current. It is because it can prevent becoming less than a value. Similarly, when the fluctuation direction of the reference command signal and the fluctuation direction of the superposition dither signal are the same, it is possible to prevent the strength of the command signal from becoming larger than the strength of the reference command signal. Note that the intensity of the dither signal for superimposition only temporarily decreases, so that the movable part does not stick.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, in the above-described embodiment, the digital current amplifier 1 generates the superposition dither signal by multiplying the dither signal and the dither setting signal. However, the present invention is not limited to this. The digital current amplifier 1 may use, for example, a fluctuation superposition dither signal registered in advance in a ROM or the like so that it can be used in place of a normal dither signal at the moment when the reference command signal changes. In this case, the digital current amplifier 1 can omit the use of the dither setting signal.

  DESCRIPTION OF SYMBOLS 1 ... Digital current amplifier 10 ... Dither oscillation part 11 ... Addition part 12 ... Subtraction part 13 ... A / D conversion part 14 ... PID control part 15 ... PWM oscillator 20. ..Solenoid valve 21 ... Voltage source 22 ... High-side MOSFET 23 ... Shunt resistor 24 ... Voltage detector 25 ... Filter

Claims (6)

A method for controlling a hydraulic excavator including a PWM oscillator that generates a PWM signal having a predetermined PWM frequency and a duty ratio corresponding to a command signal,
A reference command signal acquisition step for acquiring a reference command signal;
A superposition dither signal generating step for generating a superposition dither signal having a dither frequency set independently of the PWM frequency;
A command signal generating step of generating the command signal by superimposing the superposition dither signal on the reference command signal;
The intensity of the superposition dither signal is reduced according to the change of the reference command signal,
Level of the command signal between instantaneous said reference command signal has changed, Ri same der the level of the reference command signal, restores the strength of the superimposed dither signal in continuous time after the change of the reference command signal Let
Detect the current flowing through the solenoid valve,
Calculating a deviation between the detected current and the level of the command signal;
Controlling the solenoid valve based on the calculated deviation;
Control method of hydraulic excavator . A dither setting signal generation step of generating a dither setting signal whose value changes in accordance with a change in the reference command signal;
In the superposition dither signal generating step, the dither signal having a predetermined amplitude is multiplied by the dither setting signal to generate the superposition dither signal.
The method for controlling a hydraulic excavator according to claim 1. The PWM frequency is higher than the dither frequency;
The control method of the hydraulic excavator according to claim 1 or 2 . A hydraulic excavator including a control device that generates a PWM signal having a predetermined PWM frequency and a duty ratio corresponding to a command signal,
A superposition dither signal generator for generating a superposition dither signal having a dither frequency set independently of the PWM frequency;
A command signal generation unit that obtains a reference command signal and generates the command signal by superimposing the dither signal for superimposition on the reference command signal;
The superposition dither signal generation unit reduces the strength of the superposition dither signal to be generated according to a change in the reference command signal,
Level of the command signal between instantaneous said reference command signal has changed, Ri same der the level of the reference command signal, restores the strength of the superimposed dither signal in continuous time after the change of the reference command signal Let
Detect the current flowing through the solenoid valve,
Calculating a deviation between the detected current and the level of the command signal;
Controlling the solenoid valve based on the calculated deviation;
Hydraulic excavator . The superposition dither signal generation unit generates a dither setting signal whose value changes in accordance with a change in the reference command signal, and multiplies the dither signal having a predetermined amplitude by the dither setting signal to generate the dither setting signal. Generate signal,
The hydraulic excavator according to claim 4 . A method for controlling a hydraulic excavator including a PWM oscillator that generates a PWM signal having a predetermined PWM frequency and a duty ratio corresponding to a command signal,
Level command signal generated by superimposing the superimposed dither signal to the reference command signal, Oite the moment when the reference command signal changes, Ri same der the level of the reference command signal, the reference command signal In a continuous time after the change, the amplitude of the level of the command signal is restored so as to be in a stable vibration state centered on the reference command signal after the change,
Detect the current flowing through the solenoid valve,
Calculating a deviation between the detected current and the level of the command signal;
Controlling the solenoid valve based on the calculated deviation;
Control method of hydraulic excavator .

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