Work machine control device

Abstract

This control device for a work machine comprises: a hydraulic pump that is driven by a prime mover, and supplies hydraulic oil to a hydraulic actuator; a volume control device that controls the volume of the hydraulic pump in accordance with a control input; a volume sensor that detects an actual volume measurement value of the hydraulic pump; and a controller that acquires a target volume value of the hydraulic pump, and outputs a control input according to the target volume value to the volume control device. A mathematical model for predicting the volume of the hydraulic pump is stored in the controller. The controller calculates a predicted volume value of the hydraulic pump, using the mathematical model, calculates an optimal control input on the basis of the predicted volume value and control input constraints, calculates an assessment value on the basis of the target volume value and the actual volume measurement value, and changes the control input constraints in accordance with the assessment value.

Description

[Technical Field]

[0001] The present invention relates to a control device for a work machine. [Background technology]

[0002] In work machines such as hydraulic excavators, a variable-volume hydraulic pump is used as a hydraulic supply source for driving a hydraulic actuator. Patent Document 1 discloses a work machine that includes a motor driven by fluid discharged from a swash plate-type hydraulic pump and travels using the power of the motor. The work machine described in Patent Document 1 sets a target position for the swash plate of the hydraulic pump based on the position of an operating member and the load on the engine, and controls a continuously variable transmission (HST) so that the position of the pump swash plate coincides with the set target position. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-18171 Summary of the Invention [Problem to be solved by the invention]

[0004] The deviation between the actual displacement of the hydraulic pump and the target displacement affects the accuracy of control of the hydraulic actuator, and the accuracy of control of the hydraulic actuator affects the workability of the work machine. For this reason, when changing the displacement of the hydraulic pump, it is desired to quickly make the actual displacement follow the target displacement.

[0005] An object of the present invention is to improve the responsiveness of the volume control of a hydraulic pump and to improve the workability of a work machine. [Means for solving the problem]

[0006] A control device for a work machine according to one aspect of the present invention includes a hydraulic pump that is rotationally driven by a prime mover and supplies hydraulic oil to a hydraulic actuator, a displacement control device that controls the displacement of the hydraulic pump in accordance with a control input, a volume sensor that detects an actual measured volume value of the hydraulic pump, and a controller that acquires a target volume value of the hydraulic pump and outputs the control input in accordance with the target volume value to the volume control device. A mathematical model for predicting the displacement of the hydraulic pump is stored in the controller. The controller uses the mathematical model to calculate a predicted volume value of the hydraulic pump, calculates an optimal control input based on the predicted volume value and constraints on the control input, calculates an evaluation value based on the target volume value and the actual measured volume value, and changes the constraint on the control input in accordance with the evaluation value. [Effects of the Invention]

[0007] According to the present invention, the responsiveness of the volume control of the hydraulic pump can be improved, and the workability of the work machine can be improved. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the system configuration of a work machine. [Figure 2] FIG. 2 is a cross-sectional view of the main pump. [Figure 3] Figure 3 is a characteristic diagram of the electrical signal and output pressure of an electromagnetic proportional pressure reducing valve. [Figure 4] FIG. 4 is a control block diagram for controlling a controlled object by model predictive control. [Figure 5] FIG. 5 is a flowchart of model predictive control executed by the pump controller according to the first embodiment. [Figure 6] FIG. 6 is a time-series waveform diagram of the control input constraints set by the pump controller according to the first embodiment. [Figure 7] FIG. 7 is a diagram showing time-series changes in the volume of the pump system according to the first embodiment. [Figure 8]FIG. 8 is a flowchart of model predictive control executed by the pump controller according to the second embodiment. [Figure 9] FIG. 9 is a time-series waveform diagram of the control input constraints set by the pump controller according to the second embodiment. [Figure 10] FIG. 10 is a diagram showing time-series changes in the volume of the pump system according to the second embodiment. [Figure 11] FIG. 11 is a diagram showing time-series changes in the volume of a pump system according to a modified example of the second embodiment. [Figure 12] FIG. 12 is a flowchart of model predictive control executed by a pump controller according to the third embodiment. [Figure 13] FIG. 13 is a diagram showing time-series changes in the volume of the pump system according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will be described with reference to the drawings.

[0010] First Embodiment -Work machinery- FIG. 1 is a diagram showing the system configuration of a work machine. FIG. 1 shows one of a plurality of hydraulic actuators 17 equipped on the work machine as a representative. The work machine according to this embodiment is, for example, a hydraulic excavator equipped with a traveling body, a rotating body rotatably attached to the traveling body, and a working implement attached to the rotating body. The working implement includes a boom, an arm, a bucket, and a plurality of hydraulic cylinders that drive these. The work machine also includes a hydraulic motor for swinging that swings the rotating body, and a hydraulic motor for traveling that travels the traveling body. The multiple hydraulic cylinders that drive the working implement, the hydraulic motor that drives the swing body, and the hydraulic motor that drives the traveling body are each hydraulic actuators 17 provided on the work machine.

[0011] -Pump system (work machine control device)- The hydraulic actuator 17 of the work machine is driven by hydraulic oil supplied from the pump system 100. As shown in FIG. 1 , a control valve 16 is provided in a discharge line 15 connecting the hydraulic actuator 17 and the pump system 100. The control valve 16 is controlled in accordance with the amount of operation of an operating device of the work machine (not shown). By controlling the control valve 16, the flow rate and direction of hydraulic oil supplied from the pump system 100 to the hydraulic actuator 17 are controlled. By driving the hydraulic actuator 17, members of the work machine, such as the working implement, swing unit, and traveling unit, operate. Therefore, the pump system 100 functions as a control device for the work machine.

[0012] The pump system 100 includes a main pump 10, which is a hydraulic pump with a variable displacement (capacity), a displacement control device 20 that controls the displacement of the main pump 10 in accordance with a control input, a vehicle body controller 40 that calculates a target displacement value for the main pump 10, and a pump controller 30 that outputs a control input to the displacement control device 20 in accordance with the target displacement value obtained from the vehicle body controller 40. The main pump 10 is driven to rotate by an engine 19, which is a prime mover, and supplies hydraulic oil (working fluid) to a hydraulic actuator 17. The pump system 100 also includes a pilot pump 18, which is a fixed displacement hydraulic pump, in addition to the variable displacement main pump 10. The pilot pump 18 is driven to rotate by the engine 19 and generates pilot pressure. Note that the prime mover may be an electric motor instead of the engine 19.

[0013] -Main pump- Fig. 2 is a cross-sectional view of the main pump 10. The main pump 10 includes a casing 7, a cylinder block 3, a plurality of pistons 4, a tilting mechanism 6, and a tilting actuator 9. As shown in Fig. 2, the main pump 10 according to this embodiment is a bent-axis piston pump. However, the main pump 10 may also be a swash plate piston pump.

[0014] The casing 7 is composed of a main casing 7a and a head casing 7b. The main casing 7a is a cylindrical member that houses the components of the main pump 10, such as the cylinder block 3 and the rotating shaft 2. The tip (right end in Figure 2) of the rotating shaft 2 protrudes from the casing 7 and is connected to the output shaft of the engine 19 (see Figure 1). A circular drive disk 2a is integrally formed with the base end (left end in Figure 2) of the rotating shaft 2. The rotating shaft 2 is rotatably supported by bearings relative to the main casing 7a. The head casing 7b closes the opening at the end of the main casing 7a.

[0015] The cylinder block 3 is connected to the drive disk 2a via a center shaft 5. The cylinder block 3 rotates together with the rotary shaft 2. A plurality of cylinder chambers 3a are formed in the cylinder block 3 in its axial direction. These plurality of cylinder chambers 3a are arranged in a ring shape surrounding the rotation center line of the cylinder block 3. A piston 4 is inserted inside each cylinder chamber 3a so that it can slide back and forth. A connecting rod 4a is provided at the base end (the right end in Figure 2) of each piston 4. A joint ball 4b is formed at the tip of each connecting rod 4a. Each of the plurality of pistons 4 is connected to the drive disk 2a via the joint ball 4b so that it can swing freely.

[0016] The tilt mechanism 6 adjusts the stroke amount (pump capacity) of the piston 4 relative to the cylinder chamber 3a. The tilt mechanism 6 includes a valve plate 6a with a cylindrical lens-shaped sliding surface 6b. A center shaft 5 and a swing pin 8 are inserted into the center of the valve plate 6a from both sides. The center shaft 5 passes through the rotation center of the cylinder block 3 and is connected to the drive disk 2a. The center shaft 5 and cylinder block 3 rotate together. The opposing surfaces of the valve plate 6a and cylinder block 3 form a rotary sliding surface, and the cylinder block 3 rotates and slides relative to the valve plate 6a around the center of the center shaft 5. The tip of the center shaft 5 (the right end in Figure 2) forms a joint ball 5a, and the center shaft 5 is connected to the drive disk 2a via this joint ball 5a so that it can swing freely.

[0017] The valve plate 6a has a sliding surface 6b that slides on an arc-shaped guide surface formed on the head casing 7b, and the cylinder block 3 and valve plate 6a swing back and forth along an arc orbit around a swing center line CL that passes through the center of the joint ball 5a. The valve plate 6a also has ports (discharge port 6c and suction port 6d) that intermittently communicate with each cylinder chamber 3a as the cylinder block 3 rotates. The discharge port 6c communicates with the cylinder chamber 3a via a cylinder communication passage 3b opposite the discharge port 6c. The suction port 6d communicates with the cylinder chamber 3a via a cylinder communication passage 3b opposite the suction port 6d. When the inclination angle (tilt angle) of the rotation center line of the center shaft 5 relative to the rotation center line of the rotary shaft 2 changes, the stroke amount (pump capacity) of the piston 4 relative to the cylinder chamber 3a changes. In other words, when the tilt angle changes, the amount of hydraulic oil supplied and discharged via the cylinder communication passage 3b changes.

[0018] The tilt actuator 9 is a sector-type variable displacement mechanism. The tilt actuator 9 includes a cylinder chamber 9a formed in the head casing 7b and a servo piston 9b slidably inserted into the cylinder chamber 9a. The servo piston 9b reciprocates within the cylinder chamber 9a in the axial direction of the cylinder chamber 9a (the axial direction of the servo piston 9b). The servo piston 9b is provided with a swing pin 8. The swing pin 8 is connected to the valve plate 6a. As the servo piston 9b moves in the axial direction, the valve plate 6a slides along the guide surface of the head casing 7b. In other words, the tilt mechanism 6 operates, and the tilt angle changes.

[0019] The interior of the cylinder chamber 9a is separated into two pressure-receiving chambers 9c and 9d by the servo piston 9b. As shown in FIG. 1, the pressure-receiving chamber 9d is connected to the pilot pump 18 via the electromagnetic proportional pressure-reducing valve 11. The pressure-receiving chamber 9c is connected to the pilot pump 18 without passing through the electromagnetic proportional pressure-reducing valve 11. A pilot primary pressure generated by the pilot pump 18 acts on the pressure-receiving chamber 9c. When the same pressure as that of the pressure-receiving chamber 9d acts on the pressure-receiving chamber 9c, the servo piston 9b moves upward in the figure due to the difference in the pressure-receiving area. When the pressure of the pressure-receiving chamber 9d is reduced, the servo piston 9b moves downward in the figure.

[0020] As shown in Figure 2, the servo piston 9b has a small diameter portion and a large diameter portion. A step is formed between the small diameter portion and the large diameter portion. When the step portion of the servo piston 9b abuts against the step in the cylinder chamber 9a, one end (upper limit) of the movable range of the servo piston 9b is determined. Furthermore, when the end face (lower end face in the figure) of the servo piston 9b abuts against the end (lower end in the figure) of the cylinder chamber 9a, the other end (lower limit) of the movable range of the servo piston 9b is determined.

[0021] -Main pump operation- When the rotary shaft 2 is driven to rotate by the engine 19, the cylinder block 3 connected to the drive disk 2a is also driven to rotate. As a result, each piston 4 reciprocates within each cylinder chamber 3a of the cylinder block 3. Each piston 4 repeats a suction stroke and a discharge stroke. As a result, the main pump 10 draws hydraulic oil from the tank 12 (see Figure 1) and discharges it as pressurized oil from the discharge port.

[0022] The discharge flow rate of the main pump 10 is adjusted by changing the tilt angle. When the position of the servo piston 9b changes, the valve plate 6a moves along the guide surface of the head casing 7b. When the position of the valve plate 6a changes, the tilt angle changes. This changes the amount of displacement of each piston 4 sliding in each cylinder chamber 3a. As a result, the flow rate discharged from the main pump 10 changes. When the servo piston 9b is displaced toward the pressure receiving chamber 9c (upper side in the figure), the tilt angle decreases, and the discharge flow rate of the main pump 10 decreases. On the other hand, when the servo piston 9b is displaced toward the pressure receiving chamber 9d (lower side in the figure), the tilt angle increases, and the discharge flow rate of the main pump 10 increases.

[0023] -Volume control device- As shown in FIG. 1, the volume control device 20 has an electromagnetic proportional pressure reducing valve 11. The electromagnetic proportional pressure reducing valve 11 has a pump port 11a, a tank port 11b, and a control pressure port 11c. The pump port 11a is connected to the discharge port of a pilot pump 18. The tank port 11b is connected to a tank 12 that stores hydraulic oil. The control pressure port 11c is connected to a pressure receiving chamber (control pressure chamber) 9d of the tilt actuator 9. The electromagnetic proportional pressure reducing valve 11 has a solenoid 11d, a spool 11e, and a spring 11f. The spring 11f biases the spool 11e in a direction opposite to the thrust generated by the solenoid 11d.

[0024] An electric signal (electrical command signal) is input as a control input to the electromagnetic proportional pressure reducing valve 11 from the pump controller 30. The electromagnetic proportional pressure reducing valve 11 generates a pilot secondary pressure that is guided to the pressure receiving chamber 9d on the large diameter side of the tilt actuator 9, using the discharge pressure (pilot primary pressure) of the pilot pump 18 as its source pressure.

[0025] Fig. 3 is a characteristic diagram of the electrical signal and output pressure of the electromagnetic proportional pressure reducing valve 11. As shown in Fig. 3, the horizontal axis represents the value of the electrical signal input to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11. The value of the electrical signal is, for example, the value of the control current (excitation current). The vertical axis represents the pressure (pilot secondary pressure) output from the electromagnetic proportional pressure reducing valve 11 to the pressure receiving chamber (control pressure chamber) 9d.

[0026] An electric signal corresponding to the pump volume target value is input to the electromagnetic proportional pressure reducing valve 11. As the value of the electric signal increases, the spool 11e is displaced in one direction (to the right in FIG. 1), connecting the pressure receiving chamber (control pressure chamber) 9d and the tank 12. This reduces the pressure in the pressure receiving chamber 9d, and the hydraulic load acting on the large diameter portion of the servo piston 9b becomes smaller relative to the hydraulic load acting on the small diameter portion of the servo piston 9b. This causes the servo piston 9b to be displaced in one direction (downward in FIG. 1). The greater the downward displacement of the servo piston 9b from its upper limit position, the larger the volume of the main pump 10. On the other hand, as the value of the electric signal to the electromagnetic proportional pressure reducing valve 11 decreases, the spool 11e is displaced in the other direction (to the left in FIG. 1), connecting the pressure receiving chamber (control pressure chamber) 9d and the pilot pump 18. This increases the pressure in the pressure receiving chamber (control pressure chamber) 9d, and the hydraulic load acting on the large diameter portion of the servo piston 9b becomes larger relative to the hydraulic load acting on the small diameter portion of the servo piston 9b. As a result, the servo piston 9b is displaced in the other direction (upward in FIG. 1). The larger the amount of upward displacement of the servo piston 9b from the lower limit position, the smaller the volumetric capacity of the main pump 10 becomes.

[0027] As shown in Fig. 3, there is a correlation between the value of the electric signal to the electromagnetic proportional pressure reducing valve 11 and the pilot secondary pressure output from the electromagnetic proportional pressure reducing valve 11, and there are upper and lower limit values ​​for the output pressure (control pressure of the tilt actuator 9) and the value of the electric signal. In this embodiment, the value of the electric signal shown in Fig. 3 is the value of the control current (excitation current) supplied to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11. In the electromagnetic proportional pressure reducing valve 11 of this embodiment, the control current value is a minimum current value I min The range from the first current value I1 to the first current value I2 is the dead zone on the lower limit side of the control input. min Above the first current value I1, the output pressure of the electromagnetic proportional pressure reducing valve 11 becomes the pilot primary pressure (upper limit of the control pressure) Pp. min is 0 (zero) or the value of the standby current. The solenoid proportional pressure reducing valve 11 changes the control current value from the second current value I2 to the maximum current value I max The upper limit of the control input is the dead zone. In other words, the control current value is greater than the second current value I2 and the maximum current value I max In the following, the output pressure of the electromagnetic proportional pressure reducing valve 11 is the tank pressure (lower limit value of the control pressure) Pt. In the range where the control current value is larger than the first current value I1 and smaller than the second current value I2, the output pressure decreases as the control current value increases.

[0028] -Volume sensor- As shown in FIG. 1, the servo piston 9b has a position (a displacement x from a reference position) of the servo piston 9b. sp ) is connected to the main pump 10. The reference position is, for example, the position where the step of the servo piston 9b abuts against the step of the cylinder chamber 9a. The position sensor 13 outputs the detected position of the servo piston 9b to the pump controller 30. As will be described later, the position of the servo piston 9b correlates with the actual volume of the main pump 10. In other words, the position sensor 13 functions as a volume sensor that detects the actual volume of the main pump 10 (actual volume measurement value).

[0029] The pump controller 30 is connected to a vehicle controller 40. The vehicle controller 40 determines a target value q of the volume of the main pump 10 (hereinafter also referred to as a volume target value). ref and outputs the calculation result to the pump controller 30.

[0030] -Controller hardware configuration- The pump controller 30 is composed of a computer equipped with processing devices such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), and DSP (Digital Signal Processor), non-volatile memory such as ROM (Read Only Memory), flash memory, and hard disk drive, volatile memory known as RAM (Random Access Memory), an input / output interface, and other peripheral circuits. These hardware components work together to run software and realize multiple functions. The pump controller 30 may be composed of a single computer or multiple computers.

[0031] The nonvolatile memory stores programs capable of executing various calculations, various thresholds, data tables, mathematical models, etc. The nonvolatile memory is a storage medium (storage device) from which the programs that realize the functions of this embodiment can be read. The volatile memory is a storage medium (storage device) that temporarily stores the results of calculations performed by the processing device and signals input from the input / output interface. The processing device is a device that loads the programs stored in the nonvolatile memory into the volatile memory and executes the calculations, and performs predetermined calculations on data taken from the input / output interface, the nonvolatile memory, and the volatile memory in accordance with the programs.

[0032] The input section of the input / output interface converts signals input from various devices (such as the position sensor 13) into data that can be calculated by the processing device. The output section of the input / output interface generates an output signal according to the calculation result in the processing device, and outputs the signal to various devices (such as the electromagnetic proportional pressure reducing valve 11).

[0033] Like the pump controller 30, the vehicle body controller 40 is configured as a computer equipped with a processing device, storage devices (volatile memory and non-volatile memory), an input / output interface, and other peripheral circuits.

[0034] -Main pump control device- The vehicle body controller 40 and pump controller 30 according to this embodiment function as a control device for the main pump 10. The control device for the main pump 10 changes the flow rate of hydraulic oil supplied from the main pump 10 to the hydraulic system in order to improve the efficiency of the hydraulic system. This is achieved by changing the volume (equivalent to the discharge flow rate per rotation) of the main pump 10 in accordance with various operating states and operating conditions of the work machine.

[0035] -Pump controller functions- The pump controller 30 detects the position x of the servo piston 9b. sp Conversion coefficient k to convert the actual volume of the main pump 10 pu is stored. Conversion coefficient k pu is the position x of the servo piston 9b sp The conversion coefficient k is determined in advance based on the geometric relationship between the components of the main pump 10. pu is a constant value. The conversion coefficient is a variable k that changes depending on the position of the servo piston 9b. pu (x sp The pump controller 30 may be configured as follows: sp and the conversion factor k pu Based on the actual volume (actual measured volume) q of the main pump 10 p Calculate (q p =k pu x sp The pump controller 30 controls the volume target value q of the main pump 10. ref and the measured volume q p Based on the measured volume q p is the volume target value q refThe electromagnetic proportional pressure reducing valve 11 is controlled so that the pressure approaches

[0036] The pump controller 30 can adjust the displacement angle (volume) of the main pump 10 by adjusting the value of the electrical signal input to the electromagnetic proportional pressure reducing valve 11. Here, when the value of the electrical signal input to the electromagnetic proportional pressure reducing valve 11 is increased, the servo piston 9b moves in a direction that increases the displacement angle. The servo piston 9b moves until the large diameter portion of the servo piston 9b abuts against the lower end surface of the cylinder chamber 9a. On the other hand, when the value of the electrical signal input to the electromagnetic proportional pressure reducing valve 11 is decreased, the servo piston 9b moves in a direction that decreases the displacement angle. The servo piston 9b moves until the stepped portion of the servo piston 9b abuts against the step in the cylinder chamber 9a. Therefore, in order to move or hold the servo piston 9b at a desired position, it is necessary to successively change the value of the electrical signal input to the electromagnetic proportional pressure reducing valve 11.

[0037] The control pressure characteristics of the tilt actuator 9 are different when hydraulic oil flows out of the pressure receiving chamber (control pressure chamber) 9d and when hydraulic oil flows into the pressure receiving chamber (control pressure chamber) 9d. Therefore, when there is a transition between a state where hydraulic oil flows out of the pressure receiving chamber 9d and a state where hydraulic oil flows into the pressure receiving chamber 9d, the control pressure characteristics of the tilt actuator 9 switch. Because the control pressure characteristics switch in this way, when the actual volume measurement value is near the volume target value, the control pressure characteristics of the tilt actuator 9 become nonlinear.

[0038] The pump controller 30 determines the volume target value q ref and the measured volume q p The volume deviation e is calculated as the deviation from the volume target value q. ref From the measured volume q p It corresponds to the absolute value of the value obtained by subtracting (e=|q ref -q p The pump controller 30 inputs the volumetric deviation e to the control system, and outputs an electric signal to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11 as a control input u for reducing the volumetric deviation e.

[0039] Here, we will explain the content of volume feedback control by a pump controller according to a comparative example of this embodiment and the problems that may arise during this control. The pump controller according to the comparative example performs volume feedback control using a control system that does not consider the upper and lower limit values ​​of the electrical signal to the electromagnetic proportional pressure reducing valve 11, or changes in the control pressure characteristics of the tilt actuator 9 when the actual volume value is near the target volume value. The specific flow of control operation is as follows.

[0040] (Operation 1) The pump controller according to the comparative example outputs an electrical signal to the electromagnetic proportional pressure reducing valve 11, which controls the tilting actuator 9, to increase the volume. In other words, the pump controller according to the comparative example increases the value of the electrical signal. (Operation 2) The hydraulic oil flows out of the cylinder chamber 9a of the tilting actuator 9, causing the tilting actuator 9 to move in a direction to increase the volume. (Operation 3) When the actual volume measurement value reaches the target volume value, the pump controller according to the comparative example sets the value of the electrical signal to control the tilting actuator 9 to 0 (zero). (Operation 4) Due to the characteristics of the electrical signal to the electromagnetic proportional pressure reducing valve 11, the structural characteristics of the electromagnetic proportional pressure reducing valve 11, the structural characteristics of the tilting actuator 9, and the control pressure characteristics of the tilting actuator 9, the tilting actuator 9 does not remain at the target position corresponding to the target volume value, but passes the target position and stops. As a result, the actual volume measurement value becomes larger than the target volume value. (Operation 5) Therefore, the pump controller according to the comparative example outputs an electrical signal to the electromagnetic proportional pressure reducing valve 11 to decrease the volume. In other words, the pump controller according to the comparative example decreases the value of the electrical signal. (Operation 6) Hydraulic oil flows into the cylinder chamber 9a of the tilting actuator 9, causing the tilting actuator 9 to move in a direction that reduces the volume. (Operation 7) As in (Operation 3) and (Operation 4) above, the tilting actuator 9 does not stay at the target position corresponding to the volume target value, but passes the target position and stops. As a result, the actual measured volume value becomes smaller than the volume target value. (Operation 8) When the above (Operations 1) to (Operation 7) are repeated from then on, the hydraulic oil in the cylinder chamber 9a of the tilting actuator 9 switches between flowing in and out, and the control pressure characteristics of the tilting actuator 9 switch.

[0041] In control by the pump controller according to the comparative example, factors that affect the tracking accuracy of the actual volume value relative to the target volume value during transient response, i.e., factors that contribute to the nonlinear characteristics of the pump volume, include the existence of a dead band in the control input corresponding to the upper and lower limits of the control pressure, and changes in the control pressure characteristics of the tilting actuator 9 when the actual volume value is close to the target volume value. The dead band in the control input causes an increase in overshoot or undershoot relative to the target volume value due to a delay in switching the control input. Furthermore, the switching of the control pressure characteristics of the tilting actuator 9 between the characteristics when hydraulic oil flows into the cylinder chamber 9a and the characteristics when hydraulic oil flows out of the cylinder chamber 9a causes an increase in the duration and amplitude of the hunting phenomenon (oscillation phenomenon) of the actual volume value relative to the target volume value.

[0042] As described above, methods that use feedback control of the actual volume measured value, such as PI control, may not be able to accurately track the actual volume measured value relative to the target volume measured value during transient response. Therefore, this embodiment uses model predictive control, which can reflect control input constraints (hereinafter also referred to as control input constraints) when designing the control system and incorporate the control input constraints (upper and lower limit values ​​of the control input) of the main pump 10 as conditions when calculating the control input. Model predictive control is performed with the aim of reducing the volume deviation e. Furthermore, the control input constraints are made variable in response to changes in the control pressure characteristics of the tilting actuator 9 when the actual volume measured value is near the target volume value. This shortens the settling time during transient response of pump volume control. Reducing the settling time can improve the delay in the operation of the hydraulic actuator and the workability of a work machine using a hydraulic actuator. The control performed by the pump controller 30 according to this embodiment will be described in detail below.

[0043] -Model predictive control- Fig. 4 is a control block diagram for controlling a control target by model predictive control. The control target (plant) 39 of the control system shown in Fig. 4 ranges from the electromagnetic proportional pressure reducing valve 11 to the displacement of the servo piston 9b. When an electrical signal is input as a control input u(k) to the electromagnetic proportional pressure reducing valve 11 as the control target 39, the servo piston 9b is displaced by the output pressure of the electromagnetic proportional pressure reducing valve 11. The displacement of the servo piston 9b is calculated based on the actual volume measurement value q of the main pump 10. p is converted to

[0044] The vehicle body controller 40 determines the volume target value q based on the operation amount of the operating lever of the hydraulic actuator 17 and the discharge pressure of the main pump 10. ref The operation amount of the operation lever is detected by an operation amount sensor. The discharge pressure of the main pump 10 is detected by a discharge pressure sensor. The vehicle controller 40 further takes into account the speed of the hydraulic actuator 17, the angle and position of the member driven by the hydraulic actuator 17, etc., to calculate the volume target value q ref The vehicle body controller 40 may calculate the calculated volume target value q ref is output to the pump controller 30.

[0045] The pump controller 30 has functions as a model predictive control unit 31, a predictor 32, and a recursive least squares solver 33. The model predictive control unit 31 calculates a volume target value q ref and the measured volume q p The optimal control input u is calculated in real time using the control input u calculated in the previous control cycle, the control input constraints, and a mathematical model for predicting the behavior of the volume of the main pump 10 (hereinafter also referred to as the prediction model).

[0046] The prediction model is a physical model for predicting the volume after a predetermined time has elapsed from the present time (future volume), and is expressed by the following equation (1): The prediction model is stored in advance in the non-volatile memory of the pump controller 30.

[0047]

number

[0048] In the state equation (1), x(k) is the state vector. The structure of the state vector x(k) can be designed arbitrarily. k represents the current (calculation point) control period (number of steps), and k+1 represents the control period one period after the current control period. A is the system matrix of the prediction model, B is the control input vector of the prediction model, and C is the output vector of the prediction model. The matrix A and vectors B and C have structures designed to match the structure of the state vector x(k).

[0049] The parameters constituting matrix A and vectors B and C, i.e., the parameters of the prediction model, use values ​​previously obtained using an identification method or values ​​updated at each sample time using an adaptive identification method. When the parameters are previously obtained using an identification method, the average value of multiple parameters obtained by changing at least one of the load pressure (discharge pressure of the main pump 10) and the temperature of the hydraulic oil may be used. This reduces deviations in characteristics even when the operating environment changes. As a result, the tilt angle of the main pump 10 can be accurately tracked to the target value.

[0050] In this embodiment, the state vector x(k) is expressed by the following equation (2).

[0051]

number

[0052] In equation (2), q p (k) is the volume measurement value obtained in the current control cycle, and q p (k-1) is the volume measurement value obtained in the control cycle immediately before the current control cycle.

[0053] The model predictive control unit 31 and the predictor 32 are connected to the control input u(k) and the actual volume measurement value q p (k) and the prediction model to calculate the predicted volume of the main pump 10 (hereinafter also referred to as the predicted volume value) q pThe predictor 32 calculates the actual volume measurement value q p (k) and volume prediction value q p Calculate the prediction error ε(k), which is the deviation from ^(k) (ε(k)=q p (k)-q p ^(k)). Volume prediction value q p ^(k) is expressed by the following equation (3) using the parameters θ(k) of the prediction model and the regressor vector φ(k). The parameters θ(k) include parameters that configure the system matrix A, control input vector B, and output vector C of the prediction model.

[0054]

number

[0055] The regressor vector φ(k) is the volume measurement value q p (k) and the control input u(k), it is expressed by the following equation (4). Note that the regressor vector φ(k) has a structure designed to match the structure of the state vector x(k), and the description in equation (4) is just an example.

[0056]

number

[0057] The recursive least squares solver 33 calculates the actual volume q p (k), control input u(k), and prediction error ε(k) are used to calculate a parameter prediction value θ^(k), which is an optimal value (predicted value) of a parameter θ(k) of a prediction model (mathematical model of a predictor) in real time by a recursive least squares method. The recursive least squares solver 33 calculates the parameter prediction value θ^(k) of the prediction model so that the prediction error ε(k) calculated by the predictor 32 approaches 0 (zero). Specifically, the recursive least squares solver 33 calculates an evaluation function J expressed by the following equation (5a): θ The parameter predicted value θ̂(k) is calculated using the following equation (5b) so that (k) is minimized.

[0058]

number

[0059] The parameter prediction value θ̂(k) includes parameters that make up the system matrix A, the control input vector B, and the output vector C. As described above, the regressor vector φ(k) is calculated from the actual volume measurement value q p (k) and the control input u(k).

[0060] The recursive least squares solver 33 rewrites (overwrites) the parameters of the prediction model stored in the non-volatile memory with the parameters included in the parameter prediction value θ^(k), which is the calculation result. As a result, the matrix A and vectors B and C of the prediction model used in the model prediction control unit 31 and the predictor 32 are updated by the parameter prediction value θ^(k) calculated by the recursive least squares solver 33. This update process is repeatedly executed at a predetermined control period. In other words, the prediction model is updated in real time by the recursive least squares solver 33. Note that if the prediction error ε(k) is 0, no update of the prediction model is substantially performed.

[0061] It is possible to control the displacement of the main pump 10 even if the prediction model is not updated. In this case, the parameters of the prediction model can be determined based on test results under certain operating conditions. The average values ​​of multiple parameters calculated in response to changes in operating conditions, such as load pressure and hydraulic oil temperature, may be used as the parameters of the prediction model. However, since the operating conditions (load pressure and hydraulic oil temperature) and the actual displacement of the main pump 10 constantly change during operation of a work machine such as a hydraulic excavator, setting the parameters of the prediction model to fixed values ​​reduces the accuracy of predictive control. In other words, a discrepancy occurs between the actual value and the predicted value due to not updating the prediction model. For this reason, it is preferable to update the parameters of the prediction model to accommodate changes in the operating conditions and the actual displacement of the main pump 10, as in this embodiment. This improves the accuracy of predictive control.

[0062] The model prediction control unit 31 calculates the volume target value q ref and the volume predicted value q calculated based on the prediction model p The model predictive control unit 31 calculates the deviation from ^ and calculates the control input u(k) so that this deviation approaches 0 (zero). Specifically, the model predictive control unit 31 calculates the evaluation function J(k) expressed by the following equation (6).

[0063]

number

[0064] Δu^ is the predicted change in the control input. H p represents the prediction interval, and H u represents the control interval. The first term on the right side of equation (6) is the prediction interval (i=1,...,H p ) the target volume q ref and the volume prediction value q p The second term on the right side of equation (6) is the sum of squares of the deviations from the control interval (i=0,...H u -1). Q and R are design parameters of the control system used to weight the first and second terms, respectively. (k+i|k) means the value corresponding to each i at step k, for example, when i=2, it means the predicted value two steps ahead when predicted at step k (current time). Note that the volume predicted value q p The initial value of ^ is the actual volume measurement value q p For example, the initial value of the predicted change amount Δu^ corresponds to the value obtained by subtracting the control input u(k-1) of the step (k-1) immediately preceding the step (k) from the control input u(k) of the step (k).

[0065] The model predictive control unit 31 calculates the volume predicted value q under the control input constraint expressed by the following equation (7): p The control input u(k) is calculated so that the evaluation function J(k) including ^ is minimized.

[0066]

number

[0067] The control input constraint is the upper limit of the control input, u max and the lower limit u min In this embodiment, the model prediction control unit 31 calculates the volume target value q ref and actual volume measurement value q p The pump controller 30 calculates a volume deviation e as an evaluation value based on the calculated volume deviation e, and changes the control input constraints according to the calculated volume deviation e. The nonvolatile memory of the pump controller 30 stores a deviation threshold value e, which is a threshold value for the volume deviation e. th The model prediction control unit 31 stores the volume deviation e and the deviation threshold value e th The value of the control input constraint is set according to the magnitude relationship.

[0068] Control input upper limit u max is the volume deviation e is the deviation threshold e th If it is equal to or greater than the first upper limit value u max1 The volume deviation e is the deviation threshold e th If it is less than the second upper limit value u max2 The first upper limit value u max1 is the second current value I2 or more and the maximum current value I max The value may be within the following range. max1 The second upper limit value u is set within the dead band range in which the output pressure of the electromagnetic proportional pressure reducing valve 11 is maintained at the tank pressure Pt (constant value) even if the value of the electrical signal is changed. max2 A value greater than the first current value I1 and less than the second current value I2 may be used for u, or a value equal to or greater than the second current value I2. max2 is the first upper limit u max1 It is sufficient if the value is smaller than

[0069] Control input lower limit u min is the volume deviation e is the deviation threshold e th If it is equal to or greater than the first lower limit u min1 The volume deviation e is the deviation threshold e th If it is less than the second lower limit u min2 The first lower limit u min1 is the minimum current value I minThe value may be in the range of the first lower limit value u min1 The second lower limit value u is set within the dead band range in which the output pressure of the electromagnetic proportional pressure reducing valve 11 is maintained at the pilot primary pressure Pp (constant value) even if the value of the electrical signal is changed. min2 A value greater than the first current value I1 and smaller than the second current value I2 may be used for u, or a value equal to or less than the first current value I1. min2 is the first lower limit u min1 and the second upper limit value u max2 The deviation threshold e used as a condition for changing the control input constraints is th is the upper limit u max When changing the lower limit u min may be different values ​​when the value is changed.

[0070] In this embodiment, the time-varying characteristics of the control input constraints have the characteristics of a discretized first-order lag system 1 / (τs+1), where s is the Laplace operator and τ is the time constant. The time constant τ can be set arbitrarily.

[0071] -Model predictive control flow- Figure 5 is a flowchart of model predictive control executed by the pump controller 30. The control flow shown in Figure 5 is started, for example, when the ignition switch of the work machine is turned on, and is repeatedly executed at a predetermined control period.

[0072] In step S110, the pump controller 30 receives the volume target value q ref In the next step S120, the pump controller 30 acquires the position x of the servo piston 9b detected by the position sensor 13. sp In the next step S130, the pump controller 30 acquires the position x of the servo piston 9b. sp conversion factor k pu By multiplying by , the actual volume measurement value q pIn the next step S140, the pump controller 30 calculates the volume target value q ref and the measured volume q p Calculate the volume deviation e.

[0073] In the next step S150, the pump controller 30 determines the control input constraint (equation (7)) in accordance with the magnitude of the volume deviation e. In the next step S160, the pump controller 30 determines the control input constraint (equation (7)) in accordance with the prediction model of the volume of the main pump 10 (equations (1) and (2)), the actual volume measurement value q calculated in step S130, and the volume deviation e. p Based on the control input u calculated in the immediately previous control cycle and the control input constraint (equation (7)) determined in step S150, the pump controller 30 calculates an optimal control input u so that the above-mentioned evaluation function J (equation (6)) is minimized. In the next step S170, the pump controller 30 outputs an electric signal corresponding to the control input u calculated in step S160 to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11.

[0074] When the process of step S170 ends, the process of this control cycle shown in the flowchart of Fig. 5 ends. In the next control cycle, the pump controller 30 again executes the processes from step S110 to step S170.

[0075] -Time series changes in control input constraints- FIG. 6 shows the control input constraints (upper limit u max and the lower limit u min ) is a time series waveform diagram. In FIG. 6, the upper limit value u max and the lower limit u min is shown by a thick solid line, and the volume deviation e is shown by a thin solid line. ref When is changed, the actual volume q p is the volume target value q ref This causes the volume deviation e to decrease. From time t1 to time t2, the volume deviation e is equal to or smaller than the deviation threshold e th Therefore, the upper limit value of the control input u max is the first upper limit u max1and the lower limit of the control input u min is the first lower limit u min1 From time t2 to time t3, the volume deviation e is equal to or less than the deviation threshold e th Therefore, the upper limit of the control input u max After a predetermined time has elapsed since time t2, the second upper limit value u max2 and the lower limit of the control input u min is the second lower limit value u after a predetermined time has elapsed since time t2. min2 This becomes:

[0076] After that, the volume deviation e increases, and from time t3 to time t4, the deviation threshold e th Therefore, the upper limit of the control input u max After a predetermined time has elapsed since time t3, the first upper limit value u max1 and the lower limit of the control input u min is the first lower limit value u after a predetermined time has elapsed since time t3. min1 After that, the volume deviation e decreases again, and after time t4, the volume deviation e becomes equal to the deviation threshold value e th Therefore, the upper limit of the control input u max After a predetermined time has elapsed since time t4, the second upper limit value u max2 and the lower limit of the control input u min After a predetermined time has elapsed since time t4, the second lower limit value u min2 Note that the delay processing due to the first-order lag prevents the control input constraints from changing immediately.

[0077] -Simulation results of this embodiment and comparative examples- The main operation and effects of the pump system 100 according to this embodiment will be described with reference to Fig. 7. Fig. 7 is a diagram showing the time series change in the volume of the pump system 100. In Fig. 7, the volume target value q refis shown by a solid line. The time series change in the volume in this embodiment is shown by a dashed line. In addition, to clarify the effects of this embodiment, the time series change in the volume controlled by a pump controller according to a comparative example of this embodiment is shown by a broken line. The control of the pump controller according to the comparative example differs from the control of this embodiment only in that the control input constraints are not changed. In other words, in the comparative example, the upper limit value u of the control input max is always the first upper limit u max1 and the lower limit of the control input u min is always the first lower limit u min1 The horizontal axis represents time (elapsed time), and the vertical axis represents the volume of the main pump 10. The curves showing the time-series changes in volume according to this embodiment and the comparative example are obtained by numerical simulation.

[0078] 7 shows the settling times Δt0 and Δt1 until the volume of the main pump 10 is stabilized. The settling times Δt0 and Δt1 are determined by the volume target value q ref The settling time is the time from when the volume deviation e changes to when it reaches a predetermined error range (volume target value q ref ±De), the volume deviation e is within the above error range (volume target value q ref ±De).

[0079] As shown in Figure 7, the volume target value q ref When the volume decreases from the predetermined amount Du to the predetermined amount D1, the volume reaches the volume target value q ref An undershoot occurs in which the volume is reduced more than (=D1). In the comparative example, the amount of undershoot is larger than in this embodiment. Furthermore, in the comparative example, volume hunting (oscillation) continues after the undershoot occurs. In other words, in the comparative example, large-amplitude oscillation continues for a long time.

[0080] In contrast, in this embodiment, the amount of undershoot is smaller than in the comparative example. Also, in this embodiment, volume hunting (oscillation) after undershoot occurs is prevented. As a result, the settling time Δt1 in this embodiment is shorter than the settling time Δt0 in the comparative example.

[0081] As described above, in this embodiment, model predictive control (MPC) is used, which can incorporate constraints on the control input as a condition for calculating the control input, in order to deal with nonlinearity due to the upper and lower limits of the electrical signal value to the electromagnetic proportional pressure reducing valve 11. p is the volume target value q ref The control input constraint is made variable to cope with the nonlinearity caused by the change in the control pressure characteristics of the pressure receiving chamber 9d of the tilt actuator 9 when the volume target value q ref This reduces the magnitude (amount of undershoot) of the undershoot that occurs when the actual volumetric capacity is made to follow the target volumetric capacity q of the main pump 10, and also prevents hunting (vibration). As a result, the settling time during transient response can be shortened. In other words, according to this embodiment, ref This improves the ability of the actual volume to follow the pressure. As a result, it is possible to improve the delay in the operation of the hydraulic actuator 17 mounted on a work machine such as a hydraulic excavator. The improvement in the delay in the operation of the hydraulic actuator 17 leads to an improvement in the workability of the work machine.

[0082] -Effects of this embodiment- According to the above-described embodiment, the following advantageous effects are achieved.

[0083] (1) A pump system (work machine control device) 100 includes a main pump (hydraulic pump) 10, a displacement control device 20, a position sensor 13, and a pump controller (controller) 30. The main pump 10 is driven to rotate by an engine (prime mover) 19 and supplies hydraulic oil to a hydraulic actuator 17. The displacement control device 20 controls the displacement of the main pump 10 in accordance with a control input u. The position sensor 13 detects an actual measured volume value q of the main pump 10.p The pump controller 30 functions as a volume sensor that detects the volume target value q of the main pump 10. ref and obtain the volume target value q ref The pump controller 30 outputs a control input u corresponding to the displacement control device 20. The pump controller 30 stores a prediction model, which is a mathematical model for predicting the displacement of the main pump 10. The pump controller 30 uses the prediction model to calculate a predicted volume value q of the main pump 10. p The pump controller 30 calculates the predicted volume value q p ^ and the constraints on the control input u (upper limit u max and the lower limit u min The pump controller 30 calculates an optimal control input u based on the volume target value q ref and actual volume measurement value q p The pump controller 30 calculates an evaluation value (volume deviation e in this embodiment) based on the evaluation value. The pump controller 30 changes the constraint on the control input u in accordance with the evaluation value.

[0084] According to this configuration, the target volume value q of the main pump 10 ref Actual volume measurement value q p In other words, it is possible to improve the responsiveness of the displacement control of the main pump 10. This improves the accuracy of control of the hydraulic actuator 17, thereby improving the workability of the work machine.

[0085] (2) The pump controller 30 includes a threshold value (deviation threshold value e) for the evaluation value (volume deviation e). th The pump controller 30 stores the evaluation value (volume deviation e) and the threshold value (deviation threshold e th ) and sets the value of the control input constraint according to the magnitude relationship. The pump controller 30 uses a first-order lag system for the time-varying characteristics of the control input constraint. This configuration makes it possible to reduce the amount of undershoot (or overshoot) and vibration amplitude compared to when the control input constraint is changed discontinuously.

[0086] (3) The control input constraint is the upper limit of the control input, umax and the lower limit u min The pump controller 30 determines whether the evaluation value (volume deviation e) is greater than or equal to the upper limit threshold e th Above this, the upper limit value u max The first upper limit value u max1 The pump controller 30 sets the evaluation value (volume deviation e) to the upper limit threshold value e th Below the upper limit u max The first upper limit value u max1 A second upper limit value u that is smaller than max2 Furthermore, the pump controller 30 sets the evaluation value (volume deviation e) to a lower limit threshold value e th Above the lower limit u min The first lower limit u min1 The pump controller 30 sets the evaluation value (volume deviation e) to the lower limit threshold value e th If less than the lower limit u min The first lower limit u min1 The second lower limit u is greater than min2 In this embodiment, the upper limit threshold and the lower limit threshold are set to the same value e th However, the upper limit threshold and the lower limit threshold may be different values.

[0087] According to this configuration, when the evaluation value (volume deviation e) becomes smaller, the upper limit value u of the control input max and the lower limit u min As a result, the upper limit value u max When only the lower limit u is changed, min Compared to when only the voltage is changed, the amount of undershoot can be reduced and the vibration amplitude can be suppressed, which means that the settling time can be effectively shortened.

[0088] (4) The pump controller 30 sets the volume target value q ref and the measured volume q p The volume deviation e, which is the deviation from the volume deviation e, is used as the evaluation value. With this configuration, the control input constraint can be appropriately changed in accordance with the change in the volume deviation e.

[0089] Note that, instead of the volume deviation e, the value of the evaluation function J(k) minimized to determine the control input u(k) may be used as the evaluation value used to change the control input constraint. The evaluation function J(k) includes the sum of squares of the deviations between the target volume value and the predicted volume value in a prediction interval of a predetermined time width. Therefore, even when the control input constraint is changed according to the value of the evaluation function J(k), the control input constraint can be appropriately changed. In this way, the volume deviation e or the value of the evaluation function may be used as the evaluation value. Therefore, in this embodiment, the degree of freedom in the configuration of the control system is high.

[0090] (5) The pump controller 30 calculates the actual volume q p and the control input u, and the prediction model (mathematical model) is updated. In this embodiment, when the characteristics of the prediction model change significantly, optimal parameter prediction values ​​are calculated to match the changed characteristics, and the prediction model for prediction is updated based on the parameter prediction values. This makes it possible to calculate a pump volume prediction value with higher accuracy using a prediction model that matches the actual characteristics. In this way, in this embodiment, by making the constraints on the control input u variable and updating the prediction model, it is possible to reduce the response time of the volume control of the main pump 10 compared to when the prediction model is not updated. As a result, it is possible to improve the work efficiency of the work machine.

[0091] Second Embodiment A pump system 100 according to a second embodiment of the present invention will be described with reference to Figures 8 to 10. Components that are the same as or equivalent to those described in the first embodiment are given the same reference symbols, and differences will be mainly described. In the first embodiment, an example was described in which only one deviation threshold value used to change the control input constraint is stored in the pump controller 30. In contrast, in this second embodiment, multiple deviation threshold values ​​used to change the control input constraint are stored in the pump controller 30. In other words, in the second embodiment, the control input constraint changes in multiple stages. This will be described in detail below.

[0092] Fig. 8 is a flowchart of model predictive control executed by the pump controller 30 according to the second embodiment, similar to Fig. 5. In the flowchart of Fig. 8, the processing of step S250 is executed instead of the processing of step S150 in the flowchart of Fig. 5. Note that the processing of steps S110 to S140, S160, and S170 is the same as in the first embodiment, and therefore description thereof will be omitted.

[0093] As shown in FIG. 8, in step S250, the pump controller 30 determines the control input constraint according to the magnitude of the volume deviation e.

[0094] In the second embodiment, the control input constraint is expressed by the following equation (8).

[0095]

number

[0096] Control input upper limit u max is the volume deviation e that is greater than the first deviation threshold e th1 If it is equal to or greater than the first upper limit value u max1 The volume deviation e is the first deviation threshold e th1 is smaller than the second deviation threshold e th2 If it is greater than the second upper limit u max2 The first upper limit value u max1 is the second current value I2 or more and the maximum current value I max The value may be within the following range. max1 The second upper limit value u is set within the dead band range in which the output pressure of the electromagnetic proportional pressure reducing valve 11 is maintained at the tank pressure Pt (constant value) even if the value of the electrical signal is changed. max2 is the first upper limit u max1 The upper limit of the control input, u max is the volume deviation e that is greater than the second deviation threshold e th2 If it is less than or equal to the third upper limit value u max3 The third upper limit u max3 is the second upper limit u max2 is a smaller value than

[0097] Control input lower limit u min is the volume deviation e that is greater than the first deviation threshold e th1 If it is equal to or greater than the first lower limit u min1 The volume deviation e is the first deviation threshold e th1 is smaller than the second deviation threshold e th2 If it is greater than the second lower limit u min2 The first lower limit u min1 is the minimum current value I min The value may be in the range of the first lower limit value u min1 The second lower limit value u is set within the dead band range in which the output pressure of the electromagnetic proportional pressure reducing valve 11 is maintained at the pilot primary pressure Pp (constant value) even if the value of the electrical signal is changed. min2 is the first lower limit u min1 The lower limit of the control input, u min is the volume deviation e that is greater than the second deviation threshold e th2 If it is less than or equal to the third lower limit u min3 The third lower limit u min3 is the second lower limit u min2 is a value greater than

[0098] In this way, the pump controller 30 of the second embodiment has an upper limit value u max Two deviation thresholds e used to change th1 ,e th2 is stored. Upper limit value u max The first upper limit value u is set according to the magnitude of the volume deviation e. max1 , the second upper limit u max2 , the third upper limit u max3 Similarly, the pump controller 30 of the second embodiment has a lower limit value u min Two deviation thresholds e used to change th1 ,e th2 is stored. Lower limit value u min The first lower limit value u is set according to the magnitude of the volume deviation e. min1 , the second lower limit u min2 , the third lower limit u min3 It is set to one of three values:

[0099] FIG. 9 is a diagram similar to FIG. 6, and shows the control input constraint (upper limit value u max and the lower limit u min ) is a time series waveform diagram of the volume target value q ref When is changed, the actual volume q p is the volume target value q ref As a result, the volume deviation e becomes smaller. From time t21 to time t22, the volume deviation e becomes smaller than the first deviation threshold value e th1 Therefore, the upper limit value of the control input u max is the first upper limit u max1 and the lower limit of the control input u min is the first lower limit u min1 From time t22 to time t23, the volume deviation e is equal to or smaller than the first deviation threshold e th1 is smaller than the second deviation threshold e th2 Therefore, the upper limit of the control input u max After a predetermined time has elapsed since time t22, the second upper limit value u max2 and the lower limit of the control input u min After a predetermined time has elapsed since time t22, the second lower limit value u min2 From time t23 to time t24, the volume deviation e is equal to or less than the second deviation threshold e th2 Therefore, the upper limit of the control input u max After a predetermined time has elapsed since time t23, the third upper limit value u max3 and the lower limit of the control input u min After a predetermined time has elapsed since time t23, the third lower limit value u min3 This becomes:

[0100] After that, the volume deviation e increases. From time t24 to time t25, the volume deviation e reaches the second deviation threshold e th2 greater than the first deviation threshold e th1 Therefore, the upper limit of the control input u max After a predetermined time has elapsed since time t24, the second upper limit value u max2 and the lower limit of the control input u min After a predetermined time has elapsed since time t24, the second lower limit value u min2From time t25 to time t26, the volume deviation e is equal to or smaller than the first deviation threshold e th1 Therefore, the upper limit value of the control input u max After a predetermined time has elapsed since time t25, the first upper limit value u max1 and the lower limit of the control input u min is the first lower limit value u after a predetermined time has elapsed since time t25. min1 This becomes:

[0101] After that, the volume deviation e decreases again. From time t26 to time t27, the volume deviation e becomes equal to or smaller than the first deviation threshold value e th1 is smaller than the second deviation threshold e th2 Therefore, the upper limit of the control input u max After a predetermined time has elapsed since time t26, the second upper limit value u max2 and the lower limit of the control input u min After a predetermined time has elapsed since time t26, the second lower limit value u min2 After time t27, the volume deviation e becomes equal to or exceeds the second deviation threshold e th2 Therefore, the upper limit of the control input u max After a predetermined time has elapsed since time t27, the third upper limit value u max3 and the lower limit of the control input u min After a predetermined time has elapsed since time t27, the third lower limit value u min3 This becomes:

[0102] The first deviation threshold e used as a condition for changing the control input constraint th1 and the second deviation threshold e th2 is the upper limit u max When changing the lower limit u min may be different values ​​when the value is changed.

[0103] In the second embodiment, similarly to the first embodiment, the control input constraint is prevented from immediately changing by delay processing due to a first-order lag. th1 The time constant τa used in the first-order delay process executed when the volume deviation e exceeds the second deviation threshold e (at times t22, t25, and t26) is th2The time constant τb used in the first-order lag processing executed when the time t23, t24, and t27 exceeds the predetermined value may be the same as or different from the time constant τb used in the first-order lag processing executed when the time t23, t24, and t27 exceed the predetermined value.

[0104] Fig. 10 is a diagram similar to Fig. 7, showing the change in volume over time of the pump system 100 according to the second embodiment. In Fig. 10, the change in volume over time of the second embodiment is indicated by a dotted line. In addition, to clarify the effects of the second embodiment, the change in volume over time of the first embodiment is indicated by a dashed line.

[0105] In the second embodiment, the amount of undershoot is smaller than in the first embodiment. Furthermore, the amplitude of vibration after the occurrence of undershoot is also smaller. As a result, the settling time Δt2 in the second embodiment is shorter than the settling time Δt1 in the first embodiment.

[0106] In this way, in the second embodiment, the pump controller 30 has a plurality of thresholds (deviation thresholds e) for the evaluation value (volume deviation e). th1 ,e th2 ) is stored. This configuration can further improve the responsiveness of the displacement control of the main pump 10. Therefore, according to the second embodiment, it is possible to further improve the workability. As in the first embodiment, in the second embodiment, the prediction model is updated by the recursive least squares method, thereby further improving the accuracy of the predictive control.

[0107] -Modification of the second embodiment- In the second embodiment, the second upper limit value u max2 and the third upper limit u max3 The magnitude relationship of is reversed, and the second lower limit u min2 and the third lower limit u min3 The magnitude relationship of u can be reversed. max2 max3 ,u min3 min2 ​​11 is a diagram similar to FIG. 10, showing the change in volume over time of the pump system 100 according to the modified example of the second embodiment. In FIG. 11, the change in volume over time of the modified example of the second embodiment is indicated by a dotted line. In addition, to clarify the effects of the modified example of the second embodiment, the change in volume over time of the first embodiment is indicated by a dashed line.

[0108] In the modified example of the second embodiment, the amount of undershoot is smaller than in the first embodiment. Also, the amplitude of vibration after the occurrence of undershoot is smaller. As a result, the settling time Δt2' in the modified example of the second embodiment is shorter than the settling time Δt1 in the first embodiment.

[0109] Thus, according to the modification of the second embodiment, similarly to the second embodiment, the responsiveness of the displacement control of the main pump 10 can be further improved.

[0110] Another modification of the second embodiment The pump controller 30 according to the second embodiment has two deviation thresholds e th1 ,e th2 In contrast to this, the pump controller 30 may change the control input constraints using three or more deviation thresholds. In this case, three or more time constants τ in the first-order lag processing may also be used.

[0111] <Third embodiment> A pump system 100 according to a third embodiment of the present invention will be described with reference to Figures 12 and 13. Components that are the same as or equivalent to those described in the first embodiment are given the same reference symbols, and differences will be mainly described. In the first embodiment, an example was described in which the time-varying characteristics of the control input constraints are a first-order lag system. In contrast, in this third embodiment, delay processing is not performed when changing the control input constraints. Instead of delay processing, a constraint characteristics table is used to continuously change the control input constraints in response to changes in the deviation threshold.

[0112] Fig. 12 is a flowchart of model predictive control executed by the pump controller 30 according to the third embodiment, similar to Fig. 5. In the flowchart of Fig. 12, the process of step S350 is executed instead of the process of step S150 in the flowchart of Fig. 5. Note that the processes of steps S110 to S140, S160, and S170 are the same as those in the first embodiment, and therefore will not be described again.

[0113] 12, in step S350, the pump controller 30 determines the control input constraints according to the magnitude of the volume deviation e. In the third embodiment, when determining the control input constraints, constraint tables 301 and 302 that define the relationship between the volume deviation e and the control input constraints are used.

[0114] The constraint tables 301 and 302 are stored in the nonvolatile memory of the pump controller 30. The constraint tables 301 and 302 contain an upper limit value u that continuously changes with respect to the volume deviation e. max and a constraint table 301 for upper limit values ​​(hereinafter also referred to as upper limit value table) that defines the characteristics of the volume deviation e. min and a constraint table 302 for lower limits (hereinafter also referred to as a lower limit table) that defines the characteristics of the above.

[0115] The volume deviation e and upper limit value u specified in the upper limit value table 301 max The relationship between the volume deviation e and the first deviation threshold e is as follows: th1 Above this, the upper limit value u max is the first upper limit u max1 The volume deviation e is equal to the second deviation threshold e th2 In the following, the upper limit u max is the second upper limit u max2 The volume deviation e is equal to the first deviation threshold e th1 to the second deviation threshold e th2 In the range up to , the upper limit value u becomes smaller as the volume deviation e becomes smaller. max becomes smaller.

[0116] The volume deviation e and the lower limit value u specified in the lower limit value table 302 minThe relationship between the volume deviation e and the first deviation threshold e is as follows: th1 Above this, the lower limit u min is the first lower limit u min1 The volume deviation e is equal to the second deviation threshold e th2 In the following, the lower limit u min is the second lower limit u min2 The volume deviation e is equal to the first deviation threshold e th1 to the second deviation threshold e th2 In the range up to the lower limit u, as the volumetric deviation e becomes smaller, min becomes larger.

[0117] 12 shows an example in which the constraint tables 301 and 302 store characteristics in which the control input constraints change linearly in response to changes in the volumetric deviation e. However, the characteristics stored in the constraint tables are not limited to linear characteristics, and may be nonlinear characteristics such as quadratic and cubic curves.

[0118] In step S350, the pump controller 30 refers to the upper limit value table 301 and determines the upper limit value u based on the volume deviation e. max Furthermore, the pump controller 30 refers to the lower limit value table 302 and sets the lower limit value u based on the volume deviation e. min Set.

[0119] Fig. 13 is a diagram similar to Fig. 7, showing the change in volume over time of the pump system 100 according to the third embodiment. In Fig. 13, the change in volume over time of the third embodiment is indicated by a dashed line. In addition, to clarify the effects of the third embodiment, the change in volume over time of the first embodiment is indicated by a dashed line.

[0120] In the third embodiment, the amount of undershoot is smaller than in the first and second embodiments. Furthermore, the amplitude of vibration after undershoot is also smaller. As a result, the settling time Δt3 in the third embodiment is shorter than the settling time Δt1 in the first embodiment and the settling time Δt2 in the second embodiment.

[0121] In this way, in the third embodiment, the constraint tables 301 and 302 that define the characteristics of the constraints on the control inputs that change continuously with respect to the evaluation value (volume deviation e) are stored in the pump controller 30. The pump controller 30 refers to the constraint tables 301 and 302, and determines the value of the constraints on the control inputs (upper limit value u) based on the evaluation value (volume deviation e). max and the lower limit u min ) is set. This configuration can further improve the responsiveness of the displacement control of the main pump 10. Therefore, according to the third embodiment, it is possible to further improve the workability. As in the first embodiment, in the third embodiment, the prediction model is updated by the recursive least squares method, thereby further improving the accuracy of the predictive control.

[0122] The following modified examples are also within the scope of the present invention, and it is possible to combine the configuration shown in the modified example with the configuration described in the above embodiment, to combine the configurations described in the different embodiments above, or to combine the configurations described in the different modified examples below.

[0123] <Variation 1> In the above embodiment, an example has been described in which the control input u is a control current (excitation current) supplied to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11. However, the control input u may be a voltage that controls the excitation current supplied to the solenoid 11d of the electromagnetic proportional pressure reducing valve 11.

[0124] <Variation 2> In the above embodiment, an example has been described in which the pilot pump 18 is provided as a pilot hydraulic source that supplies pressure to the electromagnetic proportional pressure reducing valve 11. However, the discharge pressure of the main pump 10 may be reduced by a pressure reducing valve and supplied to the electromagnetic proportional pressure reducing valve 11. In other words, the control pressure that controls the volume of the main pump 10 may be generated by the pressure of the hydraulic oil discharged from the main pump 10 itself.

[0125] <Variation 3> In the above embodiment, the pump controller 30 adjusts the upper limit value u of the control input in accordance with the evaluation value.max and the lower limit u min However, the present invention is not limited to this. The pump controller 30 changes the upper limit value u of the control input in accordance with the evaluation value. max and the lower limit u min In other words, the pump controller 30 may change only one of the upper limit value u of the control input in accordance with the evaluation value. max and the lower limit u min It is sufficient that at least one of the above is changed.

[0126] <Variation 4> In the above embodiment, an example has been described in which the control valve 16 is provided between the main pump 10 and the hydraulic actuator 17. However, the present invention may be applied to a hydraulic system in which the main pump 10 and the hydraulic actuator 17 are connected in a closed circuit without providing the control valve 16. In this configuration, the responsiveness of the displacement control of the main pump 10 becomes more important. Therefore, the effects of the present invention are more pronounced.

[0127] <Variation 5> In the above embodiment, an example has been described in which the work machine is a hydraulic excavator. However, the work machine is not limited to a hydraulic excavator and may be a wheel loader, road construction equipment, or the like.

[0128] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments. [Explanation of symbols]

[0129] 9...tilting actuator, 9a...cylinder chamber, 9b...servo piston, 9c...pressure receiving chamber, 9d...pressure receiving chamber (control pressure chamber), 10...main pump (variable displacement type hydraulic pump), 11...electromagnetic proportional pressure reducing valve, 13...position sensor (volume sensor), 17...hydraulic actuator, 18...pilot pump (pilot hydraulic source), 19...engine (prime mover), 20...volume control device, 30...pump controller (controller), 31...model predictive control section, 32...predictor, 33...recursive least squares method solver, 39...controlled object (plant), 40...vehicle controller, 100...pump system, 301...upper limit value table (constraint table), 302...lower limit value table (constraint table), A...system matrix, B...control input vector, C...output vector, e...volume deviation (deviation between volume target value and volume actual measurement value), e th ...Deviation threshold (threshold for evaluation value, threshold for lower limit value, threshold for upper limit value), e th1 ...First deviation threshold (threshold for evaluation value), e th2 ...second deviation threshold (threshold for evaluation value), q p …actual volume, q p ^…volume prediction value, q ref …Volume target value, u…Control input, u max …upper limit of control input (control input constraint value), u max1 …first upper limit, u max2 …second upper limit, u max3 …Third upper limit, u min …lower limit of control input (control input constraint value), u min1 …first lower limit, u min2 …second lower limit, u min3 ...Third lower limit, x...State vector, Δt0~Δt3...Settling time, ε...Prediction error, θ...Parameter prediction value

Claims

1. a hydraulic pump that is rotationally driven by a prime mover and supplies hydraulic oil to the hydraulic actuator; a displacement control device that controls the displacement of the hydraulic pump in response to a control input; a volume sensor for detecting an actual volume measurement value of the hydraulic pump; a controller that acquires a volume target value of the hydraulic pump and outputs the control input corresponding to the volume target value to the volume control device, The controller stores a mathematical model for predicting the displacement of the hydraulic pump; The controller using the mathematical model to calculate a predicted displacement value for the hydraulic pump; calculating an optimal control input based on the volume prediction value and the control input constraints; calculating an evaluation value based on the target volume value and the actual volume measurement value; Changing the constraint on the control input in accordance with the evaluation value A control device for a work machine.

2. The control device for a work machine according to claim 1, a threshold value for the evaluation value is stored in the controller; The controller setting a value of the constraint on the control input in accordance with the magnitude relationship between the evaluation value and the threshold value; The time-varying characteristics of the control input constraints are set as a first-order lag system. A control device for a work machine.

3. The control device for a work machine according to claim 1, the controller stores a constraint table that defines characteristics of constraints on the control input that continuously change with respect to the evaluation value; The controller The constraint table is referenced, and a value of the constraint on the control input is set based on the evaluation value. A control device for a work machine.

4. The control device for a work machine according to claim 1, The controller uses the deviation between the target volume value and the actual volume value as the evaluation value. A control device for a work machine.

5. The control device for a work machine according to claim 1, The controller calculating the control input so as to minimize an evaluation function including a sum of squares of deviations between the volume target value and the volume predicted value in a prediction interval having a predetermined time width; The value of the evaluation function is used as the evaluation value. A control device for a work machine.

6. The control device for a work machine according to claim 1, the constraints on the control input include upper and lower limits on the control input; The controller When the evaluation value is equal to or greater than a threshold for an upper limit value, the upper limit value is set to a first upper limit value; When the evaluation value is less than the upper limit threshold, the upper limit is set to a second upper limit that is smaller than the first upper limit; If the evaluation value is equal to or greater than a lower limit threshold, the lower limit is set to a first lower limit; When the evaluation value is less than the lower limit threshold, the lower limit is set to a second lower limit that is greater than the first lower limit. A control device for a work machine.

7. The control device for a work machine according to claim 1, The controller updates the mathematical model using the actual volume measurements and the control inputs. A control device for a work machine.

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