JP7313633B2 - Position control device and position control method - Google Patents

Description

The present invention relates to a position control device and a position control method.

2. Description of the Related Art In machines such as excavators driven by hydraulic actuators, control methods have been developed for automatically moving buckets, working equipment, etc. to target positions. The response characteristics of hydraulic actuators, including hydraulic actuators, have strong non-linearity and change greatly depending on whether the relief valve is opened or closed. Therefore, it is difficult to realize automatic positioning control with a simple control law.

For example, the methods of Non-Patent Documents 1 and 2 have been proposed as control methods based on standard linear control theory. Since the methods of Non-Patent Documents 1 and 2 are based on linear approximation of actuator dynamic characteristics, it is difficult to perform appropriate operations when the reference position and the target position are greatly separated.

In order to perform appropriate control even when the reference position and the target position are greatly separated, a method has been developed in which a temporary target position is set near the current position and the original target position is reached while the reference position is changed smoothly over time (for example, Patent Document 1).

In addition, a method of switching the control law depending on whether the difference between the target position and the current position is large or small (for example, Non-Patent Document 3), a method of switching the control law by opening and closing a relief valve (for example, Non-Patent Document 4), etc. have been proposed.

In addition, as in Non-Patent Document 5, a method is proposed in which a nonlinear dynamic characteristic model of an actuator is used to find an optimum control input for realizing a desired speed by convergence calculation.

JP 2019-19567 A

Yaoyao Wang, Linyi Gu, Bai Chen, Hongtao Wu, “A new discrete time delay control of hydraulic manipulators”, Proceedings of Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering, Vol.231, No.3, p.168-177, 2017 Navit Niksefat, Nariman Sepehri, “A QFT fault-tolerant control for electrohydraulic positioning systems”, IEEE Transactions on Control Systems Technology, Vol.10, No.4, p.626-632, 2002 Jianpeng Shi, Long Quan, Xiaogang Zhang, Xiaoyan Xiong, “Electro-hydraulic velocity and position control based on independent metering valve control in mobile construction equipment”, Automation in Construction, Vol.94, p.73-84, 2018 Kazushige Koiwai, Shinya Hama Naga, Toru Yamamoto, Takao Nanjo, Yoichiro Yamazaki, "Event-Driven Torque Control for Hydraulic Excavators", Transactions of the Society of Instrument and Control Engineers, Vol.54, No.2, p.261-268, 2018 Kwangmin Kim, Minji Kim, Dongmok Kim, Dongjun Lee, “Modeling and velocity-field control of autonomous excavator with main control valve”, Automatica, Vol.104, p.67-81, 2019

In the control method of Patent Document 1, it is necessary to generate reference position data in advance as time-series data in order to set a reference position that changes with time. Therefore, when the target position changes moment by moment, it is difficult to deal with cases such as when the current position deviates greatly from the reference position due to disturbance.

In addition, the method of switching the control law depending on the situation, as in Non-Patent Documents 3 and 4, complicates the structure of the controller and requires careful setting of control parameters so that discontinuity does not occur before and after switching, which makes design difficult.

Further, in the method of using the non-linear dynamic characteristic model of the actuator as it is, as in Non-Patent Document 5, complicated convergence calculations are performed, resulting in an increase in calculation cost.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a position control apparatus and a position control method using a simple control algorithm, which can cope with changes in the target position and deviations in the trajectory due to disturbances, and can perform position control with a low calculation cost.

In order to achieve the above object, a position control device according to a first aspect of the present invention includes:
Equipped with a control unit that controls a hydraulic actuator that drives the machine to be controlled,
The control unit
calculating a reference speed, which is the target speed of the next time step of the machine, based on at least one of the target position and the target speed of the machine and at least one of the current position and the current speed;
saturating the reference speed so that it falls within a achievable range at the next time step based on the dynamic characteristics of the machine, the maximum allowable force generated by the hydraulic actuator, and the current speed;
A manipulated variable of the hydraulic actuator is calculated based on the quasi-static characteristics of the hydraulic actuator, the dynamic characteristics of the machine, the saturated reference speed and the current speed.

Also, the position control device according to the second aspect of the present invention includes:
Equipped with a control unit that controls a hydraulic actuator that drives the machine to be controlled,
The control unit
calculating a predicted position and a predicted speed of the machine at a time step ahead of a predetermined step based on the quasi-static characteristics of the hydraulic actuator and the dynamic characteristics of the machine;
calculating a reference speed, which is the target speed of the next time step ahead of the predetermined step, based on at least one of the target position and the target speed of the machine and at least one of the predicted position and the predicted speed;
saturating the reference speed so that it falls within a achievable range at a time step next to the time step after the predetermined step, based on the dynamic characteristics of the machine, the maximum allowable force generated by the hydraulic actuator, and the predicted speed;
A manipulated variable of the hydraulic actuator is calculated based on the quasi-static characteristics of the hydraulic actuator, the dynamic characteristics of the machine, the saturated reference velocity and the predicted velocity.

Further, comprising a plurality of hydraulic actuators,
The control unit calculates and controls the operation amount for each of the hydraulic actuators, thereby moving a predetermined portion of the machine to a target position.
You can do it.

Further, the hydraulic actuator is a hydraulic actuator,
You can do it.

A position control method according to a third aspect of the present invention includes:
a reference speed calculation step of calculating a reference speed, which is a target speed of the machine for the next time step, based on at least one of a target position and a target speed and at least one of the current position and current speed of a machine to be controlled driven by a hydraulic actuator;
a reference speed correction step of saturating the reference speed so that it falls within a realizable range at the next time step based on the dynamic characteristics of the machine, the maximum allowable force generated by the hydraulic actuator, and the current speed;
a manipulated variable calculation step of calculating a manipulated variable of the hydraulic actuator based on the quasi-static characteristics of the hydraulic actuator, the dynamic characteristics of the controlled object, the saturated reference speed, and the current speed.

According to the position control device and the position control method of the present invention, position control is performed by calculating the manipulated variable using the quasi-static characteristics of the hydraulic actuator, the dynamic characteristics of the machine, and the realizable reference speed, so the position control can be performed with a simple control algorithm. Further, the position control device and the position control method of the present invention are capable of coping with changes in the target position and trajectory deviations due to disturbances, and position control can be performed at low computational costs.

BRIEF DESCRIPTION OF THE DRAWINGS It is a side view which shows the outline|summary of the excavator which concerns on Embodiment 1 of this invention. 1 is a block diagram showing the configuration of a control system according to Embodiment 1; FIG. FIG. 4 is a conceptual diagram showing a method of controlling a plurality of hydraulic actuators; 4 is a flow chart showing the flow of position control according to Embodiment 1. FIG. 9 is a graph showing simulation results by a control algorithm according to Embodiment 2; It is a block diagram which shows the structural example of an n step predictor.

(Embodiment 1)
A position control device and a position control method according to embodiments of the present invention will be described below with reference to the drawings.

(control algorithm)
First, the control law according to the present embodiment, that is, the control algorithm for determining the manipulated variable u of the hydraulic actuator when a machine driven by a hydraulic actuator is the controlled object and the controlled object is moved to a target position will be described.

Specifically, consider the system shown below.
where M is the mass, p is the displacement, τ is the force generated by the hydraulic actuator, and f represents all other forces. Equations (1a) and (1b) represent the dynamics model of the machine.

Equation (1c) represents a quasi-static characteristic model of the hydraulic actuator. Here, the quasi-static characteristic model in the present invention refers to a characteristic model represented by a relational expression between velocity and reaction force when a constant external force and steady velocity are assumed. The manipulated variable u is a command value of the valve opening to the hydraulic actuator. From the equilibrium relationship between the flow rate and pressure of the liquid in the hydraulic actuator, the generated force τ, the velocity v and the manipulated variable u of the hydraulic actuator approximately satisfy the expression (1c). The constant C is a coefficient due to the valve and indicates the relationship between the pressure difference and the flow rate. The constant F is the maximum force generated by the cylinder of the hydraulic actuator. When the force τ generated by the hydraulic actuator exceeds the maximum force F, the relief valve opens to saturate the force τ. The constant _Fm is the maximum force generated by the cylinder of the hydraulic actuator assuming the relief valve does not open. Normally, F _m ≧F, but F _m =F may be used.

(1) Mathematical Preparation If C>0, F _m >F, Fε(0, F _m ], ε>0, vεR, and v _a εR, then the following equations are equivalent to each other (Theorem 1).

(2) Controller Next, a general expression of the control algorithm according to this embodiment will be described. To create a controller for the system described in equations (1a)-(1c) above, a nominal model of the plant is constructed. In the discrete-time domain, the nominal model of the plant can be written as
where the hated symbol represents the nominal or estimated value of the relevant unknown quantity, k is the discrete-time index, and ^ _fk is the estimate of the external force on the machine. Let T be the sampling interval of the controller.

Theorem 1 above shows that equation (7) can be equivalently rewritten as equation (8) below.

Equation (8) means that if |v ^* _k+1 −v _k −T̂f _k /̂M|<T̂F/̂M is satisfied for a desired velocity v ^* _{k+1 to} be achieved at a certain next time step, the manipulated variable u _k can be obtained using the following formula.

Therefore, consider a controller that gives the desired velocity v ^* _k+1 to equation (9). If the mass is ^M and the maximum force of the hydraulic actuator is ^F, bang-bang control is considered to be suitable in terms of achieving the minimum arrival time under the constraint of the force generated by the hydraulic actuator. Assuming that the mass estimate ̂M and the position p are available, bang-bang control can be achieved by the following control law.

where _pd is the target position. This control law can be regarded as a kind of sliding mode control law.

Applying this controller to the nominal plant results in the following system.

By discretizing equations (11) and (12) using the implicit Euler method, it can be expressed in the following closed form.

Here, the value of vk ₊₁ can be regarded as the predicted speed of the next time step that can be realized by bang-bang control. By combining this value with equation (9), the following control algorithm is obtained as a controller similar to bang-bang control.

By rearranging equations (16) to (18), the following equations are obtained as a finite-time convergence type control algorithm according to the present embodiment.
Here, A is the target acceleration of the convergence motion to the target position, and is preferably set as A=̂F/̂M. Here, ^C is the nominal value (estimated value) of the characteristic value C of the actuator, but it can be selected as a value approximating the value obtained by dividing the steady speed at the maximum input by ^F.

In the above control algorithm, v ^* _k+1 and ^v ^* _k+1 are temporary values that do not need to be stored continuously in the controller. Position p _k and velocity v _k are the actual values measured by the sensors. Also, the force ^ _fk is an estimated value estimated from some sensor information. If the force ^ _fk cannot be estimated, then ^ _fk = 0 may be set.

Also, if ^F _m = ^F in equation (21), the number in the sat function can be infinite. To avoid this, the following equation (22) may be used instead of equation (21).

Here, ε may be a very small value, for example, a very small value compared to the minimum absolute value of detectable velocity.

In the control algorithm according to the present embodiment, as the reference speed calculation step, the reference speed ^v ^* _k+1, which is the target speed for the next time step, is obtained from the target position _pd,k and the current position _pk using equation (19). Subsequently, in the reference speed correction step, using equation (20), the reference speed ^v ^* _k+1 calculated in the reference speed calculation step and the current speed _vk are used to calculate the reference speed corrected based on the maximum allowable force generated by the hydraulic actuator, that is, the desired speed v ^* _k+1 that falls within the realizable range at the next time step. Then, in the manipulated variable calculation step, the manipulated variable _uk of the hydraulic actuator is calculated from the reference speed v ^* _k+1 calculated in the reference speed correction step and the current speed _vk using equation (21).

As described above, the control algorithm according to the present embodiment is derived by combining three equations as simultaneous equations: the simple dynamic characteristics of a machine driven by a hydraulic actuator, the quasi-static characteristics of the hydraulic actuator, and a certain type of sliding mode control law. Since this control algorithm does not require time-series data to be given in advance, it is possible to cope with situations such as when the target position changes moment by moment, or when the trajectory deviates greatly due to an unexpected disturbance.

The quasi-static characteristic model of the hydraulic actuator, which is the basis for the derivation of the control algorithm, integrates and describes the opening and closing of the relief valve. As a result, the resulting calculation formula has a simple structure that does not involve case division. Therefore, the calculation can be simplified in a system in which the relief valve is frequently operated, such as swing motion control of construction machinery. Also, since each step of the control algorithm does not include complicated convergence calculations, the calculation cost can be reduced.

(Configuration of control system)
In the present embodiment, as an example of a specific configuration of a control system, a case of performing position control of a bucket of an excavator driven by a plurality of hydraulic actuators will be described.

A control unit 30, which is a position control device according to the present embodiment, is mounted on the excavator 1 shown in FIG.

The excavator 1 includes a lower travel body 11 , an upper revolving body 12 and a working device 20 . The lower running body 11 is a part for running the excavator 1, and is, for example, a crawler. The upper rotating body 12 is attached to the lower traveling body 11 via a rotating motor 27 so as to be able to rotate. The swing motor 27 is connected to the lower traveling body 11 and the upper swing body 12 to rotate the upper swing body 12 . The upper revolving body 12 is provided with an operator's cab where the operator operates the excavator 1, a working device 20, and the like.

The work device 20 includes a boom 21 rotatably attached to the upper revolving body 12, an arm 22 rotatably attached to the boom 21, and a bucket 23 rotatably attached to the arm 22 for excavation or the like.

The work device 20 also includes a boom cylinder 24 connected to the upper revolving body 12 and the boom 21 to operate the boom 21, an arm cylinder 25 connected to the boom 21 and the arm 22 to operate the arm 22, and a bucket cylinder 26 connected to the arm 22 and the bucket 23 to operate the bucket 23. The boom cylinder 24, the arm cylinder 25, the bucket cylinder 26, and the swing motor 27 (hereinafter also referred to as actuators 24 to 27) are hydraulic actuators driven by hydraulic pressure.

The control unit 30 is mounted on the excavator 1, and includes a control section 31, a storage section 32, a display section 33, and an input section 34, as shown in the block diagram of FIG. The control unit 30 is connected to the position sensor 28, the speed sensor 29, the actuators 24 to 27, etc., and controls the operation of each part of the excavator 1. FIG.

The control unit 31 is a computer device including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a crystal oscillator, etc., and controls the operation of the excavator 1 . The control unit 31 reads various operation programs and data stored in the ROM of the control unit 31, the storage unit 32, etc. into the RAM and operates the CPU, thereby realizing each function as the control unit 31 shown in FIG. Thereby, the control unit 31 operates as a calculation unit 311 and an operation control unit 312 .

The calculation unit 311 calculates an operation amount u of each of the actuators 24 to 27 for operating the work device 20 based on the measured values output from the position sensor 28 and the speed sensor 29 and the target position of the bucket 23, more specifically, the target position of the tip of the bucket 23 (hereinafter referred to as the bucket tip 23a), which is a predetermined portion of the excavator 1.

The motion control unit 312 controls the actuators 24 to 27 based on the operation amount u calculated by the calculation unit 311 to operate the upper rotating body 12, the boom 21, the arm 22, and the bucket 23.

The storage unit 32 is a non-volatile memory such as a hard disk or flash memory, and stores parameters representing dynamic characteristics of the excavator 1, a control algorithm for calculating the operation amount u, and the like. The dynamic characteristics of the excavator 1 according to the present embodiment are simplified and are expressed as the dynamic characteristics of a mass point or rigid body that moves under force.

The display unit 33 is a display device such as a liquid crystal panel or organic EL (Electroluminescence), and displays various setting parameters, detection values of the position sensor 28 and the speed sensor 29, and the like. The display unit 33 according to this embodiment is a liquid crystal panel installed in the operator's cab of the excavator 1 .

The input unit 34 is an input device for inputting various setting parameters for operating the excavator 1, such as the target position of the bucket tip 23a. The input unit 34 is, for example, a touch panel arranged on the display unit 33 .

The position sensor 28 is a sensor that detects the position of the work device 20 of the excavator 1 to be controlled, and the position sensor 28 according to the present embodiment includes a swing angle sensor 284 that detects the angle of the upper swing body 12, a boom angle sensor 281 that detects the boom angle, an arm angle sensor 282 that detects the arm angle, and a bucket angle sensor 283 that detects the bucket angle. The control unit 31 calculates the length of the boom cylinder 24, the arm cylinder 25, and the bucket cylinder 26 (hereinafter also referred to as cylinders 24 to 26) and the angle of the swing motor 27 from the angles of each part detected by the boom angle sensor 281, the arm angle sensor 282, the bucket angle sensor 283, and the swing angle sensor 284, and controls the position of the bucket tip 23a based on the calculated lengths of the cylinders 24 to 26 and the angle of the swing motor 27.

The speed sensor 29 is a sensor that detects the speed of each part of the work device 20. The speed sensor 29 according to the present embodiment includes a turning angular speed sensor 294 that detects the angular speed of the upper swing body 12, a boom speed sensor 291 that detects the telescopic speed of the boom cylinder, an arm speed sensor 292 that detects the telescopic speed of the arm cylinder, and a bucket speed sensor 293 that detects the telescopic speed of the bucket cylinder.

Position control processing of the bucket tip 23a by the control unit 30 according to the present embodiment will be described below. As shown in the block diagram of FIG. 3, a control algorithm for calculating the manipulated variable u of each cylinder 24 to 26, which is a hydraulic actuator, will be described as an example. It should be noted that although only the cylinders 24 to 26 are used in the following embodiment, the present invention is not limited to this. The coordinates of the target position _pd may be used to configure a controller that adds the swing angle of the upper swing body 12 to control the position of the bucket tip 23a. More specifically, as shown in FIG. 2, a swing angle sensor 284 as the position sensor 28 and a swing angular velocity sensor 294 as the speed sensor 29 may be used to operate the swing motor 27, which is a hydraulic actuator, to perform position control of the bucket tip 23a in combination with the operations of the boom 21, the arm 22, and the bucket 23.

In the control algorithm of the present invention, the control unit 31 calculates the operation amount u of each cylinder 24 to 26 based on the given target position, desired behavior, current position, current speed, and the like of the object to be controlled. The desired behavior is, for example, the time constant of the convergence motion of the controlled object to the target position.

(control flow)
The flow of position control of the bucket tip 23a of the excavator 1 will be specifically described with reference to the flowchart of FIG.

The operator of the excavator 1 inputs and sets the target position _pd of the bucket tip 23a from the input unit 34 (step S11). The target position _pd may be input by inputting coordinates on the input unit 34, which is a touch panel, or by setting the coordinates of the bucket tip 23a manually moved using the operation lever as the target position _pd . The target position _pd may be set by reading the coordinates on the design plane stored in advance in the storage unit 32 .

Also, the operator inputs and sets parameters such as a time constant H representing a desired behavior. These parameters may be set by reading values stored in advance in the storage unit 32 .

The control unit 31 calculates the target length of each of the cylinders 24 to 26 at the target position _pd from the input target position _pd by inverse kinematics (step S12). Then, as shown in FIG. 3, the position of the bucket tip 23a is controlled by controlling the expansion and contraction of the cylinders 24 to 26 so that the lengths of the cylinders 24 to 26 become the respective target lengths.

As a reference speed calculation step, the control unit 31 calculates the reference speed ^v ^* _k+1 of the next time step (step S13). More specifically, the control unit 31 acquires angle data of each part of the work device 20 from the boom angle sensor 281, the arm angle sensor 282, and the bucket angle sensor 283 (hereinafter also referred to as angle sensors 281 to 283). The calculation unit 311 calculates the current position _pk , which is the length of each of the cylinders 24-26, based on the obtained angle data. The control unit 31 calculates the reference speed ^v ^* _k+1 of each cylinder 24 to 26 based on the calculated current position p _k (m), the set target position p _d,k (m), the control period T (s), and equation (19). The control period is not particularly limited, but is, for example, 10 msec.

Subsequently, the control unit 31 corrects the reference speed ^v ^* _k+1 for the next time step as a reference speed correction step (step S14). Specifically, the control unit 31 acquires the current speed _vk of each of the cylinders 24 to 26 from the boom speed sensor 291, the arm speed sensor 292, and the bucket speed sensor 293. The calculation unit 311 calculates the corrected reference speed v*k+1 for each of the cylinders 24 to 26 based on the obtained current speed _vk (m/s), the reference speed ^ ^{v *} _{k+1 calculated} in the reference speed calculation step of step S13, and the equation (20).

Subsequently, the control unit 31 calculates the manipulated variable _uk of each of the cylinders 24 to 26 as the manipulated variable calculation step (step S15). Specifically, the calculation unit 311 calculates the manipulated variable u _k based on the current speed v _k (m/s), the reference speed v ^* _k+1 calculated in the reference speed correction step of step S14, and equation (21).

The operation control unit 312 of the control unit 31 outputs the calculated operation amount _uk to the cylinders 24 to 26 to operate the boom 21, the arm 22 and the bucket 23 to move the bucket tip 23a (step S16).

When the next time step is reached, the control unit 31 newly acquires the current positions p _k of the cylinders 24 to 26 from the position sensor 28 . If the difference between the acquired current position p _k and the target position p _d,k is equal to or less than a preset value (YES in step S17), the control unit 31 terminates the position control.

If the difference between the obtained current position p _k and the target position p _d,k is larger than the preset value (NO in step S17), the control unit 31 returns to the reference speed calculation step in step S13. Then, the control unit 31 calculates the operation amount _uk at the time step according to the control algorithm, and moves the bucket tip 23a. By repeating this, the control unit 31 performs position control so that the position of the bucket tip 23a becomes the target position _pd .

As described above in detail, in the position control device and the position control method according to the present embodiment, position control is performed using a control algorithm including a reference speed calculation step, a reference speed correction step, and a manipulated variable calculation step created based on the dynamic characteristics of the machine to be controlled, the quasi-static characteristics of the hydraulic actuator, and the sliding mode control law. As a result, position control is performed by calculating the manipulated variable using the quasi-static characteristics of the hydraulic actuator, the dynamic characteristics of the machine, and the realizable reference speed, so the position control can be performed with a simple control algorithm that does not include cases.

Moreover, the position control device and the position control method according to the present embodiment do not require time-series data to be given in advance, so that it is possible to cope with changes in the target position and deviations in the trajectory due to disturbances. In addition, since the control algorithm according to the present invention does not include complicated convergence calculations, it is possible to perform position control with low calculation cost.

(Embodiment 2)
Although a finite time convergence type control algorithm such as bang-bang control is used in the first embodiment, the present invention is not limited to this, and other control algorithms can be used. In this embodiment, a control algorithm that achieves smooth exponential convergence to a target position will be described.

(control algorithm)
The asymptotic convergence type controller according to the present embodiment can be realized by the following control law.
where H is the convergence time constant. This control law can also be regarded as a kind of sliding mode control law, like the control law (equation (10)) according to the first embodiment.

Applying this controller to the nominal plant, it can be expressed as follows.

By discretizing equations (24) and (25) using the implicit Euler method, it can be expressed in the following closed form.

Here, the value of v _k+1 can be regarded as the expected velocity that can be achieved by the controller represented by equation (23). The following control algorithm is obtained as an asymptotic convergence type controller by combining this value with Equation (9).

Also, in equation (30), if F _m =F, then the number in the sat function can be infinite. To avoid this, equation (22) may be used instead of equation (30).

(Numerical simulation)
FIG. 5 is a graph showing the results of a numerical simulation performed using the asymptotic convergence control algorithm. In this simulation, consider a system in which a mass point of mass M=1.1×10 ³ kg is driven by a hydraulic cylinder. A physical model of the hydraulic cylinder is a quasi-static characteristic model represented by Equation (1C).

Here, the value of constant C representing the characteristics of the hydraulic cylinder is 2×10 ⁻⁵ m/(N·s), and the value of constants F and F _m representing the maximum thrust (maximum generated force) of the hydraulic cylinder is F=F _m =36×10 ³ N.

A periodic external force with a frequency of 1 Hz and an amplitude of 10×10 ³ N was continuously applied to the mass point M. Furthermore, an external force of 38×10 ³ N is applied in the negative direction during time t=2.0 to 3.0 s.

The controller parameters were H=1.0 s, ^M=1.0×10 ³ kg, ^C=3×10 ⁻⁵ m/(N·s), ^F=^F _m =40×10 ³ N. Ideally, the values of these parameters are selected so that ^M = M, ^C = C, ^F = F, and ^ _Fm = _Fm . However, since it is difficult to accurately know the values of M, C, F, and _Fm , which are the values to be controlled, they are intentionally set to have errors in this simulation.

FIG. 5 shows simulation results when the target position p _d =1 m. The graph of the position p shows the behavior of the mass point M toward the target position p _d =1 m, and it can be seen that it converges correctly after the large disturbance at time t=2.0 to 3.0 s is removed. Moreover, even when an error is set in the parameters of the controller and an unknown disturbance is added, the convergence is correct, and it can be seen that appropriate control is performed by the control algorithm according to the present invention. The force _fm generated by the actuator oscillates sinusoidally because the controller generates a force that resists the sinusoidal external force.

As described above, the asymptotic convergence type controller of the position control device and the position control method according to the present embodiment can perform position control with a simple control algorithm, can cope with changes in the target position and trajectory deviations due to disturbances, and can perform position control with a small calculation cost. In addition, the position of the controlled object can be controlled by a control algorithm that realizes smooth and exponential convergence.

In each of the above embodiments, the speed sensor 29 is used to measure the expansion and contraction speeds of the cylinders 24 to 26, but the present invention is not limited to this. For example, the calculation unit 311 may calculate the speed of each cylinder 24-26 based on the angle data measured by each of the angle sensors 281-283.

Further, in the above-described embodiments, either one of the finite time convergence control algorithm and the asymptotic convergence control algorithm is selected and applied as the control algorithm applied to each of the cylinders 24 to 26, but the present invention is not limited to this. For example, a finite time convergence control algorithm may be applied to the boom cylinder 24 and the arm cylinder 25, and an asymptotic convergence control algorithm may be applied to the bucket cylinder 26, or position control may be performed in combination with other control algorithms. Thereby, a control algorithm suitable for the dynamic characteristics of each part including the hydraulic actuator can be selected and applied to each hydraulic actuator.

In addition, neither the finite time convergence type control algorithm nor the asymptotic convergence type control algorithm according to the above embodiment does not use the current speed to calculate the reference speed, but it is also possible to obtain the reference speed by another algorithm that uses the current speed. That is, the reference speed may be calculated based on at least one of the target position and target speed of the machine and at least one of the current position and current speed.

Also, the parameter ̂M and the estimated external force ̂f of the dynamic model of the machine may change over time. For example, in the case of the motion control of the excavator in FIG. 1, since ^M is an inertia parameter, it changes according to the length of each cylinder 24-26 (angle of each joint of the excavator). In this case, ^M can be estimated from the nominal value at the time of design and angle information of each joint. Also, the estimated external force ^f can be estimated as the sum of the centrifugal force, the Coriolis force, the frictional force, etc. obtained from the measured values of the speed of each link and the nominal values at the time of design.

Generally, hydraulic systems have delays in response (dead time). Specifically, there is a dead time of about 0.01 to 0.1 seconds before the command value transmitted from the controller is reflected in the valve opening of the hydraulic actuator. In this case, by replacing the current position and current speed according to the above-described control algorithm with the predicted position and predicted speed at a time step ahead of a predetermined number of steps, it is possible to reduce the adverse effects of wasted time. The predicted position and predicted velocity can be obtained using a dynamic characteristic model of the machine (equations (1a) and (1b)) and a quasi-static characteristic model of the hydraulic actuator (equation (1c)).

An implementation using the predicted positions described above can be represented as in FIG. The predictor in FIG. 6 can be derived from equation (7) representing the plant nominal model. Equation (7) can be equivalently rewritten using Theorem 1 as follows.

Equation (31) above can be used as a predictor to predict the velocity v _k+1 one step ahead. Also, by substituting v _k+1 obtained by equation (31) into equation (15), it can be used as a predictor that predicts the position p _k+1 one step ahead. As shown in FIG. 6, by using n predictors connected in series, a predicted position and a predicted speed n steps ahead can be obtained. The n-step predictor in FIG. 6 can be represented by the algorithm shown below.

When it is estimated that a controlled object comprising a hydraulic actuator and a moving part driven by the hydraulic actuator includes n steps of dead time, the influence of the time delay can be reduced by using ^p and ^v obtained by the above algorithm in place of p _k and v _k in the control laws (28) to (30), respectively.

INDUSTRIAL APPLICABILITY The present invention is suitable for position control of machines operated by hydraulic actuators. In particular, it is suitable for automatic positioning control of construction machines operated by hydraulic actuators.

1 Excavator 11 Undercarriage 12 Upper Revolving Body 20 Work Device 21 Boom 22 Arm 23 Bucket 23a Bucket Tip 24 Boom Cylinder 25 Arm Cylinder 26 Bucket Cylinder 27 Revolving Motor 28 Position Sensor 281 Boom Angle Sensor 282 Arm Angle Sensor 283 Bucket Angle Sensor 284 Revolving Angle Sensor 29 Speed Sensor 291 Boom Speed Sensor 292 Arm speed sensor 293 Bucket speed sensor 294 Turning angular speed sensor 30 Control unit 31 Control unit 311 Calculation unit 312 Operation control unit 32 Storage unit 33 Display unit 34 Input unit

Claims (5)

Equipped with a control unit that controls a hydraulic actuator that drives the machine to be controlled,
The control unit
calculating a reference speed, which is the target speed of the next time step of the machine, based on at least one of the target position and the target speed of the machine and at least one of the current position and the current speed;
saturating the reference speed so that it falls within a achievable range at the next time step based on the dynamic characteristics of the machine, the maximum allowable force generated by the hydraulic actuator, and the current speed;
calculating an operation amount of the hydraulic actuator based on the quasi-static characteristics of the hydraulic actuator, the dynamic characteristics of the machine, the saturated reference speed and the current speed;
Position control device. Equipped with a control unit that controls a hydraulic actuator that drives the machine to be controlled,
The control unit
calculating a predicted position and a predicted speed of the machine at a time step ahead of a predetermined step based on the quasi-static characteristics of the hydraulic actuator and the dynamic characteristics of the machine;
calculating a reference speed, which is the target speed of the next time step ahead of the predetermined step, based on at least one of the target position and the target speed of the machine and at least one of the predicted position and the predicted speed;
saturating the reference speed so that it falls within a achievable range at a time step next to the time step after the predetermined step, based on the dynamic characteristics of the machine, the maximum allowable force generated by the hydraulic actuator, and the predicted speed;
calculating an operation amount of the hydraulic actuator based on the quasi-static characteristics of the hydraulic actuator, the dynamic characteristics of the machine, the saturated reference speed and the predicted speed;
Position control device. comprising a plurality of hydraulic actuators,
The control unit calculates and controls the operation amount for each of the hydraulic actuators, thereby moving a predetermined portion of the machine to a target position.
The position control device according to claim 1 or 2. wherein the hydraulic actuator is a hydraulic actuator,
The position control device according to any one of claims 1 to 3. a reference speed calculation step of calculating a reference speed, which is a target speed of the machine for the next time step, based on at least one of a target position and a target speed and at least one of the current position and current speed of a machine to be controlled driven by a hydraulic actuator;
a reference speed correction step of saturating the reference speed so that it falls within a realizable range at the next time step based on the dynamic characteristics of the machine, the maximum allowable force generated by the hydraulic actuator, and the current speed;
a manipulated variable calculation step of calculating a manipulated variable of the hydraulic actuator based on the quasi-static characteristics of the hydraulic actuator, the dynamic characteristics of the controlled object, the saturated reference speed, and the current speed;
Position control method.