JPH01110884A - Flow quantity-pressure control device for variable delivery quantity pump - Google Patents

Abstract

PURPOSE:To hold a setting stop pressure in a short time by providing a prediction control means which instructs a delivery stop of a pump when the residual delivery volume, obtained in a prediction arithmetic means, agrees with the surplus delivery volume. CONSTITUTION:In the case of a flow quantity and pressure control device for a variable delivery quantity pump 1, when a delivery pressure starts rising by stopping a cylinder as a control load, the existing delivery volume Vr, necessary for the delivery pressure reaches from the present point of time to d setting stop pressure, is predictively calculated being based on a rising speed in every predetermined period. While the surplus delivery volume Ve, for the pump to deliver by its action delay when the pump performs its delivery stop in the present point of time, is predictively calculated, and when the existing delivery volume Vr increases to the surplus delivery volume Ve or more, the delivery stop of the pump is instructed. In this way, no overshoot is generated even when the delivery pressure reaches the setting stop pressure.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is directed to controlling the flow rate pressure of a variable discharge pump that switches from the previous flow rate control to pressure control to maintain the stop pressure at a constant value when the load on a cylinder or the like stops. Regarding a control device.

(Prior art) Conventionally, as this type of flow rate pressure control device, for example, the fifth
There is something like the one shown in the figure.

In FIG. 5, reference numeral 1 denotes a variable displacement pump, and by changing the input voltage or input current, for example, the angle of the swash plate can be changed, thereby changing the piston stroke and thereby changing the displacement.

2 is a servo amplifier for flow rate control, 3 is a servo amplifier for pressure control, 4 is a switch for switching the output of the servo amplifiers 2 and 3, 5 is a voltage comparator for switching and controlling switch 4, and 6 is a control This is a cylinder that acts as a load.

In such a flow rate pressure control device, during normal flow rate control, the switch 4 is switched to the A side, and the swash plate angle θ from the angle sensor attached to the swash plate of the variable displacement pump 1, i.e. The pump discharge flow rate Q is detected and the flow rate indication value (
The deviation from the set flow rate) QC is obtained at addition point 7 and input to the servo amplifier 2, and the discharge ♀ of the variable discharge amount pump 1 is feedback-controlled to maintain the flow rate command value QC. As a result, the cylinder 6 is Driven by movement speed.

When the cylinder 6 is driven by such flow rate control and reaches the stroke end and is mechanically stopped, the pressure inside the cylinder 6 starts to rise rapidly.

The voltage comparator 5 is given, as a reference voltage, the pressure command value pc minus a predetermined value α (PC-α) from the addition point 8, and the discharge pressure P that has increased when the cylinder 6 stops at the end of its stroke. is slightly lower than the pressure indication value pc (
PC-α), the output of the voltage comparator 5 is inverted, the switch 4 is switched to the B side, and the deviation from the addition point 9 (Pc-
Pressure control is performed to control the discharge amount of the variable discharge amount pump 1 so as to maintain the stop pressure P at the pressure command value 1)c using the output of the servo amplifier 3 based on P).

(Problem to be Solved by the Invention) However, in such a conventional flow rate pressure control device, switching from flow rate control to pressure control is performed when the discharge pressure P is slightly lower than the pressure command value PC (PC -α), for example, as shown in FIG. 6, when the flow rate command value Qc for flow rate control is a large flow rate, or when the cylinder volume when reaching the stroke end is small, Even if the pressure J control is performed, more fluid than necessary is discharged due to a delay in the response of the pump, resulting in an extremely large overshoot ΔP with respect to the pressure command value pc.

On the other hand, to reduce overshoot, servo amplifier 3
If the gain of is set very low, the stop pressure will be equal to the pressure command value p.
There was a problem in that the stationary stop time until it stabilized at c became longer, and the control accuracy deteriorated.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned problems of the conventional art. It is an object of the present invention to provide a flow rate pressure control device for a variable discharge amount pump that has excellent control response and control accuracy and can shift to pressure control that maintains a set stop pressure in a short period of time.

In order to achieve this object, the present invention performs flow control to control the pump discharge amount to maintain a set flow rate until the control load stops, and sets the discharge pressure that increases when the control load stops to the set stop pressure. In a flow rate pressure control device for a variable discharge pump that switches to pressure control to control the pump discharge amount so as to maintain the pump discharge amount, the current discharge pressure reaches the set stop pressure from the rising rate of discharge pressure when the control load stops Predictive calculation means for predicting and calculating each of the remaining discharge volume required until then, and the surplus discharge volume that would be discharged due to a delay in pump operation when the discharge is stopped at the present time, at predetermined intervals; Predictive control means for instructing the pump to stop pumping or to control the pump to a fixed discharge amount based on the stopped leakage flow rate when the obtained remaining discharge volume and surplus discharge volume match.

(Function) In the flow rate pressure control device for a variable discharge amount pump of the present invention having a small number of such configurations, when the discharge pressure starts to rise due to the stoppage of the cylinder as a control load, the rate of increase is increased at predetermined intervals. Based on this, the remaining discharge volume vr required from the current moment to reach the set stop pressure is predicted and calculated, and the surplus discharge volume ve that would be discharged due to the pump operation delay when the pump discharge is stopped at the present moment is predicted and calculated. death,
When the remaining discharge volume yr exceeds the surplus discharge volume ■e, for example, a command is given to stop the discharge of the pump.

Therefore, even if there is a delay in pump operation due to a stoppage of discharge,
The surplus discharge volume Ve discharged due to the operation delay is the remaining discharge volume yr necessary to reach the set stop pressure.
Since they match or are substantially equal, no overshoot occurs at all even when the discharge pressure reaches the set stop pressure, and by switching to pressure control at this stage, the stop pressure can be quickly maintained at the set value.

Furthermore, until the discharge is stopped by predictive control, the discharge pressure is rapidly rising due to the flow rate control, and the transition time to pressure control for maintaining stop accuracy is extremely short, making it possible to achieve a high control response.

(Example) FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a variable displacement pump, and the piston stroke can be changed by changing the inclination angle θ of the swash plate according to voltage input or current input.
This allows the discharge flow rate to be varied. Reference numeral 2 denotes a servo amplifier for controlling the flow rate, and the flow rate command value Qc as a set flow rate given when the changeover switch 4 is switched to the A side, and the discharge flow iQ based on the swash plate inclination angle θ of the variable discharge amount pump 1. An output is generated according to the deviation signal from the addition point 7 into which is input, and the discharge amount of the variable discharge amount pump 1, that is, the swash plate inclination angle θ, is feedback-controlled so as to maintain the discharge flow ff1Q at the flow rate instruction value Qc.

Furthermore, as will be explained later, the servo amplifier 2 can forcibly control the servo output for controlling the ejection amount using an external signal.

3 is a servo amplifier for pressure control, which produces an output according to the deviation between the pressure command value pc as the set stop pressure obtained from the addition point 9 and the discharge pressure P of the variable discharge amount pump 1 detected by the pressure sensor. , the output of the servo amplifier 3 is given to the variable displacement pump 1 via the addition point 7 and the servo amplifier 2 with the switch 4 switched to the B side, and the discharge pressure P of the variable displacement pump 1 is set to a pressure command value. Feedback control is performed to maintain the PC.

Reference numeral 10 denotes a prediction calculator which, when the piston rod 6a of the cylinder 6 comes into contact with the object 11 and stops due to flow rate control, calculates the discharge pressure from the previous flow rate control to a pressure command value P.
When switching to pressure control that maintains a predetermined stop pressure determined by c, the discharge amount of the variable discharge amount pump 1 is optimally controlled so that the stop pressure determined by the pressure command value PC is reached without causing an overshoot exceeding the stop pressure. Perform predictive calculations for

That is, the prediction calculator 10 calculates the piston rod 6 of the cylinder 6.
When a comes into contact with the object 11 and stops, the discharge flow rate Q and discharge pressure P of the variable discharge volume cylinder □ pump 1 are sampled at every predetermined sambling cycle Ts, and from these sampling values, the discharge pressure due to the stoppage of the cylinder 6 is calculated. The remaining discharge capacity required until the discharge pressure P reaches the set stop pressure PC from the current time (sampling point) based on the rising speed,
That is, the remaining discharge capacity Vr is predictively calculated.

At the same time, the prediction calculator 10 calculates the surplus discharge volume ve that would be discharged due to a delay in pump operation when the variable discharge amount pump 1 stops discharging at the present moment (sampling time).
Calculate the prediction.

Reference numeral 12 denotes a predictive control circuit, which compares the residual discharge volume VIV r predicted and calculated every sample period Ts by the predictive calculator 10 with the surplus discharge volume ve, and finds that the residual discharge volume vr matches the surplus discharge volume \/e. The fixed discharge 11 corresponds to the leakage flow rate at the stop position of the cylinder 6, or commands the servo amplifier 2 to stop the discharge when the leakage flow rate exceeds the specified time.
4 Command the output of QL. Furthermore, the predictive control circuit 12
is the discharge stop or fixed discharge IQL for the servo amplifier 2.
It has a control function of switching the switch 4 from the A side to the B side for controlling the flow rate after issuing a command to discharge the fluid, and switching to pressure control using the output of the servo amplifier 3. Switching to this pressure control is performed when the discharge pressure P of the variable discharge amount pump 1 matches the pressure command value PC, or when a predetermined time T to V has elapsed.

Next, referring to FIG. 2, the prediction calculator 10 shown in FIG.
The principle of control of the variable discharge amount pump 1 by the predictive control circuit 12 will be explained together with its operation.

FIG. 2 shows that the cylinder 6 is moved to the object 11 in response to the discharge amount controlled by the variable discharge amount pump 1 based on the flow rate instruction value Qc.
The figure shows the changes in discharge pressure and flow rate when the discharge pressure and flow rate stop due to contact.

That is, if the cylinder rod 6a of the cylinder 6 comes into contact with the object 11 at time to, the movement of the piston of the cylinder 6 is blocked, and at this time, the discharge amount pump 1 is controlled to produce a flow rate Q that matches the flow rate instruction value Qc. , the internal pressure of the cylinder, that is, the pump discharge pressure increases from the time to when the cylinder 6 stops.

This increase in discharge pressure when the cylinder is stopped is P=1/Vβ
foQdttenp.

However, ■ is the load volume, β is the compressibility of the working fluid, and if the discharge flow rate Q is constant, P = (Q/Vβ)t+p.

As shown in FIG. 2, it rises linearly.

Therefore, in the prediction calculator 10 of FIG. 1, a predetermined sampling period TS is set from time to when the cylinder 6 stops
The discharge flow IQ and the discharge pressure P are sampled at each time.

Here, the discharge pressure at the current sampling time point is pn, and the discharge pressure before the sampling period TS is pn.
-1, each can be expressed by the following equations.

P'n-(Q/Vβ) is 10P.

Pn-1=(Q/Vβ)(t-tp)+P.

Therefore, in order to find the rate of increase in the discharge pressure from Pn-1 to Pn, which gives the slope (Q/Vβ), the difference between the two is taken, and the slope, that is, the rate of pressure increase, is determined by the following formula. .

Pn -Pn-1= (Q/Vβ)tpQ/Vβ= (
Pn -Pn-1) /lpThis makes the current tn
The remaining time tr until the pressure command value pc, which is the set stop pressure, is reached is: (Pn - Pc ) /lr = (Pn - Pn-1
) /1ptr = ((Pc'-Pn) / (P
n -Pn-1))t.

As a result, from the current time tn to the remaining time tr, the volume of the fluid discharged by the variable discharge amount pump 1, that is, the remaining discharge volume vr, can be predicted and calculated as Vr = Q - tr. Can be done.

By the way, the discharge pressure P has changed from the current time tn to the pressure command value P.
Even if the variable discharge amount pump 1 is commanded to stop the discharge after the time tr reaching C and the swash plate angle is changed to stop the discharge or reduce the discharge amount to a fixed discharge amount based on the leakage flow rate when the cylinder is stopped, the variable discharge amount pump No. 1 is unable to immediately stop the discharge or reduce the discharge to a predetermined amount due to a delay in the operation of the pump itself, resulting in over-discharge and an increase in the stop pressure by the excess discharge amount. Therefore, the prediction calculation unit 10 shown in FIG. 1 calculates the surplus discharge volume ■e that would be discharged due to a delay in pump operation when the pump discharge is stopped at the present time. Calculating the surplus discharge volume e due to the pump operation delay is extremely difficult because the performance varies from pump to pump and the operation delay varies depending on the operating conditions. For example, the surplus discharge volume Ve can be expressed by the following formula.

Ve = QTp (1-e-'ff) However, Q
; Discharge amount Tp just before the discharge stop; Time constant t of the pump; Elapsed time from the stop command Here, if e Tp is t>2Tp, it can be regarded as e470, and therefore Ve now QTp.

Therefore, the prediction calculator 10 measures the discharge flow rate Q, that is, the pump swash plate angle θ, at the same time as sampling the discharge pressure P to calculate the surplus discharge volume Vr, and assumes that the discharge is stopped at this point. The surplus discharge volume Ve is calculated.

The remaining ejection volume Vr and the surplus ejection volume ve calculated at each predetermined sampling period by the prediction calculation unit 10 in this manner are each provided to the prediction control circuit 12 for comparison and determination.

That is, when the remaining discharge volume Vr and surplus discharge volume Ve obtained from the prediction calculator 10 become Vr = Ve, the predictive control circuit 12 causes the servo amplifier 2 to stop the discharge or to control the leakage flow rate in the hydraulic system on the cylinder 6 side. command to reduce the discharge amount to a fixed amount corresponding to minutes. A fixed time Tw = 2TI corresponding to 2 to 3 times the time constant Tp of the variable discharge amount pump 1
)~3Tp has passed or until the discharge pressure substantially matches the pressure command value PC, the control calculation by the feedback loop is stopped, and when the fixed time TW has passed or pc~
When the pressure becomes P, the switch 4 is switched to the B side to allow the servo amplifier 3 to perform the original stop pressure control.

The control by the prediction calculator 10 and the prediction control circuit 12 will be explained in detail with reference to FIG.
Since the discharge flow rate corresponding to the constant flow rate instruction value Qc has been obtained by flow rate control from the time to when the contact point came into contact with the target object 11 and stopped, the discharge pressure increases linearly, and the predetermined sampling period Ts At each time, the prediction calculator 10 calculates the remaining ejection volume r and the surplus ejection volume ve, and outputs them to the prediction control circuit 12. The predictive control circuit 12 determines the remaining discharge volume Vr.
For example, at time tn, Ve-Vr is monitored to see if it matches or exceeds the surplus discharge volume ve.
If, for example, the servo amplifier has a fixed flow rate Q corresponding to the leakage flow rate of the hydraulic system on the cylinder 6 side when stopped.
In response to this command, the variable discharge amount pump 1
The swash plate angle was changed, and the discharge flow rate decreased toward the fixed flow rate QL, and the rate of increase in the discharge pressure, which had been increasing linearly with this decrease in discharge volume, was suppressed, and the rate predicted at time tn was suppressed. Since the remaining discharge volume yr required to reach the pressure command value PC is equal to the simultaneously predicted surplus discharge volume Ve, the discharge pressure reaches the pressure command value PC without overshooting. Then, 2T from time tn
When the fixed time TW corresponding to p~3Tp has elapsed, or when the discharge pressure P substantially matches the pressure command value Pc, the switch 4 is switched to the B side to switch to pressure control by the servo amplifier 3, and the flow rate control is switched to Even when switching to pressure control, overshoot does not occur, so switching shock does not occur at all, or even if it does occur, it is so small that it can be ignored.

FIG. 3 is a block diagram showing a specific example of the prediction calculator 10 and the prediction control circuit 12 in the example of FIG. an analog multiplexer 14 that sequentially inputs the following signals at predetermined intervals, an A/D converter 15 that converts the output of the analog multiplexer 14 into a digital signal, calculations of the residual discharge sound 'IA V r and surplus discharge volume ve, and the results of these calculations. A microprocessor 1 provides a control output to a servo amplifier 2 and a switch 4 based on a comparison of
Consists of 6.

The control by the microprocessor 16 shown in FIG. 3 is shown in the flow chart of FIG.

That is, in the flowchart of FIG. 4, first, in step S1, it is determined whether or not the cylinder 6 comes into contact with an object 11, such as a stopper, and stops. Check whether the time has been reached, and when the sample time has been reached, proceed to step S3, read the flow ωQ and pressure P at that time, and only in the next step S, remaining discharge volume vr and surplus discharge volume ■e
is calculated, and the two are compared in step S5. Step S
5, when Vr becomes equal to or greater than VQ, step S
Proceeding to step 6, the servo amplifier 2 is commanded to stop the discharge or to reduce the discharge to the fixed discharge ff1QL, and in the next step S7, the elapse of the fixed time TW or whether the discharge pressure P matches the pressure command value Pc is monitored. When this condition is met, the discharge stop command or fixed discharge command is canceled in step S8, and the switch 4 is switched to the B side in step S9, thereby shifting to pressure control by the servo amplifier 3.

Note that the stop determination in step S1 is not performed, and vr, ■
An arithmetic comparison of e may be performed.

Next, another embodiment for calculating the surplus discharge volume ye of the variable discharge amount pump 1 calculated by the prediction calculator 10 of FIG. 1 will be described.

That is, as mentioned above, the calculation of the surplus discharge volume ve of the variable discharge mother pump 1 is expected to be inaccurate, but if the pump structure is the same, that is, if the model is the same, there will be little variation depending on the pump, and the behavior will be almost the same. For example, it is a function of the flow ff1Q immediately before the ejection stop command, ve=f(Qnow θ). In other words, the surplus discharge volume ve can be approximately determined by the flow ωQ or the swash plate angle θ just before the pump stops.

Therefore, if the initial value Q or θ immediately before the pump stops is known, the surplus discharge volume Ve can be determined, so instead of calculating the surplus discharge volume ■e based on the temporary delay described above, ・Use the initial value Q as a variable, The surplus discharge volume Ve at that time is experimentally determined, a table memory is created in which the experimental value ■e@ is written using the initial value Q as an address, and the table data is output to the memory of the microprocessor 16 shown in FIG. 3, for example. By reading out the excess discharge volume ■e corresponding to the initial value Q, even more precise control becomes possible.

Furthermore, the remaining discharge volume V in the prediction calculator 10 of FIG.
The calculation of r is based on the current pressure pn and the pressure one cycle ago pn-
1 was used to predict the remaining time Tr until the pressure command value pc is reached, but in addition to this, the pn
-1 and p n-2 two periods ago and p n-2 two periods ago
The calculation accuracy of the surplus discharge volume Vr can be further improved by averaging a plurality of values using pn-3 and the like three cycles before.

Furthermore, as shown in FIG.
is assumed to be constant such that Q=QC due to flow rate control, but by increasing the flow rate Q near time to, the response speed until reaching the pressure command value PC can be further increased.

In this case, if the flow rate ff1Q is constant, the excess discharge volume ■e, ■e=f(θ) is a function of two parameters: ■e=f(θ−(dθ/dt)) Then, create a table memory for determining the surplus discharge volume ve by setting dθ/dt = Qn - Qn-1, read the remaining discharge volume ve from the table memory using the initial value Q and (Qn - Qn-1), Furthermore, the control response can be improved by increasing the rate of pressure rise until reaching the stop pressure determined by the pressure command value pc.

(Effects of the Invention) As explained above, according to the present invention, the remaining discharge volume and discharge stop necessary from the pressure increase rate at the time of stopping the control load to the set stop pressure of the current discharge pressure are performed at the present moment. The system calculates the surplus discharge volume that would be discharged due to the pump operation delay when the pump operation is delayed, and when the two match, the discharge is stopped or the discharge volume is reduced to a fixed discharge volume based on the stop leakage flow rate, which causes overshoot. It is possible to shift to the control state of the set stop pressure without any trouble, and it is possible to obtain extremely good control characteristics.

In addition, in conventional devices, complicated adjustments such as lowering the pressure control feedback gain had to be made after the system was manufactured in order to prevent overshoot, but in the present invention, pressure control feedback There is no need to adjust gain or the like, and post-manufacturing adjustment can be extremely simplified.

Furthermore, it was impossible to apply conventional devices to precision devices where overshoot should not occur;
According to the present invention, highly accurate control is possible without using any other hydraulic pressure control valve or the like for absorbing overshoot.

Furthermore, in the present invention, if control characteristics are required that not only do not cause overshoot, but also actively generate overshoot, the remaining discharge volume and surplus discharge volume are required to prevent overshoot. The required overshoot can be reduced by changing the operation such as stopping the discharge when the values match, but by changing the operation in such a manner that the remaining discharge volume is smaller than the surplus discharge volume by a predetermined amount, Vr>Ve. Control characteristics can be easily realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the control operation of FIG. 1, and FIG. 3 is a concrete diagram of the predictive calculator and predictive control circuit shown in FIG. FIG. 4 is a block diagram showing the embodiment; FIG. 4 is a flowchart showing control processing according to the embodiment of FIG. 3; FIG. 5 is a block diagram showing a conventional example; FIG. 6 is an explanation showing conventional control operation. It is a diagram. 1: Variable discharge mother pump 2: Nervo amplifier (for flow control) 3: Servo amplifier (for pressure control) 4: Switch 6: Cylinder (control load) 7.9: Loading point 10: Prediction calculator 12 Two prediction control Circuit 14: Analog multiplexer 15: A/D converter 16 Two microprocessors

Claims (2)

[Claims] (1) Flow rate control is performed to control the pump discharge amount so as to maintain the set flow rate until the control load stops, and the pump discharge amount is controlled so that the discharge pressure that increases when the control load stops is maintained at the set stop pressure. In a flow rate pressure control device for a variable discharge volume pump that switches to pressure control, the remaining discharge volume required for the current discharge pressure to reach the set stop pressure from the rate of increase in discharge pressure when the control load is stopped, and Predictive calculation means that predicts and calculates each surplus discharge volume that would be discharged due to a delay in the operation of the pump when the discharge is stopped at the current time; and the remaining discharge volume and surplus discharge obtained by the prediction calculation means. A pressure flow rate control device for a variable discharge rate pump, comprising: predictive control means for instructing control to a fixed discharge rate based on stopping discharge of the pump or stopping leakage flow rate when the volumes match; (2) The predictive control means is characterized in that it includes means for switching to the pressure control after a predetermined period of time has elapsed after commanding discharge stop or fixed discharge amount control, or when the discharge pressure matches the set stop pressure. A flow rate pressure control device for a variable discharge amount pump according to claim 1.