EP1126182B1 - Electrically-controlled positioning drive - Google Patents

Description

State of the art

The invention relates to an electrically controllable actuator, in particular for hydraulic or pneumatic actuators, which are acted upon by a manually adjustable by an operator setpoint, according to the preamble of the main claim.

For example, in vehicles or other mobile machines frequently electrically-proportionally controlled hydraulic valves are used. Here, the target value specification for the hydraulic valve is usually manually realized in that the driver makes the control of the hydraulic valves by remote control by pressing appropriate controls, such as a joystick, a lever or a similar element. It is then processed via the control element read by means of an electronic setpoint by digital processing in an electronic control unit and then serves as a setpoint signal for the corresponding output stages, which feed the electromechanical transducers of the hydraulic valves.

This per se known electronic treatment serves to influence the static transmission properties of the actuator, e.g. for characteristic curve detection or for generating a zoom function. A comparable actuator is described for example in the company publication by Götz, Lackmann, "Electrohydraulic control technology in theory and practice", 1987, Robert Bosch GmbH, pages 6 to 9 described.

The document DE-A-198 01 338 describes a control device for the positioning of a cylinder piston by means of a proportional valve. The control device allows the damped start of an end stop. For this purpose, the position of the piston is constantly determined and determines therefrom by differential formation, a speed and an acceleration value of the piston. By means of a summation point, a deviation signal for the deviation between a desired position and the measured position is first generated. In another summation point, this value is corrected as a function of the speed and the acceleration, thus producing a control signal for the proportional valve. To optimize the driving behavior, the amplification factors of the individual contributions of the control signal are modified.

Hydraulic control for compensating for position and velocity variations of hydraulically-moving machine elements due to oil pressure fluctuations is described in US-A-5 218 895. The control of a hydraulic motor via a solenoid valve. A control signal for the solenoid valve is modified to match the actual speed of the hydraulic motor, which is constantly being measured, with the speed setpoint. If necessary, the speed specification is calculated from a position deviation.

Especially when the actuator is operated via smooth operating elements, feedback effects can cause vibrations in the actuator. For example, if the hydraulic valve is used in a vehicle wherein the predetermined function to be controlled loads the vehicle with a mechanical force and is dependent on the operation of the hydraulic valve or its timing, a change in the valve operation results in a change in the load state of the vehicle. If this, for example, the vehicle axles are loaded, it may cause a movement of the structure of the vehicle. This movement transfers to the manually operable control and causes a change in the setpoint. As a result, the cause, that is to say the force effect on the vehicle, can be further intensified and thus forms a feedback which leads to a vibration.

A control circuit for the tailplane control in aircraft is described in the document US-A-3 201 675. A command rate limiter with an input sum point, a limiter and an integrator is connected between a control element and a servomotor which adjusts the tail. As a result, the angle change rate of the tail is limited to a default value.

It is the object of the present invention to provide an electrically controllable actuator with an improved control behavior.

This object is solved by the features of claim 1.

Further embodiments are the subject of the dependent claims.

Advantages of the invention

The aforementioned electrically controllable actuator with a control element for reading a setpoint in an electronic control circuit and an electromechanical converter for controlling a mechanical Actuator is advantageously designed such that the electronic control circuit includes a setpoint damping circuit with which a limitation of the adjustment speed at a setpoint change is feasible.

Furthermore, the setpoint damping circuit has a summing point circuit at the input and an integrator at the output, which together are referred to as a PT1 element (first-order delay element). In this case, the summation point circuit receives at a positive input the setpoint signal of the control element and at a negative input the fed-back output signal of the downstream integrator. To limit the adjustment of the setpoint change according to the invention, the limiter circuit is connected between the summing point circuit and the integrator.

With the invention, it is thus possible in a simple manner to simultaneously carry out a low-pass filtering and a limitation of the maximum rate of change of the setpoint signal for setpoint damping. For this purpose, the aforementioned modified PT1 element is used, which is implemented in the electronic control circuit. In this case, the circuit components can also be realized without great additional expenditure by changing the software structure of the digital electronic control circuit, which is generally digital.

In addition, a logic interrogation circuit is arranged between the output of the limiter circuit and the integrator, which is acted upon at further inputs with the reference signal and the output signal of the integrator. With this embodiment, it can be achieved that in the event that the setpoint signal is equal to "zero" and the output signal of the integrator is not equal to "zero", the output of the logic interrogation circuit is set to the upper value (for x <0) or to the lower value (for x> 0) of the limiter.

In the above-described logic interrogation circuit, it is therefore also checked in particular whether the value "zero" is specified as the desired value. If this is the case, the operator would like to end the operating function as quickly as possible, and thus it makes sense to reset the output of the control circuit at the maximum speed to the zero value. In the other case, the interrogation circuit passes the output signal of the limiter circuit to the integrator.

In the case of an extended circuit, a block for influencing the setting time, for example, between the summation point circuit and the limiter circuit, can also be used. Multiplication by a constant factor, can be arranged.

Good results can be achieved with the circuit according to the invention when the actuators have hydraulic or pneumatic valves in mobile working machines, e.g. Stacker or similar vehicles are, in which case the digital electronic control unit can also be implemented in the circuit of the valve electronics.

The proposed method for setpoint attenuation is particularly advantageous because it almost completely prevents oscillations by the feedback mechanism described above, in which a change in the valve actuation leads to a change in the load state of a vehicle with an influence on the setpoint value.

The responsiveness to actuation of the control is very convenient for the operators of the vehicles because the reaction to intended setpoint changes occurs immediately. Limiting the adjustment speed causes critical accelerations or to avoid decelerations of the load on the vehicle and when approaching the desired set point, this is ideally achieved with decreasing speed and finite change in acceleration, ie without a jerk.

In summary, it can be stated that the damping effect of the circuit arrangement according to the invention is based essentially on the low-pass characteristic of the PT1 element. Due to the effective amplitude reduction in the range of the possible natural vibration frequencies of the overall system a stable behavior in the operation of an actuator in a man-machine system is achieved.

These and other features of preferred embodiments of the invention will become apparent from the claims and from the description and drawings, wherein the individual features are realized individually or in each case in the form of sub-combinations in the embodiment of the invention and in other fields and can represent advantageous and protectable versions for which protection is claimed here.

drawing

• Figur 1 ein Blockschaltbild eines Grundaufbaus eines mit einem Sollwertsteller steuerbaren hydraulischen Stellantriebs und
• Figur 2 ein Blockschaltbild einer Sollwertdämpfungsschaltung als Bestandteil einer elektronischen Steuerschaltung für den Stellantrieb.

An embodiment of the invention electrically controllable actuator will be explained with reference to the drawing. Show it:

• Figure 1 is a block diagram of a basic structure of a controllable with a setpoint adjuster hydraulic actuator and
• Figure 2 is a block diagram of a setpoint damping circuit as part of an electronic control circuit for the actuator.

Description of the embodiment

In Fig. 1 there is shown a block diagram showing the circuitry for actuating a hydraulic control valve to perform mechanical movements in a mobile work machine, e.g. a forklift or similar vehicle, the basic structure being known from the prior art mentioned at the beginning.

To generate a setpoint, a control element 1, e.g. a joystick or the like., Present and in an electronic control circuit 2 corresponding signals, preferably digital signals, generated, with which an electromechanical transducer is applied. The output of the electromechanical transducer acts here on the valve piston of a hydraulic valve 3, with which a load 6 is mechanically controllable.

The vehicle, not shown here is charged by the control of the hydraulic valve 3 with a mechanical force, which is dependent on the operation of the control element 1 or the time course and thus also leads to a change in the total load condition of the vehicle. This can lead to a movement of the structure of the vehicle, which movement can be transferred to the manually operable control element 1 and thus a change in the desired value can not be ruled out by influencing the operating element 1 or the operator. As a result, the cause, ie the force acting on the vehicle, can continue amplify and thus represents a, here schematically indicated by the dashed line 7 feedback, which can lead to a vibration.

FIG. 2 shows a nominal value damping circuit 10, which may be part of the digital electronic control circuit 2, preferably in a software implementation. The setpoint signal u is applied here to a plus input 11 of a summation point circuit 12. The output of the summing point circuit 12 is guided via a circuit 13 for influencing the setting time to a limiter circuit 14, with which a limitation of the maximum rate of change of the setpoint signal is feasible.

The output of the limiter circuit 14 is fed to an input 15 of a logic interrogation circuit 16 at the second input 17, the setpoint signal u is applied. The output of the interrogation circuit 16 is passed via an integrator 18 to the output 19 of the setpoint attenuation circuit 10, to which the output signal x is applied. The output signal x is fed to a minus input 20 of the summing point circuit 12 and to a third input 21 of the interrogation circuit 16.

With the interrogation circuit 16 it is achieved that in the event that the setpoint signal u is equal to "zero" and the output signal x of the integrator is unequal to "zero", i. x <> 0, the output of the logic interrogator circuit is set to the upper value (for x <0) or to the lower value (for x> 0), so that in this case the interrogation circuit and the integrator function like a ramp act with constant slope.

In the logic interrogation circuit 16, therefore, it is also checked in particular whether the value "zero" is specified as the setpoint u by the operator of the operating element 1. If this is the case, the operator would like the operating function as possible quit quickly and thus it makes sense to reset the output of the control circuit 2 with the maximum speed to the zero value. In the other case, the interrogation circuit 16 passes the output signal of the limiter circuit to the integrator.

Claims (3)

1. Electrically controllable actuating drive, having an operator control element (1) for reading a setpoint value (u) into an electronic control circuit (2), and an electromechanical transformer (3) for controlling a mechanical actuator (4, 5), with
   the electronic control circuit (2) comprising a setpoint-value attenuation circuit (10) with which the adjustment rate can be limited when the setpoint value changes,
   the setpoint-value attenuation circuit (10) having a summation-point circuit (12) at the input and an integrator (18) at the output, the summation-point circuit (12) receiving the setpoint-value signal (u) at a positive input (11) and the fed-back output signal (x) from the downstream integrator (18) at a negative input (20), and
   a limiter circuit (14) being connected between the summation-point circuit (12) and the integrator (18),
   characterized in that
   a logic interrogation circuit (16) is arranged between the output of the limiter circuit (14) and the integrator (18), and the setpoint-value signal (u) and the output signal (x) are applied to further inputs (17, 21) of the said interrogation circuit, and in that the output signal of the logic interrogation circuit (16) is respectively set to the upper value (for x<0) or to the lower value (for x>0) of the limiter circuit (14) if the setpoint-value signal (u) is zero and the output signal (x) of the integrator (18) is not zero.
2. Electrically controllable actuating drive according to Claim 1, with
   a module (13) for influencing the setting time being arranged between the summation-point circuit (12) and the limiter circuit (14).
3. Electrically controllable actuating drive according to either of the preceding claims, with the actuators (4, 5) being hydraulic or pneumatic valves in mobile working machines.

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