WO1991014219A1

WO1991014219A1 - Process and device for controlling a motor-driven actuator

Info

Publication number: WO1991014219A1
Application number: PCT/DE1991/000199
Authority: WO
Inventors: Hans-Peter Schabert; Erwin Laurer
Original assignee: Siemens Aktiengesellschaft
Priority date: 1990-03-13
Filing date: 1991-03-06
Publication date: 1991-09-19
Also published as: DE4008002A1; DE4008002C2

Abstract

With motor-driven actuators for a control element (4) having a defined locking position, for example a fixed end stop, care must be taken to ensure that in the locked position the control element is clamped with a defined torque. According to the invention therefore, the maximum torque available on the motor (2) is increased after the control element starts to move into a locked position. In an advantageous embodiment of the process for an actuator with an electric motor, the reaching of the locked position is monitored by measuring the motor current and the torque is increased by controlling an actual voltage applied to the electric motor. A device for carrying out the process is also disclosed.

Description

Method and device for controlling a motor-operated actuator

The invention relates to a method and a device for controlling a motor-operated actuator as is known, for example, from EP-B1-0 193 776.

Electric actuators for an actuator, for example a valve, a slide valve or a shut-off valve, are usually driven by a three-phase asynchronous motor, the torque of which rises to the overturning moment or standstill torque when the actuator moves into a blocking position and the motor does not previously depend on the torque was switched off. Under normal conditions of use, this blocking position is a fixed end stop of the actuator. However, the blocking position can also be given by a foreign body jammed in the actuator. The actuator can also be constructed in such a way that the actuating movement takes place between two fixed end stops OPEN and CLOSED, as is the case, for example, with a shut-off valve with a rear seat.

Due to the swing energy of the motor braked from the tipping speed, an additional deceleration torque is added to this tipping moment of the motor. Depending on the stiffness, friction and resilience in the valve and in the gearbox of the actuator, there may be a deceleration torque that is more than 30% of the overturning torque. At the

Reopening of the actuator has to be overcome additionally because it leads to a stronger tensioning of the actuator in the blocking position, for example a valve stem in its mother thread, and makes it difficult to reopen (break loose). Conventional actuators are therefore equipped with a complex torque-dependent switch-off device in which an axially displaceable and spring-loaded traveling screw actuates a limit switch when a predetermined torque is exceeded. You want for the strained fitting not exceed a ge velvet torque of 26 Nm, for example, then you can both end positions of the valve, the Abschalt¬ device to a cut-off point of 26 / 1.3 "= 20 Nm ^■ provide ein¬. However, this setting means that the valve does not start in the opposite direction with 26 Nm, but only with about 20 Nm. This then leads to the problem that the valve can not be opened, but stuck, especially after long periods of rest.

To overcome these difficulties, it is known from EP-B1-0 193776 to reduce the supply voltage of the electric drive motor in the remaining area of the actuating movement compared to the supply voltage in the initial area of the actuating movement by at least 10%. This reduction can be triggered depending on the distance or time. As a result of this measure, the full predetermined starting torque of the three-phase asynchronous motor is also available when starting the opposite direction.

In this known method, however, the torque with which the valve is fixed in the end position depends on a deceleration torque which results from the vibration energy of the motor and the mechanical properties of the valve and the gearbox. If these properties change, for example as a result of an increase in the coefficient of friction, this can lead to the valve being only insufficiently clamped and fixed in its end position.

The invention is based on the object of specifying a method and a device for controlling a motor-driven actuator for an actuator, in which guaranteed is that the actuator is fixed in the end position with a reproducible torque.

The above-mentioned objects are achieved according to the invention with the features of claims 1 and 16 respectively. By increasing the possible standstill torque after the start of driving into a blocking position, i.e. After the engine has stopped braking, the actuator is clamped in the end position with a defined torque which is practically independent of the momentum energy absorbed during the actuating movement. The increase in the possible standstill torque can still be initiated during the slowly decelerating movement of the actuator. The increase in the possible standstill torque is preferably so slow that the maximum possible standstill torque which is provided does not take effect until the motor has come to a complete standstill.

The increase in the possible standstill torque can also only be initiated when the motor is already in the locked position. As a result of this increase, the valve is re-tensioned by a slight additional movement. The possible standstill torque is the torque that the motor can develop at standstill with a given supply, for example with an electric motor the supply voltage. The possible is true

The standstill torque essentially coincides with the starting torque available with the same supply. Until the motor comes to a definitive standstill, there is a deceleration distance or a deceleration angle that depends on the structural conditions of the actuator and the actuator. For example, the possible standstill torque is increased to a value that is, for example, at least 5%, preferably is at least 10% higher than the standstill torque that is possible with the unbraked movement. In order to further facilitate starting in the opposite direction, in a preferred embodiment of the method the possible standstill torque after the start of moving into the blocking position is regulated to a value which is smaller than the maximum standstill torque available when required in the starting phase of the actuating movement.

The actuator can contain, for example, a pneumatic motor or an electric motor, for example a single-phase or single-phase AC machine or a DC machine. A three-phase asynchronous motor, in particular a squirrel-cage motor, is preferably provided as the electric motor, the starting torque of which essentially corresponds to the overturning torque or is greater than the overturning torque. The starting torque and the standstill torque are approximately the same.

The standstill torque is preferably controlled by controlling an actual voltage applied to the electric motor. In the case of a three-phase asynchronous motor, the effective value of a delta voltage applied to a motor winding can be provided as the control variable, for example.

The individual phases of the actuating movement, in particular moving into the blocking position, are recorded by monitoring the speed of the motor. The possible standstill torque is preferably increased after the rotational speed has dropped by at least 20% below a nominal value specified for the actuating movement before the start of entry into a blocking position. In a preferred embodiment of the invention, the motor current flowing in a winding is provided as an indicator of the rotational speed. The measurement of the motor current can be carried out anywhere in the supply line for the electric motor, for example in a control cabinet unit, which also contains the electronics required for regulating the actual voltage. The actual voltage is controlled via a time-variable target voltage, which is always increased to a predetermined value when the motor current exceeds a predetermined limit value. At the beginning of the actuating movement, the setpoint voltage is preferably increased to a value which is greater than the value to which the setpoint voltage is raised when the blocking position is reached at the end of the actuating movement. If the motor current falls below a predetermined limit value, the target voltage is reduced. This measure limits the swing energy of the actuator. The limit values of the motor current provided as switching points are preferably approximately 1.5 to 2.5 times, in particular 2 times the nominal current.

Since the actual voltage applied to the electric motor is carried by a mains-independent target voltage, it is also ensured that the entire actuating process can be carried out independently of the fluctuations in the mains voltage.

In a particularly advantageous embodiment of the method, the motor temperature, in particular the temperature of a winding of the electric motor, is additionally recorded and used as a disturbance variable for regulating the motor voltage in order to ensure a constant standstill torque.

The regulation of the torque of the electric motor is preferably carried out by a phase control of semiconductor valves.

To further explain the invention, reference is made to the drawing, in which

1 shows an arrangement for performing the method according to the invention is illustrated in a block diagram. 2 shows an advantageous arrangement of semiconductor valves, which is particularly suitable for controlling the electric actuator in opposite directions of movement. Based on the in

FIGS. 3 and 4 show time diagrams in which the motor current, the actuating path, the actual voltage on the motor and the target voltage are plotted against time, the method according to the invention is explained in more detail.

According to FIG. 1, an electric actuator contains an electric motor 2, which drives an actuator 4, for example a shut-off valve, via a gear (not shown in the figure). An asynchronous three-phase motor, in particular a squirrel-cage motor, is preferably provided as the electric motor 2, the starting torque and the overturning torque of which essentially coincide. The electric motor is connected to the supply voltage of a three-phase network 12 via a semiconductor valve arrangement 6, a reversing contactor 8 and a fuse 10. The semiconductor valve arrangement 6 is bridged by a bypass contactor 7, with which the motor can be connected directly to the network 12 in a emergency situation by means of a special command.

The actuator is preferably a compact drive with a self-switching loose gear, as disclosed, for example, in EP-B1-0 193 776.

A control device 20 is provided for phase control of the semiconductor valve arrangement 6, which provides ignition signals for the semiconductor valves, for example triacs or thyristor circuits. At least one of the three phases is provided with a device 22 for detecting the motor current flowing in this phase, for example a current transformer. In the example of the figure, this device 22 is followed by a comparison device 24, in which it is determined whether the flowing, for example effective motor current I exceeds or falls below a predetermined limit value I. Depending on the result of this comparison, the comparison device 24 then forwards a digital control signal to the control device 20. The control device then as a function of this comparison result determines a target value for the actual voltage applied to the motor 2, measured with a measuring device 26. The firing angles of the firing signals provided by the control device 20 for the semiconductor valve arrangement 6 are regulated by the control device 20 in such a way that the actual voltage measured by the measuring device 26 is readjusted in accordance with the target voltage specified by the control device 20.

The control device, together with a disconnector, de reversing contactor 8, the fuses 10 and the semiconductor valve arrangement 6, are accommodated in a common switchgear assembly.

In an advantageous embodiment of the invention, the motor, for example on one of its windings, is provided with a device 28 for temperature measurement, which forwards an electrical signal corresponding to the motor temperature or the winding temperature to the control device 20. This signal is then used in the control device 20 as a disturbance variable for correcting the setpoint voltage in order to compensate for the standstill torque which drops when the winding is hot. A measured variable corresponding to the motor temperature can be carried out, for example, by a temperature sensor arranged on the electric motor 2 in the vicinity of a winding.

In a preferred embodiment according to FIG. 2, a semiconductor valve arrangement 6 with semiconductor valves 6a, b, c and d is provided, with which the connections of the electric motor 2 to the phases L2 and L3 can be interchanged. In this arrangement, the reversing contactor function can be performed by the semiconductor valve arrangement. Line 6 are taken over, so that a separate reversing contactor 8 (FIG 1) is no longer required.

3 shows the actual voltage U _M applied to a winding of the electric motor, the setpoint voltage U _s specified by the control device at a specific motor temperature, the motor current I and the travel path s of the actuator in a diagram versus time. The torques currently output by the engine are not shown. These are approximately proportional to the product of the motor current I and the actual voltage U _M. At time t _Q the control device receives a switch-on command. The target voltage is then set to a value U _S2 that is smaller and independent of the actually applied mains voltage U _Q. With a time delay characteristic of the actuator, the measured actual voltage U _M rises steeply. The actual voltage U _M corresponds, for example, to the effective voltage across a winding.

0 As of the switch-on time t _Q , the motor current I also rises steeply as the starting current. If the motor current I has a limit value I

- G reached, which is preferably between 1.5 and 2.5 times, in the example of the figure twice the nominal current I characteristic of the electric motor used, the setpoint voltage U _{s is set} to a value U by the control device _s *, increased to ensure sufficient starting torque to break free the actuator. In one embodiment, this value is U _ς -, approximately 1.15 times U _S2 - The actual voltage U _M and the motor current I continue to rise, the motor current I reaches a maximum and then begins to decrease . This is the case when the actuator is released from the end stop. If the motor current I falls below a predetermined limit value I ', this is an indication that the actuating movement is underway and the motor speed is being driven. 5 This limit value I 'is preferably equal to the limit value I yy for the first switching time t and in the example of the figure is also twice the nominal current I.

The figure falls below the limit value I at a point in time t. At this point in time t -, the setpoint voltage is reduced from U ^ to the value Uς ₂ in the control device. The motor current I continues to drop, because during this phase of the actuating movement only the braking torques caused by internal frictional forces in the transmission and in the actuator can be overcome. By lowering the target voltage U _< - and thus also the actual voltage U _M applied to the motor, both the kinetic energy of the running motor and the maximum torque that can be generated when the motor is blocked, which corresponds to the breakdown torque in a three-phase asynchronous motor , reduced.

The travel s increases linearly with time. When driving into a blocking position, usually the end stop of the actuator, the motor current I begins to rise again due to the increased torque requirement. A current dip in the motor voltage U _{M is} associated with this current rise and is regulated by the control device.

At a time t, the motor current I reaches a limit value I "which indicates that the actuator is starting to jam. The limit value I" preferably also corresponds to the limit values at the preceding switching times t- and t.

At time t _* , the control device then increases the target voltage U _s to the value U- - ^ and the actuator is fixed in the end position with a torque which corresponds to the standstill torque of the motor supplied with an actual voltage U _M , which is slightly smaller than the target voltage U _c 1. After a humming time A specified by the control device, for example about 2 s, the stationary motor is then switched off at time t ₇ . A time window t 1 to t _{6 is also} set in the control device after the switching command occurring at time t ₀ , in which an end of the travel path and thus a exceeding of the limit value I are expected in normal operation. If the limit value I is not exceeded within this time window t ^ to t ^ and a corresponding control signal is not triggered, this can be caused by the fact that the actuator has not moved at all. In this case it must be ensured that the stationary engine is also switched off in good time before it overheats. This then takes place after a maximum switch-on time tg which, for example, results from the end time t _{g of} the time window t. to t ₆ by adding a humming time B, for example about 3s.

In a further advantageous embodiment of the method according to the invention, according to FIG. 4, an increase in the target voltage to a value U _so at time t is provided, which is greater by a predetermined amount DU _ς than the value U _ς , the target voltage U _ς when reached the end position. In one embodiment, U _{SQ is} approximately 1.3 times U _ς2 . In the control device, a time window for this purpose is t _Q - t ₂ is set in which an increase in the Soll¬ voltage U _e to the value U _S2 to an increased value U _so BE DONE is men when I a given within this time window, the motor current Limit exceeded. If the motor current I exceeds the predetermined limit value I outside of this time window, the nominal voltage U _s is increased from the value U _S2 only to the value U _s . By means of this measure, a starting torque can be made available in the start-up phase that is greater than the standstill torque with which the actuator was moved into the blocking position.

Short time constants, for example, can be used to change the values for the target voltage and to adjust the actual voltage. wise 100 ms. However, larger time constants or a smoothly regulated transition depending on the engine speed are also possible.

Claims

1. A method for controlling a motor-driven actuator bes for an actuator (4), in which in various Zeitab¬ sections of the actuating movement control of a possible motor (2) of the actuator Er¬ follows Er¬, characterized in that the possible standstill torque after Beginning of driving into a blocking position is increased.

2. The method according to claim 1, dadurchgekenn¬ characterized in that the possible standstill torque is regulated after de the start of driving into a blocking position to a value which is greater than the sum of a possible standstill torque before the start of driving in and a deceleration torque which occurs when braking arises from the kinetic rotational energy of the actuator.

3. The method of claim 1 or 2, d a d u r c h e- k e n n z e i c h n e t that the possible standstill torque after the start of driving into a blocking position is regulated to a value which is smaller than the standstill torque possible in the start-up phase of the actuating movement.

4. The method according to any one of the preceding claims, that the control of the possible standstill torque takes place in an actuator with an electric motor (2) by controlling an actual voltage (U) applied to the electric motor (2).

5. The method according to any one of the preceding claims, d a- characterized in that the Hineinfah¬ ren in the blocking position is detected by monitoring the speed of the motor (2).

6. The method according to claim 5, d a d u r c h g e k e n n z e i c h n e t that the possible standstill torque is increased after the speed has dropped by at least 20% below a nominal value specified for the actuating movement before the start of driving into the blocking position.

7. The method according to claim 6, dadurchgekenn¬ characterized in that the speed is monitored by a measurement of the ^' motor current (I) in an actuator with an electric motor.

8. The method according to any one of claims 4 to 7, characterized in that a time-variable target voltage (U _ς ) is provided for guiding the actual voltage (U _M ).

9. The method according to claim 8, characterized in that the target voltage U is increased to a predetermined value (U _SQ , U _sl ) when the motor current (I) has a predetermined limit value (Ig, 'I "g) exceeds.

10. The method according to claim 9, d a d u r c h g e k e n n¬ z e i c h n e t that always when the motor current (I) d

Limit value (I) within a predetermined time window y (ti-t-) after a switch-on time (t _Q ) exceeds that

Target voltage (U _ς ) is increased to a value (U _ς .-,) which is greater than a value (U _ς -,) to which the target voltage (U _ς ) is increased if the limit value (I) is outside this Time window

(t-i-tg) is exceeded.

11. The method according to any one of claims 8 to 10, characterized in that the target voltage (U _ς ) is reduced to a predetermined value (U _ς2 ) when the motor current (I) _{falls below} a predetermined limit value (I ').

12. The method according to any one of claims 8 to 11, so that the limit values (Ig, I ', I ") are approximately 1.5 to 2.5 times the nominal current (I).

13. The method according to any one of claims 4 to 12, d a- characterized in that the motor temperature is detected as a disturbance variable for the regulation of the actual voltage (U _M ).

14. The method according to claim 13, d a d u r c h g e k e n n z e i c h n e t that the temperature of a winding of the electric motor (2) is monitored.

15. The method according to any one of claims 4 to 14, that the control of the torque of a single- or multi-phase AC motor is carried out by a phase control of semiconductor valves (6).

16. Device for controlling a motor-driven actuator for an actuator (4) with a method according to one of claims 1 to 12, characterized in that control means (6, 20) for regulating the standstill torque of the motor (2) and means ( 22) are provided, which indicate the start of driving into a blocking position, the control means (6, 20) increasing the standstill torque after the means (22) indicate the beginning of driving into the blocking position.

17. The apparatus of claim 16, d a d u r c h g e¬ k e n n z e i c h n e t that means (22) for detecting the speed of the motor (2) are provided.

18. The apparatus according to claim 17, dadurchge¬ indicates that the means (22) at one Actuator with an electric motor comprise a device for measuring the motor current (I).

19. The apparatus of claim 17, d a d u r c h g e- k e n n z e i c h n e t that a measuring device (24) is provided for measuring the engine temperature.

20. Device according to one of claims 16 to 19, d a- characterized in that for controlling the torque in an actuator with a single or multi-phase AC motor semiconductor valves (6) are provided, which a control circuit (20) for Phases ¬ cut control is assigned.

21. Actuator with a device according to one of claims 16 to 20, so that the actuator contains a three-phase asynchronous motor, the standstill torque of which is at least as large as its overturning moment.