EP1830370A2 - Device for controlling an electromagnetic actuating device - Google Patents

Abstract

The method involves overdriving an actuator with a capacity that has a time limitation, where the capacity lies above rated capacity of an actuator drive. A control unit (60) determines the rated capacity on the basis of a number of various inductive loads of different rated capacities based on available current and level of supply voltage of the actuator while being in an over-driven state. The actuator is controlled by a switching unit (10) under pulse width modulation.

Description

Field of the invention

The invention relates to a device for controlling an electromagnetic actuator such as a solenoid, in particular a solenoid to hydraulic or pneumatic control valves, preferably in the field of plastic injection molding machines according to the preamble of claim 1.

State of the art

In the industrial sector, hydraulic switching valves with a supply voltage of 24V _DC are traditionally used. The same applies to pneumatics in industrial applications. Prescribed by the vehicle electrical system, the supply voltages of switching valves in the mobile area are usually 12V _DC . However, the range of valves and their switching logic is comparable.

From the DE 40 31 427 A1 For example, a method and a device are known which, with the aid of pulse-width-modulated supply voltage, permit energy-reduced operation with readjusted power adaptation of an electromagnetic actuator. This method reduces the power cyclically to a minimum power (P ₀ ) and can thus reach the limit of the holding torque of the actuator. For this purpose coil current and coil voltage are measured and the power in the coil is reduced continuously or in fixed stages until the actuator moves, ie the counterinduction in the coil is detected by the coil current. This power P ₀ is provided with an offset and delivered to the coil as a minimum power. The method is independent of the connected load, with small inductive loads, the recognition of the actuator movement is difficult because of the low mutual induction by coil current and voltage. There is also a risk that in critical applications under high load or at spontaneously acting disturbances at least partially moves the load out of the desired state.

The DE 41 09 233 C2 shows a control electronics with pulse width modulated output signal for driving electrical actuators of a hydraulic system, which determined without overexcitation on the basis of the determined impedance, the characteristics of the actuator and these are controlled by the pulse width modulation. (see also DE 101 04 754 A1 ).

From the DE 39 10 810 A1 a circuit arrangement is known in which with an adjustable pulse width modulation (PWM) a reduced-power operation of electromagnetic actuators is realized.

Disclosure of the invention

Based on this prior art, the present invention seeks to identify valve spools according to their rated voltage and make them available for industrial use.

This object is achieved by a method for controlling an electromagnetic actuator having the features of claim 1.

By a time-limited over-excitation, ie operation with a power that is well above the rated power of the electromagnetic actuator, valves lower nominal power can be operated at higher switching speed even under higher voltage. On the basis of the occurring current and voltage characteristics when applying the supply voltage to the actuator can be closed to the actuator or the valve, which is then operated according to pulse width modulation at its rated power. Preferably, the supply voltage is at least as high as the rated voltage of the actuator. Due to the overexcitation, variations in the duty cycle via different actuators of a series and / or different operating points (for Valves eg pressure, flow rate, temperature, viscosity of the medium) minimized.

This makes it possible to identify valve coils of different nominal voltages and to make them usable at various supply voltages for industrial use. By adapting the switch-on duration by means of the pulse-width-modulated supply, the electromagnetic actuators can be utilized for a wide range of different supply voltages. The height of the supply voltage is essentially limited only by the permissible insulation voltage of the coil. In operation, fluctuations in the supply voltage are compensated by adjusting the duty cycle, so that the average coil current remains constant.

At the moment of switch-on, the current in the connected inductive load increases in an e-function. With the movement of the actuator, that is, the deflection of the actuator from the rest position to the active end position, there is a short-term interruption of the current increase, which can be evaluated for function monitoring.

Further advantages emerge from the subclaims and the following description.

Brief description of the figures

Fig. 1

ein Blockschaltbild einer erfindungsgemäßen Schaltung,

Fig. 2

ein Schaltbild einer Schaltung in einer gegenüber Fig. 1 konkretisierten Ausführungsform,

Fig. 3 - 5

Diagramme von Spannung und Strom über der Zeit an verschiedenen Ventilspulen als Last.

In the following the invention will be explained in more detail with reference to the attached figures.
Show it:

Fig. 1

a block diagram of a circuit according to the invention,

Fig. 2

2 shows a circuit diagram of a circuit in an embodiment concretized relative to FIG. 1,

Fig. 3-5

Diagrams of voltage and current over time on different valve coils as a load.

Description of preferred embodiments

Before describing the invention in detail, it should be understood that it is not limited to the particular components of the device or the methodology discussed within the scope of the method, as these components and methods may vary. The terms used herein are intended only to describe particular embodiments and are not intended to be limiting. When the singular or indefinite articles are used in the specification and claims, these also refer to the majority of these elements unless the context clearly makes otherwise clear. The same applies in the opposite direction.

The method described below is preferably used on actuators of valves on an injection molding machine for processing plasticizable materials, in particular on a plastic injection molding machine.

In the drive circuit 80 according to FIG. 1, a supply voltage U _{V is applied} via the outputs 80.4, 80.5 to a connected load 100 via at least one switching element 10. This load is in the exemplary embodiment, for example, the coil of an actuator of a valve with actuator and slider. The circuit is connected via input 80.2 to the supply voltage U _V and via input 80.3 to GND. The switching element 10 is switched on or off via a control 60 via terminals 60.2. In addition to the switching element 10, a current sensor 20 is provided. If the switching element 10 is closed, current flows from the supply pin 80.2 via current sensor 20, switching element 10 and via the connected load 100 to GND. The electromagnetic actuator turns on.

When switching on a time-limited overexcitation, ie an operation with a power which is well above the rated power of the electromagnetic actuator, so that valves operate low rated power even at higher voltage with greater switching speed. On the basis of the occurring current and voltage characteristics when applying the supply voltage to the actuator can be closed to the actuator or the valve, which is then operated according to pulse width modulation at its rated power. Preferably, the supply voltage is at least as high as the rated voltage of the actuator.

The thereby flowing current is the control element 60 provided by the current sensor 20 as information available. In addition, the height of the supply voltage U _{V is} measured. From the two information current (here coil current) and voltage (here supply voltage), the impedance of the load 100 can be calculated. The device for detecting current and supply voltage can be integrated in the control element 60 or be present externally. The current sensor 20 may also be integrated in the switching element 10.

The decision with which power the load (coil of the electromagnetic actuator) must be operated is determined in the control element 60 on the basis of the calculated impedance.

Detects the control 60 as a load a coil lower nominal power, the switching element 10 is switched by the control 60 in the clock mode and thus adapted via a pulse width modulated voltage, the power to the load of the coil. The duty cycle within the clock mode is also dependent on the applied supply voltage U _V. With increasing supply voltage, the duty cycle is reduced and vice versa. As a result of this adaptation, the average coil current is kept constant even when the supply voltage U _{V is} variable.

The control is a variety of different inductive loads of different rated power known. The detection of the respective control element via the current and the height of the supply voltage in the overexcited state. The switching frequency of the pulse width modulation (PWM) is selected so high that the inductive load acts like the storage inductor of a switching regulator. At the valve coil, a "quasi" DC current sets in with little residual ripple. Coil current and supply voltage are preferably measured in each cycle. The supply voltage U _V must be at least as high as the nominal voltage of the connected Load. If the supply voltage exceeds the rated power of the control element, it is dynamically switched to cycle mode (and back again). The control elements can thus be operated significantly above rated voltage (limited only by the insulation resistance of the insulation of the coil wire). The PWM is dynamically adapted to the supply voltage. Thus, with a voltage source loads of different nominal voltage can be operated.

By means of the coil current, the switching of the load can be detected and thus valve clamps, e.g. by foreign bodies. The monitoring of the coil current can be used as a short-circuit detection, as an electronic fuse. This increases the short circuit safety of the actuator itself

The circuit device may have an additional control input 80.1, by which the switching on and off of the circuit itself can be controlled

In the embodiment of FIG. 2, two switching elements 10, 30 are provided in the drive circuit 80. Both switching elements, which are designed here as a MOSFET switch, logically as normally open, are switched on and off via control 60 via terminals 60.2, 60.3. In the circuit example, in addition to the switching element 10, there is provided a current sensor 20 (here, for example, a shunt resistor). Indicated at 70 is an internal extinguishing element.

If both switching elements 10, 30 are closed, current flows from the input 80.2 via switching element 10, current sensor 20, via the connected load 100 and via switching element 30 to GND. The electromagnetic actuator turns on. The thereby flowing current is the control element 60 from the current sensor 20 via the A / D converter 40 to the control 60 at the input 60.5 provided as information. In addition, the level of the supply voltage is measured and provided via the A / D converter 50 for voltage measurement to the control element 60 at the input 60.4. From the two information current and voltage, the inductive load is determined.

The circuit works as follows. According to FIG. 3, a digital control signal is present at the input 60.1 of the control element at the time _tIN1 . The control simultaneously closes both switching elements 10, 30. Thus, the voltage U _LAST (U _V - losses on the switching elements 10, 30 and the current sensor 20) at the connected load 100 (valve coil). The coil current I _LOAD increases in an e-function until the time t ₁ . By the movement of the actuator of the actuator from the rest position towards the active end position, there is a short-term interruption of the current increase, until the time t _2, the actuator is in the end position. The current increase reaches the maximum value at time t ₃ . At time t ₃ identifies the control on the basis of the coil current and the supply voltage, the rated power of the connected load 100. In the example of Fig. 3, no power adjustment by means of PWM is required. In addition, the inflection point occurring at the moment of time t ₂ at the time of switch-on can be used to increase the current for function monitoring of the actuator, since this inflection point occurs as a result of the movement of the actuator. In most cases, the curve of the current over time at this point is not monotonically increasing or possibly even unsteady

If a coil of lower rated voltage is connected as the load according to FIG. 4, after the actuator is safely in the end position, it is switched to the cyclic mode. The current and thus the effective power across the coil is reduced to the nominal value of the device to prevent thermal destruction of the coil. In this case, there is a digital control signal at input 60.1 of the control element at time t _IN2 . The control simultaneously closes both switching elements 10, 30. Thus, the voltage U _{LAST is applied} to the connected load 100. The coil current I _LAST increases in an e-function up to the time t ₄ . By the movement of the actuator of the actuator from the rest position towards the active end position, there is also a short-term interruption of the current increase, until the time t _5, the actuator is in the end position. The current increase reaches the maximum value at time t ₆ . At time t ₆ , the control identifies the rated power of the connected load 100 based on the coil current and the supply voltage and clocks at least one of the switching elements 10, 30 at the times t ₇ , t ₈ . as a result, when the voltage U _{LAST is} pulsed, the coil current I _LOAD is reduced.

Reduced during operation, the supply voltage, the duty cycle as shown in Fig. 5 at time t ₉ is increased accordingly and the coil current remains constant, ie, with clocked voltage applies to the current I _LAST in the controlled state regardless of the amount of supply voltage U _V : $$\int I\left(t\right)dt=\mathit{const}\mathrm{,}$$

The overexcitation of the electromagnetic actuator minimizes the variations in duty cycle across various devices in a series and / or different operating points.

LIST OF REFERENCE NUMBERS

10, 30

switching element

20

current sensor

40

A / D converter for current measurement

50

A / D converter for voltage measurement

60

control

60.1,60.4,60.5

entrance

60.2,60.3

connections

70

internal extinguishing element

80

drive circuit

80.1

control input

80.2,80.3

entrance

80.4,80.5

output

100

load

t _ON1

time

t ₁ , t ₂ , .., t ₁₀

time

I _LAST

coil current

U _LOAD

voltage signal

U _V

supply voltage

Claims (11)

Method for controlling an electromagnetic actuator with a circuit device, comprising: an input (80.2) for connection to a supply voltage (UV), an input (80.3) for connection to GND, two outputs (80.4, 80.5) for connecting an actuator, at least one switching element (10, 30) for interrupting the power supply, a device (20) for detecting the current, a control element (60) for measuring current and supply voltage and for controlling the at least one switching element (10, 30), the actuating element, which is actuated by the at least one switching element (10, 30) under pulse width modulation, characterized in that the control element is overexcited for a limited time with a power which is above the rated power of the actuator, and that the control (60) based on current and the height of the supply voltage of the control element in the overexcited state, the rated power based on a variety known to the control , various inductive loads of different rated power determined. A method according to claim 1, characterized in that by means of the at least one switching element (10,30) is generated a pulse width modulated voltage for adjusting the power to the specific power in the connected electromagnetic actuator. A method according to claim 1 or 2, characterized in that the circuit means has an additional control input (80.1), by which the switching on and off of the circuit device can be controlled Method according to one of the preceding claims, characterized in that the device (20) for detecting current and supply voltage integrated in the control element (60) or is present externally or that the means (20) for detecting the current in the switching element (10) is integrated Method according to one of the preceding claims, characterized in that the duty cycle of the at least one of the switching elements (10,30) generated, clocked voltage signal (U _LAST ) of the height of the supply voltage (U _V ) depends. Method according to one of the preceding claims, characterized in that when clocked voltage for the current (I _LAST ) in the controlled state, regardless of the level of the supply voltage (U _V ) applies: $$\int I\left(t\right)dt=\mathit{const}\mathrm{,}$$

Method according to one of the preceding claims, characterized in that when turned on (t _2, t ₅₎ of the at least one turning point in the rise of the current for monitoring the function of the actuator is used. Method according to one of the preceding claims, characterized in that the switching frequency of the pulse width modulation is selected so high that the actuator acts as the storage inductor of a switching regulator. Method according to one of the preceding claims, characterized in that the coil current and supply voltage are preferably measured in each cycle. Method according to one of the preceding claims, characterized in that the supply voltage (U _V ) is greater than or equal to the rated voltage (U _load ) of the actuating element. Method according to one of the preceding claims, characterized in that the method is used on an injection molding machine for processing plastifizierbarer materials, in particular on a plastic injection molding machine.

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