DE102016220686A1 - Method and circuit arrangement for determining a position of a movable armature of an electromagnetic actuator - Google Patents

Abstract

The invention relates to a method for determining a position of a movable armature (103) of an electromagnetic actuator (101), wherein the armature by means of energizing a coil (102) of the electromagnetic actuator (101) is movable, wherein a semiconductor switch (M1), a current sense resistor circuit (RS) and the coil (102) are connected in series, wherein the position (x) of the armature (103) is determined taking into account a frequency of a vibrating signal in a vibratory electrical system, wherein the coil (102) as a frequency-influencing element of the oscillatory electric system is used, wherein a potential at a node between the coil (102) and the current sense resistor circuit (RS) is controlled by means of the semiconductor switch (M1) to a desired value.

Description

The present invention relates to a method and a circuit arrangement for determining a position of an armature of an electromagnetic actuator, which is movable by means of driving a coil of the electromagnetic actuator.

State of the art

Electromagnetic actuators with armature and coil, in which the armature is movable by the coil is energized, are known. Frequently find such electromagnetic actuators in solenoid valves, eg. For hydraulic applications, use. In this case, such solenoid valves can be used as proportional valves by the coil, for example, is controlled pulse width modulated. In this case, due to the inductance, a mean current in the coil. As a counter force to the magnetic force can be provided a spring, but, for example, another coil is conceivable.

However, the actual position of the armature and thus, for example, a control slide or the like connected to the armature often does not coincide with the theoretically predetermined position due to the control. This may be due, for example, soiling or different pressures in the hydraulic lines, which act on the anchor back.

In the not pre-published DE10 2015 213 206.4 For example, a method and a circuit arrangement for determining a position of a movable armature of an electromagnetic actuator are proposed, wherein the position of the armature is determined from a frequency measurement of a charging and discharging current profile of the electromagnet. For example, the coil current is measured by means of a shunt resistor.

It has been found that the measurement when using a typical amplifier circuit with operational amplifiers is both noisy and not very temperature stable. In non-inverting operational amplifier circuits, e.g. multiply the (temperature-dependent) offset voltage into the result. At inverting amplifiers at least still additive. Both types of amplifiers have inherent noise. In addition, noise of the measured variable is recorded and amplified. The described dependence on the offset voltage generates a temperature dependence of the frequency in the oscillation circuit. The noise produces jitter of the output signal which is at the expense of the dynamics e.g. can be compensated by averaging the frequency measurement.

Disclosure of the invention

According to the invention, a method and a circuit arrangement for determining a position of a movable armature of an electromagnetic actuator with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

An inventive method is used to determine a position of an armature of an electromagnetic actuator, which is movable by energizing a coil of the electromagnetic actuator. For this purpose, the position of the armature is determined taking into account a frequency of a vibrating signal in a vibratory electrical system, wherein the coil is used as a frequency-influencing element of the oscillatory electrical system.

Only a slight shift of the position of the armature in the electromagnetic actuator generates even a small change in the current or its course in the coil. Although such a small change is theoretically measurable, this is virtually impossible to carry out, since a resolution of suitable scanning devices usually is not sufficient for this purpose. However, the invention now makes use of the fact that such a small change in the current manifests itself in the frequency of the current profile and thus the frequency of the oscillatory system, since the changes add up each period and are thus easier to measure. In particular, in this way, the coil of the electromagnetic actuator itself can be used to determine the position of the armature and there is no need additional measuring device. This saves costs.

The invention now forms this subject of DE10 2015 213 206.4 in that the magnitude of the voltage across the coil is controlled by a semiconductor switch connected in series with the coil, in particular transistor, is regulated to a desired voltage. If a current measuring resistor circuit, such as a simple shunt resistor, is connected upstream of the coil, the voltage (to ground) at its coil-side pole is known, namely the nominal voltage. The voltage (to ground) at its semiconductor switch side pole corresponds to the sum of the target voltage and the voltage drop across the current sense resistor circuit, which in turn is characterized by the electrical resistance of the current sense resistor circuit and the current flowing through them. The current in turn corresponds to the current through the coil.

Thus, simply by controlling the potential at the node between the coil and the current sense resistor circuit to a set point and detecting the voltage at the semiconductor switch side pole of the current sense resistor circuit, the current through the coil can be determined and determined to determine the frequency and therefrom the armature position , Since an electrical resistance of the current sense resistor circuit due to the regulation no longer affects the current through the coil, the resistance value can be optimally selected for the measurement. There is no need for a transimpedance amplifier or similar. be used for the measurement.

The potential at the node between the coil and the current sense resistor circuit is supplied to a control circuit whose output is connected to the control input (gate, base) of the semiconductor switch. The control circuit may comprise an operational amplifier to eliminate inadequacies of the transistor, e.g. the temperature and component dependency of the base-emitter voltage or the current gain in bipolar transistors or the threshold voltage in MOSFET, compensate. However, this is not used for the measurement.

The invention offers the advantage that the measurement can take place without the use of operational amplifiers. This significantly improves the temperature response, i. the temperature dependence decreases and jitter is significantly reduced. The circuit becomes less expensive and less susceptible to interference, i. robust against interference. Further advantageously, a coil terminal is grounded, so that the coil can be energized externally in addition to the measurement.

Advantageously, to determine the frequency of the oscillating signal in the oscillatable electrical system, the voltage at the node between the coil and the current sense resistor circuit is alternately switched between two values when a resulting coil current reaches an upper and lower threshold, respectively and the frequency of the oscillating signal uses the switching frequency. The two values can be used in the simplest case, the target voltage and zero or a separate power supply. This is a particularly simple way to realize such a vibratory system.

It is advantageous if a measuring voltage corresponding to the coil current and a reference voltage are supplied to a comparator, and wherein the comparator is used to switch the voltage across the coil by driving the semiconductor switch. This is an easy way to generate the alternating voltage. The measuring voltage is generated by the current measuring resistor circuit.

As an alternative to the comparator, the switching of the voltage at the coil takes place by means of a flip-flop circuit controlled by the coil current. For this purpose, it is possible to use switches, for example transistors, with which the alternating voltage is generated by capacitors which are alternately charged and discharged by the rising and falling coil current. Again, an alternating voltage can be generated in a simple manner and the frequency of the coil current can be tapped.

The position of the armature is preferably determined from the frequency by determining an inductance of the coil from the frequency taking into account an ohmic resistance of the coil and from this the position. This is particularly possible if the coil is used as the only frequency-influencing component and / or the frequency influence by other components is known. The increase in the current in the coil when the voltage is applied and the drop of the current at zero voltage or separate power supply are dependent only on the ohmic or DC resistance and the inductance of the coil and the DC resistance of the current measuring resistor circuit. In particular, the method is thus independent of fluctuations in the supply voltage. The higher the inductance, the slower is, for example, the increase. By means of the frequency it is thus possible, with a known ohmic resistance, to infer the inductance of the coil. The inductance in turn depends on the position of the armature relative to the coil. The relationship between inductance and position of the armature can be stored, for example, in a corresponding table. This provides an easy way to Determining the position of the armature. For a detailed explanation, reference is made to the figure description at this point.

Preferably, the current sense resistor circuit is operable having at least two different electrical resistance values. In particular, after switching off the current is waited for restarting to a current value near zero. The timing of the coil current is particularly flat in this range, so that noise in the circuit has a relatively large influence on the timing of the triggering of the comparator. In this case, ie when small currents are to be measured, the use of a current measuring resistor circuit with a particularly high resistance is expedient in order to achieve a correspondingly large measuring voltage drop. This increases the precision of the oscillating circuit due to the lower temporal jitter and reduces the dependence on tolerances (also over temperature) of the measuring resistor. The oscillation is still stable at the lower switching point (near zero). The design of the comparator is simplified.

Preferably, the current sense resistor circuit is operated with a first (smaller) of the at least two different electrical resistance values while the coil current reaches the upper threshold value and is operated with a second (larger) one of the at least two different electrical resistance values while the coil current reaches the lower threshold value.

The switching between the resistance values can be e.g. inexpensively by bridging a resistor with a second semiconductor switch, e.g. MOSFET done whose control input can be connected to the control input of the arranged in the main current path semiconductor switch.

Advantageously, the position of the armature comprises a position corresponding to an end position of the armature without an armature moving energization of the coil. Without such, the armature moving energization, the voltage whose frequency is detected, is not affected, allowing a more accurate measurement is possible. In this way, it is very easy to check an end position of the armature. In addition, the position of the armature can be determined from the frequency very simply by comparing a measured frequency with a frequency which corresponds to an end position of the armature in the de-energized state. The frequency corresponding to this end position of the armature can, for example, be determined and stored once for a solenoid valve. Furthermore, a frequency of an end position can also be used when energized. It should be noted that this does not come into question solenoid valves whose safe state (eg. Closed) is present at fully energized coil. However, this is not the case for the vast majority of applications, since the safe state is usually the de-energized state.

Preferably, a position of a component connected to the armature is determined from the position of the armature. In particular, the electromagnetic actuator for controlling a solenoid valve, in particular a proportional solenoid valve, in particular for hydraulic applications, wherein the armature is connected to a spool, used, and thereby determines from the position of the armature, a position of the spool. As already mentioned, the exact position of the spool is often of interest in such solenoid valves. The position of the armature makes it very easy to deduce the position of the component or spool by taking into account the geometrical dimensions.

A circuit arrangement according to the invention is used to determine a position of an armature of an electromagnetic actuator, which can be moved by energizing a coil of the electromagnetic actuator. In this case, the circuit arrangement has drive means which are set up to control an oscillatory system having the coil as a frequency-influencing element, frequency detection means which are set up to determine a frequency with which a signal oscillates in the oscillatable system, and evaluation means which are adapted to determine from the frequency a position of the armature on. In particular, the circuit arrangement may be constructed such that the coil is the only frequency-influencing element of the oscillatable electrical system.

It is advantageous if the drive means are further configured to switch a voltage on the coil alternately between two values, taking into account a coil current. In such a circuit arrangement is thus a kind of oscillator circuit, in which the coil serves as a time-determining element.

The circuit arrangement preferably also has means in order to carry out a method according to the invention.

Concerning. the advantages of a circuit arrangement according to the invention and the use thereof according to the invention, reference is made to the above statements on the method according to the invention to avoid repetition.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically by means of exemplary embodiments in the drawing and will be described in detail below with reference to the drawing.

list of figures

• 1 schematically shows a solenoid valve, in which a method according to the invention is feasible.
• 2 schematically shows a circuit arrangement according to the invention in a preferred embodiment.
• 3 shows by means of purely schematic voltage curves, the generation of a voltage across a coil according to a method of the invention in a preferred embodiment.

Detailed description of the drawing

In 1 is schematically a solenoid valve 101 shown, in which a method according to the invention is feasible. The solenoid valve 101 , which in the present case is designed as a proportional valve, has an electromagnetic actuator 101 on which in turn a coil 102 and an armature movable therein 103 having.

With the anchor 103 is a control valve 104 connected in a valve body 106 can be moved back and forth. The spool 104 is by means of a spring 105 against one end of the valve housing 106 supported. By controlling the electromagnetic actuator 101 becomes the anchor 103 moves and thus the valve spool 104 against the spring 105 pressed. In this way, the position x of the anchor can be 103 or the valve spool 104 change. This can be the control of the coil 102 For example (via connections not shown here) carried out pulse width modulated.

By the movement of the valve spool 104 becomes a flow through the valve body 106 from a terminal A to a terminal B is set. It is understood that the connections of such a valve can also be configured differently. Likewise, more ports controlled by a valve spool may be present.

In 2 schematically is a circuit arrangement according to the invention 200 shown in a preferred embodiment. For the coil 102 in the present case, its inductance L and its ohmic or DC resistance R _L are shown. The sink 102 is connected in series with a current sense resistor circuit RS and a semiconductor switch (eg bipolar transistor) M1 and connected to a supply voltage terminal V +. A diode D3 serves to prevent a feeding back into the supply voltage when the coil is energized. To the coil 102 is applied by means of the semiconductor switch M1, a voltage V2, which can be switched back and forth between two values or switched.

In the present case, the voltage V2 is switched on and off by the semiconductor switch M1. A control input of the semiconductor switch M1 is for this purpose with a control circuit 230 connected. The control circuit 230 acts for one of the control means 210 provided voltage (switching signal) voltage stabilizing, in particular also over the temperature, and has an operational amplifier K5. A control input of the circuit 230 is connected to a node between the coil and the current sense resistor circuit RS to regulate the level of the voltage V2 there.

In the present case, the resistance circuit RS has a series connection of two resistors R23 and R10, the resistor R10 being bridged by means of a semiconductor switch (eg MOSFET) M2 can. The control input of the semiconductor switch M2 is also connected to the output of the control circuit 230 connected.

Between current sense resistor circuit RS and semiconductor switch M1, a measurement voltage U _{I is} tapped and the drive means 210 fed. The driving means 210 have a comparator or comparator K2, which is supplied via a supply voltage V + and at whose non-inverting input a reference voltage U _R is applied, which is generated via a voltage divider with the resistors R2 and R3 from a supply voltage V + and via a resistor R1 with its own output voltage is fed back.

At the inverting input of the comparator K2 is applied via a resistor R37, the measuring voltage U _I , which is a current in the coil 102 flows corresponds. In this way, the drive means generate 210 in the manner of a Schmitt trigger, a square wave signal with which ultimately the semiconductor switch M1 is turned on and off.

The rest in the 2 shown and not yet mentioned resistors and capacitors, which are not provided with a reference numeral, can be suitably selected. It should be emphasized in particular that in the circuit arrangement 200 shown capacitors only serve to limit the bandwidth of the operational amplifier or comparators and do not affect the frequency of the oscillating coil current.

The driving means 210 control the semiconductor switch M1 (here as a series transistor) so that it turns the coil 102 applied with a square wave signal of known voltage, thus at the circuit point between coil 102 and current sense resistor RS is applied. The the coil 102 flowing current also flows through the current sense resistor circuit RS. The voltage across the current sense resistor circuit is evaluated. A difference measurement is not required because the voltage at the node between coil 102 and current sense resistor circuit RS yes, namely the regulated square wave voltage.

The voltage at the upper terminal of the current sense resistor circuit RS is composed of the regulated square-wave voltage and the voltage component caused by the current. This signal can be returned directly to the comparator K2. The dimensioning of the switching thresholds is expediently adapted so that an offset is taken into account by the square-wave voltage. In contrast to a pure shunt voltage measurement, in which the voltage corresponds to the current and therefore can be directly compared, in the preferred embodiment of the invention on the coil side of the current measuring resistor circuit, the square wave signal is regulated by the OP K5. The voltage drop across the current sense resistor circuit caused by the current appears as an offset on this square wave signal. When choosing the comparator thresholds, the measured square wave signal is thus expediently taken into account.

In 3 the generation of the voltage V2 is shown by purely schematic voltage curves. In each case, a voltage U is plotted against the time t in two diagrams.

The measuring voltage U _I , which is the coil current in the coil 102 corresponds, is, as explained, determined.

über die Zeit t an. R_L bezeichnet dabei den ohmschen Widerstand der Spule 102. Erreicht der Spulenstrom I bzw. die diesem entsprechende Messspannung U_I nun bspw. zu einem Zeitpunkt t₁ einen oberen Schwellwert U_R,₂ und übersteigt somit die Messspannung U_I die Referenzspannung, wie im oberen Diagramm der 3 gezeigt, so wird die Spannung an der Spule durch den Komparator K2 bspw. auf Null bzw. Masse geschaltet und der Spulenstrom I fällt ab gemäß der Formel $$I\left(t\right)\frac{U}{R_L}\text{exp}\left[-\frac{t\cdot R_L}{L}\right].$$

If, for example, initially at a time t _0, a voltage U to the coil 102 is applied, the coil current I increases according to the formula $$I\left(t\right)\frac{U}{R_L}\left(1-\text{exp}\left[-\frac{t\cdot R_L}{L}\right]\right)$$

over time t. R _L denotes the ohmic resistance of the coil 102 , If, for example, the coil current I or the measuring voltage U _I corresponding thereto reaches an upper threshold value U _R , ₂ at a time t ₁ , the measured voltage U _I thus exceeds the reference voltage, as in the upper diagram of FIG 3 shown, the voltage at the coil by the comparator K2, for example, is switched to zero or ground and the coil current I drops according to the formula $$I\left(t\right)\frac{U}{R_L}\text{exp}\left[-\frac{t\cdot R_L}{L}\right],$$

After the coil current I or the measuring voltage U _I corresponding thereto has now eg reached a lower threshold U _R , ₁ at a time t ₂ and thus the measuring voltage U _{I has} the now lower reference voltage (the reference voltage depends on the output voltage of the comparator) undershoots, the voltage V2 is switched to the coil by the comparator K2 back to the previously applied voltage. to 3 It should be noted that the reference voltage U _R with the two limit values U _R , ₁ and U _R , ₂ here oscillates by half the supply voltage V +, if the two resistors R2 and R3 are selected to be the same size and the operational amplifier is a rail-to-rail Type is. The magnitude of the hysteresis of the Schmitt trigger is defined by R1.

The frequency with which the coil current I or with which the voltage V2 applied to the coil is switched back and forth can, for example, with frequency detection means 260 at the output of the drive means 210 or the comparator K2 tapped and evaluation means 270 be supplied. In the evaluation means can now indirectly from the frequency (eg via the inductance L of the coil 102 ) or directly (eg by comparison with reference values) the position x of the anchor 103 be determined.

The frequency or an order of magnitude of the frequency can be adjusted by a suitable choice of the sizes of the components involved in the circuit arrangement approximately to a desired value. The ultimately measured, exact value of the frequency of course depends on the inductance of the coil or the anchor position.

In particular, after switching off the current is waited for restarting to a current value near zero. The timing of the coil current is particularly flat in this range, so that noise in the circuit has a relatively large influence on the timing of the triggering of the comparator. In this case, ie when small currents are to be measured, the use of a current measuring resistor circuit with a particularly high resistance is expedient in order to achieve a correspondingly large measuring voltage drop. This increases the precision of the oscillating circuit due to the lower temporal jitter and reduces the dependence on tolerances (also over temperature) of the measuring resistor. The oscillation is still stable at the lower switching point (near zero). The design of the comparator K2 is simplified.

Therefore, the resistance circuit RS herein has a series connection of two resistors R23 and R10, whereby the resistor R10 can be bypassed by means of a semiconductor switch (e.g., MOSFET) M2. This allows a high resistance (R23 + R10) to be used at low currents and a small resistance (R23 only) at high currents. At least while reaching the respective switching point should be present according to the desired resistance.

The semiconductor switch M2 switches in the illustrated preferred embodiment whenever the voltage across resistor R23 exceeds the threshold voltage of M2. Comparator thresholds, R23 and M2 should therefore be suitably dimensioned so that the switching does not take place just when the coil current (and thus the voltage Ul) is in the vicinity of the comparator thresholds. Then: At the upper comparator threshold is measured with a measuring resistor consisting of R23 (comparator threshold takes into account offset by square wave signal). The lower comparator threshold is measured with a measuring resistor consisting of R23 and R10.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102015213206 [0004, 0009]

Claims (15)

Method for determining a position of a movable armature (103) of an electromagnetic actuator (101), wherein the armature can be moved by energizing a coil (102) of the electromagnetic actuator (101), wherein a semiconductor switch (M1), a current sense resistor circuit (RS) and the coil (102) are connected in series, the position (x) of the armature (103) being determined taking into account a frequency of a vibrating signal in a vibratory electrical system, the coil (102) being used as a frequency-influencing element of the oscillatable electrical system, wherein a potential at a node between the coil (102) and the current sense resistor circuit (RS) is controlled to a target value by means of the semiconductor switch (M1). Method according to Claim 1 wherein, for determining the frequency of the oscillating signal in the oscillatable electrical system, a voltage across the coil (102) is alternately switched between two values when a resulting coil current (I) reaches an upper or lower threshold, respectively; and the frequency of the oscillating signal, the switching frequency is used. Method according to Claim 2 Wherein a coil current (I) corresponding measuring voltage (U _I) and a reference voltage is supplied (U _R) of a comparator (K2), and wherein the comparator (K2) for switching the voltage across the coil (102) is used. Method according to Claim 2 or 3 wherein the switching of the voltage across the coil (102) is effected by means of a flip-flop circuit (310) controlled by the coil current (I). Method according to one of the preceding claims, wherein from the frequency, the position (x) of the armature (103) is determined by an inductance (L) of the coil is determined from the frequency taking into account an ohmic resistance (R _L ) of the coil, and From the inductance (L) of the coil, the position (x) of the armature (103) is determined. Method according to one of the preceding claims, wherein the current sense resistor circuit (RS) is operated at least two different electrical resistance values. Method according to Claim 6 in reference to at least Claim 2 wherein the resistance circuit (RS) is operated with a first one of the at least two different electrical resistance values while the coil current (I) reaches the upper threshold value, and wherein the resistance circuit (RS) is operated with a second one of the at least two different electrical resistance values the coil current (I) reaches the lower threshold. Method according to one of the preceding claims, wherein the position (x) of the armature (103) comprises a position corresponding to an end position of the armature (103) without energizing the coil (102) moving the armature (103). Method according to one of the preceding claims, wherein a position (x ') of a component (104) connected to the armature (103) is determined from the position (x) of the armature (103). Method according to one of the preceding claims, wherein the electromagnetic actuator (101) for controlling a solenoid valve (100), in particular a proportional solenoid valve, further in particular for hydraulic applications, in which the armature (103) is connected to a control slide (104), is used, and from the position (x) of the armature (103) a position (x ') of the spool (104) is determined. Circuit arrangement (200) for determining a position (x) of a movable armature (103) of an electromagnetic actuator (101), which is movable by energizing a coil (102) of the electromagnetic actuator (101), wherein a semiconductor switch (M1), a current sense resistor circuit (RS) and the coil (102) are connected in series with driving means (210, 230) adapted to drive a vibratory electric system having the coil (102) as a frequency-influencing element and a potential at a circuit point between coil (102) and current sense resistor circuit (RS) to a target value, frequency detection means (260) adapted to determine a frequency with which a signal oscillates in the oscillatory system, and Evaluation means (270), which are adapted to determine from the frequency of a position (x) of the armature (102). Circuit arrangement (200) according to Claim 11 wherein the drive means (210, 230) are further adapted to switch a voltage (V2) on the coil (102) alternately between two values, taking into account a coil current (I). Circuit arrangement (200) according to Claim 12 in which the drive means (210, 230) comprise a comparator (K2) which is connected to the current sense resistor circuit (RS) with an inverting input for taking into account the coil current (I) and to which a reference voltage (U _R ) is applied at a non-inverting input. is applied. Circuit arrangement (300) according to one of Claims 11 to 13 wherein the current sense resistor circuit (RS) is operable to have at least two different electrical resistance values. Use of a circuit arrangement (200) according to one of Claims 11 to 14 to carry out a method according to one of Claims 1 to 10 ,

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