DE2258862A1 - CONTROL CIRCUIT FOR RAPID EXCITATION OF ELECTROMAGNETIC SYSTEMS, IN PARTICULAR OF A STEPPER MOTOR - Google Patents

Description

Control circuit for high-speed excitation of electromagnetic systems, in particular of a stepping motor The invention relates to a control circuit for high-speed excitation electromagnetic systems, in particular one that can be switched on by electrical impulses Stepper motor, the rotor of which is spatially opposed to one another by exciting individual of several staggered stator coils can be switched forward with a voltage source Can be connected via power transistors, which one after the other from a pulse generator can be controlled via an impulse distributor.

With such stepper motors, the rotor is set in rotation, that the stator coils, which are spatially offset from one another, are arranged one after the other in time Generate a magnetic field over a certain period of time.

The dynamic properties of these stepper motors are strong Ground from the control circuit. Will z03. : high step frequencies required, so the coils in very nutshell get excited and de-excited for a short time, to achieve a rapid increase and decrease in torque.

The required rapid rise and fall in electricity is based on the Lenz's rule opposes the self-induction of the coil. To build up the magnetic field To accelerate, i.e. to shorten the rise time, are already so-called fast excitation circuits become known, in which initially a higher than the required nominal operating voltage is placed on the coil.

This improves the current rise time di / dt.

For example, a capacitor can be used with the coil for this purpose bridged series resistor can be connected in series. During the series resistor according to the relationship # = L / R the electrical time constant is reduced, bridged the capacitor at the time of switching on the series resistor Rv, so that at the Coil is initially at full operating voltage. After charging the capacitor the differential voltage between Jenn voltage and the overvoltage falls across the series resistor away.

There is also the option of using two different operating voltages to be provided, namely a higher high-speed excitation voltage and a permissible nominal voltage, with the help of a switch gate controlled by a timer one after the other to the Coil.

The majority of the circuits known so far have the disadvantage that in spite of the considerable effort, you only have the tension, not the most important Regulate the size, namely the coil current. When using series resistors falls on this from a considerable power loss, whereby the efficiency deteriorates will and the power supply must deliver a high continuous output.

Finally, it is to improve the efficiency and to increase it The step frequency of such stepper motors is just as important as that in the coil stored magnetic energy E = 1/2 LI² is reduced in a very short time, This results in a rapid drop in torque when the respective coil is switched off to reach. The problem here is that transistors are used as switching elements that only allow limited switch-off voltages. Because the level of the cut-off voltage according to the C-calibration u = - L. di / dt is inversely proportional to the switch-off time, With short switch-off times, it can easily reach values that lead to destruction of the transistor lead. With such circuits it is also important, to limit the disconnection voltages in their llöhe despite the shortening of the disconnection times.

The present invention is based on the object of a control circuit to create an increase in efficiency while avoiding the disadvantages mentioned above as well as the Schrfttfrequenzen of the stepper motors to be controlled allows, but not the coil voltage but the coil current is to be regulated.

In itself, a circuit is known in which the mean value of the Motor current between two values with the help of a two-point constant current controller is kept constant.

However, the known circuit is very complex and therefore expensive 9 because separate assemblies are required for the control.

This circuit becomes essential to the present invention Simplified that the power transistors in the motor circuit both for switching over the respective stator coil as well as for two-point constant current control day-controlled, that is, without additional control elements, directly for current regulation 0 The two-point control causes the transistor power loss compared to the power loss of a continuous controller is lower because the respective The auxiliary transistor is either fully conductive or fully blocked when switching on the full operating voltage is applied to the coil, which is a multiple of the nominal voltage the coil current rises steeply according to an exponential function. Dl; rch the current control it is limited when the prescribed nominal current is reached0 from this point in time from the current is switched off and on in short intervals, I'm chopped "so that the induction effect of the coil results in a constant direct current, to which a current that is not detrimental in its effect has a relatively low ripple, which is caused by the hysteresis of the two-position controller, is superimposed.

If in the proposed way the power transistors for current regulation are used, it is recommended to control them via a UNG gate, whose first gate each with the pulse distributor and its second gate each with the Output of a comparator are connected, which the output stage transistors in such a way controls that it opens in the manner explained above when the rated current is reached and are closed0 For this purpose is applied to the first input of the comparator a constant target voltage acting as a reference voltage and at the second input an actual voltage proportional to the stator coil current.

A particular advantage of this circuit is that to control the Coil current and thus for setting the Engine torque only the reference voltage needs to be changed.

To produce the desired hysteresis behavior, the output of the comparator is connected to its second input via a positive feedback resistor which results in the desired two-point control. For example, can the circuit can be designed so that the stator coil current has a ripple current a frequency of e.g.

5 kHz is superimposed.

A particularly simple circuit structure results if, as further it is proposed that the emitter of the auxiliary transistors with the voltage source are connected across a common emitter resistor at which the voltage is for the comparator is tapped 0 In this circuit arrangement, the current flowing through each coil at the common resistor an actual voltage, which is compared with the soft voltage in the comparator.

If the actual voltage is lower than the target voltage, the means of of the pulse distributor selected power transistor conductive. The coil current increases consequently on, which increases the actual voltage occurring at the emitter resistor will. If the actual voltage has reached the target voltage, the respective output stage transistor becomes locked.

Only when the actual voltage has increased by one through the positive feedback resistor the power transistor becomes reopened and the explained process is repeated anew.

Since in this circuit arrangement the at the common emitter resistor falling voltage with the power transistor closed «, u becomes zero, is after another proposal of the invention between the emitter resistor and to the second input, the comparator, a replica of the inductance is arranged. she causes the actual voltage at the second input of the comparator to be similar as the coil current drops after an exponential function, so that the power transistor is not opened again immediately.

In a manner known per se, the simulation consists of two in the longitudinal branch arranged ohmic resistors and a capacitor in the shunt arm.

As already mentioned at the beginning, this is also the case with such circuits It is important that the cut-off voltages are safe for the transistor be limited.

In order to achieve this, in the exemplary embodiment according to the invention Circuit between the collectors and the bases of the power transistors Zener diodes arranged, which together nib the power transistors as controlled Freilarfdioden works.

It turns the magnetic energy stored in the coil into dismantled in the shortest possible time.

On the other hand, it is in accordance with the invention when regulating the coil current It is not practical if the current drops too quickly, as is the case with the combination caused by power transistor and zener diode, as in this case the transistor is switched on most of the time because the dissipated by the rapid de-energization Energy of the coil needs to be replaced. This would result in a relatively high output gain out of the power supply.

In order to prevent this, the invention also provides a so-called erase circuit proposed that the high-frequency switching on and off the control device a slow one The F, nergy stored in the coil is reduced and no rapid degradation when changing from one stator coil to the other which then enables an effective combination of Zener diode and power transistor.

These quenching circuits consist of arranged parallel to the stator coils semiconductors controlled by the pulse distributor, in series with one for the cut-off current the coil are connected in the forward direction arranged diode. As controlled Semiconductors are suitable e.g. Transistors, thyristors or similar switching elements, in which the use of the diode can possibly be dispensed with These switching elements are, controlled by the pulse distributor, conductive as long as the respective power transistor is controlled by the pulse distributor, the respective line transistor is when switching off through the impulse distributor as a result of the self-induced voltage of the Coil over the Zener diode arranged between the collector and the base for quick de-excitation only blocked to the extent that the permissible collector-emitter voltage is not exceeded will.

The measures proposed by the invention are not suitable only for switchable stepper motors, but are basically for high-speed excitation or de-excitation of electromagnetic systems, e.g. also suitable for electromagnets, which are now required on a large scale for tax purposes.

Ger subject of the invention is below with reference to one in the drawing illustrated circuit diagram of a circuit arrangement according to the invention.

The controlled stator coils S1, S2 and S3 are each via the power transistors T1, T2 and T3 and the common emitter resistor RE with the connection terminals B1 and B2 of a DC voltage source connected, for example from a Graetz rectifier consists. A so-called control logic SL is provided to control the power transistors. which essentially consist of a pulse generator (not shown) and a pulse distributor consists. The outputs of the control logic are each connected to a gate g21, g31, the respective UD gates G1, G2 and G3 are connected, the outputs of which are g12, g22 and g32 lead to the bases of the power transistors TI, T2 and T3. The remaining gates g13, g23 and g33 are connected to the output K3 of the comparator K, both of which Inputs Kl or K2 on the one hand the reference voltage URef and on the other hand the Actual voltage UI falling across the common emitter resistor RE is supplied0 Between the second input K2 of the comparator and the emitter resistor RE is an X element with the resistors R1 and R2 around the series branch and the capacitor Cl arranged in the cross arm, this T-link represents a simulation of the inductance of the stator coils S1, S2 or S3. It has the effect that when the transistors are blocked Tl, T2 or T3 the input voltage at terminal S2 of the comparator similar to the current of one of the stator coils drops according to an exponential function.

Furthermore, there is between the input K2 of the comparator and its output K3 a positive feedback resistor RH is provided that the hysteresis behavior explained at the beginning which controls the current.

Serve to reduce the magnetic energy stored in the coil when switching on and off at high frequency, i.e.

i.e. when regulating the current through the two-position controller, Extinguishing orders, those from the transistors T4, T5, and T6 and those connected in series with them Diodes D4, D5 and D6 exist, the latter inversely operating the transistors Prevent T4, T5 and T6. The transistors T4, T5 and T6 are connected via equipotential bonding circuits n, P2 or P3 from the control logic SL, which consists of a pulse generator and distributor driven in such a way that they are only conductive when the associated power transistors T1, T2 and T3 are controlled by the pulse distributor.

If the associated power transistor, e.g. the transistor T1, of the control device is switched on in the manner explained, so that germs in the coil S1 stored magnetic energy through the open transistor T4 and the now Diode D4 lying in the forward direction are dismantled 0 when the next one is activated Transistor, e.g. of transistor T2, on the other hand transistor T4 is blocked again, so that the magnetic energy stored in the coil 51 passes through the transistor T1 is dismantled.

Claims (9)

Claims Control circuit for high-speed excitation of electromagnetic systems, in particular for a stepper motor that can be switched on by electrical impulses, its rotor by excitation of some of several that are spatially offset from one another Stator coils can be switched to a voltage source via power transistors can be connected, which one after the other from a pulse generator via a pulse distributor are controlled, the mean value of the stator coil current using a Two-point constant current control is kept constant, characterized in that the power transistors (T1, T2, T3), although for switching over the respective stator coil as well as for two-point constant current control. 2. Circuit arrangement according to claim 1, characterized in that the power transistors (T1, T2, T3) controlled via AND gates (G1, G2, G3) whose first gate (g11, g21, g31) each with the pulse distributor and their second gate (g13, g23, g33) each connected to the output (K3) of a comparator (K) are, at the first input (K1) is a reference voltage (URef) acting constant Setpoint voltage and at its second input (K2) one proportional to the stator coil current Actual voltage is present. 3o. Circuit arrangement according to Claims 1 and 2, characterized in that that the reference voltage for coil current regulation can be changed 0 4. Circuit arrangement according to claim 2 or 3, characterized in that the output (K3) of the comparator (K) with its second input (E2) to generate a hysteresis behavior a positive feedback resistor (Rg) is connected. 5. Circuit arrangement according to claims 2, 3 or 4, characterized in that that the emitters of the power transistors (T1, T2, T3) with the voltage source (B) are connected via a common emitter resistor (RE) to which the Actual voltage (UI) for the comparator (K) is tapped. 6. Circuit arrangement according to claim 5, characterized in that between the second input (K2) of the comparator (K) and the common emitter resistor (RE) to simulate the coil inductance; iv, it would be a T-link consisting of two Ohmic resistances (R1, 'R2) in the series branch and a capacitor (C1) in the shunt branch, is arranged. 7. Circuit arrangement according to one or more of claims 1 to 6, characterized in that for quick de-energization of the stator coils (51,52,53) between the bases and the collectors of the power transistors (T1, T2, T3) Zener diodes (Dl, D2, D3) are arranged. 8. Circuit arrangement according to one or more of claims 1 to 7, characterized in that parallel to the Stator pulses (S1, S2, S3) each have a semiconductor that is starred by the pulse distributor, in particular one Transistor (T4, T5, T6), is arranged in series with a diode (D4, D5, D6). 9. Circuit arrangement according to claim 7 and 8, characterized in that that the controlled parallel to the respective stator coil (S1, S2, S3) arranged Semiconductor (T4, T5, T6) is conductive as long as the stator coil (S1, S2, S3) from Pulse distributor is controlled, and that the respective power transistor at Shutdown by the pulse distributor as a result of the self-induction voltage generated the coil via the zener diode (D1, D2, D3) is blocked for rapid transfer to the extent that the permissible collector-emitter voltage is not exceeded.