Untitled record

Speed ​​Control Apparatus for a DC Series Motor Motor There are known speed control apparatuses for a DC series motor in which the speed control of the DC series motor is provided by a controllable rectifier powered from an AC power source.

Furthermore, the use of inductive encoders for speed control of electric motors by appropriate control of a rectifier located in the motor circuit is known per se. Finally, differential transformers are also known as inductive sensors.

The main object of the invention is to provide a device for controlling the speed of the pre-marked type, in which a greater freedom in the arrangement of the controlled rectifier in the circuit is possible. In a device for controlling the speed of a supplied via a controllable rectifier from an AC power DC series motor, the rectifier is controlled according to the invention via a diode by the sum of the armature voltage and an adjustable AC voltage, which is taken as a secondary voltage to a primary side connected to the AC power source inductive sensor.

In a practical embodiment of the invention, a differential transformer may be used as the inductive transmitter having two primary windings connected in series and inductively counteracting the AC source, and further comprising a secondary winding coupled to the primary windings by an adjustable armature ,

According to a further embodiment of the invention, a transformer is provided as an inductive sensor having a connected to the AC power source and a secondary secondary winding, which is inductively coupled to the primary winding by an adjustable armature.

By changing the inductive coupling becomes a stepless control voltage change, which allows for their electrical isolation from the supply voltage, a greater freedom in the arrangement of the controlled rectifier in the circuit. This further results in the advantage of a reduced energy spread, and the reliable operation of the device is increased by the elimination of any sliding contacts.

The invention will be explained in more detail below with reference to the drawing, for example. F i g. 1 is a schematic diagram of a device according to the invention; F i g. 2 gives an amendment to the one in FIG. 1 embodiment shown again; F i g. FIG. 3 shows a modification of FIG. 2 illustrated embodiment.

According to F i g. 1 is a DC series motor which, connected in series, has a field winding 10 and an armature winding 11 connected in series with an anode 12 and the cathode 13 of a silicon controlled rectifier 14 to an AC power source LL. A differential transformer as inductive sensor 15 has two primary windings 16 and 17, which are connected in series, but inductively opposing each other to the power source LL. An ohmic resistor 18 may, as shown, be connected in series with the primary windings 16 and 17 to reduce the voltage applied to the windings. The necessary impedance may of course be provided alone in the primary windings 16 and 17, of course.

A secondary winding 19 of the transformer is arranged symmetrically between the primary windings 16 and 17, and an adjustable armature 20 is used to change the mutual inductive coupling between the windings. When the armature 20, for example, in its in F i g. 1 is shown, causes the same coupling between each of the primary windings 16 and 17 and the secondary winding 19, the wastage of the resulting flow (due to the inductively opposing windings 16 and 17), so that in the secondary winding 19, no voltage is induced.

If the armature 20 from the in F i g. 1 position is shown, the coupling between the windings 16 and 19 is increased and that between the windings 17 and 19 is reduced. This differential action causes an alternating voltage of a predetermined phase position to be induced in the secondary winding 19, wherein the magnitude of the voltage is substantially linearly proportional to the armature movement. In a corresponding way, when the armature 20 of the in F i g. 1 in the secondary winding 19 induces an alternating voltage whose phase position is opposite to that which is caused by the upward movement of the armature 20 from the center position, and their size is also substantially linearly proportional to the armature movement.

The secondary winding 19 of the transformer therefore provides a control AC voltage of reversible phase and a magnitude proportional to the armature movement. This control voltage is applied in series with the DC voltage at the armature winding 11 between the control terminal 21 and the cathode 13 of the silicon controlled rectifier 14. In this circuit, a diode 22 is arranged, which has such a polarity that it passes only a positive voltage to the control terminal 21.

Since the rectifier 14 is only conductive when the control terminal 21 and the anode 12 with respect to the cathode 13 are positive, and since this condition is met only in the one direction of movement of the armature 20 from its center position, it follows that any other position the armature 20 generates no such control voltage, so that the motor stops in this area of ​​the armature movement. In this way, it is easily possible by means of the differential transformer to obtain a position corresponding to zero for the armature 20. When the armature 20 is moved in the direction in which a control voltage of the correct phase position for igniting the rectifier 14 is supplied, a stepless speed control is obtained, which is substantially linearly proportional to the armature movement.

Due to the fact that in this circuit, the control voltage is electrically isoiiert from the supply voltage, in the arrangement of the controlled rectifier 14 itself a certain freedom is possible. For example, the circuit according to F i g. 1 functionally not be changed if the field winding 10 between the anode 12 and the junction of the winding 17 with the one terminal of the power source LL would be arranged in series.

F i g. FIG. 2 shows a modification of the device according to FIG. 1, which differs from this essentially in that the inductive sensor 15, the primary winding 16 is omitted, which is a simple transformer with two windings and modified coupling instead of the differential transformer of F i g. 1 results. In this device, only one primary winding 17 is used. The coupling between the primary winding 17 and the secondary winding 19 can in turn be changed by moving the armature 20. The operating characteristics are substantially the same as those of the differential transformer control circuit shown in FIG. 1, with a single exception. The minimum speed of the motor in the device according to F i g. 2 is determined by the smallest coupling between the primary winding 17 and the secondary winding 19. Since there is always a certain coupling between these two windings, it is impossible to forcibly produce a zero control voltage so that, instead of the standstill, a slow rotation of the motor shaft can result.

An advantage of the device according to FIG. 2 is that the linear movement of the armature 20 causes a logarithmic change in the control voltage, whereby the control range for low speeds without the use of complicated mechanical link connections can be extended.

Further modifications of the circuit according to F i g. 1 are possible by the addition of one or two capacitors 24, 25 (shown in dashed lines in FIG. 1), which are connected in parallel to the primary windings 16 and 17. These capacitors have the effect of changing the speed-torque characteristic by shifting the phase position of the control voltage.

Similarly, in the device according to FIG. 2, a capacitor 26 (shown in dashed lines) may be added to shift the phase position of the control voltage relative to the voltage of the current source LL.

F i g. FIG. 3 shows a device substantially similar to that shown in FIG. 2, with the exception that a DC series motor can be used, in which two field windings 10a, 10b are provided, which are connected symmetrically on each side of the armature winding 11. In this case, the winding 10 b forms part of the control circuit between the control terminal 21 and the cathode 13 of the controlled rectifier 14th It has been found that the arrangement of one field winding 10b in the control circuit does not appreciably degrade the speed-torque characteristic and is a circuit arrangement applicable to two-field winding motors, which is simpler than one in which the controlled rectifier 14 is connected between the armatures and the one field winding would be switched. The device according to F i g. 3 is therefore also within the scope of the invention.