Apparatus for Automatically Switching Off and Disconnecting an Electric Motor Shaft Drive Accelerating a Winding Bobbin Once a Circumferential Cylinder Drive Has Become Effective

The present invention relates to textile winding bobbin driving systems, and more particularly, to an apparatus for automatically switching off and disconnecting an electric motor shaft drive which accelerates a winding bobbin and automatically substituting for the shaft drive a synchronized circumferential cylinder drive which engages the winding bobbin as the diameter of the bobbin increases with textiles spun thereon.

Circumferential drives with driving cylinders are very frequently used for spinning the winding bobbins in the chemical fiber industry, since constant thread withdrawal velocities can be maintained relatively easily thereby. These circumferential drives are not always capable of accelerating the empty winding bobbin from standstill to the nominal speed in a relatively short time, however. Therefore, additional shaft drives are utilized which are disconnected once the circumferential cylinder drive has become effective. The change in the torque supplied by the shaft-drive motor due to the activation of the circumferential cylinder drive motor can then be used as a measure of the time at which the shaft drive should be disconnected and turned off. The problem arises, however, that the torque corresponding to the time when the shaft drive motor should be disconnected depends on numerous parameters such as the number of threads to be wound simultaneously, the thread thickness, the thread velocity and the air gap between the bobbin and the driving cylinder.

Accordingly, it is an object of the present invention to provide an apparatus which will automatically disconnect the shaft drive at the proper time dependent on the numerous parameters which affect torque requirements.

According to the present invention, this problem is solved by the provision that after the acceleration of the bobbin by the shaft drive, and after winding of fibers around the bobbin has begun, but before the circumferential cylinder drive has become effective by engaging the bobbin, a value proportional to the torque supplied by the shaft drive motor can be stored and the signal to disconnect the shaft drive outputted if the measured instantaneous value of the torque of the shaft drive motor after the cylinder drive has become effective exceeds the stored value by a predetermined amount. In other words, the signal proportional to torque stored after deposition of the thread on the bobbin but before engagement of the cylinder drive is the desired value at which the shaft drive motor will be disconnected and switched off after engagement of the cylinder drive when both drives are operating in parallel. This value takes into account all of the prevailing conditions.

Synchronous motors fed by frequency converters are generally used as shaft drives. The frequency converter may consist of, for example, a group of rectifiers which change the A.C. line voltage to D.C. connected to a D.C. to A.C. inverter by an intermediate D.C. link. As substitutes for the direct measurement of torque, signals proportional to torque such as the active current in the d-c link circuit of the converter or, for cost reasons, the reactive current at the output of the frequency converter can be measured, by for example, a suitable current transformer or voltage dropping resistor.

To exclude the dynamic torque changes occurring shortly after the deposition of the threads has begun from being stored as the desired torque value, the signal to store is advantageously given a short time after the winding process has begun.

So that the shaft drive motor is not prematurely switched off, for instance, due to relatively different circumferential velocities between the driving cylinder and the winding bobbin, the conditions precedent to switching-off the shaft drive are advantageously checked for their presence only after a predetermined time by appropriately designed circuitry.

The circuit arrangement, according to the invention, can be realized particularly simply by the provision that a signal proportional to the actual current value prevailing after the thread is deposited on the winding bobbin is transferred into a storage amplifier such as a sample and hold circuit, the output signal of which is compared with the instantaneous value of the current by a comparator which in turn generates the command to switch off the shaft drive if the measured value agrees with the stored value. Advantageously, the signal will be generated if the instantaneous value exceeds the stored value by a certain predetermined amount.

Additional objects and features of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in connection with the accompanying drawings.

FIG. 1 is a block diagram of the circuit arrangement; and

FIG. 2 is a graph of the current drawn by the shaft drive motor.

With reference to FIG. 1, a synchronous motor 4 drawing current from a frequency converter 6 with an intermediate d-c link drives a winding bobbin 1 via a controlled clutch 41. By increasing the frequency and voltage output of the converter 6, the bobbin is thereby accelerated to the nominal velocity, which may correspond, for instance, to a circumferential velocity of 4000 meters per minute. If the motor has reached the desired speed, the thread 2 to be wound, which is drawn, for instance from an extruder not shown, is deposited on the winding bobbin 1 at the time t.sub.1, as shown in FIG. 2, by a thread-depositing device 3. The motor current I which is proportional to the torque of the motor 4 thereby increases after short-time dynamic transients have decayed, to the steady-stage value I.sub.a.

A signal proportional to this value is fed via a low-pass filter 92 to a storage amplifier 91 such as a sample and hold circuit. The current value may be measured at the converter output by a suitable current transformer 9, as shown, or in the intermediate D.C. link, as shown by the dotted line 10, by a suitable voltage dropping resistor or other method not shown. Simultaneously, the thread depositing device 3 generates a signal which opens the switch 911 after a delay time t.sub.v1 at the time t.sub.a via the contacts 31 and delay stage 99. The delay stage 99 may consist of a rising edge triggerable monostable multivibrator or single shot outputting a pulse with a pulse width equal to t.sub.v1 driven by trigger circuit 32. The value proportional to the current drawn by the shaft drive motor prevailing at that instance which is proportional to torque, is thereby stored in the storage amplifier 91.

With the increasing diameter of the winding bobbin due to the fibers wound thereon, the gap s between the circumference of the winding bobbin at the beginning of the winding process and the driving cylinder 8 of the cylinder drive driven by motor 5 gradually decreases. The circumferential drive motor 5 is likewise a synchronous motor which is fed from the frequency converter 7. If the gap s disappears at the instant t.sub.2, peripheral contact occurs between the winding bobbin and the driving cylinder 8. Because the circumferential velocities of the winding bobbin and the driving cylinder are well synchronized, the motor 4 is first relieved by the motor 5, so that the measured current I drawn by the motor 4 is reduced according to FIG. 2. With increasing winding diameter, the circumferential velocity of the winding bobbin 1 increases, so that the motor 5 is dragged by the motor 4. The current I of the motor 4 rises again. As indicated in FIG. 2, this current again reaches the stored initial value I.sub.a at the time t.sub.3. This value is exceeded at the time t.sub.4 by an experimentally determined adjustable value .DELTA.I, at which time the signal to disconnect the shaft drive is generated. This is accomplished by the provision that the output of the storage amplifier 91 and the instantaneous value of the current I of the motor 4 at the output of the filter 92 are compared by comparator 94 which, in case of agreement of both values, delivers a signal. The adjustable value .DELTA.I can be taken into account by an appropriate design of the comparator 94 or of the storage amplifier 91.

In order that premature signals to switch off the shaft drive are not generated, the output signal of the comparator 94 is fed to AND gate 95 along with the output signal of a delay stage 98 which is triggered when the switch 31 is closed, and the trigger circuit output caused by the closing of the switch 31. The output of AND gate 95 is then fed into a suitable buffer amplifier stage 101 driving a relay 96. Thus, the signal to switch off the motor 4 cannot be given until at least a time t.sub.v2 after time t.sub.1. When all three conditions are met, i.e., the winding process has begun, corresponding to a positive signal at the output of trigger circuit 32, the comparator output corresponds to agreement of the compared currents and time t.sub.v2 has passed, the output of the AND circuit will go positive, picking relay 96 and delivering the signal via line 97 to the frequency converter 6 to switch off the motor 4 and to the clutch 41 to mechanically separate the winding bobbin from the driving shaft.