GB2228774A

GB2228774A - Drive train monitoring and braking system

Info

Publication number: GB2228774A
Application number: GB8925131A
Authority: GB
Inventors: Anton Munzebrock
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1988-11-07
Filing date: 1989-11-07
Publication date: 1990-09-05
Anticipated expiration: 2009-11-07
Also published as: DE3838058C3; FR2638728B3; GB8925131D0; DE3838058A1; GB2228774B; DE3838058C2; FR2638728A1

Description

1 Drive Monitoring System for a Drive Train The invention relates to a

monitoring system for a drive train between a motor and a load application point such as a cable drum. Typically, such a drive train includes a shaft, clutch or similar transmission system.

When the motor is driving in a train of the above type, the transfer of force and power runs from the motor to the load. When braking, the load drives and the flow of force and power is reversed, with the result that the motor or its brake must absorb energy. If the drive train between load and motor or load and brake is interrupted, the load moves in uncontrolled fashion. In many cases, particularly in the case of hoist mechanisms, this gives rise to a dangerous condition which should be detected and remedied as early as possible.

The cable drums of hoist mechanisms are often allocated safety brakes, as disclosed in German Patent Specification No. 31 37 523. However, these only respond in the case of grossly excessive speed and, during the subsequent braking, lead to high stressing of the supporting structure.

The aim of the invention is to design a safety device in such a way that it monitors the flow of force b6tween the input and the output side or braking and output side of a drive train and, in the case of an interrupted flow of force, detects this condition as early as possible and immediately brings about the intervention of the brake. To this end, the invention provides a drive monitoring system in a drive train between a motor and a load application point in which a first rotary pulse generator is arranged on a shaft from the motor to a service brake therefor, the first pulse generator being connected to a second rotary pulse generator at the load application point via a monitoring logic unit, and the logic unit being operative, in the 2 event of a pulse difference, to switch in a brake at the load application point. Thus, use of the invention can bring about the intervention of the brake in the event of even the slightest speed deviations and thus prevents sudden overloading upon braking the previously accelerated load.

In preferred embodiments of the invention, the monitoring logic unit contains pulse counters which are associated with the pulse generators, are provided with counter adjusters, and are connected to a flip-flop storage which is connected via a relay and a triggering line to an air-core solenoid of the brake at the load application point. The brake is typically spring- loaded. The pulses of the pulse generators are evaluated by the monitoring logic unit by means of at least one preadjustable pulse counter, the pulses of the generator on the output side acting as synchronizing signals for the preadjustable pulse counter, so that with each synchronizing pulse the preadjustable counter is loaded with its initial value and between two synchronizing pulses the pulses of the generator on the input side continuously decrement the initial value loaded. Between two synchronizing pulses, it is determined whether a certain threshold value of the counter is being reached and it is thereby established whether the drive train has been interrupted.

An embodiment of the invention will now be described by way of example and with reference to the accompanying schematic drawing wherein:

Figure 1 shows the arrangement of a drive train for a cable hoist mechanism; and Figure 2 shows the elements of the monitoring logic unit in the arrangement of Figure 1.

As shown in Figure 1, a motor 3 drives a transmission 7 via a shaft 2 and is braked by a service brake 4 on the same shaft. A cable drum 8 is driven via 3 the transmission 7, with the result that a load is raised or lowered in accordance with the direction of rotation of the motor. With the drive train uninterrupted, the speeds of drum shaft 6 and motor shaft 2 have a fixed relationship which is determined by the transmission ratio. In the event of an interruption of the drive train, e.g. due to breakage of the transmission, this fixed speed dependency no longer applies, with the result that, depending on load conditions, very rapid changes in speed can occur. The pulse generators on the input side and on the output side supply pulse frequencies proportional to the speed. The ratio of the pulse frequencies is a product of the number of generator pulses per rotation of the motor shaft and of the drum shaft respectively and of the transmission ratio of the transmission in accordance with the following formula:

fm/fr = (nm/nr) x i fm being the pulse frequency of the generator 1 on the motor shaft and fr being the pulse frequency of the generator 5 on the drum shaft. Here, nm and nr are the number of generator pulses per shaft rotation and i is the transmission ratio. The ratio of the pulse frequencies is thus proportional to the transmission ratio and fbr the special case where both generators produce the same number of pulses per rotation is equal to i. The pulses of the generators 1 and 5 are transmitted to the monitoring logic unit 10 via pulse lines 17 and 18.

By means of the monitoring logic unit 10, the ratio --of motor speed and drum speed is determined from the generator pulses and compared to the known transmission ratio i. Figure 2 shows a correspondingly constructed monitoring logic unit 10 which, in the event of pulse deviation, brings about the intervention of the brake 9 of the drum 8 via a triggering line 19.

The pulses of the motor pulse generator 1 are 4 counted in two pulse counters 11 and 12. The pulse counters are preferably decrementers. They decrement the initial counter contents which are accepted by the input CI and can be adjusted by means of the counter adjusters 13 and 14. The pulses of the drum pulse generator 5 synchronize and control the acceptance of the initial counter contents via the inputs 5 of the pulse counters, so that between two pulses of the drum pulse generator 5 the initial counter contents of the two pulse counters are decremented by the number of the motor pulse generator. Each of the pulse counters has a carry output CO, which changes over if the contents of the counter fall below zero and thus indicates "counter overflow".

Because of the fixed ratio already described of the pulse frequencies fm and fr for a given transmission ratio i, a constant number of pulses of the motor pulse generator 5 will always decrement the initial counter contents of the pulse counters 11, 12 between two pulses of the drum pulse generator 5. According to the inven- tion, the initial counter contents 13 and 14 are chosen so that, for the given transmission ratio i, the first pulse counter 11 just fails to reach counter overflow and the initial counter contents are then set lower for the second pulse counter 12, with the result that at the time of the next drum pulse the counter overflow has always been reached. The state of the carry outputs CO of the two pulsd counters-11 and 12 at the time of a drum pulse indicates whether the number of pulses set by means of the counter adjuster 13 has been exceeded since the last drum pulse and whether the number of pulses of the motor pulse generator 1 set by means of the counter adjuster 14 has been reached.

In the case where the drive train is not interrupted, the first pulse counter 11 must not overrun and the second pulse counter 12 must always overrun. Monitoring of this malfunction-free condition is effected using a flip-flop storage 15 which with each pulse of the drum pulse generator 5 detects the condition of the carry -1 outputs of the two pulse counters and, in the non-malfunction-free condition, switches off the relay 16, with the result that the associated output contact opens and interrupts the circuit of the air-core solenoid 20 of the brake 9 of the drum 8. As shown, the brake 9 is loaded by a spring 21.

In the case where the pulse generators 1 and 5 produce the same number of pulses per rotation, the first counter adjuster 13 will be set to an integer i+X and counter adjuster 14 will be set to an integer i-X. The value X will expediently be chosen so that torsional vibrations resulting from the spring action of the drive train do not trigger the malfunction monitoring system.

A simple variation of the drive monitoring system described, in which the pulse counter 11 and the associated counter adjuster 19 are omitted, is possible. In this embodiment, the monitoring system only responds when the ratio of input speed to output speed is smaller than the ratio set, i.e. the drum is rotating too fast, for example because of a breakage of the transmission, and as a result the number of pulses set by means of the counter adjuster 14 is not being reached.

Generators with different numbers of pulses can also be used or different values of X can be chosen, in order to achieve optimum matching to particular drive configurations.

A 1 6

Claims

1. A drive monitoring system in a drive train between a motor and a load application point in which a first rotary pulse generator is arranged on a shaft from the motor to a service brake therefor, the first pulse generator being connected to a second rotary pulse generator at the load application point via a monitoring logic unit, and the logic unit being operative, in the event of a pulse difference, to switch in a brake at the load application point.

2. A system according to Claim 1 wherein the monitoring logic unit has a pulse counter adjustable by a counter adjuster of the first pulse generator, the pulse counter being connected to a flip-flop storage which is connected via a relay and a triggering line to an air-core solenoid of the brake at the load application point.

3. A system according to Claim 1 wherein the monitoring logic unit has a pulse counter, preadjustable by a counter adjuster of the second pulse generator and a further pulse counter adjustable by a counter adjuster of the first pulse generator, the pulse counters being connected to a flipflop storage which is connected via a relay and a triggering line to an air-core solenoid of the brake at the load application point.

4. A system according to any preceding Claim wherein the brake at the load application point is spring-loaded.

5. A drive monitoring system substantially as described herein with reference to the accompanying drawing.

6. A drive train between a motor and a lifting device including a monitoring system according to any preceding Claim.

7. A drive train according to Claim 6 wherein the lifting device is a cable drum.

Published 1990 wThe Patent =ice. State House. 6671 High R-:tibnrn.london WC1R4TP.Parther copiesmk.,be obtainedfrom ThePatent=lce Sales Branch. St Mary Cray. Orpington. Kent BR5 3RD Prir ted by Multiplex techniques ltd. St MarY Cray. Kent. Con. 1'87 i