GB2225568A - Device for limiting the downward travel of a lift at low tripping speeds with transmission gearing - Google Patents

Description

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i 1 9 9 2 5 568 1 "Device for limiting the downward travel of a Lift- The invention relates to a device for Limiting the downward travel of a Lift that includes a Limiter wheeL driven at a speed corresponding to that of the Lift cage that actuates, via a rotating cam plate, a pendulum which, if the speed of rotation of the Limiter wheel is too high, swings so far out that a pawl thereon strikes against one of a plurality of stops that are rotating with the Limiter wheel and Locks it, thereby tripping a device for arresting the Lift cage.

Such a device is described in European Patent 121 711. In this device the cam plate and the stops are arranged on the Limiter wheel and rotate at the same speed as the Limiter wheel. As a rule the cam plate has four cams arranged uniformly around its periphery and associated with an equaL number of stops.

The known device very reliably prevents a too rapid descent of the lift cage and is suitable for tripping speeds of 0.4 to 3.2 mls. It is however difficult to set lower tripping speeds since the acceleration of the pendulum by the cams on the cam plate is too small, so that the period of oscillation of the pendulum is too long.

It is an object of the invention to improve a device of the abovementioned kind so that it also operates at low tripping speeds, preferably in the range from 0.10 to 0. 40 mls.

To this end, according to the invention transmission gearing is arranged between the cam plate and the Limiter wheel in a device of the abovementioned kind. The stops are connected to the Limiter 2 wheel and are directly driven by it at the same speed of rotation, while the cam plate is driven via the transmission gearing at a higher speed of rotation so that the cam or cams on the cam plate can impart to the pendulum a high enough acceleration for it to Lock the Limiter wheel at a predetermined, adjustable tripping speed and trip the device for arresting the Lift cage.

In this way the pendulum is caused to oscillate by the more rapidly rotating cam plate, and if the tripping speed is exceeded it engages directly with the stops and Locks the Limiter wheel so that the cage arresting-device is tripped without subjecting the transmission gearing and the cam plate to excessive strain when Locking occurs. Thus the transmission gearing need only be of a suitable size to drive the cam plate, and it can therefore very easily comprise gear wheels of plastics material. The transmission ratio of the transmission gearing between the cam and the Limiter wheel may advantageously be about 4:1. This transmission ratio can be obtained in only a small space by means of two pairs of gear wheels having a 2:1 diameter ratio. If four stops are distributed uniformly around the Limiter wheel, the cam plate need only have one cam in order to cause the pendulum to swing synchronously with the rotation of the stops.

p 1 a t e To enable the Lift drive to be disengaged in advance and possibly to enable a bearer rope brake, e.g. a jaw brake, to be engaged before the Limiter wheel reaches the tripping speed, a safety switch with its switching point suitably set can be arranged in the range of oscillation of one arm of a pendulum.

The arrester catch, which is acted on by the fork- shaped damping spring, can also serve to actuate a 1 3 switch arranged in the range of the arrester catch when the Limiter wheel reaches the tripping speed.

The invention will now be described in more detail, by way of example, with reference to an embodiment illustrated in the drawings, in which:

Fig. 1 Fig. 2 shows a side view, and shows a front view of the device according to the invention.

A pendulum 2 is carried in bearings on a bearing pedestal 1; it is supported through an extension (not shown) on a spring (not shown), housed in an arrester catch 3, whose tension can be varied by means of an adjusting screw 18. After setting, the adjusting screw 18 is secured against rotation by means of a lock nut 19.

Fixed to the end of one arm 14 of the pendulum is a pin 20, on the free end of which a penduLum roller 4 is rotatabLy mounted. The penduLum 2 has a pawl 15 at its other end. In a circumferential groove in the pendulum roller s'+ there is an O-ring 5 which roLLs on the periphery of a cam plate 11 on which there is a cam (not shown). A safety switch 6 is mounted within the range of movement of a further cam 8 arranged on the pendulum arm 14. A Limiter wheel 9 having a rope groove is rotatabLy mounted between the bearing pedestals 1 and carries on one side four uniform Ly distributed stops 13 and on its other side a gear wheeL of a transmission gear 12. A pair of gear wheels 22 of the transmission gear 12 is rotatabLy mounted on a bracket 21 and acts on a gear wheel that rotates with the cam plate 11, the pairing of the gear wheels being selected to give an overall transmission ratio of 4:1.

4 The pendulum 2 and the arrester catch 3 are mounted on an axle 16 that is mounted to rotate in the bearing pedestal 1 and carries a switch cam 17 at its other end. The switch cam 17 is held between the limbs of a forkshaped damping spring 10 that bear on its side faces. A further limit switch 7 may if desired be arranged in the region of the arrester catch 3 when this is provided with a corresponding switch cam.

The device according to the invention operates as follows:

An endless rope (not shown) of which the closed strand is driven by the Lift cage and runs over the Limiter wheel 9, runs parallel to a Lift. The pendulum 2 is caused to swing by the action of the cam on the cam plate 11. Below an adjustabLe tripping speed the pendulum roller 4 does not Lift from the cam, so that below this tripping speed the-pawL 15 of the pendulum 2 cannot come within reach of the rotating stops 13. If the speed of rotation of the Limiter wheel 9 exceeds the set tripping speed, the pendulum 2 is so greatly accelerated by the cam on the cam plate 11, which is turning at four times the speed of rotation, that the roller 4 and thus the pendulum 2 is no Longer able to follow the contour of the cam plate 11 but instead lifts off. The pawl 15 then engages behind one of the stops 13 and locks the limiter wheel 9, whereby the device for arresting the lift cage is tripped by the endless rope.

In the case of lifts which have to be provided with preliminary switching off means that acts before the arrest switching and puts the main driving motor out of operation, this can be done by the safety switch 6.

Thus before the speed limiting device reaches the tripping speed, the more pronounced up-and-down osciLLatory movement of the pencluLum 2 causes the safety switch 6 to be operated through the cam 8 fixed to the penduLum 2. The switching point is set by adjusting the safety switch 6. The safety switch couLd aLso be connected to a brake acting on at Least one of the ropes hoLding the Lift cage.

Besides the safety switch 6 the limit switch 7 is operated by the switch cam 17 when the tripping speed is reached.

Since the cam pLate 11 rotates at four times the speed of the Limiter wheeL 9 the acceLeration imparted by the cam or cams of the cam pLate 11 to the pencluLum roLLer 4 and thus the penduLum 2 is aLso Large enough, even at Low tripping speeds, to bring about Locking of the Limiter wheeL 9 by the pawL 15 that has come within reach of one of the stops 13. The gearing 12 is not stressed by this, and it can be smaLL in size and have pLastics materiaL gear wheeLs; it requires no maintenance.

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Claims (1)

1. What we claim is:

   1. A device for Limiting the downward travel of a Lift that includes a Limiter wheel driven at a speed dependent on that of the Lift cage, which actuates, via a rotating cam plate, a pendulum which, if the speed of rotation of the Limiter wheel becomes too high, swings so far out that a pawl thereon comes up against one of a plurality of stops that are rotating with the Limiter wheel and Locks the wheel and trips an arrester device for the Lift cage, wherein a transmission gear is arranged between the cam p Late and the Li miter whee L and the stops are directly driven by the Limiter wheel at the same speed of rotation.

   2. A device according to claim 1, wherein the transmission ratio of the transmission gearing is about 4..l.

   3. A device according to claim 1 or claim 2, wherein four stops are arranged on the Limiter wheel and a cam is arranged on the cam plate.

   4. A device according to any one of claims 1 to 3, wherein the pendulum, an arrester catch and a switch cam are mounted on a common axle, and the side faces of the switch cam are pressure-loaded by limbs of a forked damping spring.

   5. A device according to claim 4, wherein a switch is actuated by the switch cam when the Limiter wheel reaches the tripping speed.

   7 A device according to one or more of claims 1 wherein a safety switch is arranged in the range of oscillation of one arm of the pendulum to operate to switch off the Lift drive before the Limiter wheel reaches the tripping speed.

   6. to 5 7. A device according to claim 6, wherein the safety switch is connected to a brake operating on the bearer rope of the lift.

   8. A device according to claim 1 substantially as described herein with reference to the accompanying drawings.

   Published 1990 at The Patent Office. State House.66 711-Iig]7.Holbor.-.. London WC1R4TP. Further copies inay be obtaired,fror.-.Tl E Fa-en' Of'!'E