GB2045204A - Lifting apparatus - Google Patents

Abstract

A lifting apparatus comprises a vertical, screw-threaded motor-driven shaft (11), and a vertically movable carriage (15) connected to said shaft by a nut (16). The limits to the carriage movement are fixed by stops (24 and 25) mounted on a movable rod (23) cooperating with a finger (30). Movements of this rod stop the motor. A safety device is provided, consisting of a nut (33) positioned below the nut (16), a pivotally mounted lever (41) and a second movable rod (34) (Figure 3, not shown) parallel to the rod (23) and carrying a finger (36). When the nut (16) is worn, it falls onto the nut (33) which takes over the control of the carriage (15). The carriage (15) is then halted in a lower position by a lever (41) which is pivoted by the nut (33) to contact the finger (36) and move rod (34) downwards so stopping the motor. <IMAGE>

Description

SPECIFICATION Lift apparatus This invention relates to a lift apparatus, for example a vehicle lift.

This apparatus comprises a lift apparatus comprising at least one post, the or each post having a vertically disposed, screw-threaded shaft, means for rotating the shaft, a load-bearing nut member screwthreadedly engaged with the shaft so as to rise or descend according to the direction of rotation of the shaft, a member rigidly connected to said loadbearing nut member and adapted to receive a load, and a safety device including a second nut member screw-threadedly engaged with the shaft at a predetermined distance below the load-bearing nut membey so as to support the load-bearing member and its load should the load-bearing nut member fail.

Known apparatus of this type suffer from the disadvantage that there is no signal to indicate any failure of the load-bearing nut member, and it is therefore possible for the safety nut member to operate as a substitute load-bearing nut member until it in its turn fails, the consequence of which could be most disastrous, for example, the fall of the load carrying member with its load.

The present invention, which has as its object to obviate this risk, is characterised in that said safety device includes means which monitor the gap separating the two nut members and cause the instantaneous or deferred termination of said drive means immediately said gap is accidentally reduced.

In the accompanying drawings: Figure 1 is an end view of a vehicle lift according to the present invention, Figure2 is a plan view of Figure 1, Figure 3 is an enlarged sectional view taken on the line Ill-Ill of Figure 5, Figure 4 is a sectional view taken on the line IV-IV of Figure 3, Figures 5 and 5A are sectional views taken on the line V-V of Figure 3 showing the normal operation of the lift, Figures 6, 6A and 6B are fragmentary views similar to Figures 5 and 5A illustrating the operation of the safety device, and Figure 7 is an electrical conduit diagram for the lift.

Each lift post 10 shown on the drawings comprises a vertical screw-threaded shaft 11 rotatably mounted between a pivot 12 and a bearing 13, a hollow beam 14, a carriage 15 mounted on ball bearings and able to move vertically without clearance within the beam 14, a nut member 16 rigid with the carriage 15 and screw-threadedly engaged with the shaft 11, telescopic arms 17 hinged to the carriage 15, and a three-phase electric geared motor 18 which rotates the shaft 11 by way of a double toothed belt 18A in one direction orthe other to effect raising or lowering of the carriage 15. The beam 14 is welded at its lower end to a horizontal plate 19 supporting the pivot 12, and welded at its upper end to a horizontal plate 20 on which the bearing 13 and geared motor 18 are mounted.

The two geared motors 18 are controlled in synchronism, through relays R1, R2, R3 and R4, by two pushbuttons 21 and 22 positoned on one of the posts 10 and forming part of a single phase circuit (Figure 7). One of these pushbuttons controls the raising and the other the lowering of the carriage 15.

The upward and downward movement of the carriage 15 is limited by a device (Figures 4,5 and 5A) comprising a rod 23 on which they are adjustably fixed two fingers 24 and 25 and two cams 26 and 27, the latter co-operating with contacts 28 and 29 connected into the single phase control circuit of the geared motors 18 (Figure 7). The Fingers 24 and 25 lie in the path of movement of a plate 30 welded on the carriage 15. The rod 23 is mounted on and extends between spaced angle irons 31 welded to the beam 14 in such a manner as to be able to move axially against the action of two spaced springs 32 from an equilibrium position in which the contacts 28 and 29 are closed.

Downward movement of the carriage is automa ticallyterminated (Figure 5) the~momentthe plate 30, having come into contact with the finger 24 and moved the rod 23 downwards against the action of the corresponding upper spring 32, causes the contact 28 to open by the action of the cam 26. In the same manner, upward movement of the carriage 15 is automatically terminated (Figure 5A) by the opening of the contact 29.

The lift illustrated also comprises a safety device mainly designed to prevent the carriage 15 and its load from falling, should the nut member 16 fail due to fracture, wear, or the like. This safety device comprises a nut member 33, also screw-threadedly engaged with the shaft 11 a predetermined distance below the load-bearing nut member 16. The purpose of the nut member 33, which normally does not support any load, is to automatically replace the load-bearing member 16 should it fail, and to enable the carriage 15 to descend to a lower level from which it possible to easily unload it.

For this purpose, the safety device comprises a rod 34 on which there are adjustably fixed three fingers 35,36 and 37, and a double cam 38 which cooperates with a contact 39 connected into the control circuit for the geared motors 18.

The rod 34 is also mounted on and between the spaced angle irons 31 parallel to the rod 23. It can move axially, as in the case of the latter, against the action of two spaced springs 40 which normally maintain it in an axial equilibrium position in which the contact 39 is closed.

The safety device also comprises a pivotally mounted lever 41, the spindle 42 of which is rigid with the carriage 15. The end of the lever 41 remote from the spindle 42 is bent to form a projection 43, and aproximately in the centre of the lever, a nose 44 is provided which is normally positioned between the nut members 16 and 33.

The fingers 35 and 37 which lie in the vertical path of movement of the projection 43 are positioned at slightly higher and lower levels respectively than the levels of the fingers 24 and 25. The finger 36 is shorter than the fingers 35 and 37, and is located in a horizontal plane slightly above the plane containing the finger 24. Because of its reduced length, the end of the finger 36 is not in the path of movement of the projection 43.

During normal operation, the fingers 24 and 25 cause the carriage 15 to halt before the projection comes into contact with the fingers 35 and 37.

The safety device becomes operative when either the load-bearing nut member 16 fails or when the limit stops have not operated normally, this action taking place in the following manner: Failure of the load-bearing nut 16 This nut member can slide or fall until it is halted by the safety nut member 33 which then supports the entire load. During this relative movement of the two nut members 16 and 33, the nose 44 comes into contact with the safety nut member 33, so causing the lever 41 to pivot as shown in Figure 6. The consequence is that when the carriage 15 has descended a certain distance from its lower limit position, the projection 43 contacts the finger 36, displaces the rod 34 downwards and causes the contact 39 to open.The current supply to the motors 18 is interrupted, and the carriage 15 is halted in a slightly elevated position such that it can be easily unloaded, and from which it is no longer possible to restart the lift by pressing the pushbuttons 21 and 22. This condition would then indicate that the load-bearing nut member 16 is broken or worn.

Failure of the limitstops If the carriage passes one or other of its normal movement limits (Figures 6A and 6B), the projection 43 contacts the finger 35 or finger 37, to displace the rod 34 downwards or upwards so opening the contact 39. The current supply to the geared motors is interrrupted and the carriage 15 is halted slightly above or below the positions which it occupies when the limit stops operate normally. When the carriage 15 is in these positions, it is no longer possible to restart the movement by pressing the pushbuttons 21 and 22. This condition therefore indicates that one or other of the movement limit stops has failed.

To prevent the fingers fixed on the rods 23 and 24 from being displaced by incompetent personnel, these rods are made inaccessible by means of a locked casing 45.

The invention is not limited to the embodiment shown on the drawing. In particular, as a modification, the finger 35 could be replaced by a block rigid with the carriage 15 which co-operates with the finger 36 if the lower limit of the carriage movement is exceeded.

Claims (6)

1. A lift apparatus comprising at least one post, the or each post having a vertically disposed, screw-threaded shaft, means for rotating the shaft, a load-bearing nut member screw-threadedly engaged with the shaft so as to rise or descend according to the direction of rotation of the shaft, a member rigidly connected to said load-bearing nut member and adapted to receive a load, and a safety device including a second nut member screwthreadedly engaged with the shaft at a predetermined distance below the load-baring nut member so asto support the load-bearing member and its load should the load-bearing nut member fail, wherein said safety device includes means which monitor the gap separating the two nut members and cause the instantaneous or deferred termination of said drive means immediately said gap is accidentally reduced.

2. A lift apparatus as claimed in claim 1,wherein said means which monitor the gap between the two nut members includes a lever pivotally mounted on the carriage, the angular position thereof being altered when the safety nut member becomes stressed.

3. A lift apparatus as claimed in claim 2, wherein said monitoring device includes a switch which is connected, when closed, into the control circuit for said drive means, and is opened by said lever when the latter occupies its altered angular position.

4. A lift apparatus as claimed in claim 3, wherein said switch is opened when the load bearing member attains a position in proximity to its lower limit position.

5. A lift apparatus as claimed in any of the preceding claims, wherein said safety device includes means which automatically open the control circuit for the drive means when one or other of the movement limit stops has not functioned.

6. A lift apparatus substantially as described with reference to, and as illustrated in, the accompanying drawings.