GB2071203A - Driving mechanism for lift doors - Google Patents

Abstract

In a driving mechanism for operating lift car doors 106, the doors are coupled to a horizontal loop of rob 3 part of which is wound around a drum 1. The drum 1 has a central axis 4 on which it can rotate and move horizontally in a slot (104) (Fig. 1, not shown), and a peripheral axis on which is can rotate and move vertically in a slot (102) (Fig. 1, not shown). These constraints cause the rope coming off the drum to move with a kind of cycloidal motion providing a region of effectively zero rope movement toward the ends of the drum rotation. Door movement is made smoother by this motion. An electric motor 14 operates through belt and pulley gearing to drive a pulley wheel 7 on which is eccentrically-mounted the drum 1. <IMAGE>

Description

SPECIFICATION Driving mechanisms This invention relates to driving mechanisms particularly for driving a member in a straight line with a non-linear velocity. The invention is particularly, but not exclusively applicable to the operation of lift doors in which it is a general requirement to bring the door or doors to and from the closed position and to and from the open position with low final and initial velocities while at the same time wasting no time in the overall operation.

It is an object of the present invention to provide a mechanism of the above kind in which there is a substantial lost-motion of the mechanism on closure which can be used for ancillary operations, such as, in the case of lift installations, the disengagement of lift car and landing doors.

According to the present invention therfore, a driving mechanism for driving a member along a straight path comprises a drum having a first axis of rotation constituted by its geometrical axis, a second axis of rotation parallel to said first axis and positioned at or near the drum periphery, the first and second axes being constrained to move in first and second directions respectively, which directions are substantially perpendicular to each other and to the axial directions, means for rotating the drum about said axes, a rope wound around the drum and extending from it tangentially in a direction parallel to said first direction, the rope being held under tension and having said member attached to it, and the arrangement being such that non-linear velocity of the member, including a portion of substantially zero velocity, is produced by continuous rotation of the drum.

In a sliding door operating mechanism according to the invention the member is a sliding door and the portion of substantially zero movement is arranged to coincide with the closed position of the door.

A driving mechanism as applied to the operation of lift car doors will now be described, by way of example, with reference to the accompanying drawings, of which: Figure 1 is a diagram of a drum and rope illustrating the possible movement of the drum; Figure 2 is a diagram illustrating a practical embodiment of the arrangement of Figure 1; Figure 3 is an elevation of a driving mechanism in accordance with Figure 2 and as coupled to lift car doors; Figures 4 and 5 are elevation and plan view of an ancillary mechanism driven by the mechanism of Figure 3; and Figure 6 is a characteristic showing the non-linear movement obtained by the mechanism of Figure 3.

Referring to Figure 1, this shows a drum 1 having a shaft 4 on the drum geometric axis. The drum has a second shaft 2 parallel to the first but positioned on (or near) the drum periphery. The first shaft 4 rides in a horizontal slot 104 while the second shaft 2 rides in a vertical slot 102. It tne drum 1 is rotated it is constrained by the limitations on the movements of its axes. It in fact slides to and fro along the horizontal slot 104, every point on the drum describing an elliptical path.

A rope 3, which term is used to include an equivalent cable, wire, belt, or like flexible tension member is wound around the drum one or more turns and extends from the drum tangentially at the point 103 in a direction parallel to that of the slot 104. It then forms a closed loop around two pulleys 5 and is maintained in tension.

As the drum rotates, the horizontal part of the rope 3 is subject to two components of motion.

The pure rotary motion of the drum causes a linear movement of the rope directly proportional to the angle of rotation, while the pure translational movement of the drum causes an oscillatory movement of the rope. The latter is just sufficient to substantially cancel the linear movement of the rope over about 30C of the drum rotation at each end of a revolution. In order to obtain this zerorope-movement at the extreme horizontal rope positions, the drum is arranged with its shaft 2 at the point 103 in the extreme rope positions, the direction of rotation being such that the direction of movement of the shaft 4 (which is then at the intersection of the slots 102 and 104) is opposite to that in which the rope is required to move (subsequently) in the upper part of the horizontal loop.

Figure 2 shows one way in which the rotation of the drum, and the vertical constraint on the drum shaft, can be effected. It will be appreciated that if the drum 1 were rotated by a motor directly the motor would have to move with the drum, and this would be impracticable. Any fixed rotary driving means must therefore be capable of accommodating the bodily movement of the drum 1.

To this end an arm 6 is pivoted on a fixed shaft 9 and the other end is pivoted on the shaft 2 of the drum. The drum 1 is fixedly mounted on a driven pulley 7, the axis of which is coincident with that of the shaft 2 on which the pulley 7 is mounted.

Thus the drum 1 and the pulley 7 are carried by the arm 6. The drum shaft 4 must be offset from the pulley axis by the distance between the shafts 4 and 2 since both spacings dictate the horizontal 'throw' of the drum 1.

A driving pulley 8 may then be mounted on the shaft 9 and the driving and driven pulleys coupled by a belt 10.

As the pulley 7 rotates, the arm 6 will oscillate up and down and the shaft 2 will move in a substantially vertical, shallow arcuate path. The path can be made more or less straight, according to the length of the arm 6, the distortion of the characteristic varying accordingly.

Referring now to Figure 3, this shows a manner of coupling the driving pulley 8 to a driving motor and the coupling of the lift car doors to the rope.

To avoid confusion the arm 6 is shown only by way of its centre-line. The arm in fact extends from the axis of the driven pulley 7 to the driving pulley 8, and beyond to provide the support for a driving motor 14. The arrangement of Figure 3 is a development of Figure 2 in that the drum 1, although normally fixed to the pulley 7, is not permanently fixed. The shaft 2 which was previously a common shaft of the drum 1 and pulley 7 is now only the shaft on which the pulley 7 is pivotally mounted in the arm 6. The drum 1 is still, however, mounted on the shaft 4 which in turn is mounted in the pulley 7 and locates in the horizontal slot 104 (not shown).

To prevent rotation of the pulley 7 independent of the drum 1 in normal circumstances, a latch mechanism is provided. A cam 17 is pivoted on the pulley 7 on a shaft 19, the cam having a detent which normally engages a roller 16 mounted on the periphery of the drum 1 and which may coincide, as shown, with the shaft 2.

The cam is urged against the roller 1 6 by a spring 18. The cam has a ramp surface out of the detent in the direction in which the drum would have to revolve to open the lift car doors. The ramp angle and the spring pressure are such that the drum remains locked to the pulley 7 under normal door closing loads, but, if the doors are jammed in a half-closed position, the drum will disengage from the pulley, the roller 16 running up the ramp and out of the detent. The pulley can then rotate free of the drum and the doors can remain open.

Subsequent operation of the motor to open the doors will cause clockwise rotation of the pulley 7 and re-engagement of the cam detent on the roller 1 6.

The same spring loaded coupling between the pulley wheel 7 and the drum 1 will permit the doors to be forced open if the power to the motor fails or the pulley 7 jams.

A contact 20 is operated by the cam 17 when the drum disengages, the contact causing reversal of the motor and opening of the doors if the power is 'on'.

The rope 3 passes around the drum 1 and horizontally between pulleys 5 as in Figure 2.

In Figure 3 the doors are shown in their 'justclosed' position with some (anticlockwise) rotation of the pulley 7 and drum 1 still to go. This rotation is effectively 'lost motion', as will be seen from the characteristic of Figure 6.

The doors 106 are supported on rollers in a running track (not shown) and are attached to the rope 3 at points 105 as shown, the left hand door to the upper part of the loop and the right hand door to the lower part.

An opening or closing operation of the doors involves one revolution of the drum 1 so that clearly the extent of door movement determines the diameter of the drum 1.

The motor 14 is coupled to the driving pulley 8 by a speed reduction system, all of which is mounted on the arm 6 to pivot with it about the axis 9. The weight of the pulley 7, drum 1 and associated components is therefore counterbalanced by the weight of the motor and reduction system. The load is therefore taken off the engagement between the drum shaft 4 and its horizontal slot 104, the engagement of which also controls the orientation of the arm 6.

Also mounted on the pulley wheel 7 is a cam 21. A crank 23 having a cam follower 22 is pivotally mounted on a fixed axis 24 so that, when the door is just closed the follower 22 is aligned with the leading edge of the cam 21. Continued anticlockwise rotation of the pulley 7 after the doors have just closed causes the crank 23 to pivot clockwise on its axis 24.

One of the features of the invention is the substantial 'lost motion of the pulley rotation after door closure which lost motion is available for ancillary purposes.

As can be seen from Figure 6, the characteristic, of car door movement against angular rotation of the pulley, is asymmetric.

There is a greater portion of lost motion of the rope at the closing end of the door movement than at the opening end. This is caused by the arcuate nature of the substantially vertical motion of the shaft 2. At the end of the rope movement where the horizontal component of the movement of the shaft 2 is in the same direction as the corresponding movement of the shaft 4, then the angle of lost motion rotation is increased.

Conversely, at the other end of the rope movement, where the horizontal component of the movement of the shaft 2 is opposite to the corresponding movement of the shaft 4 the lost motion is reduced. The closed condition of the doors is therefore arranged to be at the former of these two situations since it is at the closed position that the lost motion is required for the ancillary purposes mentioned.

The arcuate nature of the vertical motion is thus turned to good advantage.

Figures 4 and 5 show a mechanism achieving such an ancillary purpose, namely, the engagement of lift landing doors to control them in synchronism with the lift car doors. The lift car doors must be able to pass any 'unwanted' lift landing doors without obstruction and, ideally, engage 'wanted' lift landing doors without backlash or lost motion.

The mechanism comprises a pair of vertical rods 25 and 26 forming a parallelogram linkage with short cross rods 27. The latter are pivotally mounted at their centres on one of the lift car doors. The linkage is shown in its 'retracted' position in Figure 4(b) and 'ejected' in Figure 4(a), a spring 30 biasing the linkage into the 'ejected' position against a stop 29 which is just overcentre to prevent horizontal forces retracting the linkage.

In its retracted position the linkage runs clearly between rollers 37 and 41 mounted on a landing door on each floor. The linkage is kept out of engagement with the landing door rollers by a crank 34 coupled to the crank 23 so that, in the closed position of the lift car doors the crank 34 depresses the left-hand rod 25 and holds the linkage in the retracted position against the spring 30. On opening the lift doors at a landing, the cam follower 22 runs out of the cam 21 during the lost motion of the pulley 7 and allows the linkage to 'eject to the position shown in Figure 4(a). It is then in engagement with both rollers 37 and 41.

On movement of the lift car doors the landing doors are carried along with them.

Despite the departure from true cycloidal motion engendered by the arcuately moving arm 6, the advantage of progressive change in acceleration from rest, giving a merely finite jerk, is retained. The stopping and starting of the doors at the ends of their travel are thus effected more smoothly than with the conventional crank design.

The latter gives rise to an instantaneous acceleration and consequently infinite jerk.

Both cycloidal and the conventional harmonic motions have appreciable movement of crank or drum accompanied by only a small movement of the door when this is at the closed position. As described above this can be used to actuate the mechanism which couples the car and landing doors. However, it has been found practicable to design the cycloidal unit so that significantly greater rotary motion is available than with a crank and this facilitates a satisfactory design of the cam 21 (Figure 3). The relatively large cam angle enables the linkages to be actuated smoothly to reduce noise.

Claims (8)

1. A driving mechanism for driving a member along a straight path, the mechanism comprising a drum having a first axis of rotation constituted by its geometrical axis, a second axis of rotation parallel to said first axis and positioned at or near the drum periphery, the first and second axes being constrained to move in first and second directions respectively, which directions are substantially perpendicular to each other and to the axial directions, means for rotating the drum about said axes, a rope wound around the drum and extending from it tangentially in a direction parallel to said first direction ,the rope being held under tension and having said member attached to it, and the arrangement being such that nonlinear velocity of the member, including a portion of substantially zero velocity is produced by continuous rotation of the drum.

2. A sliding door operating mechanism according to Claim 1, wherein said member is a sliding door and said portion of substantially zero movement is arranged to coincide with the closed position of the door.

3. A mechanism according to Claim 1 or Claim 2, wherein said rope is formed in a substantially continuous loop having two parallel portions stretched between two pulley wheels, one of said parallel portions being tangential to the drum and being interrupted by one or more loops around the drum.

4. A mechanism according to any preceding claim wherein said means for rotating the drum comprises a driven pulley fixedly attached to said drum, the axes of the pulley and said second axis of the drum being coincident, an arm pivotally coupled to a shaft on said second axis and also to a remote shaft, a driving pulley mounted on said remote shaft, belt means coupling said driving and driven pulleys, and means for driving said driving pulley.

5. A mechanism according to Claim 4, wherein said means for driving said driving pulley comprises a motor mounted on an extension of said arm and coupled to said driving pulley, the arrangement being such that the motor tends to counter-balance the weight of the drum and driven pulley.

6. A mechanism according to Claim 4 or Claim 5, wherein said driven pulley has mounted thereon a cam which, during said portion of substantially zero movement, engages a cam follower pivoted on a fixed pivot axis, rotation of said cam follower providing driving means for ancillary operations.

7. A mechanism according to any of Claims 4, 5 and 6 wherein said drum is rotatable about its second axis on a shaft mounted on said driven pulley and is normally fixed against rotation with respect to the driven pulley by a latching arrangement comprising a cam member and a follower member urged into mutual engagement, one of these members being mounted on the drum and the other on the driven pulley, the cam member being so shaped that the driven pulley is in positive engagement with the drum for one direction of rotation of the driven pulley and is free to escape engagement with the drum against a spring bias in the other direction of rotation of the driven pulley.

8. A sliding door operating mechanism substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.