GB2468737A

GB2468737A - Tension-sensing safety mechanism for hoist

Info

Publication number: GB2468737A
Application number: GB0916066A
Authority: GB
Inventors: Lord Peter Malcolme Bond
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-03-17
Filing date: 2009-09-15
Publication date: 2010-09-22
Also published as: GB0916058D0; GB0904522D0; GB0916066D0; GB2468738A; GB2468736A; GB0916069D0; GB0916063D0; GB2468735A

Abstract

A powered hoist such as a ceiling hoist for a chandelier includes means 43, 16 to sense tension in a hoisting rope 3 and to disable a motor 9 driving a winch drum 22 in the event of an unsafe condition. Proximity sensor or microswitch 43 which generates a control signal in the event of the load reaching the floor and the tension in the wire hoisting rope 3 indicating that the load is not safely supported or the hoisting rope being insufficiently taut within the hoist and risking the wire rope 3 unwinding and touching an electrically live terminal of the hoist. Proximity sensor or microswitch 16 senses tension in a second section of wire rope 3 exceeding a safe value and generates a second control signal. Microswitch 43 may be activated by a pulley 8 sliding against a spring 42 and microswitch 16 may be activated by a pulley 10 rotating an arm 13 against a spring 19.

Description

Hoist arrangement The present invention relates to hoists, and relates particularly but not exclusively to ceiling hoists, ie hoists intended to be mounted on the ceiling of a building.

Chandeliers and other permanently-installed products such as shop displays, advertising banners, lighting assemblies, mannequins etc are commonly suspended from very high ceilings and arc therefore difficult to access, yet need to be serviced, maintained, cleaned or rearranged on a regular basis.

Usually these various suspended units will be expected to remain in place for many years, if not decades, and must remain accessible for maintenance and servicing during their entire life time. Maintenance of a permanently suspended unit requires the employment of specialist workers proficient at working high off the ground, sometimes in very inaccessible places. Such specialists are rare, and their cost of labour very high due to the risks taken and expertise required. Insurance costs are also prohibitive.

Accordingly there is a requirement for a compact and visually unobtrusive hoist capable of raising and lowering a load of greater than (say) 50kg, and supporting the load permanently and safely in the raised position. Furthermore it is highly desirable that the hoist can be operated in a fail-safe manner by relatively unskilled personnel.

Attention is directed to co-pending applications GB, GB and GB, each entitled "Hoist Arrangement," in the name of the present applicant which claim and disclose various inventions which address different aspects of these requirements.

An object of the present invention is to provide a hoist in which the load on the hoisting rope or the like is sensed and utilised to generate at least one control signal for controlling the hoist motor in order to ensure safe operation.

Such a control signal can be utilised to ensure that if the weight of the suspended unit exceeds the safe weight load of the hoist, the hoist does not operate.

Such a control signal can also be utilised to ensure that when the suspended unit is lowered, if it touches the floor, then the hoist is stopped automatically, to eliminate the risk of the unit being damaged, by lying over on its side or by the hoist cable becoming entangled in the suspended item. Chandeliers, shop displays, and lighting systems tend to have projecting parts which could easily entangle a wire rope and become damaged if raised.

Such a control signal can also be utilised to prevent operation of the hoist without weight on the hoisting rope or the like, to avoid the risk of the hoisting rope unravelling in the hoist housing and causing damage to the hoist, or worse, contacting a live connection in the hoist body with a clear risk of electrocution of anybody touching the hoisting rope or the suspended unit.

Accordingly the invention provides a hoist comprising a hoist mounting and a pendant assembly suspended from the mounting by a hoisting rope or the like, the pendant assembly having means for attaching it to a load and being hoistable by a powered winch drum to a raised position, the hoist being provided with at least one sensor arranged to sense the tension in the hoisting rope or the like and to generate a control signal which disables the powered winch drum in the event of an unsafe operating condition.

The term "hoisting rope or the like" is intended to encompass any windable elongate hoisting element, eg a chain, as well as a rope of wire or other material.

Preferably said at least one sensor generates said control signal in the event of one or both of: a) the load reaching the floor and the tension in said hoisting rope or the like indicating that the load is not safely supported on the pendant assembly, and b) said hoisting rope or the like being insufficiently taut within the hoist.

Typically the tension in the rope should be greater than 2.5 N to ensure sufficient tautness within the hoist.

Preferably said at least one sensor generates a control signal in the event of the tension in said hoisting rope or the like exceeding a safe value.

Preferably a first sensor is responsive to tension in a first section of said hoisting rope or the like to generate a first control signal in response to one or both of a) or b) as defined above, and a second sensor is responsive to tension in a second section of said hoisting rope or the like exceeding a safe value to generate a second control signal, said second section being intermediate said first section and a winding on said winch drum.

Preferably said at least one sensor comprises a proximity sensor arranged to sense a movable element acted on by a run of said hoisting rope or the like within the hoist.

Preferably indicator means are arranged to indicate to a user that said proximity sensor has failed.

n one embodiment said movable element is a pulley around which said hoisting rope extends, said pulley having an axle mounting which is biased against the force exerted on the pulley by tension in said hoisting rope or the like.

Optionally said axle mounting is carried on a slide which is biased by spring means.

Optionally said axle mounting is carried on a lever which is biased by spring means.

Optionally the biasing force exerted by said spring means is adjustable.

Preferably said mounting is a ceiling mounting which has a housing which abuts a housing of the pendant assembly when the pendant assembly reaches the upper limit of its travel. This enhances the appearance of the hoist, which can be made to resemble a ceiling rose, for example.

Preferably the pendant assembly is coupled to a winch drum which is driven by a worm drive, friction in the worm drive being sufficient to prevent the pendant assembly from falling in the event of a power failure to the winch drum.

This feature obviates the need for a brake which would increase the size of the ceiling mounting.

A preferred embodiment of the invention is described below by way of example only with reference to Figures 1 to 11 of the accompanying drawings, wherein: Figure 1 is a perspective view from below of a chandelier hoist in accordance with the invention; Figure 2 is a perspective view from above showing a locking assembly and weight sensing alTangement in the ceiling mounting portion of the chandelier hoist of Figure 1; Figure 3 is a perspective view from above showing the interior of the ceiling mounting portion of the above hoist; Figure 4 is a perspective view from below of the ceiling hoist with its cover removed, showing the drive arrangement for the rope layering mechanism; Figure 5 is a perspective view from above, showing the pendant lowered and suspended from certain supporting components in the ceiling mounting portion; Figure 6 is a perspective view from below, showing the pendant with its cover removed and raised into locking engagement with the supporting components of the ceiling mounting portion; Figure 7 is a perspective view from above of the rope layering mechanism in the ceiling portion; Figure 8 is a side elevation of the pilot utilised in the rope layering mechanism of Figure 7; Figure 9 is a plan view of the pilot of Figure 8; Figure 10 is a side elevation of the drive shaft of the rope layering mechanism of Figure 7, and Figure 11 is a diagrammatic side elevation showing the opposite orientations of the pilot during its ascent of one helical guide channel and descent of the other helical guide channel of the drive shaft of Figure 10.

Referring to Figures 1 and 5, the hoist comprises a pendant 12 incorporating a suspension pulley 38 which is supported in a loop of wire rope 3 from a ceiling mounting 11. Ceiling mounting 11 is supported from the ceiling (not shown) by an annular ceiling mounting plate 1. The free end of wire rope 3 (the left-hand run 3L as shown in Figure 5) is secured to an anchor pin 47 of a housing block 46 of the ceiling mounting.

The parallel right-hand run of the wire rope runs through a tubular guide pin 34 to a series of pulleys which operate various safety sensors of the hoist arrangement. The path of the wire rope will be described before describing the safety sensors in detail.

The first pulley is no-weight sensor pulley 8 which is mounted for rotation on a horizontal axle 51. Axle 51 is parallel to the plane of the left-hand and right-hand runs of the wire rope 3 and is carried by a slide bracket 44 on a mounting bolted to housing block 46. Slide bracket 44 is urged towards this plane (ie forwardly in Figure 5) by a compression spring 42.

The wire rope 3 runs horizontally from no-weight sensor pulley 8 to an over-weight sensor arm pulley 10 (Figure 3) and loops round this pulley to a rope-guide pulley 6 to a wirc rope drum 22. Drum 22 is driven via reduction gcaring by an electric motor 9 to raise and lower pendant 12. A downwardly-projecting lug 27 extends from a pulley mounting yoke 37 on the underside of pendant 12 and carries a chandelier or other electrically powered load (not shown) to which it can be rigidly attached.

The slide bracket 44 of no-weight sensor pulley 8 is provided with a laterally- projecting tab 28 which is aligned with the actuating button of a proximity micro-switch 43. Normally (ie when the wire rope 3 is tensioned by the weight of eg. a chandelier) the tension in the horizontal run of the wire rope between pulleys 8 and overcomes the force exerted by compression spring 42 and slide bracket 44 is stopped in its extreme rearward position with tab 28 being sensed by the proximity micro-switch 43. In this condition micro-switch 43 is ON and completes a circuit to drive motor 9 (via an electronic relay, not shown) so the chandelier can be raised or lowered.

When the wire rope 3 is not tensioned by the weight of a chandelier, typically when the chandelier has been lowered to the floor and it is therefore not desirable for the wire rope to continue spilling out, compression spring 42 urges slide bracket 44 forwardly so that tab 28 activates the proximity micro-switch 43 and switches OFF power to the downward pole (anticlockwise pole) of the drive motor 9. Further lowering which would cause uncoiling of the wire rope 3 on drum 22 and/or potential damage to the chandelier is thereby prevented.

The vertically-aligned shaft of over-weight sensor arm pulley 10 is carried on the short leg of a generally L-shaped over-weight sensor arm 13 which is in turn pivotally mounted for rotation about a vertical axis 53 which intersects the short leg near a heel portion of the arm. Accordingly the tension in the parallel runs of wire rope 3 looping round pulley 10 urges arm 13 clockwise (as viewed in Figure 3) and urges the long leg thereof against an adjustable compression spring 19. A normally ON proximity switch 16 mounted on a bracket 17 is switched OFF in the event that its spacing from the long leg of L-shaped sensor arm 13 falls below a predetermined value (as a result of too great a tension in wire rope 3) and thereby switches OFF power to motor 9. In this manner, the motor 9 is protected from loads in excess of the safe weight load of the hoist. This feature also prevents the motor 9 from being overloaded, or from over-straining the wire rope, eg as a result ofjamming of pulley 8.

The rope layering arrangement will now be described with reference to Figures 4 and 7. Referring to Figure 4, a drive shaft 68 of gear 2 protrudes downwardly through an opening in the bottom plate of the ceiling mounting and carries a drive pulley 69 which drives a timing belt 59. As will be described subsequently, gear 2 is part of a gear train driven by a drive motor 9 (Figure 3) and is therefore coupled to wire rope drum 22 which feeds out and draws in the wire rope 3 as the pendant 12 is lowered and raised. The rope layering mechanism ensures that the wire rope 3 forms regular tightly wound layers on drum 22 throughout this process.

Referring again to Figure 4, belt 59 runs over an intermediate idler pulley 61 to a drive pulley 55 of the rope layering mechanism shown in Figure 7. Timing belt 59 is omitted from Figure 7 for the sake of clarity. A stepped drive shaft 58 (Figure 7) is secured to drive pulley 55 and runs in a suitable bearing carried by a drive housing 7. Drive shaft 58 has a double-helix worm drive portion 54 which includes a left-handed helical cut or channel superimposed on a right-handed helical cut or channel in the mid-portion of the cylindrical surface of the shaft. As best seen in Figure 10, these two helical channels merge at two points 62 with the result that a continuous channel is formed, starting at the lower point 62 and following a helical path up the shaft 58, and then, at the upper point 62, following a helical path of the opposite sense down the shaft 58 until it reaches the lower point 62 again. The right-handed helical channel is intersected at regular intervals by the left-handed helical channel (and vice versa) but as the shaft 58 is continuously rotated a pilot element can follow one helical channel up the shafi until it reaches upper point 62 and then follow the other helical channel down the shaft until it reaches lower point 62.

Such a pilot is shown as item 56 in Figures 8 and 9, and comprises a stepped cylindrical base carrying a diametral ridge 59 on its smaller end face. Ridge 59 has an arcuate concave profile which is complementary to the cylindrical surface of the helical channels in worm drive portion 54. Pilot 56 is retained in an inner recess in a sleeve 52 as shown in Figure 7, with its ridge 59 running in one of the helical channels. The pilot 56 is held sufficiently loosely to enable it to rotate freely about its central axis (perpendicular to the plane of Figure 11), such that its ridge 59 can tilt between the opposite inclinations of the two helical channels, according to whether it is ascending or descending shaft 58 (as indicated by the arrows in Figure 11). It tips over between these two orientations at points 62.

The sleeve 52 slides axially on shaft 58 and carries an enlarged bearing portion 52a (Figure 7) in which driven shaft 57 is mounted, the shaft 57 carrying a guide pulley 6. As best seen in Figure 3, the wire rope 3 (not shown in Figure 7) runs from the guide pulley 6 to drum 22 and is caused by the engagement of the worm drive portion 54 and the pilot 56 to ascend by one rope diameter per turn of the drum 22 while the wire rope 3 is forming a rising coil on the drum, and to descend by one rope diameter per turn of drum 22 while the wire rope is forming a fatling coil on the drum (ie during the succeeding layer of wire rope). th this manner, coils of the wire rope 3 are laid down uniformly on drum 22 in successive layers of alternating left-handed and right-handed helices as the hoist is raised and the wire rope is prevented from riding up on itself during this process. The number of turns of each helical channel in portion 54 corresponds to the number of turns of wire rope 3 in each layer on drum 22. The pitch of each helical channel is equal to the diameter of the wire rope. However in other embodiments both the travel of the pilot and the pitch could be smaller, and provide a lesser degree of guidance to the wire rope which would still be sufficient to facilitate rope-layering on drum 22. This can be accomplished by varying the size of pulley 55, thereby varying the turn ratio of the helical drive in accordance with the wire rope diameter.

Not only does the above arrangement eliminate the risk of tangles, bird nesting, or even of the wire rope falling' off the drum 22 altogether as it piles up then collapses, but also it ensures smooth raising of the pendant 12, by preventing the coils of wire rope from collapsing into themselves periodically.

The drive and alignment arrangements of the hoist will now be described with reference to Figures 3 to 6.

Referring to Figure 3, a small high power, high speed electric drive motor 9 carries a worm drive 5 on its output shaft which is coupled to a worm drive gear 4, thereby stepping down the drive at a ratio of 50:1 or more. Gear 4 is coupled to a step-down gear train culminating in a rope drum gear 18 which is secured to rope drum 22.

This gear train has a ratio of at least 50:1 per step. The drawing shows three steps each with ratios of 50:1 thereby giving an overall increase in torque of 125,000 to the electric motor loading. Using this method of gearing, it is possible for a small motor to lift very high loads. If more torque is required, the step down ratios can be increased, or more steps introduced. Since run 3L (Figure 5) of rope 3 is anchored and suspension pulley 38 is carried in a loop of rope, this pulley arrangement doubles the above step-down ratio. After taking into account friction losses, the above arrangement is capable of lifting a safe weight load well in excess of 600kg the limit being set in practice by the thickness of the wire rope.

The above drive system, incorporating a low power electric motor driving step-down gearing from a worm drive, is very compact. The diameter of the ceiling mounting 11 is only 350 mm and its depth is only 120 mm. Furthermore the worm drive obviates the need for a brake, since in the event of a power failure, friction in the worm drive is greater than the small torque transmitted back from the load via the gearing.

Besides doubling the lifting capacity of the hoist, the loop of wire rope 3 around pulley 38 serves to align the pendant 12 about a vertical axis, and in particular prevents rotation of a chandelier or other load (eg as a result of the wire rope twisting). In many applications, exact alignment about the vertical axis is required and to this end the pendant 12 incorporates peripheral guide slots 48 (Figure 5) formed in a mounting plate 50 which accommodate the vertical runs of wire rope 3 extending to suspension pulley 38. The guide slots 48 have semicircular ends centred on the wire rope 3. The wire rope runs through vertical tubular guide pins 34 (Figures 5 and 6) which are mounted on housing block 46 and these have tapered lower ends which, if there is any slight misalignment of the suspension unit 12 as it is hoisted towards the housing block 46 engage the semicircular ends of the guide slots 48, to ensure correct alignment.

A tapered orientation and security locking tongue 35 projects upwardly from the top of pendant 12 (Figures 1, 5 and 6) and engages a closely fitting complementarily-shaped housing 40 (Figure 1) in housing block 46 when the pendant 12 approaches the housing block 46. This ensures exact alignment of housing block 46 and pendant 12, not only in the horizontal plane about the vertical axis, but also in both vertical planes. Locking tongue 35 is permanently and securely fixed directly to the pendant 12 itself.

In order to ensure that the fully raised pendant 12 and its attached chandelier or other load are not supported just by the wire rope 3 when in the resting state, the security locking tongue 35 is provided with a transverse hole 63 (Figure 1) and top of travel sensor proximity switches 14 which control an electrically operated locking solenoid 41 which allows a spring-loaded locking pin (not shown) to be inserted in hole 63 only when tongue 35 is fully raised. When the suspended pendant assembly reaches its top of travel limit and triggers the top of travel sensor proximity switches 14, they cut the power supply to solenoid 41. The solenoid thereby releases the spring loaded locking pin which passes through the hole 63 in the locking tongue 35. This ensures the pendant unit 12 is suspended on the housing block 46 not the rope 3, and the motor 9 can only run in the lowering (downward) direction, which must come as a separate instruction from the operator. Only when the solenoid 41 is powered up does the locking pin retract from the locking tongue 35. The solenoid 41 is only powered up when the hoist is being operated. At all other times, the securing pin is held firmly in place by the spring.

Should the solenoid fail and the locking pin be forced into the locking position while the hoist is in operation and before the suspended pendant is raised, this is detected by a further proximity sensor switch 45 which immobilises the hoist until a service engineer can remedy the fault.

Furthermore when the proximity sensor switches 14 detect tongue 35 they selectively disable the upwards (clockwise) rotation of the drive motor 9 through an electrical relay (not shown), but still enable the downwards (anticlockwise) rotation of the drive motor, so the pendant unit 12 can be lowered but will not rise any more.

If proximity switch 45 does not sense the locking pin, it causes a green power onl fault indicator LED 33 (Figure 1) to change colour to red, thereby warning the operator of the need for a service engineer visit. The proximity switches 14 disable clockwise (lifting) power to motor 9 via an electrical relay (not shown) the instant they sense the presence of the tongue 35 to ensure the suspension unit and pendant can not be raised further, which would overload the wire rope. The proximity switches 14 are connected in series so that if one fails, the other ensures that the pin is inserted in the hole 63 by the spring and any further upward motion is impossible.

Referring to Figure 5, power to the pendant 12 and its associated chandelier or other load is provided by means of six pickup contacts 36 on a generally annular mounting plate 50 which engage live power transfer contacts 39 on a mounting plate 24 of suspension unit 11 only when the pendant is fully raised. This is a further safety feature which ensures that there are no live parts on the pendant or chandelier in the lowered condition. In addition to the six pairs of contacts 36 and 39 which provide six live feeds to the chandelier, one mating earth contact and one mating neutral contact are provided on the mounting plate and suspension unit.

To ensure that any faults which may occur to the hoist during its working life, all sensitive components, such as the micro-proximity switches, are wired through a relay which will notify LED 33 (Figure 1) mounted on the outside of the suspension unit 11 and cause it to glow red. A red waning will thereby inform the operator that he/she needs to contact a maintenance engineer, even if the hoist still operates, as it would do for instance if micro switch 45 failed to sense the locking pin, or the switch itself failed or if one of micro-proximity switches 14 failed, or the locking pin did not otherwise operate correctly.

As best seen in Figures 1 and 5, the ceiling mounting 11 and the pendant assembly 12 are covered by respective lightweight shells (eg of moulded of plastics material) which are removable and held in place by simple tension clips (not shown). The shells are dome-shaped and abut each other when the pendant assembly 12 is raised.

In this abutting configuration they look like a standard ceiling rose, but can easily be unclipped to allow access for maintenance and inspection of the hoist mechanism.

The hoist is designed to be operated via a remote controller (not shown), or via a hard wired wall mounted switching system.

Claims

Claims 1. A hoist comprising a hoist mounting and a pendant assembly suspended from the mounting by a hoisting rope or the like, the pendant assembly having means for attaching it to a load and being hoistable by a powered winch drum to a raised position, the hoist being provided with at least one sensor arranged to sense the tension in the hoisting rope or the like and to generate a control signal which disables the powered winch drum in the event of an unsafe operating condition.
2. A hoist according to claim 1 wherein said at least one sensor generates said control signal in the event of one or both of: a) the load reaching the floor and the tension in said hoisting rope or the like indicating that the load is not safely supported on the pendant assembly, and b) said hoisting rope or the like being insufficiently taut within the hoist.
3. A hoist according to claim 1 or claim 2 wherein said at least one sensor generates a control signal in the event of the tension in said hoisting rope or the like exceeding asafevalue.
4. A hoist according to claim 3 as dependent on claim 2 wherein a first sensor is responsive to tension in a first section of said hoisting rope or the like to generate a first control signal in response to one or both of a) or b) as defined in claim 2, and a second sensor is responsive to tension in a second section of said hoisting rope or the like exceeding a safe value to generate a second control signal, said second section being intermediate said first section and a winding on said winch drum.
5. A hoist according to any preceding claim, wherein said at least one sensor comprises a proximity sensor arranged to sense a movable element acted on by a run of said hoisting rope or the like within the hoist.
6. A hoist according to claim 5 comprising indicator means arranged to indicate to a user that said proximity sensor has failed.
7. A hoist according to claim 5 or claim 6 wherein said movable element is a pulley around which said hoisting rope extends, said pulley having an axle mounting which is biased against the force exerted on the pulley by tension in said hoisting rope or the like.
8. A hoist according to claim 7 wherein said axle mounting is carried on a slide which is biased by spring means.
9. A hoist according to claim 7 wherein said axle mounting is carried on a lever which is biased by spring means.
10. A hoist according to claim 8 or claim 9 wherein the biasing force exerted by said spring means is adjustable.
11. A hoist according to any preceding claim wherein the pendant assembly is coupled to a winch drum which is driven by a worm drive, friction in the worm drive being sufficient to prevent the pendant assembly from falling in the event of a power failure to the winch drum.
12. A hoist according to any preceding claim wherein said hoist mounting is a ceiling mounting and has a housing which abuts a housing of the pendant assembly when the pendant assembly reaches the upper limit of its travel.
13. A hoist according to any preceding claim which is a chandelier hoist carrying a chandelier.
14. A hoist according to any preceding claim wherein said hoisting rope or the like is a wire rope.
15. A hoist substantially as described hereinabove with reference to Figures 1 to 6 of the accompanying drawings.