GB2123792A - Safety means for a hoist cage - Google Patents

Abstract

In a hoist system of the kind comprising a mast 4 made from a number of sections which are successively assembled to a desired height, and a hoistable cage 2 guided for movement by guide means on the mast and usable as a working platform for assembling the mast, the cage carries means for sensing undesired discontinuities of the guide means, and switch means responsive to the sensing means for stopping movement of the cage when such a discontinuity is sensed by the sensing means. A switch 12 on the lift, for stopping the lift motor, is operable via a link 40 by the rotation of a pivoted arm 22 carrying a roller 34 which normally runs on a rack 20, when a rack and pinion drive is employed. The switch can alternatively be operated from the cage via cable 48 and link 40, or by a cam rail at the top or bottom of the mast, which contacts a finger 18 extending from the switch. <IMAGE>

Description

SPECIFICATION Hoist system and safety means therefor The present invention relates to a hoist system having safety means for a hoist cage guided for movement along guide means. Said guide means may form part of a mast structure comprising a number of mast sections which are successively assembled to a desired height using the cage as a platform.

Hoists of this type are used in industrial environments, building sites, excavation and the like. Such hoists generally are either of the rack and pinion or the wire rope type.

Typically the cage carries a final limit switch having the function, during normal duty of the hoist, of automatically switching off the mains supply to the hoist system when the cage travels beyond upper and lower end positions along said mast. For that purpose actuating means for the switch, usually in the form of cam rails, are attached to the uppermost and lowermost mast sections.

During erection of the mast structure the successive intermediate mast sections which are being attached to the growing mast structure are not provided with any limit switch actuating cam rail. There may be, however, means for preventing the cage from being accidentally or inadvertently moved upwards beyond the upper mast section.

It has occurred in some cases, during assembly of the mast structure, that the erectors have failed to put all the fixing bolts for the upper mast section in place before travelling upwards with the cage. The result has been that the upper mast section has come loose under the weight of the cage, resulting in the cage dropping to the ground.

According to one aspect of the present invention a safety means for a hoist cage is provided which senses undesired discontinuities of guide means along which the hoist cage is guided for movement, and actuates means for stopping movement of the cage when an undesired discontinuity is sensed.

Other aspects of the invention are a hoist system including a hoist cage and a mast comprising a number of mast sections as set forth above, and including safety means according to the first-mentioned aspects; and a hoist cage having such sensing means.

The safety means can be of the contactless variety, e.g. including optical, sonic, inductive or capacitive sensors. In that cage actuation of the stopping means can take place via some form of electrical-mechanism transducer.

A simple and reliable form of the safety means, however, comprises a contact member continuously moving in contact with a guide of the guide means. In that case spring means can be arranged for urging the contact member into contact with the guide, and an actuating member for the stopping means can be linked to the contact member.

The stopping means can be the conventional final limit switch carried by the cage and having the function, during normal duty of the hoist, of automatically switching off the mains supply to the hoist system when the cage travels beyond upper and lower end positions along the mast.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic side view, with a portion broken away to show a detail of its interior, of a building hoist cage located near the top of a hoist mast, of which only the upper part is shown; Figure 2 is a plan view of the arangement illustrated in Figure 1; Figure 3 is a view from the mast side of the hoist cage, the lateral end portions of which have been broken away; Figure 4 is a perspective view of a safety device included in the hoist system according to Figures 1-3 on a larger scale; and Figure 5 is a view from above of the device of Figure 4.

The hoist illustrated in the Figures includes a hoist cage 2 guided for movement along a hoist mast 4 comprising a number of mast sections 4', 4", 4"', etc., attached end to end by means of bolts (not shown). Each mast section is in the form of a framework, rectangular in cross-section, and including four corner posts. The cage 2 carries guide roller 6, the location of which appears from a comparison between Figures 13, and which serve as connecting means with the mast structure at the same time allowing movement of the cage 2 along the mast. More particularly the roller 6 roll against two vertical guides 8 of the mast structure made up of two of said corner posts of each mast section. The cage 2 also carries two hooks 10 extending partly, with some play, around the circumference of the guides 8.

The cage 2 in its interior careies a so-called final limit switch 12 having the function, during normal duty of the hoist, of automatically switching off the mains supply to the hoist system should the cage travel beyond upper and lower end positions along the mast structure. For that purpose actuating means in the form of cam rails (not shown) are attached to the uppermost and lowermost mast sections. A control shaft 14 of the limit switch carries a control handle 1 6 extending into the interior of the cage 2, to be available for manual actuation, and a finger 18 in line with the handle 16 extending through a vertically extending oblong opening (not shown) in the back wall of the cage 2.Should the cage 2 travel beyond the said upper or lower end positions, the finger 18 will ride up on the corresponding cam rail, thereby operating the switch 12 to interrupt the mains supply to the hoist system.

For installing the hoist structure the mast 4 is erected by successively attaching the mast sections 4', 4", 4"' etc., on the top of each other, using the roof of the hoist cage 2 as a working platform. The cage 2 is moved upwardly stepwise on each installed mast section until the top has been reached.

In the disclosed embodiment the drive of the hoist system is of the rack and pinion type.

Included in this drive arrangement is a toothed rack 20 carried by the mast 4, i.e. each mast section carries its own rack section.

The arrangement thus far disclosed is well known to persons skilled in the art, as are also details not described.

Near its uppermost end, on the side facing the mast structure 4, the cage 2 carries a two armed lever 22 mounted on a pivot 24. A sidewardly extending arm of the lever 22 is upwardly biased by a coil spring 26 acting between the free end 28 of the said arm and a support 30 carried by the cage 2. The other arm of the lever 22 at its free end 32 carries a roller 34 rolling in contact with a face 36 of the rack 20 remote from its teeth, indicated 38 in Figure 4.

A bar 40 is connected at one end to the sidewardly extending arm of the lever 22 and at its other end to the finger 18 of the control member 14 of the swtich 12. More particularly, the bar 40 near its upper end has a slot 42 extending in the length direction of the bar 40 and through which a pin 44 extends, which pin is carried by the lever 22 between the pivot 24 and the end 28. At the other end of the bar 40 the finger 1 8 extends through a hole 46 in the bar.

A cable or other line 48 is tied to the upper end of the bar 40 and its other end is accessible from the roof of the cage 3, which roof has a fence (not shown) and is used as a working platform in some instances, e.g. during assembly of the hoist system, as described above.

When the cage 2 is at approximately the location on the mast 4 illustrated in the drawings, the finger 1 8 of the switch 1 2 normally cooperates with the cam rail fixed to the uppermost mast section, to interrupt the main supply and thereby stop further upward travel of the cage 2 above the upper end of the mast. During erection of the mast structure, however, the individual intermediate mast sections are not provided with any such cam rail. Normally this will not be dangerous, since when the hoist reaches the top the drive pinion engaged with the teeth 38 of the rack 20 will be disengaged from said teeth, and thus, the cage cannot travel further.

An an extra safety measure, however, the mains supply of the hoist system will be shut off aiready before the cage reaches this point. This occurs when the roller 24 reaches the top of the rack 20, whereby the lever 22 is pivoted clockwise around the pivot 24 under the action of the force of the coil spring 26. Due to the connection between the bar 40 and the lever 22 the bar 40 is then lifted upwardly at the same time also pulling the finger 1 8 of the switch 12 upwardly, thus actuating the switch to interrupt the mains supply. The pivoting of the lever 22 has been indicated with dashed lines 50 in Figure 4.

Should, for some reason, the attachments between the mast sections 4" and 4"' fail, the hooks 10 form a further safety means for gripping around the members 8 and thus keeping the cage on the mast.

Due to the shape of the slot 42 the bar 40 has a path of free movement with respect to the lever 22 corresponding to the length of the slot 42.

Thus, normal actuation of the finger 46 by the lowermost of the abovementioned cam rails will not be restrained by the bar 40 and its connection with the lever 22.

The cable or other line 48 and its connection via the bar 40 to the finger 18 forms a means for interrupting the mains supply from the top of the cage 2 in an emergency.

It should be realized that the safety arrangement illustrated in more detail in Figures 4 and 5 also has the more general function of detecting other discontinuities of the mast structure besides the mast ending. As the member sensed for the purpose of detecting any irregularities, portions of the mast structure other than the rack 20 can also be used to co-operate with the sensing roller 34 or any other sensing means. It lies within the scope of the invention to use also optical, sonic, capacitive and inductive sensing systems of a type well-known per se. A safety device of the kind described above, however, forms a very suitable sensing means due to its simplicity and ruggedness.

Claims (13)

Claims

1. A hoist system including a hoist cage and a mast having guide means along which the cage is guided for movement, the mast comprising a number of mast sections which are successively assembled to a desired height using the cage as a platform, safety means for sensing undesired discontinuities of the guide means, and switch means responsive to the safety means for stopping movement of the cage when an undesired discontinuity is sensed by the safety means.

2. A hoist cage having means for movably carrying it along guide means, safety means for sensing undesired discontinuities along the guide means, and means responsive to the safety means for stopping movement of the cage when an undesired discontinuity is sensed by the safety means.

3. A safety means for a hoist cage for sensing undesired discontinuities of guide means along which the hoist cage is guided for movement, and actuating means for stopping movement of the cage when an undesired discontinuity is sensed.

4. A device as claimed in any of Claims 1 to 3 in which the safety means is of the contactless variety.

5. A device as claimed in any of Claims 1 to 3 in which the safety means comprises a contact member continuously moving in contact with a guide of the guide means.

6. A device according to Claim 5 in which the contact member is a roller.

7. A device according to Claim 5 or Claim 6 comprising spring means urging the contact member into contact with the guide, and an actuating member for the stopping means linked to the contact member.

8. A device according to Claim 7 in which the actuating member has a path of free movement with respect to the contact member for allowing actuation of the stopping means by means other than the safety means and independently thereof.

9. A device according to any of the preceding claims in which the stopping means is a final limit switch also having a normal function during normal duty of the hoist of automatically switching off the mains supply to the hoist system when the cage travels beyond upper and lower end positions along the mast.

10. A device according to Claim 9 wherein the safety means is intended to actuate the final limit switch when the cage reaches the top of the guide means and the normal function fails.

11. A device according to Claim 7 or any of Claims 8 to 10 when appendant to Claim 7 comprising means for allowing manual actuation of the stopping means via the actuating member also when no discontinuity of the guide means is sensed.

12. A device according to Claim 11 wherein the means allowing manual actuation comprises a line connected to the actuating member and leading to the roof of the cage.

13. A hoist system substantially as described with reference to the accompanying drawings.