Hand truck World

A swivel castors having a locking device to arrest rotation of its wheel or swivelling of its fork, the device comprising a mounting sleeve and, extending therethrough and through the fork head, an axially movable locking pin having a vertically adjustable top member acted on by a cam received in the mounting sleeve. The top member of the locking pin is guided in the mounting sleeve so as to be axially movable and non-rotatable and is prevented from co-rotating with the locking pin by way of the mounting sleeve. The top member is vertically movable and adjustable by way of the screw thread by rotation of the locking pin relative to the mounting sleeve as for example, by rotation of the fork head.

In a castor having a locking device to arrest rotation of its wheel and/or swivelling of its fork, the improvement wherein the device comprises a mounting sleeve, an axially movableand rotatable locking pin extending through the mounting sleeve and through its fork head, said locking pin having an axial screw thread at its top portion and a vertically adjustable, non-rotatable top member threadedly mounted thereon, a cam disposedin the mounting sleeve and acting on the top member, means connected to the locking pin for rotating the locking pin relative to the mounting sleeve wherein the mounting sleeve has means guiding the top member for axial movement while preventingcorotation with the locking pin, whereby the top member can be moved vertically and adjusted vertically by way of the screw thread by rotation of the locking pin relative to the mounting sleeve.

Description
The invention relates to a castor having a locking device forarresting its wheel. In the case of a pedestal castor, the locking device serves to arrest rotation of the wheel. In the case of a swivel castor, the locking device can be used to inhibit swivelling of the castor fork and therefore of the wheel. Thelocking device associated with a swivel castor can also be used to completely arrest rotation of the wheel and swivelling of the castor fork and therefore of the wheel. A locking device of this kind for arresting wheel rotation and/or wheel forkswivelling comprises an axially movable locking pin which extends through the fork head and through the castor mounting pin, a cam or the like being operative on the top part of the locking pin. Movement thereof axially brings locking members disposedin the hollow of the wheel fork into engagement with one another and thus causes wheel rotation and/or swivelling to be arrested.

Castors of this kind usually form part of centrally lockable castors, of use more particularly for mobile hospital beds. Centrally lockable castors of this kind are usually operated from a central locking mechanism through the agency of alinkage controlling the cams acting on the pins for locking the castors. If operation is to be satisfactory and all the castors of the bed or other device or appliance are to be adjusted consistently despite tolerances, adjustment work is necessary.

To facilitate adjustment, German Gebrauchsmuster No. 7 016 058 discloses the idea of making the castor mounting pin in the form of a sleeve and of accommodating and mounting the cam or the like therein so that the cam becomes a component of thecastor. The castor can therefore be adjusted by the maker during assembly to ensure direct co-operation between the locking pin and the cam or the like. For the purposes of such adjustment the axially movable locking pin has an axial screw thread witha vertically adjustable top member in the form of a commercially available cap nut which is first adjusted, then locked by means of a lock nut, a camming surface of the cam acting on such member. The castor is therefore adjusted by the maker ready forfitting, and so tolerances in the bed frame or the like do not impair the operation.

However, in the course of time wear affects the wheel tires, the actuating elements, more particularly the cam, and the locking members of the castor locking device, so that readjustment may be needed after relatively lengthy use. To obviate theneed to dismantle the castor from the bottom of the leg of the bed frame or the like, it is known from German Gebrauchsmuster Specification No. 7 837 296 for the brake element received in the hollow of the castor fork to have an adjusting mechanism. Thelatter increases the cost of the castor and readjustment calls for skill and the use of a tool.

It is the object of the invention to obviate the need for any such additional adjusting mechanism and so to simplify readjustment of the castor that work can be carried out as required by unskilled labour without any special tool.

The invention solves the problem by a special way of arresting rotation of the adjustable top member of the locking pin, the screw thread vertically adjustable top member of the axially movable locking pin being so disposed thereon as to bealways loosely adjustable–i.e., not locked by a lock nut during assembly of the castor.

The novel castor which has a locking device to arrest rotation of its wheel and or swivelling of its fork, the locking device comprising a mounting sleeve and, extending therethrough and through the fork head, an axially movable locking pin whichfor adjustment purposes has an axial screw thread having a vertically adjustable top member acted upon by a cam or the like disposed in the mounting sleeve, is characterised according to the invention in that the top member of the locking pin is soguided in the mounting sleeve as to be axially movable and non-rotatable and is prevented from co-rotating by means of the mounting sleeve, and the top member can be moved vertically and adjusted by rotation of the locking pin and of its screw thread inthe mounting sleeve.

Since the freely axially movable top member of the locking pin disposed inside the mounting sleeve is retained thereby as by a tool, the castor can be readjusted as necessary by means of such top member, despite its inaccessibility, just byadjusting the castor fork head by hand in the mounting sleeve in one or the other direction, there being no need to dismantle the castor from the bottom of the leg of the bed frame or the like. All that is necessary for this readjustment is totemporarily slacken or unscrew the securing screw in the bottom of the leg.

A rugged form of the invention is characterised in that the locking pin has a screw thread pin as adjusting screw thread and the vertically adjustable top member has a corresponding internal screw thread. Conversely, the locking pin can beformed with a tapped bore as adjusting screw thread and the vertically adjustable top member can have a corresponding screw thread pin. Fine adjustment is possible if the adjusting screw thread is a fine pitch screw thread.

Since the adjustable top member of the locking pin is so retained by the mounting sleeve in the interior thereof as to be non-rotatable, the invention makes it possible for there to be between the cam and the adjustable top member of the axiallymovable locking pin not just a point contact but a relatively widge edge contact, a feature which is advantageous for transmitting substantial actuating pressures and which reduces wear of the camming surface of the cam.

In a further development along these lines of the underlying idea of the invention, the novel castor is characterised in that the top member non-rotatably guided by the mounting sleeve tapers towards the top to give a ridge adapted to engage withthe camming surface of the cam.

This feature enables the apex of the top member of the locking pin to follow the shape of the camming surface of the cam more intimately, with the result not only that operation of the locking device becomes more accurate but also that thecamming surface of the cam can now be shaped for a different pattern of actuating sequences, with a profiling such that the various locking operations occur with precision.

In the embodiment in the form of a totally lockable castor for hospital beds, the castor has the locking device for arresting at choice rotation of the wheel 1and/or swivelling of the castor fork.