Guiding wheel assembly, especially for a hospital bed

A guiding wheel assembly, mainly for a hospital bed, including a wheel (1) with a horizontal rotation axis (6) installed on an arm (7) that is fixed to the frame (5) with the use of an axis (4) allowing swinging in the vertical plane. The wheel (1) is firmly fixed in the straight direction. The arm (7) is provided with a track (3), against which a pressing element (8) leans. The pressing element (8) is fixed with a pin (9) to the frame (5) in a swinging way.

This is a national stage application under 35 U.S.C. §371 of International Application

PCT/CZ2007/000089 filed 25 Sep. 2007 and published in English, claiming the benefit of Czech Republic application PUV2006-18253 filed 9 Nov. 2006, the entire disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a guiding wheel assembly, mainly for a hospital bed, comprising a wheel with a horizontal rotation axis installed on an arm that is fixed to the frame with the use of an axis allowing swinging in the vertical plane.

BACKGROUND ART

Some hospital beds are equipped with wheels to enable transport of patients between individual workplaces of the hospital. In the corners of the bottom frame of such a bed there are four travelling wheels that are freely turning around the vertical and horizontal axis. Such a design makes it possible to move the bed easily in all directions, but during the movements along hospital corridors it is difficult to keep the straight direction. This is why some beds are equipped with the fifth, so called guiding wheel that can be locked in the straight direction, so the bed keeps the straight direction.

The guiding wheel is usually positioned in the middle of the undercarriage, it is spring loaded and pressed to the floor with the force of approx. 200 to 500N. The control, i.e. locking of the guiding wheel in the straight direction may be either separate or derived from the control of the main wheels, or it may be self-locking.

A disadvantage of structures with separate control where the wheel is lowered onto the floor in such a way that the control force must overcome the force of the pressing spring is that the control force is relatively high while the accumulated energy of the compressed spring causes impacts during the control as well as noise when the wheel hits the floor.

In structures with a horizontal rotation axis combined with a vertical axis and locking control derived from the control of main wheels the locking in the straight direction is “pre-selected”, but it is only activated when the bed starts moving after the part with the vertical axis turns to the straight direction due to the turning of the guiding wheel and the lock engages. An advantage is a low control force. A disadvantage in this case is delayed locking as the wheel is not locked in the straight direction until the corresponding parts of the locking mechanism are turned towards each other.

In structures with a horizontal rotation axis combined with a vertical axis and self-locking of the guiding wheel in the straight direction e.g. a spring-loaded ball is used against which a groove is created in the required place where the ball may fit into to prevent free turning of the guiding wheel around the vertical axis. An advantage is that you do not need any other control since the wheel is locked automatically in the straight direction as soon as the ball fits into the corresponding groove. A disadvantage is that if it is necessary to move the bed in another than straight direction, you must exert an increased pressure on the bed to make the spring-loaded ball get out of the groove to deactivate the locking of the guiding wheel while the straight direction is locked again when during the turning of the wheel around the vertical axis the ball gets to the groove again. This is also related to the risk of spontaneous unlocking of the guiding wheel when passing through a bed due to an excessive side force.

In cheaper version of beds the fifth guiding wheel is not installed at all and locking in the straight direction is achieved by locking of one of the four main travelling wheels. However, this solution requires higher skills of the personnel with regard to moving the bed and at the same time larger handling areas for turning (wider corridors) since the free end of the bed gets considerably out of direction.

Summary of the Invention

The above mentioned disadvantages are solved with a guiding wheel assembly, mainly for a hospital bed, comprising a wheel with a horizontal rotation axis installed on an arm that is fixed to the frame with the use of an axis allowing swinging in the vertical plane, characterized in that the wheel is firmly fixed in the straight direction and the arm is provided with a track, against which a pressing element leans, while the pressing element is fixed with a pin to the frame in a swinging way.

An advantage of this solution is that the guiding wheel is locked or unlocked immediately while the control forces are kept to the minimum. In addition, such a guiding wheel can be easily equipped with an electric drive as thanks to the design structure the power supply is simple.

To minimize the control forces it is advantageous if the track on the arm has the shape of a circle with its centre on the pin at least on a part of its surface.

In an advantageous embodiment behind the axis the arm continues as a lifting protrusion allowing lifting the guiding wheel over the floor.

In another advantageous version the pressing element comprises a spring.

For easy handling the pressing element may be equipped with a control pedal.

Description of the Preferred Embodiment

FIGS. 1 to 4show a frame5of a hospital bed that has four traveling wheels in the corners that can freely turn around the vertical and horizontal axis. In the middle of the frame5there is the fifth, so called guiding wheel1. The assembly of the guiding wheel1(seeFIGS. 5 to 7) comprises side supporting metal sheets that are firmly fixed to the frame5. The horizontal rotation axle6of the guiding wheel1is installed on an arm7that is fixed between the supporting side metal sheets of the frame5with the use of the axle4. The arm can swing in the vertical plane about this axle4, which is a first axle, with the axle6being a second axle about which the wheel rotates.

On the upper side of the arm7a track3is provided that the pressing element8presses on. As shown inFIGS. 5,6and7, the pressing element8comprises a wound spring11, and a pin9which may include a first inner part12, and a second outer part13positioned around the first inner part12and which is shiftable relative to the first inner part12, this being reflected by a comparison of the relative positions of the first inner part12and the second outer part13as shown inFIGS. 5,6and7. A part of the pin9is swingably mounted to the frame5and thus with the use of the pin9, the pressing element8is attached to the frame5in a swinging way. The second outer part13of the pressing element8may include an engagement portion14which is biased toward the track3by the spring11. The spring11is concentrically positioned around the first inner part12and the second outer part13of the pressing element8as shown in the drawings. The track3on the on the upper side of the arm7has the shape of a circle with the center on the pin9. After the axle4the arm7continues as a lifting protrusion2that is an integral part of the arm7. The pressing element8is equipped with a control pedal for its turning between individual positions.

After pressing of the control pedal10(seeFIG. 5) the engagement portion14of the pressing element8moves to the end of the arm7which is a first position on the track3proximate the second substantially horizontal axle6and the spring11presses the guiding wheel1with the maximum pressing force (approx. 300 to 400 N) to the floor. In this way the hospital bed keeps the straight direction (or the direction given by the operator) although the traveling wheels can freely turn about the vertical axis.

After moving the engagement portion14of the pressing element8to an intermediate or third position proximate to and above the first axle4of the arm7(seeFIG. 6) in spite of the same pressure of the spring11exerted on the arm7(circular shape of the track3) the resulting force on the guiding wheel is nearly zero and the guiding wheel1does not prevent the movement of the bed in any direction.

Through further lifting of the control pedal10the engagement portion14of the pressing element8moves to a second position on the portion of the track3on the lifting protrusion2(seeFIG. 7) and lifts the arm7together with the wheel1above the floor. In this second position the lifted wheel1does not prevent the bed from crossing barriers.