The invention relates to an adjustable treatment table, hospital or care bed of the type defined in the introductory portion of claim 1.

EP 498 111 B2 to J. Nesbit Evans & Co. Ltd. discloses a hospital bed, in which the mattress supporting face may be adjusted by two electrical ac¬ tuators, and in which the frame, in which the mattress supporting face is mounted, may be raised and lowered as well as tilted over a transverse axis (Trendelenburg positions) by two additional actuators. The actuators are connected to a control box containing a mains-based power supply as well as a rechargeable battery pack, just as the control box contains a con¬ trol unit. Handsets for the patient as well as a handset for the staff are con¬ nected to the control unit, alternatively, or additionally, a control box (ACP) may be arranged at the foot end of the bed. In addition, the bed may be equipped with a foot control at each side, typically with two-three operating pedals. An example of a bed with a foot control is shown in WO 01/47340 to Hill-Rom Services, Inc.

There has been a number of accidents where a patient has fallen down on the foot control, whereby one or more functions have been activated. After the activation, the patient has e.g. got his head caught in the bed structure, and there have been instances which have had a fatal result.

The object of the invention is to avoid these problems.

This is achieved according to the invention by arranging the bed as stated in claim 1. When an operating sequence for the foot pedals is required in order to activate a function, unintentional activation because of a fall on the pedals or lean on these in an attempt to get up after a fall is prevented. It has been found that the sequence may be made very simple, e.g. two

successive presses on the pedal with an intermediate pause have been found to be sufficient to protect against unintentional activation because of a fall on the pedals.

This sequence protection may e.g. be implemented directly in the foot con¬ trol or in the control box. Alternatively, it may be positioned in the ACP. Here, there is the additional option of disconnecting the function entirely by disabling the foot control.

An exemplary embodiment of the invention will be described below with ref¬ erence to the drawing. In the drawing:

Fig. 1 shows three sequences in the operation of a foot pedal on a hos¬ pital bed, and

fig. 2 shows a diagram of a circuit of the invention.

Three situations are outlined in the accompanying drawing, where the first one shows a sequence for the enabling of the function. First, the foot pedal is operated briefly, is released and operated again and kept down until the function has been performed, e.g. raising of the bed, more particularly rais¬ ing of the mattress frame to a desired level. The other situation shows a disabling of the related function, here the foot pedal is kept down for an extended period of time, e.g. corresponding to a patient falling down on the pedal. The last one, the third operation, is disabling, too, here the foot pedal is kept down for a certain period of time, is released and kept down again, e.g. corresponding to a patient pressing on the foot pedal in an attempt at getting up. It will be appreciated that all other operating modes than pre¬ cisely the first outlined one, are disabling, i.e. the function is not performed.

In case of enabling, i.e. the first situation, it has been found expedient that

the first press on the foot pedal is not below about 50 msec and not above about 500 msec, while, the pause, i.e. released pedal, before the next activation is to be minimum 150 msec. For proper use, the duration of the press on the foot pedal and the pause does not exceed 500 msec.

The realization may take place in the form of analog circuits or be micro¬ processor-based, where the function is written into the software.

With reference to fig. 2, an example of a realization in the form of an analog circuit will be described below.

A FET transistor Q3 is the switch which decides whether a channel may be or may not be activated. The control current to the channel runs through this, and if it is interrupted, no control signal will be applied to the control box.

The control box contains a relay K1-B, which activates the motor of the ac¬ tuator when it is drawn.

For the FET Q3 to be switched on, a sequence must be performed. Failure to comply with the sequence means that various circuits prevent Q3 from being switched on.

The FET Q3 is switched on, when it receives a sufficiently high voltage. At the moment when the foot switch SW1-B is activated, the entire relay volt¬ age is applied across the circuit.

The two capacitors C2 and C3 are charged through the resistor 3 and in part the resistor R4. The voltage across C2 increases ten times as fast as the voltage across C3, since it has a capacity which is ten times greater.

If the voltage across C2 is allowed to increase to about 0.7 volt, the latch, the transistors Q2-A and Q2-B, will be activated and from now on prevent the FET Q3 from being switched on, as the control voltage is permanently connected to earth.

If the foot switch SW1 is released after a suitable period of time before the latch Q2-A and Q2-B is activated, the capacitor C2 will be discharged rap¬ idly through the resistor R4. The capacitor C3, on the other hand, maintains its voltage, since the discharge only takes place very slowly.

If the foot switch SW1 is activated again after the capacitor C2 has been discharged, the charging of the capacitor C3 continues until the FET Q3 is switched on, and the control unit is activated.

When the FET Q3 has been activated, the voltage across the circuit will be so low that the capacitor C2 is discharged again close to 0 volt.

If the foot switch SW1 is activated several times in succession, also the cir¬ cuit will be activated. The function of the transistor Q4 is to block activation if the voltage across the circuit is high too many times. During the period when the voltage is high, the capacitor C4 is charged through the resistors R7-R8-R9, and if the activation voltage to Q4 is reached, the latch Q2-A and Q2-B is instantaneously triggered through the diode D2, following which further function is blocked.

Here, just one foot switch and one relay for an actuator have been indi¬ cated, but it will be appreciated that it is readily within the abilities of a per¬ son skilled in the art to extend the circuit to several foot switches and sev¬ eral actuators on the basis of the disclosure.