NL2013068B1 - Patient supporting system comprising a holding brake, holding brake. - Google Patents

Abstract

The invention relates to a patient support system comprising a frame mounted to a floor and an upright column movably mounted to the frame. lt comprises a holding brake device to hold the column in a set position, comprising a static component and a movable component, movable with the column in a reference plane. The holding brake device prevents the movable component to move in an activated condition and allows it to move in an inactivated condition, and comprises two first, static brake plates extending side by side from the static component in the reference plane, and two second movable brake plates extending from the movable component in the reference plane, overlapping the first brake plates. The first and second brake plates are arranged alternatingly. A pressure assembly applies a normal force to the brake plates to activate the brake device and releases said normal force to inactivate the brake device.

Description

Title: Patient supporting system comprising a holding brake, holding brake

Description

The current invention, according to a first aspect thereof, relates to a medical device attached to a static frame and comprising a movable part and a holding brake device to hold the movable part in a set position.

Medical devices according to the introduction are known. A known patient support system for patient positioning at X-ray systems, especially a cardio/Vascular system for example, has a frame that is mounted to the floor. Mounted to the frame is an upright column that is rotatable around a longitudinal axis thereof. On top of the column is a rectangular table top, for in use supporting a patient lying at the table top. The table top is mounted to the column at or near an end of the table top. The table top is arranged to rotate together with the column. A holding brake is mounted to the frame, to, in an activated condition thereof, prevent rotation of the column and the table top in set position. The known holding brake, which may also be considered as a locking system, comprises a toothed ring that rotates with the column and a rack having teeth that cooperate with the teeth of the toothed ring. In the inactivated condition of the holding brake, the toothed ring is freely movable to allow rotation of the column with the table top and that engages the rack. In the activated condition of the holding brake the rack is locked, with the result that the teeth of the rack, and thus also the teeth of the toothed ring are fixed in position to prevent rotation of the column and the table top. A disadvantage of the known device, however, is that the holding brake is vulnerable for play and hysteresis in the movement direction when the brake is applied, especially noticeable when there is a large leverage between the objects that are being braked. To increase the holding power of the known holding brake a stronger and thus more voluminous actuation device or even an additional brake is required.

The current invention aims to provide a medical device according to the introduction with a holding brake device which is less vulnerable for play/hysteresis than the known device and/or that can be varied in maximum holding power without substantially affecting the space required for the holding brake device. According to the invention this is achieved with a patient support system according to claim 1. In this document, the activated condition of the holding brake device is the condition in which the holding brake device locks the column against moving with respect to the frame. Thus, in a so-called “normally on” arrangement, the holding brake device is switched “off” in the activated condition.

Known holding brakes of medical devices, such as patient support systems, incorporate at least one guidance mechanism to let friction surfaces of the holding brake touch each other in a parallel way in order to get good surface to surface contact. Such guidance mechanisms cause the play/hysteresis in the movement direction when the brake is applied.

In a holding brake device according to the current invention no such guidance system is present. Instead, the first and second brake plates can be spaced apart to minimize resistance when rotating the table top in the inactivated condition of the holding brake device. However, it is not even required to space the brake plates apart. The distal ends of the brake overlap and of course the overlapping brake plates create material distance between two neighbouring brake plates of the same kind, at the location of overlap. This may be achieved by bending neighbouring plates away from each other. Even if some adjacent brake plates would be in contact in the inactivated condition of the holding brake device, they are not used as a guidance mechanism and the contact causes only minimal resistance.

When, as in a preferred embodiment the brake surfaces are made of thin sheet metal, the brake surfaces can be designed ‘not stiff perpendicularly to the movement direction. Therefore they easily form good friction surface to friction surface contact, while being fixed (which implies there is no play). In the movement direction they are stiff, so when trying to push through the brake, there is really little deflection. This gives the feel that the object being braked is standing still, even with a big force applied.

The first and second brake plates can be designed to provide opposing friction surfaces and to deflect easily to form good friction surface to friction surface contact if the pressure assembly applies a normal force to the brake plates. The holding force of the holding brake device according to the invention is a function of the normal force exerted to the brake plates, the coefficient of friction of the friction surfaces and the number of friction surfaces between the brake plates. Because the relatively large number of brake plates, and thus friction surfaces, only a relatively low normal force is required to result in a relatively high braking power. The dimensions of the mutually contacting surface areas and the number of first and second brake plates can be easily increased to increase the holding power, without substantially affecting the rotatability of the table top in the inactivated condition of the holding brake device. Because the brake plates are relatively thin, increasing the number of brake plates requires only very little additional space. Thus, the objective of the current invention is achieved. While the arrangement of a holding brake device according to the invention is able to generate a relatively high holding force, it is not excluded that additional holding brake devices could be added to further increase the holding power, or as an (additional) safety brake. US 2005/0068137 A1 discloses a holding brake arrangement with a movable sheet as part of a medical device and enables moving and positioning of the device. The sheet is sandwiched between a fixated sheet and an electromagnet. When the electromagnet is switched on, an electromagnetic holding force is generated and the electromagnet clamps the movable sheet against the fixation sheet. There exist two friction surfaces, one between the electromagnet and the movable sheet and one between the movable sheet and the fixation sheet. If the electromagnet is switched off, and the electromagnet is no longer in contact with the movable sheet, and thus the movable sheet can move again.

In a preferred embodiment according to the current invention a brake plate is preferably made of metal. In general metal plates especially if the surface is a little buffed comprise a friction coefficient which is suitable for use in a holding brake device. A relatively small normal force can result in good holding characteristics. However, other suitable materials can be used for the holding brake plates.

The holding capacity of a second brake plate are preferably made of a dissimilar material, preferably two different kinds of metal. However, it would be possible to the same material for the first brake plates than for the second brake plates.

The holding capacity of a holding brake device according to the current invention is proportional to the number of friction surfaces available in the device. Therefore, the holding brake device preferably comprises at least three, more preferably at least four first brake plates. In other words, the holding brake device preferably has at least three friction surface pairs. With two first brake plates and two second brake plates there are already 3 friction surface pairs.

For the same reason the holding brake device of the patient support system according to the current invention preferably comprises at least three, more preferably at least four second brake plates. The first and second brake plates preferably are arranged alternatingly, wherein the number of second brake plates is preferably equal to, or one more or less than, the number of first brake plates. It is possible to arrange the first or second brake plates without an intermediate second or first brake plate respectively. In that case two opposing friction surfaces of the brake plates of the same kind will not influence the holding power of the holding brake device.

In a preferred embodiment of a patient support system according to the current invention a surface of an outer brake plate facing away from the other brake plates is covered with a resilient material. This resilient material help to prevent and to level out peak contact stress at the friction surfaces.

The resilient layer is preferably made of rubber.

To assure a good holding capacity in a relatively compact brake device, the thickness of the brake plates is in the range of 0.02-4.0 mm, preferably in the range of 0.05-2.0 mm and even more preferably in the range of 0.75-1.5 mm. The brake plates should not be vulnerable to damage. On the other hand, the thicker the brake plates, the more difficult the brake plates will deflect, for example when a normal force is applied to the brake plates, or if the normal force is released activate and inactivate respectively the holding brake device.

In a preferred embodiment according to the current invention two adjacent first brake plates and/or two adjacent second brake plates are spaced apart, or at least overlapping parts of the brake plates are spaced apart. A spacing between brake plates is preferably provided by a holding brake device wherein a spacer is arranged between two adjacent first brake plates and/or between two adjacent second brake plates. The spacer helps to create room for a brake plate of the other type to be present between the adjacent brake plates. As a result the brake plates can extend straight, thus without deflecting, for example from a mounting block in which the brake plates are mounted. Spacers can keep the first and second brake plates relatively parallel to each other, so the force to make good friction surface to friction surface contact is even less than without them. Besides that, spacers can be made of inexpensive sheet metal, so cost price impact of adding spacers is little. The spacer has preferably the same thickness as the brake plates.

In a preferred embodiment of the current invention the pressure assembly comprises an electromagnetic actuator to activate and/or inactivate the holding brake device. The electromagnetic actuator can be used to activate the holding brake device in the powered condition of the electromagnetic switch in a normally open system. However, for safety reasons it is preferred to inactivate the holding brake device when the electromagnetic actuator is powered in a normally closed arrangement.

Additionally or alternatively the pressure assembly may comprise a mechanical spring, such as a helical pressure spring in a normally closed arrangement of the holding brake device, for example. The helical pressure spring will apply a normal force to the brake plates. If an electromagnetic switch is powered, the electromagnetic switch will release the normal force of the helical pressure spring to inactivate the holding brake device.

In a preferred embodiment of the holding brake device according to the current invention the first, static brake plates are ring-shaped and are arranged such that a rotation axis of the movable part of the column of the patient support system extends perpendicularly through the centre or the ring-shaped brake plates. In such an arrangement the second movable brake plates extend to in between the first static brake plates. In the activated condition of the brake the normal force prevents the medical device to rotate about the rotation axis. In the inactivated condition of the holding brake device the patient support system is allowed to rotate. However, an arrangement wherein, instead of the first, static brake plates, the movable brake plates are ring-shaped can be considered as well.

Alternatively, or additionally, the movable part of the patient support system is arranged to be translatable, and the brake plates are arranged rectangular. In such an arrangement the patient support device is able to translate in an inactivated condition of the holding brake device.

Alternatively or additionally the path of movement of the movable part of the medical device is complex, and static first brake plates extend at least substantially correspondingly to the path of movement of the movable brake plates, wherein complex is to be interpreted as any other arrangement than a linear path that can be generated in case of a linear drive, or a circular path that can be generated by a rotational drive. In that case, if the patient support device can be moved along the complex path. The movable brake plates will stay between the static brake plates.

According to a second aspect the current invention relates to a holding brake device for use in a medical device, especially in a patient support system, developed to position and support a patient lying on the support system comprising a frame that is, in use, mounted to a floor and an upright column that is mounted to the frame and that is movable with respect to the frame. In a preferred embodiment the column is at least rotatable with respect to the frame and the holding brake is arranged to, in use, hold the frame from moving, for example. The holding brake device comprises at least one static component and at least one movable component, movable with respect to the at least one static component in a reference plane, the holding brake device being arranged to prevent the at least one movable component to move parallel to the reference plane in an activated condition of the holding brake device and to allow the at least one movable component to move parallel to said reference plane in an inactivated condition of the holding brake device, at least two static brake pates extending from the at least one static component and parallel to the reference plane and, seen perpendicularly to the reference plane, side by side and apart, and at least two second movable brake plates extending from the at least one movable component and parallel to the reference plane, and at least in the activated condition of the holding brake device partly overlapping the first brake plates, wherein the first and second brake plates are arranged alternatingly, and a pressure assembly that applies a normal force to the brake plates to activate the brake device and releases said normal force to inactivate the brake device has advantages that correspond to the advantages discussed above with respect to the first aspect of the current invention.

According to a third aspect the current invention is related to the use of a holding brake device according to the second aspect of the current invention in a medical device, for example a patient support system according to the first aspect of the current invention. Again, the advantages of the third aspect of the current invention correspond to that of the first and second aspect of the current invention.

The invention will now be described in more detail with reference to the figures that show a preferred embodiment of a patient support table according to the invention and wherein:

Fig. 1 is a perspective view of a patient table according to the invention;

Fig. 2 is a perspective view of a compact linear drive for a table top of the patient support table of fig. 1;

Fig. 3 is a perspective view, partly in cross section, of the compact linear drive of fig. 3 with the housing removed;

Fig. 4 is a perspective view of the compact linear drive according to fig. 2 in the patient table and cooperating with a rack;

Fig. 5a is a schematic side view of a levelling device that is integrated in the patient support table of figure 1 in a neutral condition;

Fig. 5b is a schematic side view of the levelling device of fig. 5a supporting a patient;

Fig. 6a is a perspective view of the guiding system of the patient support table of fig 1, with the column at a first location;

Fig 6b is a perspective view of the guiding system of fig. 6a with the column in an opposite location;

Fig 7a is a perspective side view of a holding brake system of the patient support table of fig. 1;

Fig. 8 is a detailed perspective side view, of part of the holding brake assembly of fig.7

In the different figures the same parts are referred to with the same reference numbers to overcome an unnecessary repetition of introduction of reference numbers. The orientation of components of the patent table must not always be taken absolutely. The orientation of some parts may differ from the unloaded condition in the loaded condition (compare figures 5a and 5b, for example). The term level, however, is to be interpreted as as horizontal as possible under the given circumstances.

Now referring to fig. 1 a patient table 1 is shown in a perspective view as an embodiment of a patient support system according to the current invention. Patient table 1 is arranged to support a patient of which an X-Ray image must be generated, especially to manoeuvre and maintain the patient in a desired location with respect to an X-Ray imaging device (not shown). The patient table 1 is mounted to a floor 2 of a medical room to which in use is fixed, and wherein is preferably sunk, mounting plate 3 as part of a frame through which the patient table 1 is installed in the medical room. A guiding system 4, which will be discussed more in detail herein later, is present between the mounting plate 3 and a column 5 that carries a table top 6. The column 5 has a housing 7 enclosing many components, amongst which a control system to control movements of the patient table 1 to, in use, move the table top 6 and a patient lying thereon to, and maintain it in, a desired position. A ring guide system 8 is enclosed in the bottom of the housing 7 of the column 5. The control system comprises a levelling device (not shown in fig 1) that will be discussed later herein to maintain the table top 6 level, or in another defined angle of inclination, in the loaded condition of the table top 6. A compact linear drive 9 on a positioning table 45 on top of column 5 serves a longitudinal movement of the table top 6 with respect to the column 5.

The patient table 1 is able to make many movements to be able to move and maintain the table top 6 with a patient in a desired position with respect to an X-Ray imaging device. The column 5 is able to translate, supported by the guiding system 4, in a direction indicated by P1 with respect to a floor of a medical room to which the mounting plate 3 is attached. The column 5 is also able to rotate about a generally vertically extending rotation axis, driven and supported by a ring guide system 8 and in a direction indicated by arrow P2. The column 5 is also able to move generally vertically in a direction indicated by arrow P3, for which movement a cylinder (not shown in fig. 1) is present in a levelling device to be discussed. The table top 6 is able to move longitudinally with respect to the column 5 in a direction indicated by arrow P4, driven by the compact linear drive 9 that is discussed later herein. The table top 6 is also able to translate transversely with respect to the column 5 in a direction indicated by arrow P5, to rotate about its longitudinal axis in a direction indicated by arrow P6 and to tilt with respect to the horizontal in a direction indicated by arrow P7. The control of the movements in the directions P5-P7 happens in a way that is known from patient tables that are commercially available and will not be discussed in detail herein.

Figure 2 shows a perspective view of the compact linear drive 9 for the table top 6 of the patient support table 1. The compact linear drive 9 comprises a motor 21, a gear box 22, a safety brake 23 and an electromechanical brake 24 as a clutch.

Fig. 3 shows the compact linear drive 9 in more detail in a perspective view, partly in cross section and with the housing of the gear box 22 removed. The motor 21, a conventional electromotor, has an output shaft 25 embodied as a worm 25. The worm 25 is in engagement with a worm gearwheel 26 which, in an operational condition, is able to rotate with a pinion shaft 27. The worm gearwheel 26 has a hollow axis, through which the pinion shaft 27 extends. As a result, a relatively compact drive arrangement is achieved. A clutch 24 embodied as an electromechanical brake 24 is operationally arranged between the worm gearwheel 26 and the pinion shaft 27. In use, the motor 21 of the compact linear drive 9 rotates the worm 26, which in turn rotates the worm gearwheel 26. In the mutually coupled condition of the worm 25, the worm gearwheel 26 and the pinion shaft 27, the worm gearwheel 26, in turn, rotates the pinion shaft 27.

The clutch 24 is embodied as an electromechanical brake. An adapter flange 29 is in connection and rotates together with the worm gearwheel 26. The lower surface of the adapter flange 29 faces to an upper surface of a friction disk 28. A leaf spring 32 is provided between the lower surface of the adapter flange 29 and the upper surface of the friction disk 28 and is pulled downward in the non-powered condition of the electromechanical brake 24. Located below the friction disk 28 is a magnet arrangement 30 comprising a permanent magnet that attracts friction disk 28. The magnet arrangement 30 further comprises an electromagnet that, in a powered condition of the electromagnet, compensates for the attractive force of the permanent magnet and the force of the leaf spring 32.

Both the lower surface of the friction disk 28 and the upper surface 33 of the magnet arrangement 30 are provided with a friction surface. In the non-powered condition of the electromechanical brake 24, the friction disk 28 and the upper surface 33 of the magnet arrangement 30 are in mutual engagement. In this condition, the pinion shaft 27 will rotate if the worm gearwheel 26 is rotated. In the powered condition of the electro mechanical brake 24 as a clutch, a gap is present between the friction disk 28 and the upper surface 33 of the magnet arrangement 30 because the attractive force of the permanent magnet is compensated by the electromagnet. Now the friction disk 28 and the upper surface 33 of the magnet arrangement are disengaged. In this condition, the pinion shaft 27 is freely rotatable and will not rotate if the worm gearwheel 26 is rotated. An arrangement in which the powered and non powered conditions are interchanged, however, is also possible.

The magnet arrangement 30, like the worm gearwheel 26 has a hollow axis that is aligned with the hollow axis of the worm gearwheel 26. This enables the pinion shaft 27 to extend through the hollow axes of both the worm gearwheel 26 and the magnet arrangement 30. As can be seen in figure 3 this results in a very compact arrangement of the linear drive 9 and the clutch 24, with only a relatively small number of components.

Fig. 4 shows a perspective view of the compact linear drive 9 according to fig. 2 in the patient table 1 and cooperating with a rack 31 to move the table top 6 of the patient table 1 in the longitudinal direction. The table top (not shown in fig. 4) is fixedly connected to and moves the rack 31. When the pinion shaft 27 is actuated (indirectly) by the motor 21, it rotates and its teeth will engage and move the rack 31.

Fig. 5a shows a schematic side view of a levelling device 11 integrated in the patient support table 1 of figure 1 in a neutral condition. The levelling device 11 cooperates with components of the patient table 1 to, at least in use, continuously keep the table top 6 level, usually horizontal. The column 5 has a base plate 41 that is rotatably supported by the ring guide system 8. The axis of rotation of the column 5 extends through the centre of the ring guide system 8. Connected to an outer edge 42 of the base plate 41, is an upright hollow post 43 in which a linear drive piston-cylinder device 44 is enclosed. The piston-cylinder device 44 is able to vertically move the table top 6 with respect to the floor 2. On top of the piston-cylinder device 44 the piston-cylinder device 44 supports an intermediate part 50 to which a positioning table 45 is pivotably connected and extends horizontally above the base plate 41. Interposed between the piston-cylinder device 44 top and the positioning table 45 is a force sensor 52 that in use measures the force exerted to the piston-cylinder device 44 by the positioning table 45. At the bottom part of the intermediate part 50 a tilt actuator 46 is pivotably connected to the intermediate part 50, and extends to and is pivotably connected to an edge 47 of the positioning table 45 that is opposed to an edge 48 of the positioning table 45 that is supported by the cylinder 44. Thus, the positioning table 45 is supported at two outer edges 47, 49. The tilt actuator 46 has a piston-cylinder device 48 that can be extended and compressed to pivot the positioning table 45 about a horizontal pivot axis 51. The positioning table 45 supports several actuators that in use manipulate the table top 6 to, and maintain it in, the desired position as is depicted by means of arrows P4, P5 and P6 in fig. 1,one of which is the compact linear drive 6 that has been discussed earlier herein in more detail. A longitudinal positioning sensor 53 disposed below the table top 6 and in a fixed position with respect to the positioning table 45 measures the longitudinal position of the table top 6 with respect to the positioning table 45.

Fig. 5b shows a schematic side view of the levelling device 11 of fig. 5a, with the table top 6 supporting a patient 12 and longitudinally extended to an extreme (left) position. Fig 5b clearly shows that the orientation of many components is changed compared to the same patient table 1 in the neutral position of fig. 5a. The weight of the patient 12 and the position of the table top 6 tend the table top 6 to become off level in the absence of any corrective movements in the patient table 1. Fig 5b. shows effects of the load of the table top 1 and corrections taken by the levelling device 11. One of the effects is that the arrangement of the table deflects under the weight of the patient 12. The extent to which the table deflects depends on several factors, amongst which the rotational stiffness of the table top 6 (which is a given constant for a specific patient table), the weight of the patient 12 and the (longitudinal) position of the centre of gravity of the load. Currently known systems correct the level of the table top independently of deflection of the table. For example by measuring the position of two reference points in the table top. This results in an inaccurate measurement and thus in an inaccurate corrective action which might result in the table top of the known patient table not being absolutely level (or exactly in a defined angle of inclination).

The levelling device 11 of the patient table 1 according to the current invention is able to make a more accurate correction. In use the controller of the levelling device 11 receives the actual force measured by the force sensor 52. This actual force is reduced with a result of a measurement of the force sensor 52 of an unloaded table top 6 and in the neutral position of the table top 6, which in fact is a constant value. The controller also receives the actual longitudinal position of the table top 6 measured by the longitudinal position sensor, i.e. the moment of the force working at the piston-cylinder device 44 top and is determined by force measurement at the position of the force sensor 52 times the longitudinal position. Those two values are multiplied and are then divided by the table support rotational stiffness (a constant) to result in a correction angle, and a corrective action is taken accordingly by the levelling device 11.

Fig. 6a is a perspective view of the guiding system 4 of the patient support table 1 of fig 1, with the column 5 at a first location. A lower front part of the housing 7 of the column 5 is taken away to make part of the guiding system 4 visible. A mounting plate 3 is fixedly mounted to the floor 2. Immovably attached to the mounting plate 3 are four guiding shoes 61a-61d, only two (61a, 61b) of which are visible in fig. 6a. The two other guiding shoes are located at the opposite side of the mounting plate 3 which in fig. 6a is hidden by the column 5. Mounted at the bottom of column 5 are two guide rails 62a, 62b, of which only guide rail 62a is visible in fig. 6a. The guide rails 62a, 62b each extend through a pair of guide shoes 61a, 61b and 61c, 61c respectively. The column 5 is movable to the position shown in fig 6b, guided by the guide rails 62 that are guided by the guide shoes 61. This movement, in use, is actuated manually by pushing against the (foot side of) the top of the table or by pulling the (foot side of) the table 1.

In the installed position of the patient table 1 the mounting plate 3 is covered by a cover (not shown in figs. 6a, 6b). The lower part of the housing 7 of column 5 extends around the whole column 5, covering the guide rails 62 and close to the floor 2 and the cover. It will be clear to the reader that in the installed condition, no components visibly project to outside the housing of the column 5 or from the floor 2 (or the cover). This contributes to a safe, ergonomic environment for medical personnel and minimizes the risk of damage to the components of the column 5. The total distance between the outermost parts of the two guide shoes 61a, 61b that cooperate with a guide rail 62a is about 1/3th of the length of the rail. As a result a projection of the column 5 in the two extreme opposite positions “overlaps itself over only this 1/3th of its length. This means that the column 5 can be moved over a distance of 2/3th of its own length.

Fig 7a shows a perspective side view of the holding brake system 13 of the patient support table 1 of fig. 1. The holding brake system 13 is mounted to an annular ring guide system 8 that enables the column 5 to rotate about the substantially vertical central axis of a ring 71 of the ring guide system 8. The column 5 has a mounting plate 3 supporting a ring 71 that is fixedly mounted to the mounting plate 3. An annular mounting block 72 is attached to the immovable ring 71 and carries a number of static brake disks 73 that are stacked and clamped to the ring 71 by a clamping ring 74 and bolts 75. This will be elucidated in more detail in figure 8. A rectangular brake plate assembly 76 is mounted to the ring 71 and can move around the ring 71. The brake plate assembly 76 comprises a mounting block 77 that supports a number of stacked dynamic brake plates 78 that extend to outside the projection of the mounting block 77, all clamped together by a clamping strip 79 and inner hexagon socket screws 80. The rectangular brake plate assembly 76 is movably attached to the column 5 of the patient table 1. The brake plates 78 extend in the direction of the ring and between the brake disks 73. The brake disks 73 and brake plates 78 are in overlapping and alternating arrangement as can be seen in fig. 8, which shows an enlarged detailed drawing of part of the holding brake system 13 which will be discussed later. When the brake plate assembly 76 moves around the ring 71, the brake plates 78 are maintained between the static brake disks 73. In this embodiment the upper brake plate 78, of course, is maintained in between the upper brake disk 73 and the pressure assembly 81.

Mounted above the overlapping parts of the brake disks 73 and the brake plates 78 is a pressure assembly 81 that is attached to the horizontal plate that is screwed onto the pivot frame connected to the column 5. The pressure assembly 81 has a bottom plate 82 and a top plate 83 which are mutually connected by pins 84. Helical compression springs 85 are arranged around the pins 84 and drive the bottom plate 82 away from the top plate 83. Arranged in the centre of the pressure assembly 81 is an electromagnet 86 that is fixed to the bottom plate 82.

Figure 8 shows a part of the holding brake system 13 in more detail. The mounting block 77 supports the brake plates 78 that are spaced apart by spacers 87 positioned between adjacent brake plates 78. A clamping strip 79 on top of the stack of brake plates 78 clamps the brake plates 78 together and to the mounting block 77. The brake plates 78 (except the upper one) extend to in between brake disks 73 that are attached to the static ring 73 mounted to the mounting plate 3 in the lower part of the patient table 1, and which is not rotatable with respect to the floor. The bottom plate 82 of the pressure assembly 81 is located above the overlapping brake plates 78 and disks 73.

In use, in the non-powered condition of the electromagnet 86 as shown in fig. 7a, the bottom plate 82 of the pressure assembly 81, together with the electromagnet is driven away from the top plate 83 by the helical compression springs 85. A gap G1 is present between the electromagnet 86 and the top plate 83. The bottom plate 82 exerts a normal force to the alternatingly stacked brake disks 73 and brake plates 78. In this condition of the pressure assembly 81 the mutually facing surfaces of the brake disks 73 and plates 78 act as friction surfaces. The number of friction surfaces can be chosen as desired (or required) by adding/removing brake plates 78 or brake disks 73 and amounts nine in the arrangement of fig. 8. A relatively small normal force is required to generate a relatively large holding force of the holding brake system 13. Thus, if the electromagnet 86 is not powered, the brake plates 78 that are rotatable with respect to the ring 71 are trapped and kept immovably in position by the static brake disks 73.

If the electromagnet 86 is powered, as shown in fig. 7b, the electromagnet 86, together with the bottom plate 82, pulls itself to the top plate. No gap (G1) is present between the electromagnet 86 and the top plate 83. Instead, a gap G2 is present between the bottom plate 82 and the upper brake disk 73. No normal force is exerted to the mutually overlapping brake disks 73 and brake plates 76 and the brake plates 78 are able to move freely with respect to the brake discs 73 and the ring without (substantial) friction between the friction surfaces.

In the figures and in the description thereof only one preferred embodiment of a patient table according to the current invention is shown and described. It will be clear, however, that many modifications, that may or may not be obvious to for the skilled person, may be made to the patient table within the scope of the invention defined in the following claims. It is possible, for example, to use a closed spring solution instead of a normally closed permanent magnet in the brake as a clutch in the compact linear actuator. The compact linear actuator could be applied in other drive arrangements in the patient table. The pinion could also be in engagement with a toothed belt, which would enable to arrange the actuator at a different location. The worm gear could be replaced by an angular arrangement of a different type that a worm gear arrangement

Claims (16)

A patient support system adapted to position and support a patient lying on the support system, for example in X-ray systems, and comprising a frame which, when used, is mounted on a floor and an upright column mounted on the frame and is movable to with respect to the frame, the patient support system comprising a retaining brake device to hold the column in a set position, the retaining brake device comprising at least one static component and at least one movable component, which is connected with the column and with respect to the at least one static component is movable in a reference plane, the holding brake device being arranged to prevent the at least one movable component from moving parallel to the reference plane in an activated state of the holding brake device and being arranged to allow the at least one movable The component moves parallel to said reference plane in an inactivated state of the holding brake device, further comprising at least two first, static brake plates extending from the at least one static component, parallel to the reference plane, and extending relative to the reference plane seen at right angles, extending side by side, and at least two second movable brake plates extending from the at least one movable component, parallel to the reference plane, and at least in the activated state of the holding brake device partially overlapping the first brake plates, the at least two first and the at least two second brake plates, at least in the inactivated position of the holding brake device, are arranged alternately, comprising a pressure assembly exerting a normal force on the brake plates to activate the brake device and canceling said normal force to deactivate the brake device. The patient support system of claim 1, wherein a brake plate is made of metal. A patient support system according to claim 1 or 2, comprising at least three, preferably at least four first brake plates. A patient support system according to claim 1, 2 or 3, comprising at least three, preferably at least four second brake plates. A patient support system according to any one of the preceding claims, wherein a surface of an outer brake plate facing away from the other brake plates is covered with a resilient layer. The patient support system of claim 5, wherein the resilient layer is made of rubber. The patient support system according to one or more of the preceding claims, wherein the thickness of the brake plate is in a range of 0.02 - 4.0 mm. A patient support system according to one or more of the preceding claims, wherein two adjacent first brake plates and / or two adjacent second brake plates are spaced apart. A patient support system according to one or more of the preceding claims, wherein a spacer is arranged between two adjacent first brake plates and / or between two adjacent second brake plates. The patient support system according to one or more of the preceding claims, wherein the pressure assembly comprises an electromagnetic circuit. A patient support system according to one or more of the preceding claims, wherein the pressure assembly comprises a spiral compression spring. A patient support system according to any one of the preceding claims, wherein the first static brake plates are annular and are arranged such that an axis of rotation of the movable part of the patient support table extends perpendicularly through the center of the annular static brake plates. Patient support system according to one or more of the preceding claims, wherein the movable part of the patient support system is arranged to be translatable, and wherein the brake plates are arranged in a straight line. A patient support system according to one or more of the preceding claims, wherein the path of movement of the movable part of the medical device is complex, and wherein the first, static brake plates extend at least substantially corresponding to the path of movement. A retention brake device for use in a patient support system and comprising at least one static component and at least one movable component movable in a reference plane with respect to the at least one static component, the retention brake device being arranged to prevent the at least one movable component moves parallel to the reference plane in an activated state of the holding brake device and to allow the at least one movable component to move parallel to said reference plane in an inactivated state of the holding brake device, wherein at least two static brake plates extend from the at least one static component and parallel to the reference plane, and extending perpendicular to the reference plane, side by side and spaced apart, and wherein at least two second movable brake plates extend from the at least e a movable component and extend parallel to the reference plane, and at least in the activated state of the holding brake device partially overlapping the first brake plates, the first and second brake plates being arranged alternately, and a pressure assembly exerting a normal force on the brake plates in order to apply the braking device and cancels said normal force to deactivate the braking device. Use of a patient support system according to one or more of claims 1 to 14 and / or a holding brake according to claim 15.