NL2013069B1 - Patient support system and clutch for a compact linear movement actuator in a patient support system. - Google Patents

Abstract

The invention relates to a patient support system developed to position and support a patient lying on the support system, for example at X-Ray systems. The patient support system comprises a frame that is, in use, mounted to a floor, an upright column mounted to the frame and supporting a substantially rectangular table top extending in the rectangular plane that is movable in said plane with respect to the column to accommodate a patient, and a controlling device with a motor and a gear assembly for moving the table top to a desired position and a clutch for activating and deactivating the gear assembly and a brake to lock the table top in the desired position. The invention further relates to a controlling system and to the use of such a patient support system and/or such a controlling system.

Description

Title: Patient support system and clutch for a compact linear movement actuator in a patient support system

Description

The current invention, according to a first aspect thereof, is related to a patient support system arranged to position and support a patient lying on the support system, for example at X-Ray systems especially Cardio/Vascular systems, comprising a frame that is, in use, mounted to a floor, an upright column mounted to the frame and supporting a substantially rectangular table top defining a plane and which is movable in said plane with respect to the column to accommodate and position a patient, and a controlling device with a motor and a gear for moving the table top to a desired position and a clutch for activating and deactivating the gear assembly. A known patient support system comprises a table wit a table top that is floatable with respect to the column, to position the table top in an X-Ray imaging device. The table top can be moved by means of the motor and manually by medical personnel, and can be locked in position, for example when the table top with the patient is in the desired position to generate an image of the patient. Performance requirements of such patient support systems, like larger user strokes, safety brake systems and safer, faster and stronger movements constantly increase. Those increasing requirements not only result in the space in the column, available for housing the equipment becoming scarce, but also in an increasing number of components. An increasing number of components, however, compromises the safety of the patient support system. In other words, more functionality in a smaller available column volume makes that a solution with all the functions stacked would not fit in the column.

Therefore, it is an objective of the current invention to provide a patient support system enabling a reduction of the number of components with respect to a comparable patient support system with at least the same functionality, and/or that can be designed more compact. This objective is achieved by the current invention in that the controlling device comprises an electromechanical brake as the clutch. An electromechanical brake in principle requires two main components, a magnet and a friction part and can thus be designed relatively compact, while a conventional clutch requires at least an actuation part and two rotating friction parts. Thus, the objective of the current invention is achieved with the features of the characterising part of claim 1.

In a preferred embodiment of the current invention the electromechanical brake is integrated in the gear assembly. Integration in the gear assembly enables to achieve a rather compact arrangement of the controlling device.

It is preferred that the electromechanical brake comprises a coiled magnet and a first friction element that is movable with respect to a second friction element of a component to be switched between a locked condition an a released condition, between an operational position wherein the first and second friction elements are mutually in engagement and a non operational position wherein the first and second friction surfaces are disengaged. In such an arrangement the second friction element can be integrated in an actuation part of the gear assembly, also enabling a relatively compact embodiment of the controlling device.

It is preferred in that aspect, that the clutch is arranged to be in the locked position when the clutch is not powered. As a result the table top of the patient support system will not be able to move (float) if the electromechanical brake is not powered. Thus, in a situation where the power supply is disturbed the table top is in a fixed condition, or at least there will be no freedom of movement in the direction in which the current actuator is intended to move the table top. This increases the safety of the patient support system. However, alternatively it could be possible to develop a patient support system according to the current invention wherein the clutch is in the locked position when the clutch is powered.

In a preferred embodiment according to the current invention the second friction element is comprised in, or fixed to, an actuation part of the gear assembly. This also enables a rather compact design of the controlling system and a reduction of the number of parts necessary for the patient support system.

It is preferred if the electromechanical brake is arranged in parallel with a hollow axis angular gear, and if the electromechanical brake also comprises a hollow axis, which is at least substantially aligned with the hollow axis of the gear wheel. When both hollow spaces are aligned it is possible to mount an output pinion of the gear assembly through the space within the electromechanical brake and the hollow axis angular gear. This also enables a very compact controlling device and a reduction of the number of parts of the controlling device since the transmission of the movement of the actuating parts to the part to be actuated can be embodied in a simple way.

In such a device it is preferred that a rotary electrical feed through is provided, preferably embodied as a slip ring, to power the electromechanical brake.

The gear assembly is preferably developed to linearly move the table top in the rectangular plane of the table top, especially in the longitudinal direction of the rectangular plane. The stroke of the table top in the longitudinal direction may be rather long and forces exerted at the electromechanical brake as a clutch can be quite large. A controlling device in a patient support system must be reliable at all times. Therefore a patient support system with a controlling device according to the current invention can be developed reliable, compact and with a relatively small number of components.

According to a second aspect the current invention relates to a controlling device for use in a medical device, especially a patient support system according to the first aspect of the invention, having a table top the controlling device comprising a motor and a gear assembly for moving the table top to a desired position, a clutch for activating and deactivating a gear assembly to actuate movement of the table top and a brake to lock the table top in the desired position, characterised in that the controlling device comprises an electromechanical brake as the clutch.

The advantages of such a controlling device correspond to the advantages discussed above with respect to the first aspect of the current invention.

According to a third aspect the current invention relates to the use of a controlling system according to the second aspect of the current invention, preferably in a patient support system according to the first aspect of the current invention. Again the advantages of the use of such a controlling system correspond to the advantages discussed herein above.

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 (11)

A patient support system adapted to position and support a patient lying on the patient support system, for example in X-ray systems, and comprising a frame which, when used, is mounted on a floor, an upright column mounted on the frame and supporting a substantially rectangular tabletop defining a plane and movable in said plane relative to the column to accommodate and position a patient, and a control device with a motor and a gear assembly for moving the tabletop to a desired position and a coupling for activating and deactivating the gear assembly, characterized in that the control device comprises an electromechanical brake as the clutch. The patient support system of claim 1, wherein the electromechanical brake is integrated in the gear assembly. A patient support system according to claim 1 or 2, the electromechanical brake comprising a magnet with a coil and a first friction element which, relative to a second friction element of a component to be switched between a locked position and a released state is movable between an operational position in which the first and the second frictional element mutually engage one another and a non-operational position in which the first and the second frictional surface do not engage each other. The patient support system of claim 3, wherein the coupling is arranged to be in the locked position when the coupling is not energized. The patient support system of claim 3 or 4, wherein the friction element is included in, or attached to, a drive part of the gear assembly. 6. Patient support system according to one or more of the preceding claims, wherein the electromagnetic brake is arranged in parallel with a transmission at an angle with a hollow shaft, and wherein the electromagnetic brake also comprises a hollow shaft which is at least substantially aligned with the hollow shaft of the gear. Patient support system according to one or more of the preceding claims, wherein a rotatable electrical lead-through is provided, preferably designed as a slip ring. The patient support system of any one of the preceding claims, wherein the gear assembly is designed to linearly move the tabletop in the rectangular surface of the tabletop. The patient support system of claim 8, wherein the gear assembly is designed to move the tabletop longitudinally into the rectangular surface of the tabletop. 10. Control device for use in a medical device, in particular a patient support system according to one of claims 1 to 9, with a table top, the control device comprising a motor and a gear assembly for moving the table top to a desired position, a coupling for activating and deactivating the gear assembly to drive movement of the table top and a brake to lock the table top in the desired position, characterized in that the control device comprises an electromechanical brake as the coupling. Use of a control system according to claim 10, preferably in a medical device, in particular a patient support system according to one of claims 1 to 9.