Linear drive with brake mechanism

Abstract

The invention relates to a linear drive comprising a spindle drive (2), the spindle drive parts (4, 5) of which are threadingly engaged, one of the spindle drive parts (4) being mounted for longitudinal movement along a drive axis (10) and having a stroke part (11) for executing a stroke. The drum brake (18) is released when a rotationally driven spindle drive part (5) is rotationally driven and is closed when the stroke part (11) is under external load. The drum brake (18) is provided with a plurality of brake shoes (24) and a brake drum (21) having a brake surface (23) for the brake shoes (24). A release actuating element (26) and a closing actuating element (27) are provided, which actuate the brake shoe (24) in opposite directions.

Description

TECHNICAL FIELD

[0001] The invention relates to a linear drive. The field of application can in particular include the medical technology sector, for example as a means for displacing a computed tomography table. The invention also relates in general to a patient table comprising a frame and a bed for a patient, which bed can be displaced by means of a linear drive. BACKGROUND

[0002] DE 2238632 C2 discloses a linear drive according to the features of the preamble of claim 1.

[0003] The linear drive comprises a lead screw drive, which is driven by an electric motor via a spur gear mechanism. A threaded nut of the lead screw drive is driven in rotation and a threaded spindle is arranged in a longitudinally displaceable manner in a housing of the linear drive and is connected to a travel portion. In the event of an external force acting on the travel portion in the direction of the spindle axis when the electric motor is switched off, an undesired rotation of the threaded nut is prevented by a brake device. The brake device has a wrap spring, which contacts a fixed housing portion and prevents the undesired rotation of the threaded nut.

[0004] The wrap spring causes grinding noise, which is undesirable depending on the field of application of the linear drive. Known linear drives use a hydrostatic displacement unit to reduce the grinding noise, but these hydrostatic displacement units require an increased design effort.

[0005] Furthermore, it has been determined that in the event of a large external force acting on the travel portion in the axial direction along the drive axis, the technical limits of the wrap spring will be reached, so that a reliable brake function of the brake device cannot be ensured. SUMMARY

[0006] It is an object of the invention to provide a linear drive which is easy to manufacture and has an improved brake device.

[0007] According to the invention, this object is achieved by a linear drive according to claim 1. Advantageous further refinements are indicated in the dependent claims.

[0008] The linear drive according to the invention has a lead screw drive, a lead screw drive portion of which is threadedly engaged and converts a rotation of one lead screw drive portion about a drive axis into a relative displacement of the lead screw drive portions along the drive axis. Preferably, the rotating lead screw drive portion is fixed in the axial direction to a frame and the other lead screw drive portion is longitudinally displaceable in the axial direction and fixed in terms of rotation relative to the frame.

[0009] Suitable for the application is a ball screw drive, the balls of which roll in ball grooves of a threaded nut and a threaded spindle, the ball grooves being helically wound around the drive axis.

[0010] Also a roller screw drive is a tried and tested screw drive that can be used for the application.

[0011] In special applications, it can be advisable to use a sliding screw unit as used in a trapezoidal screw drive. In these cases, the threaded nut and the threaded spindle are each provided with a trapezoidal thread, which are threadedly engaged with one another.

[0012] For particularly small thread pitches, a planetary roller screw drive can be required, the planetary rollers of which engage with the thread of the threaded spindle on the one hand and with the groove profile of the nut on the other hand with their planetary roller profile. If a planetary roller screw drive with constant thread pitch is to be used, in many cases a planetary roller carrier is rotationally driven, which accommodates the planetary rollers arranged distributed around the circumference. In this case, the planetary roller carrier can also be referred to as a screw drive part. In this embodiment, the threaded spindle can be arranged in a non-rotatable and longitudinally displaceable manner and provided with a stroke part.

[0013] One screw drive part is rotationally driven via a drive shaft, wherein the other screw drive part is arranged in a longitudinally displaceable manner along the drive axis and designed to perform a stroke. The rotationally driven screw drive part is preferably formed by the threaded spindle described above, which can be mounted in a rotatable manner in the housing. It is also possible to rotationally drive the threaded nut described above and, for example, to mount the threaded nut in a rotatable manner in the housing. It is also conceivable that the other screw drive part is formed by the threaded spindle, which is guided in a non-rotatable and longitudinally displaceable manner in the housing.

[0014] The drive shaft can be part of a traction drive, wherein a motor shaft of an electric motor drives the drive shaft via a traction means, such as a toothed belt pair. The drive shaft is preferably arranged coaxially to the rotationally driven screw drive part.

[0015] Furthermore, the linear drive is provided with a brake device, which opens under the rotational drive of one rotationally driven screw drive part and which closes under an external axial load of the stroke part and counteracts displacement of the stroke part.

[0016] The brake device is designed as a drum brake having a plurality of brake shoes and a brake drum with brake surfaces for the brake shoes. The brake device comprises a release actuating element and a closure actuating element, wherein the actuating elements actuate the brake shoes in opposite directions.

[0017] The release actuating element of the brake device is located on the drive side of the linear drive and engages with the brake shoes under rotational drive of the drive shaft. The release actuating element is connected to the drive shaft and follows the rotational movement of the drive shaft.

[0018] The closure actuating element of the brake device is actuated under external axial load of the travel portion. The closure actuating element is connected to the rotationally driven lead screw drive portion, which is subjected to a torque due to the thread engagement when the travel portion is subjected to the external axial load. The closure actuating element is actuated independently of the rotational drive. For example, if the drive moves in the direction of the applied force, the closure actuating element is permanently actuated, but the opening actuating element is also actuated so that the friction of the brake is just high enough to ensure that the speed predetermined by the motor is not exceeded.

[0019] In a preferred further development, the drive shaft actuates the release actuating element in both rotational directions, i.e. independently of the rotational direction of the drive shaft, and drives the rotationally driven lead screw drive portion.

[0020] If the drive shaft is rotationally driven, i.e. driven via the motor, a drive-side torque acts on the drive shaft, under which the release actuating element is actuated.

[0021] If the drive shaft is unloaded, i.e. the motorized drive is switched off, the rotational drive is switched off. As mentioned at the outset, one lead screw drive portion is subjected to a torque due to the thread engagement with the other lead screw drive portion under the axial load of the other lead screw drive portion. The one lead screw drive portion actuates the closure actuating element under this torque.

[0022] For example, if the lead screw drive portion is formed by a threaded nut and a threaded spindle in thread engagement with the threaded nut, and the threaded spindle is rotationally driven, the threaded nut arranged in a non-rotatable and axially displaceable manner is axially loaded under its external axial load due to the connected travel portion. In this case, this external axial load is transmitted to the rotationally driven threaded spindle. The thread engagement generates a torque acting on the threaded spindle about the drive axis. Under this torque, the threaded spindle actuates the closure actuating element for the drum brake. To this end, the closure actuating element can have a clutch portion fixed to the threaded spindle.

[0023] It is conceivable that an arrangement is provided in which the brake drum and the brake shoes are located one behind the other in the axial direction. In this case, the actuation of the brake shoes takes place in axially opposite directions.

[0024] Preferably, an arrangement of a brake drum known per se is provided, in which arrangement the brake shoes are actuated in opposite radial directions. A cost-effective further development provides two brake shoes. However, it is conceivable to arrange more than two brake shoe segments distributed in a circumference, which are actuated in the described manner.

[0025] Under motorized load on the drive shaft, the release actuating element is set in rotation and engages the brake shoes. Regardless of the direction of rotation, the brake shoes are deflected in the direction away from the brake surface under the driving force of the actuating element.

[0026] For example, under external axial load on the stroke section when the drive is switched off, the axial force acting on the stroke section can generate a force component in the circumferential direction, i.e. a torque, on the rotationally driven screw drive part as a result of the thread engagement of the two screw drive parts. The unwanted rotation of this screw drive part is prevented by the fact that the closing actuating element engages the brake shoes and always deflects the brake shoes in the direction of the brake surface of the brake drum, regardless of the direction of rotation of the external axial force acting on the brake shoes. The force between the brake shoes and the brake drum depends on the size of the acting torque generated by the external axial force acting on the stroke section. The greater the external axial load, the greater the acting brake force with which the axial displacement of the stroke section in the direction of the acting load is prevented.

[0027] The brake shoes are therefore exclusively deflected in the direction away from the brake surface by the release actuating element and exclusively in the opposite direction, i.e. towards the brake surface, by the closing actuating element.

[0028] In the preferred arrangement, the brake shoes are arranged in the brake drum in a known manner and are actuated in the radial direction.

[0029] In an advantageous manner, the brake device allows an advantageous further development by which, on the one hand, the driving load is transmitted from the drive shaft to the rotationally driven screw drive part via the brake shoes and by which, on the other hand, the external load of the stroke section is transmitted to the brake drum via the brake shoes. The driving load is applied to the drive shaft, for example, if a part of the linear drive is an electric motor which drives the drive shaft via a transmission.

[0030] The rotational connection between the drive shaft and the rotationally driven screw drive part is preferably established by means of the brake shoes, which transmit the driving torque from the drive shaft to the rotationally driven screw drive part. In this further development, the flow of forces is conducted via the brake shoes.

[0031] Thus, the drum brake assumes a dual function: On the one hand, the brake shoes serve to transmit the power between the drive and the output portion when the drive shaft is being rotated driven and the stroke portion is performing a stroke on the output side. On the other hand, the brake shoes serve to generate a sufficiently high braking force when the restoring torque acts on the rotationally driven screw drive portion in the case of an external axial force acting on the stroke portion. At this torque, the brake shoes are pressed against the braking surface of the brake drum. If this restoring torque is greater than the drive torque on the drive side, the closing actuation element is actuated.

[0032] An advantageous further development provides a brake device which is prepared for braking, in which the brake shoes are pressed against the braking surface when the linear drive is unloaded. This means that the brake shoes rest against the braking surface of the brake drum and prevent an undesired adjustment movement of the stroke portion. Preferably, the brake shoes are spring-loaded against the braking surface.

[0033] Preferably, two brake shoes are provided, which are arranged opposite one another about the drive axis. Preferably, the brake drum encloses the two brake shoes such that the braking surface of the brake drum is contacted when the brake shoes are displaced radially outward. The advantage of the brake drum being located radially outward is that a larger diameter and a correspondingly larger circumferential section for the braking surface can be obtained, so that a sufficiently large braking force can be generated.

[0034] Compression springs can be arranged between the two brake shoes, the spring force of which is effective in the radial direction. For example, helical compression springs can be used, one end of which is supported on one brake shoe and the other end of which is supported on the other brake shoe. These helical compression springs are under spring preload and press the two brake shoes radially outward away from one another against the braking face of the brake drum. In this arrangement, the braking surface is arranged on the inner circumference of the brake drum.

[0035] The linear drive preferably has a housing which accommodates the screw drive, one screw drive portion of which is designed as a rotationally driven spindle and the other screw drive portion of which is designed as a threaded nut which is guided in the housing in a non-rotatable and longitudinally displaceable manner and is connected to the stroke portion which can be moved out of the housing.

[0036] In this preferred arrangement, the brake drum is arranged in a fixed manner to the housing. In this arrangement, the rotationally driven drive shaft is connected to the threaded spindle via the brake shoes; thus, the drive power is transmitted via the brake shoes.

[0037] In a preferred design, the release actuation element comprises a first stop and a first counter-stop assigned to the brake shoes and to the drive shaft. For example, the drive shaft can carry a stop portion in the form of a pin, a bolt or a claw, which can engage in recesses in the brake shoes and come into form-fitting contact with the walls of these recesses in order to initially introduce a drive torque into the brake shoes. The torque is transmitted via the contact between the stop and the counter-stop. The recesses can be formed by grooves, holes or elongated holes.

[0038] The first stop and the first counter-stop are arranged in such a way that, irrespective of the direction of rotation of the drive shaft, the brake shoes are radially guided towards one another and away from the brake surface of the brake drum.

[0039] The contact of the stop portion with the wall has a radial distance from the screw drive axis and thus forms a lever arm.

[0040] In a preferred further development, the closure actuation element is provided with a clutch portion which is connected to one rotationally driven screw drive portion in a non-rotatable manner and which has a lever forming a second stop which engages in a gap formed by the brake shoes, wherein a second counter-stop is formed by walls delimiting the gap on the brake shoes, one of the walls being formed on one brake shoe and the other of the walls being formed on the other brake shoe.

[0041] The clutch portion can be an integral part of the threaded spindle, i.e. produced integrally with the threaded spindle or as one piece. For example, if the threaded spindle is made of solid material, one end portion can be machined to form a polygonal piece which is suitable as a lever for actuating the brake shoes.

[0042] In these further developments, the drive shaft transmits the drive power via the stop portion in a form-fitting manner to the brake shoes and via the brake shoes to the clutch portion and via the clutch portion to the rotationally driven screw drive portion.

[0043] If the rotationally driven screw drive portion is formed by a threaded spindle in the preferred design, the clutch portion can be provided with a receiving hole in which the threaded spindle engages with an end face. Fixing means are used to connect the threaded spindle to the clutch portion in a non-rotatable manner.

[0044] The clutch portion can engage with its lever in a gap formed by the two brake shoes. The lever can be designed as a dihedral piece which form-fittingly engages with the brake shoes, which press against the dihedral angle or polygonal piece under the force of the first stop and rotationally drive the dihedral angle or polygonal piece.

[0045] The two brake shoes can be designed to be flat or planar on their circumferential sides facing each other and to define a gap in which the lever engages with these planar circumferential sides.

[0046] The lever can be clamped between the two brake shoes under a rotary drive. The lever arm is preferably longer than the width of the gap, so that the lever cannot rotate freely relative to the brake shoes.

[0047] The clutch portion can be provided at the end face with a pin which engages in a bore in the drive shaft in order to allow sufficient pivoting of the clutch portion and the drive shaft about the drive axis for actuating the drum brake.

[0048] In other words, the closing actuation element preferably has a second stop and a second counter stop which are assigned to the brake shoes and one lead screw drive portion. The second stop can be formed by the dihedral or polygon mentioned above. The second counter stop can be formed by a wall of the associated brake shoe. If two brake shoes are preferably provided, the walls of the two brake shoes face each other and define a gap into which the second stop engages.

[0049] The second stop and the second counter stop are thus functional elements which realize the dual function of the brake device described at the outset. On the one hand, the second stop and the second counter stop serve to transmit the power when the drive shaft is driven in rotation. On the other hand, the second stop and the second counter stop serve to generate a sufficiently high braking force, since the second stop, which is preferably designed as a dihedral, of the rotationally driven lead screw drive portion is subjected to a torque about the drive axis and presses against two adjacent walls of the two brake shoes, which are deflected radially away from each other under this torque against the braking surface of the brake drum.

[0050] Preferably, the drive shaft and the one rotationally driven lead screw drive portion are connected to each other via a pivot bearing, so that the drive shaft and the one rotationally driven lead screw drive portion can be pivoted about the lead screw drive axis. This can be achieved in a simple manner by the drive shaft having a bore or a hollow cylindrical receptacle arranged coaxially with the drive axis, into which a bearing pin of the lead screw drive portion arranged coaxially with the drive axis engages. In this way, a certain size of pivoting movement can be provided in order to release and actuate the drum brake.

[0051] A preferred further development provides a linear drive, the stop portion of which is formed by bolts or clamping jaws protruding axially from the drive shaft and fixed to the drive shaft in a circumferential distribution, wherein in each case two bolts engage in elongated holes of the two brake shoes forming recesses, and wherein the elongated holes with the bolts are arranged at a radial distance from a plane in which the drive axis lies, and wherein each bolt on one side of the plane is arranged diametrically opposite to a bolt on the other side of the plane, and wherein under rotational drive a diametrically arranged pair of bolts displaces the two brake shoes towards each other against the spring force.

[0052] The second stop formed by the dihedral preferably engages between the two brake shoes. When the drive shaft is driven in rotation, a diametrically arranged pair of bolts actuates the two brake shoes in radial direction towards each other, so that the dihedral between the two brake shoes comes into sufficiently firm contact with the walls of the two brake shoes to transmit the drive power in a reliable manner. When an external axial load is applied in the opposite direction, a torque acts on the rotationally driven lead screw drive portion. If this torque is sufficiently high, the dihedral lever pries the two brake shoes radially in the direction of the brake surface of the brake drum apart. The term "sufficiently high" means that the rotationally driven lead screw drive portion should rotate in the opposite direction under the external axial load. This is prevented by the drum brake.

[0053] In other words, the rotationally driven lead screw drive portion can have a lever forming a second stop at an end face, which engages in a gap formed by the brake shoes, wherein a second counter-stop is formed on the brake shoes by the walls delimiting the gap, one of the walls being formed on one brake shoe and the other of the walls being formed on the other brake shoe.

[0054] The lever is preferably designed as a dihedral, the flat sides of which come into contact with the two walls of the two brake shoes for transmitting the torque, wherein the dihedral can be arranged radially within the release actuating element, i.e. preferably radially between the two recesses of the two brake shoes mentioned above, wherein the bolts or clamping jaws of the drive shaft engage in these recesses.

[0055] The linear drive according to the application is particularly suitable for a patient table, such as is known for a computed tomography table. A patient table of this type comprises a frame and a patient bed movably connected to the frame. The housing of the linear drive is movably mounted on the frame and the travel portion of the linear drive is movably mounted on the bed. The housing and the travel portion can each be provided with a bearing eye. The frame and the bed can be provided with a connection point for the bearing eye. For example, the bearing eye can be connected to the frame and the bed via a pin, so that the bearing eye can pivot on the connection point.

[0056] In the case of a CT scanner, the frame can have a carriage on which a bed, i.e. a section on which a patient lies or sits, is supported. The bed can be moved about several axes to reach a desired position: displacement along the longitudinal axis of the bed, along the vertical axis and along the transverse axis is possible.

[0057] With the linear drive according to the application, the set position of the bed can be maintained in a reliable manner; an unintended retraction of the bed, for example due to acting gravity, is excluded. After the table or bed has been moved to the desired position, the linear drive can be de-energized, without the table descending due to gravity. The brake device according to the application prevents this undesired descent or lowering in a reliable manner. BRIEF DESCRIPTION OF DRAWINGS

[0058] The application is explained in more detail below on the basis of exemplary embodiments illustrated in a total of 11 figures. In the drawings: Figure 1 a longitudinal section of the linear drive is shown, Figure 2 a cross section of the linear drive according to Figure 1 is shown, taken along the line A-A, Figure 3 two perspective views of the linear drive are shown, Figure 4 two perspective views of the brake device of the linear drive are shown, Figure 5 a cross section of the brake device according to Figure 4 is shown, Figure 6 a longitudinal section of the brake device according to Figure 4 is shown, taken along the line C-C, Figure 7 a perspective view of the drive shaft of the linear drive is shown, Figure 8 a perspective view of the output portion of the linear drive is shown, Figure 9 a view of the brake shoe of the brake device is shown, Figure 10 a brake device as shown in Figure 4 is shown, wherein the direction of action of the drive force is indicated, and Figure 11 a brake device as shown in Figure 4 is shown, wherein the direction of action of the brake force is indicated. DETAILED DESCRIPTION

[0059] Figures 1 to 3A linear drive is shown in longitudinal sectional view and in cross-sectional view and in perspective view. In the housing 1 of the linear drive a spindle drive 2 is mounted which in the exemplary embodiment is formed by a ball screw drive 3 known per se. The spindle drive 2 comprises two spindle drive parts 4, 5 which are threadingly engaged with one another - in the exemplary embodiment a threaded nut 6 forms one spindle drive part 4 and a threaded spindle 7 forms the other spindle drive part 5.

[0060] The threaded spindle 7 is driven in rotation and is mounted in the housing 1 in a rotatable manner by means of a double row ball bearing 8. The threaded nut 6 is arranged in the housing 1 in a non-rotatable manner and is guided in a longitudinally displaceable manner. For this purpose a guide groove 9 is provided in the housing 1 which is arranged axially parallel to a drive axis 10 of the spindle drive 2. In the exemplary embodiment the drive axis is the spindle axis of the threaded spindle 7. A spring 19 which is firmly attached to the outer circumference of the threaded nut 6 engages in the guide groove 9.

[0061] An electric motor 13 is attached to the housing 1 and drives a drive shaft 16 which is arranged coaxially to the threaded spindle 7 via a traction drive 15 using the motor shaft 14 of the electric motor.

[0062] Between the drive shaft 16 and the spindle drive 2 a brake device 17 is arranged which is formed by a drum brake 18 via which the power is transmitted between the rotary drive and the stroke part 11 and via which a braking force is transmitted when an external axial load acts on the threaded nut 6 and the threaded spindle 7 is subjected to a sufficiently large counter torque under this load. Figures 5 to 11

[0063] The approximately tubular stroke part 11 is firmly connected at an end face to the threaded nut 6. The stroke part 11 passes through the housing 1 at one end face and is provided at the other end face with a connection pin 20 to which an external machine part (not shown) can be connected. The tubular stroke part 11 surrounds the threaded spindle 7 in the housing 1 and moves in axial direction relative to the housing 1 under rotary drive of the spindle drive 2.

[0064] The threaded spindle 7 is provided at its end facing the drive shaft 8 in a non-rotatable manner with a clutch part 12 Figure 8 The clutch part 12 connects the threaded spindle 7 to the drive shaft 16 via the drum brake 18.

[0065] Figure 4 ​The drum brake 18 is shown in two perspective views from the outside. The brake drum 21 can be seen, as well as the drive shaft 8 and the clutch portion 12. In this exemplary embodiment, both the drive shaft 8 and the clutch portion 12 are functionally part of the drum brake 18.

[0066] Figure 5 A cross section of the drum brake 18 is shown. The cylindrical inner circumference of the brake drum 21 is lined with brake pads 22, the inner circumferential surfaces of which form the brake surface 23.

[0067] Two brake shoes 24, which are arranged about the drive axis 10, are engaged in the brake drum 21. Both brake shoes 24 are provided on the outer circumference with a friction surface 25 for braking contact with the brake surface 23.

[0068] The drum brake 18 has a release actuating element 26 and a closure actuating element 27, wherein the actuating elements 26, 27 actuate the brake shoes 24 in opposite radial directions depending on whether the rotary drive is activated or an external axial load is acting on the stroke portion 11, which is not shown here. The release actuating element 26 releases the drum brake 18 and enables a non-braking drive by the electric motor 13, regardless of the direction of rotation. The closure actuating element 27 closes the drum brake 18 and counteracts any unwanted axial displacement of the stroke portion 11.

[0069] Figure 5 It is also shown that the drum brake 17 is equipped with a preloading device 28, which ensures that the brake is ready when the linear drive is unloaded and presses the brake shoes 24 against the brake surface 23.

[0070] The preloading device 28 has a helical compression spring 29, which is supported under elastic axial preloading on both brake shoes 24 and springs both brake shoes radially outward in the direction of the brake surface 23. In order to ensure that both brake shoes 24 are perfectly guided relative to one another, a guide pin 30 is provided, which is arranged axially parallel to the helical compression spring 29 and which is fixed to one brake shoe 24 on the one hand and displaced along a guide hole 31 of the other brake shoe 24 on the other hand.

[0071] With regard to the explanations of the actuating elements 26, 27, reference is made to the other Figures 6 to 11 .

[0072] The release actuating element 26 comprises a first stop 32 and a first counter-stop 33, which are assigned to both brake shoes 24 and the drive shaft 16.

[0073] Figure 5A first stop 32 is shown, which is formed by two stop portions 34, and in the exemplary embodiment by a total of four bolts 35 arranged axially parallel to each other and securely connected to the drive shaft 16.

[0074] Figure 7 The drive shaft 16 is shown as a separate part, with a bolt 35 protruding axially on the end face of the drive shaft facing the drum brake 18 (one bolt 35 is indicated by a dashed line).

[0075] Each of the two brake shoes 24 is provided with an elongated hole 37 formed by a recess 36, and two bolts 35 are engaged in each elongated hole. Figure 5 ).from Figure 5 It can be seen that a certain amount of rotational clearance is possible for the drive shaft 16 relative to the brake shoes 24. It is clearly visible that the bolt 35 shown on the left side of the figure rests against the radial inner wall 38 in the upper elongated hole 37, which forms the first reverse stop 33. On the other hand, the second bolt 35, engaged in the elongated hole 37, is spaced apart from the wall 38. Of the two bolts 35 engaged in the lower elongated hole 37, only the bolt 35 shown on the right rests against the radial inner wall 38. If the drive shaft 16 rotates clockwise relative to the two brake shoes 24, one bolt 35 contacts the radial inner wall 38, while the other bolt 35—previously resting against the wall—does not contact the wall 38.

[0076] An elongated hole 37 with bolts 35 is arranged at a radial distance from the plane containing the drive axis 10, wherein each bolt 35 on one side of the plane is arranged diametrically with a bolt 35 on the other side of the plane, and wherein, under rotary drive, the pair of bolts arranged diametrically cause the two brake shoes 24 to displace toward each other against the spring force.

[0077] Figure 6 A longitudinal section is shown of a drive shaft 16 and an axially adjacent clutch portion 12, which is non-rotatably connected to a threaded spindle 7. The drive shaft 16 and the clutch portion 12 are pivotally mounted relative to each other about a drive axis 10. The pivot bearing 41 has: a cylindrical pin 42 formed at an end face on the clutch portion 12; and a bearing opening 43 formed on the drive shaft 16, in which the pin 42 engages and enables pivoting movement.

[0078] Figure 5 Also shown is a closing actuation element 27, which has a second stop 39 and a second reverse stop 40. The second stop 39 is formed on the clutch portion 12. The second reverse stop 40 is formed on the two brake shoes 24.

[0079] Figure 8 A perspective view of the clutch portion 12 is shown, and for example, the interaction with the second counter-stop 40 is shown in Figure 10 The second stop 39 is formed by a lever 44 in the form of a dihedral angle 45 (see also Figure 10 ). The lever 44 engages in a gap 46 formed by the brake shoes 24, wherein the second counter-stop 40 is formed on the brake shoes 24 by walls 47 delimiting the gap 46, one of the walls being formed on one brake shoe 24 and the other of the walls being formed on the other brake shoe 24. The flat sides of the lever 44 come into contact with the two walls 47 of the two brake shoes 24 when a torque is introduced to actuate the drum brake 18.

[0080] Figure 8 It is shown that the clutch portion is provided with the above-mentioned pin 42 on one end face and with an axial hole 48 for receiving an end portion of the threaded spindle 7 on the other end face. Fixing means, not shown, are provided to mount the clutch portion 12 to the threaded spindle 7.

[0081] Figure 10 It is clearly shown that the lever 44 is arranged centrally between the two elongated holes 37 of the brake shoes 24.

[0082] Finally, Figure 9 It is shown that one of the two brake shoes 24, which are identical in the exemplary embodiment. It can be clearly seen that the elongated hole 37, the wall 47 and a portion of the gap 46 into which the lever 44 engages.

[0083] The operating mode of the drum brake 18 is explained below.

[0084] When the electric motor 13 actuates the linear drive, the drive shaft 16 rotates and the bolt 35 of the drive shaft hits the walls 40 of the brake shoes 24 in the above-described manner and presses the walls of the brake shoes towards each other, i.e. away from the brake surface 23. The two brake shoes 24 press the walls 47 (second counter-stop 40) of the brake shoes, which delimit the gap 46, against the flat sides of the lever 44 and transmit the drive power of the drive shaft 16 to the clutch portion 12, which is firmly connected to the threaded spindle 7. Figure 9 It is shown that the case in which the arrow indicates the direction of rotation of the drive shaft 16.

[0085] For example, if the rotary drive, i.e. the electric motor 13, is switched off and an external axial load acts on the stroke portion 11, a counter-torque is exerted on the threaded spindle 7. This case is shown in Figure 11The lever 44, which is connected to the clutch part 12 of the screw spindle 7 in a non-rotatable manner, can be clearly seen to press against the walls 47 of the two brake shoes 24 at the diagonal point and to pry the walls of the two brake shoes away from one another in the direction of the brake surface 23 of the brake drum 21, which is firmly connected to the housing 1, i.e. radially away from one another. The indication arrows show the lines of action of the forces. During the braking contact, rotation of the screw spindle 7 is prevented and thus unintentional displacement of the travel portion 11 is prevented.

[0086] The drum brake 18 thus takes over the power transmission between the drive shaft 16 and the lead screw drive 2 by means of the brake shoes 24 and the screw 35 of the release actuating element 26 and by means of the clutch part 12 of the closure actuating element 27 and the lever 44 of the clutch part. The drum brake 18 also takes over the braking force by means of the clutch part 12 of the closure actuating element 27 and by means of the brake shoes 24 and the brake drum 21, which ensures a reliable locking of the lead screw drive 2 when the travel portion 11 is subjected to external axial forces.

[0087] List of reference signs 1 housing 2 lead screw drive 3 ball screw drive 4 lead screw drive portion 5 lead screw drive portion 6 threaded nut 7 screw spindle 8 double-row ball bearing 9 guide groove 10 drive axis 11 travel portion 12 clutch part 13 electric motor 14 motor shaft 15 traction drive 16 drive shaft 17 brake device 18 drum brake 19 spring 20 connecting pin 21 brake drum 22 brake pad 23 brake surface 24 brake shoe 25 friction surface 26 release actuating element 27 closure actuating element 28 preloading device 29 helical compression spring 30 guide pin 31 guide hole 32 first stop 33 first counter stop 34 stop portion 35 screw 36 recess 37 elongated hole 38 wall 39 second stop 40 second counter stop 41 pivot bearing 42 pin 43 bearing opening 44 lever 45 dihedral angle 46 gap 47 wall 48 axial hole CLAIM (AMENDED IN ACCORDANCE WITH ARTICLE 19 OF THE TREATY) 1. Patient table, comprising a frame and a bed for a patient movably connected to the frame, and comprising a linear drive, whose housing (1) is movably mounted on the frame, and which is provided with a screw drive (2), whose screw drive parts (4, 5) are in threaded engagement, and which converts the rotation of one screw drive part (5) about a drive axis (10) into the relative displacement of the screw drive parts (4, 5) along the drive axis (10), wherein the one screw drive part (5) is rotationally driven via a drive shaft (16), and wherein the other screw drive part (4) is arranged in longitudinally displaceable fashion along the drive axis (10) and has a stroke part (11) movably mounted on the bed for performing a stroke, and which is provided with a brake device (17) that is released under the rotational drive of the one rotationally driven screw drive part (5) and which is closed under the external load of the stroke part (11) and which resists the displacement of the stroke part (11), wherein the brake device (17) is designed as a drum brake (18) having a plurality of brake shoes (24) and a brake drum (21) with brake surfaces (23) for the brake shoes (24), and which has a release actuating element (26) and a closure actuating element (27), wherein the actuating elements (26, 27) actuate the brake shoes (24) in opposite directions. 2. Patient table according to claim 1, the drive shaft (16) of the patient table actuating the release actuating element (26) in both rotational directions and the rotationally driven lead screw drive part (5) of the patient table actuating the closure actuating element (27) in both rotational directions under external load of the travel part (11). 3. Patient table according to claim 1 or claim 2, the drive load of the patient table being transmitted from the drive shaft (16) to the rotationally driven lead screw drive part (5) via the brake shoe (24) and the external load of the travel part (11) of the patient table being transmitted to the brake drum (21) via the brake shoe (24). 4. Patient table according to any one of claims 1 to 3, the drum brake (18) of the patient table being prepared for braking and pressing the brake shoe (24) against the brake surface (23). 5. Patient table according to any one of claims 1 to 4, the release actuating element (26) of the patient table having a first stop (32) and a first counter stop (33), which are assigned to the brake shoe (24) and the drive shaft (16). 6. Patient table according to any one of claims 1 to 5, the closure actuating element (27) of the patient table having a second stop (39) and a second counter stop (40), which are assigned to the brake shoe (24) and the one lead screw drive part (5). 7. Patient table according to claim 5, the drive shaft (16) and the one lead screw drive part (5) of the patient table being mounted in a pivotable manner to each other about the lead screw drive axis (20) via a pivot bearing (41), wherein the first stop (32) is designed as a stop portion (34) which is firmly connected to the drive shaft (16) and wherein the first counter stop (33) is formed by a wall (38) of a recess (36) in the brake shoe (24), into which the stop portion (34) engages. 8. Patient table according to claim 7, the stop portion (34) of which is formed by bolts (35) projecting axially from the drive shaft (16) and fixed to the drive shaft (16) distributed in a circle, wherein in each case two bolts (35) engage in the recesses (36) of two brake shoes (24), and wherein the recesses (36) with the bolts (35) are arranged at a radial distance from the plane in which the drive axis (20) lies, and wherein a pair of bolts is formed by two bolts (35), one of which (35) is arranged on one side of the plane and the other of which (35) is arranged diametrically opposite the one (35) on the other side of the plane. 9. Patient table according to claim 6, the closure actuation element (27) of which has a clutch portion (12) connected to the one rotationally driven lead screw drive portion (5) in a rotationally fixed manner and having a lever (44) forming the second stop (39), which engages in a gap (46) formed by the brake shoes (24), wherein the second counter-stop (40) is formed on the brake shoes (24) by walls (47) delimiting the gap (46), one of the walls being formed on one brake shoe (24) and the other of the walls being formed on the other brake shoe (24). 10. Patient table according to any one of claims 1 to 9, the housing (1) of which accommodates the lead screw drive (2), one lead screw drive portion (5) of which is designed as a rotationally driven threaded spindle (7) and the other lead screw drive portion (4) of which is designed as a threaded nut (6), which is guided in the housing (1) in a rotationally fixed and longitudinally displaceable manner and connected to the travel portion (11) which can be removed from the housing (1), wherein the brake drum (21) of the drum brake (18) is arranged in a fixed manner to the housing, and wherein an electric motor (13) drives the drive shaft (16) via a traction drive (15).

Claims

1. A linear actuator having a lead screw actuator (2) having lead screw actuator portions (4, 5) threadedly engaged, and converting rotation of one lead screw actuator portion (5) about an actuator axis (10) into relative displacement of the lead screw actuator portions (4, 5) along the actuator axis (10), wherein, One lead screw drive section (5) is rotatably driven via a drive shaft (16), and wherein another lead screw drive section (4) is arranged longitudinally displaceable along the drive axis (10) and has a stroke section (11) for performing a stroke, and the linear drive is provided with a braking device (17) that is released under the rotational drive of the rotary-driven lead screw drive section (5) and closed under external load of the stroke section (11) and resists displacement of the stroke section (11), characterized in that the braking device (17) is designed as a drum brake (18) having a plurality of brake shoes (24) and a brake drum (21) with a braking surface (23) for the brake shoes (24), and the drum brake having a release actuating element (26) and a closing actuating element (27), wherein the actuating elements (26, 27) actuate the brake shoes (24) in opposite directions.

2. The linear actuator according to claim 1, wherein the drive shaft (16) of the linear actuator actuates the release actuator (26) in two rotational directions, and the rotary drive screw drive portion (5) of the linear actuator actuates the closing actuator (27) in two rotational directions under the external load of the stroke portion (11).

3. The linear drive according to claim 1 or claim 2, wherein the drive load of the linear drive is transmitted from the drive shaft (16) to the rotary drive screw drive portion (5) via the brake shoe (24), and the external load of the stroke portion (11) of the linear drive is transmitted to the brake drum (21) via the brake shoe (24).

4. The linear actuator according to any one of claims 1 to 3, wherein the drum brake (18) of the linear actuator is prepared for braking and presses the brake shoe (24) against the brake surface (23).

5. The linear actuator according to any one of claims 1 to 4, wherein the release actuation element (26) of the linear actuator has a first stop (32) and a first reverse stop (33), the first stop and the first reverse stop being assigned to the brake shoe (24) and the drive shaft (16).

6. The linear actuator according to any one of claims 1 to 5, wherein the closing actuation element (27) of the linear actuator has a second stop (39) and a second reverse stop (40), the second stop and the second reverse stop being assigned to the brake shoe (24) and the lead screw drive portion (5).

7. The linear actuator according to claim 5, wherein the drive shaft (16) of the linear actuator and the lead screw drive portion (5) are pivotally mounted to each other about the lead screw drive axis (20) via a pivot bearing (41), wherein, The first stop (32) is designed to be securely connected to the stop portion (34) of the drive shaft (16), and wherein the first reverse stop (33) is formed by the wall (38) of the recess (36) in the brake shoe (24), the stop portion (34) engaging in the recess.

8. The linear actuator according to claim 7, wherein the stop portion (34) of the linear actuator is formed by bolts (35) or clamps protruding axially from the drive shaft (16) and is circumferentially fixed to the drive shaft (16), wherein, In each case, two bolts (35) engage in the recesses (36) of the two brake shoes (24), and wherein the recesses (36) having the bolts (35) are arranged at a radial distance from the plane containing the drive axis (20), and wherein a pair of bolts is formed by two bolts (35), one of the bolts (35) being arranged on one side of the plane, and the other bolt (35) being arranged on the other side of the plane opposite in diameter to the first bolt (35).

9. The linear actuator according to claim 6, wherein the closed actuating element (27) of the linear actuator has a clutch portion (12) non-rotatably connected to the rotary-driven lead screw drive portion (5), and the clutch portion has a lever (44) forming the second stop (39), the lever engaging in a gap (46) formed by the brake shoe (24), wherein, The second reverse stop (40) is formed on the brake shoe (24) by a wall (47) defining the gap (46), one of the walls being formed on one brake shoe (24) and the other wall being formed on the other brake shoe (24).

10. The linear actuator according to any one of claims 1 to 9, wherein the housing (1) of the linear actuator houses the lead screw actuator (2), one lead screw actuator portion (5) of the lead screw actuator is designed as a rotary-driven threaded spindle (7), and the other lead screw actuator portion (4) of the lead screw actuator is designed as a threaded nut (6), the threaded nut being guided in the housing (1) in a non-rotatable and longitudinally displaceable manner and connected to the stroke portion (11) removable from the housing (1), wherein, The brake drum (21) of the drum brake (18) is arranged to be fixed to the housing, and wherein the electric motor (13) drives the drive shaft (16) via the traction driver (15).

11. A patient table having a linear actuator according to claim 10, the patient table comprising a frame and a bed for a patient movably connected to the frame, wherein, The housing (1) of the linear drive is movably mounted on the frame, and its travel portion (11) is movably mounted on the bed.

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