Linear drive having shock compensation

A directly coupled linear drive having a drive unit and a sliding element that are disposed in a frame, the sliding element, actuated by the drive unit, being capable of effecting a movement in a direction of translation with respect to the frame and having a blocking device for blocking the sliding element in the frame in the event of a shock load to the sliding element, the blocking device having a body coupled to the sliding element that absorbs the shock load and is disposed such that the shock load of the body counteracts the shock load of the sliding element.

FIELD OF THE INVENTION

The invention relates to linear motors in general and more specifically to directly coupled linear drives, such as a friction-coupled linear drive or a magnetic drive. Examples of friction-coupled linear drives, for which the invention finds application, include electromechanical linear motors having a drive element that is made of an electrostrictive or magnetostrictive material. Also known are polymer actuators that are made of a combination of polymer and metallic materials and that allow an electrically controllable movement of a polymer body.

BACKGROUND OF THE INVENTION

WO 2004/001867 describes an example of a piezoelectric motor that provides a linear drive for an actuator. The motor uses a piezoelectric drive element that operates at high speed and with high precision. The piezoelectric motor described in WO 2004/001867 A1 comprises a stator that consists of two series-connected bending sections and a power transmission element which is mounted on the stator and transmits the bending action of the drive element to a sliding element. The drive element is aligned parallel to the sliding element and is made of an electrostrictive material, such as a piezoelectric material. These kinds of materials change their shape when exposed to an electric voltage or a magnetic field. The bending sections of the drive element are disposed symmetrical to the power transmission elements, the two bending sections performing a bending action that is similar to a traveling wave when an electric voltage is applied. The wave-like movement is transmitted via the power transmission elements to the sliding element and moves the sliding element incrementally. The movement of the drive elements is transmitted via the power transmission elements to the sliding element in that the power transmission elements and the sliding element are in frictional contact. The electromechanical motor may be used as a regulating device that achieves fast and precise lateral displacement of the sliding element and thus of an actuator connected to it. Piezoceramics have very short response times and thus very short operating times. One possible application for a friction-coupled miniature motor of this type is in a locking system, where the sliding element is used as an actuator to close a lock cylinder.

These kinds of friction-coupled linear drives and other directly coupled linear drives—in other words drives that do not involve a rotational movement being translated into a translation movement but rather in which the translation movement is directly generated—are generally used for moving an actuator in a direction of translation. Directly coupled linear drives have the disadvantage that it is possible to manipulate the movement of the actuator by applying an external force. In particular, when exposed to a shock or impact load or any other mechanical stress, such as vibration that is applied to the linear drive from an external source, the actuator may slip along the drive unit because the directly coupled linear drive has only a limited self-restraining effect. This self-restraining effect is found in the region of static friction between the sliding element and drive unit. For linear drives in which a rotational movement is translated by a thread into a translation movement, an external force varies in its effect. If the thread pitch, for example, is low, an external force, such as a shock load, immediately results in damage to the thread. If the pitch of the thread is high, a shock load results in the actuator slipping through, similar to directly coupled linear drives.

If used, for example, for actuating a lock cylinder, the fact that the actuator could be manipulated by a simple external shock load or an externally applied vibration would of course be highly disadvantageous. Safety standards require that electronic locks as well withstand shock loads of some 1500 times the acceleration of gravity (1500 g) or more. One g corresponds to an acceleration of 9.81 m/sec2.

It is an object of the invention to provide a linear drive that cannot be manipulated by the application of external forces, such as shock loads and vibrations, and at the same time can maintain its original performance.

SUMMARY OF THE INVENTION

The invention provides a linear drive having a drive unit and a sliding element that are disposed in a frame. The sliding element is actuated by the drive unit so as to effect a movement in a direction of translation with respect to the frame. According to the invention, a blocking device is provided for blocking the sliding element with respect to the frame in the event of shock or impact loads to the sliding element. In a first embodiment of the invention, this blocking device has a compensating body coupled to the sliding element that is equally exposed to the shock load and disposed such that an acceleration of the compensating body caused by the shock load counteracts an acceleration of the sliding element caused by the shock load and compensates this shock load. In another embodiment variant, the blocking device has a compensating body that is likewise exposed to the shock load and disposed such that the movement of the compensating body due to the shock load counteracts a movement of the sliding element due to the shock load. In general terms, the invention thus provides as a blocking device a moveable mass that is disposed in relation to the sliding element of the linear drive such that it counteracts a movement of the sliding element caused by an external shock load. For this purpose, the blocking device does not need its own power supply nor does it require any means for recognizing the shock load and triggering the blocking device, but rather, according to the invention, the blocking device is activated directly and immediately by the shock load that also acts on the sliding element of the linear drive and—without the blocking device according to the invention—could cause an undesirable movement of the sliding element.

In a first preferred embodiment of the invention, the compensating body is coupled with the sliding element via a lever arm that is preferably supported by means of a bearing point on the frame, one end of the lever arm interacting with the sliding element and the other end of the lever arm interacting with the compensating body. The system consisting of the compensating body, lever arm and sliding element is adjusted such that the sum of the torques that act on the lever arm through a shock load in the direction of translation, is zero or at least approximately zero. In other words, the mass of the compensating body and the mass of the sliding element, taking into account the lever principle, are in equilibrium. A shock load that acts in the direction of translation of the linear drive on the compensating body and on the sliding element equally, will not cause any displacement of the sliding element nor of the compensating body because these two are in equilibrium thanks to the lever arm. This blocking effect is achieved independent of friction.

The compensating body may be carried on the frame, within the frame, or outside it. It may be adapted in shape to the frame or to a housing of the linear drive and take the shape, for example, of an elongated cube or a segment of a cylinder. To achieve a compensating body for small-scale constructions that has a high mass, a comparatively heavy material is preferably used, for example a metal such as brass, in manufacturing the compensating body.

When the compensating body and the sliding element are coupled using a lever arm, care must be taken that the lever arm is supported on the frame such that no bouncing occurs in the event of a shock load. This can preferably be realized by suspension of the lever arm in the bearing point, using, for example, an axle.

In an alternative embodiment, the compensating body is coupled with the sliding element using a Bowden cable or via a toothed wheel and a toothed rack, substantially the same blocking effect being achieved as with the lever arm described above. In this alternative embodiment, the mass of the compensating body should be equal to or at least approximately equal to the mass of the sliding element.

In the example of the above-mentioned piezoelectric motor, a coupling of the compensating body and the sliding element by using a toothed wheel and toothed rack is particularly suitable for a drive unit that acts on one side of the sliding element, wherein the toothed rack may be provided on the opposite side of the sliding element.

In another embodiment of the invention, the blocking device has a spring device that is coupled with the compensating body and designed such that it is deflected by the shock load so as to be able to engage with the sliding element. This second embodiment of the invention is based on the deflection of a spring in the event of a shock load, the deflection amplitude on the one hand being determined by the compensating body coupled to the spring and on the other hand by the design of the spring itself. The spring is designed such that in the event of a shock load it becomes engaged with a defined point of the sliding element and blocks it. The mass of the compensating body, the design of the spring and the spring constant are preferably adjusted to the impact force that can be expected.

It is expedient if the spring device is fixed on the frame and has at least one spring arm that extends in the direction of the sliding element. The compensating body is disposed on the spring arm.

In a particularly advantageous embodiment, the spring device has a spring ring that has a number of spring arms extending radially inwards, a compensating body being disposed on each spring arm. This spring ring encloses the sliding element, so that on deflection of the spring arms, the sliding element is blocked at its circumference simultaneously from different sides.

In another embodiment, the spring device has a leaf spring that is connected at one end to the frame and carries the compensating body at the other end. The leaf spring is preferably designed with a recess through which the sliding element passes.

In yet another embodiment, the spring device has a suspension spring that is connected to the frame via two pendulum arms. The suspension spring has a central hole through which the sliding element is led.

In yet another embodiment, the blocking device has a bent leaf spring that is designed such that it is stretched by a shock load so as to become engaged with the sliding element. One end of the bent leaf spring is connected to the frame and its other end becomes engaged with the sliding element at an end face of the sliding element, for example, in order to block at least one direction of movement of the sliding element.

Whereas the known friction-coupled linear drives, such as piezoelectric linear drives, can absorb a force of impact of up to a maximum of 100 G through their friction coupling, thanks to the invention, reliable blocking of the sliding element for shock loads of over 500 G, and even up to 1500 G and beyond can be achieved.

DETAILED DESCRIPTION OF EMBODIMENTS

FIGS. 1 and 2show a side view as well as an isometric view of the friction-coupled linear drive according to one embodiment of the invention. InFIGS. 1 and 2, first a drive housing10and a sliding element of the linear drive, more specifically an actuator12connected to the sliding element, are illustrated. A blocking pin14is mounted on the actuator12, the blocking pin14being used in the locking application mentioned at the outset to block the lock cylinder. Damping elements taking the form of elastomer members16are mounted on the outside circumference of the drive housing10. The elastomer members which in the illustrated embodiment take the approximate shape of cuboid blocks may be directly molded or bonded to the housing10, or connected in some other manner to the drive housing10. Instead of using the illustrated elastomer members, damping strips may be mounted in an axial direction or in a circumferential direction on the outside surface of the drive housing10. In an alternative embodiment, instead of the elastomer members16, one or more O-rings may be mounted on the circumference of the drive housing10. These may be held in position by grooves or by using positioning lugs.

In the final assembled position of the friction-coupled linear drive according to the invention, the elastomer members16come to lie between the drive housing10and a hole or a housing of the application (not illustrated) in which the drive is installed. In the event of mechanical stress, particularly a shock load, vibration and suchlike, the elastomer members16absorb a part of this mechanical stress and reduce it through their deformation in the direction of excitation. Here, the elastomer members16are designed such that they are particularly effective in dampening external excitation that acts parallel to the direction of movement of the linear drive. There has to be sufficient space available in the final assembled position to allow the linear drive to move in the direction of excitation in the event of mechanical stress, in order to reduce the stress energy. This measure alone decreases the susceptibility of the linear drive to any shock load and reduces the risk of the sliding element moving due to external excitation.

In the case of the illustrated embodiment having block-shaped elastomer members16, the geometry of the supporting surface of the elastomer member16determines the effective deformation. These kinds of elastomer members can dampen shock loads in such a way that the shock load does not cause any undesirable displacement of the sliding element. For heavier shock loads, however, their damping effect is inadequate.

Thus according to the invention, the first embodiment has a blocking device taking the form of a compensating body18coupled to the actuator12, the blocking device being connected to the actuator12using a lever arm20. The lever arm20is supported at a bearing point22on the drive housing10, the lever arm20being pivotable about this bearing point22.

In the event of an external shock load to the actuator and thus to the sliding element36, from the left, for example, in the drawing plane, this impact has an equal effect on the sliding element36as it does on the compensating body18, so as to push both of them towards the right in the drawing plane. Since the sliding element36and the compensating body18are coupled to each other via the lever arm20and the bearing point22, the torques generated in the bearing point22at the ends of the lever arm20cancel each other out, so that the system as a whole remains in equilibrium. In the event of a shock load, this goes to produce a self-retarding system where the position of the sliding element36and thus of the actuator12cannot be manipulated through any external influence.

FIG. 3shows a modification of the linear drive ofFIGS. 1 and 2, related components being indicated by the same reference numbers. In the view ofFIG. 3, in addition to the components illustrated inFIGS. 1 and 2, a connecting component24taking the form of a flexible circuit board is shown, the connecting component24providing the terminal for power supply and signal lines.

In the embodiment ofFIG. 3, the lever arm20is hinged to the drive housing10using a swivel pin26, so that it is supported in a more stable manner and any bouncing of the lever arm20can be avoided in the event of a shock load. The lever arm20is coupled to the actuator12using a long slot28and a stub shaft30, so that it can follow the movement of the actuator12into the drive housing10and out of it again (to the right and left in the drawing plane).

As an alternative, the lever arm20may also abut an end face of the blocking pin14facing the drive housing10on the side of the actuator12(not illustrated). This makes it possible to restrain impact movements whose direction of excitation would push the sliding element36into the drive housing10, i.e. only in one direction. A variant of this kind is much more cost-effective since no machining of the actuator12for its coupling to the lever arm20is required. With regard to the functioning of the system comprising the sliding element, actuator12, lever arm20and compensating body18, the same applies as described with reference toFIG. 3.

FIG. 4shows a further embodiment of the linear drive according to the invention in a sectional view, the linear drive ofFIG. 4being designed as an electromechanical motor, particularly a piezoelectric motor. Related components are indicated by the same reference numbers.

The electromechanical motor shown inFIG. 4comprises a stator34, i.e. a stationary component, and a sliding element36, i.e. a moving component, that can move with respect to the stator in a direction of translation, in the direction of the motor axis. The main components of the stator34include a frame component38and a drive unit40. The drive unit40comprises two parallel electromechanical drive elements42, each of which is associated with a power transmission element44. The electromechanical drive elements42are made of a material whose form changes when an electric voltage or, in another embodiment, a magnetic field is applied to the drive element42. Examples of these kinds of materials include electrostrictive materials, particularly piezoelectric and magnetostrictive materials as well as polymer actuators. The drive elements42are preferably made of a piezoelectric material that changes its shape when an electric voltage is applied and, vice versa, emits an electric voltage on deformation. In the illustrated embodiment, the power transmission elements44are tube-shaped. They should possess a certain elasticity in the direction perpendicular to the drive element42. They may be connected to the drive element by means of bonding, for example.

As explained in more detail below, the drive unit interacts with the sliding element36whose main components include a supporting component46and a drive rail48. The supporting component46is preferably formed as an injection-molded plastic part and holds the drive rail28at its two end faces. The supporting component may be made, for example, of a thermoplastic, such as polyetherimide, having a teflon component of some 10-20%. Other materials lie within the scope of the invention, high abrasion resistance and a low coefficient of friction being desirable. The drive rail48is preferably made of a ceramic, such as aluminum oxide ceramic, having high abrasion resistance. To increase the coefficient of friction of the surface of the drive rail, the surface may be provided with a groove pattern or some other kind of fluting.

The supporting component46is used to hold the drive rail48and moreover to receive a sensor magnet50as well as an adapter piece52. The sensor magnet50is used to measure the position of the sliding element36, as explained in more detail below. The adapter piece52is used for connecting an actuator66that is moved by the electromechanical motor in the direction of translation.

The drive rail48, the sensor magnet50and the adapter piece52are preferably held in the supporting component46in a non-positive and positive fit using snap-in connections or by injection-molding.

A first sliding bearing54is formed between the supporting component46and the frame component38; a second sliding bearing56is formed between the adapter piece52held in the supporting component46and the frame component38. The supporting component46is thus preferably made of a plastic having a low coefficient of friction, such as a teflon-containing plastic.

The sensor magnet50interacts with a Hall sensor58, or other magnetic sensors, in order to measure the position of the sliding element36with respect to the frame component38. The Hall sensor58and the drive elements42are mounted on a flexible printed circuit board (FPC)62that is placed about the frame component38. The circuit board62is held in position by a clamp64. The circuit board62may be extended laterally to allow signal and power supply lines to be led out of the motor. The connecting component24is then provided by the circuit board62.

The Hall sensor58makes it possible to detect the magnetic field intensity of the sensor magnet50over the entire traveling distance of the sliding element, this magnetic field density being proportional to the lateral displacement of the sliding element. This makes it possible to determine the current position of the sliding element as an analogue quantity; limitation to discrete positions not being necessary.

The frame component38is held in the drive housing10in a non-positive and positive fit by means of a snap-in connection. The drive housing10may simply be slid over the frame component38until the snap-in fasteners snap in, and ensures good protection for the electromechanical motor.

The motor operates as follows: The two drive elements42are disposed parallel to the drive rail48on each side of the drive rail. Each drive element42comprises two bending sections on each side of the centrally disposed power transmission elements44. The two bending sections are thus arranged in series along the surface of the drive rail48in the direction of the intended movement of translation (in the direction of the motor axis). These bending sections are preferably made up of bimorph piezoelectric elements that can be bent in a direction perpendicular to the direction of translation. Each bimorph piezoelectric element comprises two parallel individually excitable active volumes, whereby a bending action is achieved through the application of different voltages to the active volumes. Concerning the basic functioning of the electromechanical motor, reference is additionally made to WO 2004/001867 A1.

The bending induces a wave that moves from a first end of the drive element42, in the direction of its other end. Without losses, the drive unit40would operate in resonance and a wave would be reflected at the other end of the drive element42. This is described in more detail in WO 2004/001867 A1 as referred to above.

The drive element42is generally driven by electric voltage impulses that are applied to the bending sections. Due to the bending action of the drive element42that continues over the length of the drive element42, a corresponding movement of the power transmission elements44is induced that is transferred to the drive rail48. Here, the power transmission elements44move both perpendicular as well as parallel to the surface of the drive rail48. The drive rail48can thereby be moved incrementally forwards and backwards in the direction of translation.

In the embodiment ofFIG. 4, the sliding element36is coupled to a compensating body70using a lever arm68. The lever arm68is pivotably mounted on the frame component38at a bearing point72, and connected to the compensating body70via a long slot74. Again in this embodiment, the sum of the torques of the system comprising the compensating body70, lever arm68and sliding element36is zero. Without the blocking system formed by the compensating body70and the lever arm68, in the event of a shock load the sliding element36could slip through between the power transmission elements44, since only friction coupling is provided here. Although the friction coupling may prove adequate for absorbing shock loads of up to 100 G for example, with heavier shock loads, it is not possible to prevent the sliding element36from slipping through. The actual shock load that can be compensated depends of course on the design and size of the linear drive. The sizes described here apply by way of example for the lock application described at the outset.

With the linear drive according to the invention, shock loads in the direction of translation act not only on the sliding element36, but also on the compensating body70, both being accelerated in the same direction, but due to the connection of the lever arm68, the system is self-retarding. Frictional forces do not occur since a movement of the sliding element36is totally prevented.

As described above, the compensating body is made of a comparatively heavy material, for example a metal such as brass, so as to provide the same leverage force as that of the sliding element for small-scale constructions. In a further development of the invention (not illustrated in the figures) a magnet may be integrated in the compensating body, the magnet having the same or approximately the same magnetic intensity as the sensor magnet50. Alternatively, the compensating body itself may be made of a magnetic material. This further development of the invention not only has the effect of enabling the compensating body to compensate an external shock load of the linear drive but also of making the linear drive immune to external manipulation with a magnet. An external magnet that interacts with the sensor magnet50could namely be used to move the sliding element36via the sensor magnet50in the direction of translation. In this modification of the invention, however, the external magnet would not only act on the sensor magnet but also on the magnetic compensating body, the system being self-retarding due to the connection via the lever arm.

In practice, a compensating body having an integrated magnet could have an influence on the magnet characteristic of the Hall sensors58, which, however, could be taken into account when evaluating the Hall signals.

The embodiment ofFIG. 4differs from the previously described embodiments particularly in that the compensating body70is disposed within the drive housing10. Since for many electromechanical motors only very little space is available for the disposal of the compensating body within the housing, it is expedient if the compensating body takes the form of a cylinder segment or any other form adapted to the space available.

The embodiment ofFIG. 4moreover differs from the previously described embodiments in that the lever arm68engages within the drive housing10with the end of the sliding element36facing away from the actuator66. This has the advantage that the actuator66has no attachments whatsoever and can thus be optimally adapted to the respective application.

FIG. 5shows a further embodiment of the linear drive according to the invention in a sectional view, the sectional view ofFIG. 5being rotated by 90° about the longitudinal axis of the drive with respect to the view ofFIG. 4. Hence, the drive unit40cannot be seen in this view, but it is possible to see the Hall sensor58that is missing in the view ofFIG. 4. Related components are indicated by the same reference numbers.

The embodiment ofFIG. 5differs from the embodiment ofFIG. 4in that the compensating body70′ is disposed outside the drive housing10. In this embodiment, the compensating body70′ is carried on the outside of the drive housing10. For the rest, the functioning of the system comprising the compensating body70′, lever arm68and sliding element36is the same as previously described with reference toFIG. 4. Bores in the drive housing10and the frame component38are large enough to allow the lever arm68, during regular operation of the sliding element36, to deflect and follow its movement.

In the embodiments ofFIGS. 4 and 5, the blocking device is designed such that it absorbs a shock load in only one direction, specifically only a shock load that acts on the actuator66, so as to move it into the drive housing10. This, however, is exactly the critical movement that as a rule should be prevented, for example, when the linear drive finds application in a door lock where the actuator66is used to close a lock cylinder. In the embodiment ofFIG. 3, on the other hand, the blocking system consisting of the lever arm20and compensating body18prevents an undesirable movement of the sliding element36in both directions of translation.

A further embodiment of the invention is shown inFIGS. 6A to 6D,FIGS. 6A and 6Bshowing an external view of the linear drive without housing andFIGS. 6C and 6Dshowing a sectional view of the linear drive, along the same sectional plane asFIG. 5. For the sake of simplicity, the drive housing and the circuit board with the electronics have been omitted. Related parts are indicated by the same reference numbers as inFIG. 5.

In the embodiment ofFIGS. 6A to 6D, a compensating body76is coupled via a lever arm78with the sliding element36. The lever arm78is supported by means of stub shafts80in a receiving portion82connected to the housing10. The lever arm78engages in the sliding element36at a shoulder of the actuator66. The functioning of the blocking device formed from the compensating body76and the lever arm78is as described with reference to the preceding embodiments. When the sliding element36and thus the actuator66move into the drive housing10, the lever arm78is deflected accordingly, as illustrated inFIGS. 6B and 6D.

A further embodiment of the linear drive according to the invention is depicted inFIGS. 7A and 7Bin an isometric view and in a sectional view. The sectional plane ofFIG. 7Bcorresponds to the view ofFIG. 4, and related components are indicated by the same reference numbers.

The embodiment ofFIGS. 7A and 7Bdiffers from the preceding embodiments in that the lever arm140is attached to the blocking pin14of the sliding element36. A compensating body142is disposed outside the drive housing10and is carried in guide rails144. The compensating body142has an opening146through which the lever arm140is passed. The opening146is formed in such a way that the lever arm140is pivotably disposed therein.

In a similar way as in the embodiment ofFIGS. 6A to 6D, the lever arm140is supported by means of stub shafts148in a receiving portion150connected to the housing10. At its end facing away from the compensating body142, the lever arm140is forked, thus forming two arms152,152′ that engage with the outside contour of the blocking pin from opposite sides.

The functioning of the blocking device formed from the compensating body142and the lever arm140is as described with reference to the preceding embodiments. If the sliding element36and thus the compensating body142is exposed to a shock load in the direction of translation, the torques generated in the bearing point (148) cancel each other out, so that the system as a whole remains in equilibrium. On the other hand, the pivotal connection of the two arms152,152′ to the blocking pin14and the design of the opening146allow the actuator12to move into and out of the drive housing10, the lever140deflecting and thus being able to follow this movement.

A further embodiment of the linear drive according to the invention is shown inFIG. 8in a sectional view. The sectional plane corresponds to the view ofFIG. 4, and related components are indicated by the same reference numbers.

In the embodiment ofFIG. 8, the drive unit40comprises only one drive element42and one power transmission element44that interacts with a drive rail84. The side of the drive rail84facing away from the power transmission element44has the form of a toothed rack and meshes with a toothed wheel86that engages with a compensating body88. The compensating body88is disposed within the drive housing10where, in the embodiment ofFIG. 4, for example, the second drive element is located. The compensating body88is slidably guided in the drive housing10and its mass is equal to the mass of the sliding element36that comprises the actuator66, the supporting component36and the drive rail84. Should the linear drive undergo a shock load in the direction of translation, this shock load acts equally on the compensating body88and the sliding element36, so as to accelerate these in the direction of translation. Since the acceleration forces on the sliding element36and compensating body88are the same, the coupling via the toothed wheel86prevents a movement of the one or the other in the direction of translation. The system is self retarding. The effect is substantially the same as in the previously described embodiments.

Alongside lock applications, friction-coupled linear motors having a one-sided drive also find application, for example, in auto focus drives. In this kind of application it is again important that the actuator66is not displaced when exposed to shock loads or vibration.

A modification of the embodiment illustrated inFIG. 8is shown inFIG. 9. The sectional plane of the sectional view ofFIG. 9corresponds to that ofFIG. 5. Related parts are indicated by the same reference numbers.

The embodiment ofFIG. 9differs fromFIG. 8in that the sliding element36is again driven by two drive elements (not illustrated in the figure) and that the compensating body90is disposed outside the drive housing10. It is coupled with the sliding element36, more specifically with the actuator66using a toothed wheel92. For this purpose, the compensating body90and the actuator66are designed like toothed racks on one side. The effect thus achieved is described as with reference toFIG. 8.

Yet a further embodiment of the invention is shown inFIG. 10. The sectional view ofFIG. 10extends through the same sectional plane as that ofFIG. 4. Related components are indicated by the same reference numbers.

The embodiment ofFIG. 10differs from the preceding embodiments in that the compensating body94is connected to the sliding element36using a Bowden cable96. The Bowden cable96is carried on the frame component38and engages with the actuator66as well as the end of the sliding element36facing away from the actuator. The mass of the compensating body94is equal to the mass of the sliding element36that comprises the actuator66, the supporting component46, the drive rail48and the sensor magnet50. In the event of a shock load to the linear drive in the direction of translation, it acts equally on the compensating body94and the sliding element36, so as to move both in the same direction. Due to the coupling via the Bowden cable96, the compensating body94and the sliding element36block each other, and the system is self retarding. The effect is basically the same as described above with reference to the other embodiments.

FIG. 11shows a front view of the linear drive ofFIG. 10to better illustrate the design of the compensating body94that takes the form of a cylinder segment and rests slidably on the drive housing10. The compensating body94is slidably guided on the drive housing10using guiding components98. Alternatively, the compensating body could also be guided within the drive housing10. This method of guiding the compensating body94can conceivably be used for all variants having compensating body that are located externally.

It basically applies to all previously described embodiments that the compensating body may be disposed and guided within or outside the drive housing. In the same way, the coupling mechanism, such as the lever arm, toothed wheel or Bowden cable, can be disposed and guided within and/or outside the drive housing. The weight of the sliding element and the weight of the compensating body should—in accordance with the lever principle where applicable—be the same.

Another embodiment of the linear motor according to the invention is shown inFIGS. 12 and 13,FIG. 12depicting an isometric view of the linear drive andFIG. 13showing a sectional view of the linear drive that extends through the same sectional plane as the view ofFIG. 4. Related components are indicated by the same reference numbers.

In the embodiment illustrated inFIGS. 12 and 13, the blocking device is formed by a spring device100that is designed in such a way that it is deflected by a shock load so as to become engaged with the sliding element36or its actuator66respectively. This spring device100of the embodiment illustrated inFIGS. 12 and 13is shown inFIGS. 14 and 15in an isometric view and a side view respectively. In this embodiment, the spring device comprises a spring ring102having a plurality of radially inwards extending spring arms104, each carrying a compensating body106. The spring ring102and the spring arms104are disposed about the actuator66. Any desired number of spring arms104may be provided, a plurality of spring arms being distributed as evenly as possible about the circumference of the spring ring102. The spring arms may be designed, as in the illustrated embodiment, as double arms or also as single arms. In the illustrated embodiment, the ring102is connected to the frame component48or the drive housing10, and the spring arms104extend with respect to the ring102at an angle α (seeFIG. 15) in the direction of the actuator66. Angle α is approximately 30° C. and preferably lies in a range of 10° to 80°. Basically every angle 0°<α<90° is conceivable.

The spring device100, including the compensating body106carried on the spring arms104, is designed such that the spring arms deflect in the event of a shock load to the linear drive in the direction of translation. Advantage is taken of the fact that a shock load causes the spring arms104to become pressed together, i.e. a becomes smaller, and at the same time to move in a radially inwards direction. Here, the spring arms104come to lie against the outside circumference of the actuator66as shown inFIGS. 12 and 13, and block the movement of the actuator66. In order to intensify this blocking or arresting effect of the spring device100, the actuator66preferably has a groove108into which the free ends of the spring arms104become engaged and/or the spring arms104are coated with a high friction material layer, such as rubber.

In realizing the embodiment of the invention illustrated inFIGS. 12 to 15, the spring constant of the spring device100and the mass of the compensating body106should be designed such that, when exposed to a shock load that can be expected, the radial movement of the spring arms104and the translation displacement of the sliding element36are matched to each other in such a way that the free ends of the spring arms104come to lie in the groove108. Suitable ratios can be determined without too much effort.

The spring device shown inFIGS. 14 and 15comprises an annular spring having radially inwards extending spring arms that are also shown inFIGS. 12 and 13. The spring device100ofFIGS. 12 to 15has a one-sided function, which means a movement of the actuator66due to a shock load is only retarded if the direction of excitation of the shock load reduces the size of the angle α of the spring arms104. This kind of spring device may also be provided with additional spring arms that extend at an angle −α with respect to the ring; this makes it possible to realize a spring device that, in the event of shock loads, can form a retarding effect in both directions of translation.

Instead of this annular spring, alternative spring devices may be used that are depicted in isometric views inFIGS. 16,17and18. The spring device ofFIG. 16comprises a leaf spring110that is connected at one end112to the frame and at the other end114carries a compensating body116. The leaf spring110has a recess118through which the sliding element36or the actuator66can be led. The leaf spring110is preferably designed such that it is bent at an angle β with respect to its end112fixed to the frame component38. The angle β is, for example, 20° and lies preferably in the range of 10° to 45°.

The leaf spring110can be used in the linear drive ofFIGS. 12 and 13instead of the spring device100, the sliding element66passing through the recess118. In the event of a shock load in the direction of translation, the leaf spring110is deflected with respect to its fixed end112, so that angle increases or decreases. At the same time, the recess118also makes a movement in a radial direction of the linear drive and can thus engage with the actuator66of the sliding element36. The actuator66in turn preferably has a groove that interacts with the recess118. The spring constant of the leaf spring110and the mass of the weight116should in turn be chosen such that the acceleration of the leaf spring110generated by the shock load brings about the effective arrest of the spring in the groove108in the actuator16.

Instead of the spring ring illustrated inFIGS. 14 and 15or the leaf spring illustrated inFIG. 16, a suspension spring120may also be used as a blocking device as depicted inFIG. 17in an isometric view. The suspension spring120has two pendulum arms122,124that are connected on one side to the frame component38and on the other side carry a pendulum ring126that in turn carries a compensating body128. A shock load to the linear drive and thus to the suspension spring120results in the pendulum ring126tilting and thus also deflecting in a radial direction. The actuator66of the sliding element36is led through the pendulum ring126, and the pendulum ring126engages with the actuator66, preferably with the groove108in the actuator66when it is deflected or tilted. Again in this embodiment, the spring constant of the suspension spring126and the mass of the weight118should be chosen such that when exposed to the stress that can be expected, the pendulum ring126comes to lie as far as possible in the groove108of the sliding element66.

A further embodiment of a blocking device for a linear drive is shown inFIG. 18. It comprises a bent leaf spring130that is clamped at one end134in the frame component38and whose other free end132can be made to engage with the sliding element36. A compensating body for absorbing a shock load is integrated in the leaf spring130in that the leaf spring130itself forms this compensating body or such a compensating body is additionally mounted on the leaf spring (not illustrated in the figure). When a shock load acts in the direction of translation on the linear drive, the same stress also acts on the leaf spring130(from above in the view ofFIG. 18for example), so that the leaf spring130is stretched by this shock load and end132moves away from end134(to the right inFIG. 18). The behavior of the leaf spring130can be taken advantage of so as to make the end132engage with a recess of the sliding element36. The end132is bent so that it catches in the recess of the sliding element36and no longer springs back independently. The sliding element36has to be moved by the drive unit40away from the spring, i.e. in the opposite direction to the direction of excitation of the shock load, in order to free it. Shape, spring constant and mass of the leaf spring130should be adapted to the shock loads that can be expected in order to ensure that the end134of the leaf spring130comes to lie in a corresponding recess in the sliding element36.

IDENTIFICATION REFERENCE LIST