Patent Publication Number: US-2023160231-A1

Title: Bumping preventing arrangement for lock device, lock device and method

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to a bumping preventing arrangement. In particular, a bumping preventing arrangement for a lock device, a lock device comprising a bumping preventing arrangement, and a method of controlling a lock device, are provided. 
     BACKGROUND 
     Unauthorized manipulation of lock devices by different types of bumping is a well-known problem for key cylinder locks. Also blocking mechanisms for dead bolts and door handles may be subjected to bumping. 
     In some prior art lock devices, a certain mechanical force “hill” needs to be passed to bump a transfer member from a locked position to an unlocked position to thereby be able to unlock the lock device without authorization. The transfer member may for example be a blocking member or a coupling member. The mechanical force hill may be the force required to overcome a force from a spring that pushes the transfer member towards the locked position. 
     In those prior art lock devices, the same mechanical force hill for unauthorized unlocking also needs to be overcome for authorized unlocking of the lock device. In the case of a spring pushing the transfer member towards the locked position, the transfer member needs to be moved against the force of the spring also for authorized unlocking. Thus, authorized unlocking often requires a substantial amount of energy to unlock. This is problematic when the transfer member is driven by a motor, and in particular if the lock device is an energy harvesting lock device with a small battery or with no battery at all. 
     SUMMARY 
     One object of the present disclosure is to provide a bumping preventing arrangement for a lock device, which bumping preventing arrangement improves security of the lock device. 
     A further object of the present disclosure is to provide a bumping preventing arrangement for a lock device, which bumping preventing arrangement provides resistance against bumping of the lock device. 
     A still further object of the present disclosure is to provide a bumping preventing arrangement for a lock device, which bumping preventing arrangement has low power consumption. 
     A still further object of the present disclosure is to provide a bumping preventing arrangement for a lock device, which bumping preventing arrangement has a compact, simple and/or reliable design. 
     A still further object of the present disclosure is to provide a bumping preventing arrangement for a lock device, which bumping preventing arrangement has a compact, simple and/or reliable function. 
     A still further object of the present disclosure is to provide a bumping preventing arrangement for a lock device, which bumping preventing arrangement solves several or all of the foregoing objects in combination. 
     A still further object of the present disclosure is to provide a lock device comprising a bumping preventing arrangement, which lock device solves one, several or all of the foregoing objects. 
     A still further object of the present disclosure is to provide a method of controlling a lock device, which method solves one, several or all of the foregoing objects. 
     According to one aspect, there is provided a bumping preventing arrangement for a lock device, the bumping preventing arrangement comprising a transfer member having a magnet, the transfer member being movable along an actuation axis between a locked position and an unlocked position; a plurality of electric conductors, each electric conductor enclosing the actuation axis; and a plurality of switches, each switch being associated with a respective electric conductor, and being arranged to selectively close an electric circuit comprising the associated electric conductor such that eddy currents are induced in the electric conductors when the magnet moves along the actuation axis from the locked position towards the unlocked position. 
     The eddy currents generate a magnetic force on the magnet acting against the movement of the magnet. The magnetic force acts as a brake against movements of the transfer member due to bumping. 
     The transfer member may move relatively easy during authorized unlocking of the lock device when the switches are open due to the absence of the magnetic force. However, for unauthorized opening or bumping when the switches are closed, the transfer member moves relatively heavy due to the induced eddy currents and the consequential counteracting magnetic force. 
     The bumping preventing arrangement thus enables a particular “unauthorized force hill” and a particular “authorized force hill”, lower than the unauthorized force hill, to be set. For example, the unauthorized force hill may be the force needed to overcome both the force of an elastic element and the magnetic force from the eddy currents, and the authorized force hill may be the force needed to overcome only the force of the elastic element. Since the force of an elastic element and the magnetic force can be set as desired, e.g. by corresponding dimensioning of the parts, also the unauthorized force hill and the authorized force hill can be set as desired. In this way, a low authorized force hill and a high unauthorized force hill can be set. This enables a high protection against bumping with a low energy consumption. A wide range of tradeoffs between a very high protection against bumping and a very lower energy consumption can also be realized by means of the bumping preventing arrangement. 
     The selective closing of the switches can be made with very low power consumption. The bumping preventing arrangement thus provides a low power bumping protection based on the eddy current principle. 
     When the electric circuits are selectively opened by opening of the switches, no eddy currents are induced in the electric conductors when the magnet moves along the actuation axis from the locked position towards the unlocked position. When the switches are open, the switches are in an unlocked state. This may be referred to as an opening mode. 
     When the switches are closed to close the electric circuits, the switches are in a locked state. This may be referred to as a protection mode. Each switch may be either electrically or mechanically controlled. 
     Each electric conductor may partly or entirely enclose the actuation axis. Each electric conductor may have the same, or substantially the same, electrical conductivity. The electric conductors may for example be made of copper, gold or silver. The electrical conductivity of the electric conductors may be at least 3×10 7  σ (S/m) at 20° C., such as at least 4×10 7  σ (S/m) at 20° C. The bumping preventing arrangement may comprise at least three electric conductors, such as three to six electric conductors. 
     Due to the cooperation between the electric conductors and the switches to selectively induce eddy currents as a result of movement of the magnet, the bumping preventing arrangement can be miniaturized for various types of lock devices. Thus, the bumping preventing arrangement enables a compact design. 
     The magnet may be a permanent magnet. The magnet may for example comprise a Neodymium alloy such as a Neodymium-Iron-Boron (NdFeB), or other alloy having a relatively high intrinsic remanence. A relatively high intrinsic coercivity may be used to protect the magnet from being demagnetized by an applied external magnetic field. 
     The electric conductors may be arranged in a stack. The stack may thus extend parallel with the actuation axis. By arranging the electric conductors in a stack, a tube of electric conductors is formed. A length of the stack along the actuation axis may be larger than a length of the magnet along the actuation axis. 
     Each electric conductor may extend in a plane substantially perpendicular to, or perpendicular to, the actuation axis. The electric conductors may thus be arranged as, or configured as, a plurality of washers. In this case, each washer may comprise an opening where one of the switches is connected. 
     The bumping preventing arrangement may further comprise an elastic element arranged to force the transfer member along the actuation axis towards the locked position. The elastic element may for example be a leaf spring or a coil spring. 
     The transfer member may be constituted by the magnet. Alternatively, the magnet may constitute only a part of the transfer member. That is, the transfer member may comprise the magnet and one or more non-magnetic parts. In any case, the transfer member may be rigid. 
     The transfer member may be a blocking member. The blocking member may block relative movement between an input member and an output member in the locked position, and unblock relative movement between the input member and the output member in the unlocked position. Thus, in the unlocked position of the blocking member, a movement of the input member is transferred to the output member. 
     Alternatively, the transfer member may be a coupling member. The coupling member may decouple an input member from an output member in the locked position, and couple the input member to the output member in the unlocked position. Thus, in the unlocked position of the coupling member, a movement of the input member is transferred to output member. The coupling member may thereby function as a clutch. 
     Each switch may comprise a transistor. The transistor may be controlled by voltage. Alternatively, each switch may be an electromechanical switch or a mechanical switch. 
     The transistor may be a metal oxide semiconductor field effect transistor, MOSFET, such as N-type metal oxide semiconductor field effect transistor, nMOSFET. 
     The transistor may be a field effect transistor of the depletion type. The depletion type field effect transistor is normally closed (on). By applying a voltage to the gate, the transistor opens the electric circuit. Depletion type field effect transistors do therefore not consume any power in the locked state. The use of depletion type field effect transistors is therefore advantageous for energy harvesting lock devices which may have limited or no available power in passive mode. 
     Alternatively, the transistor may be a field effect transistor of the enhancement type. The enhancement type field effect transistor is normally open (off). By applying a voltage to the gate, the transistor closes the electric circuit. Enhancement type field effect transistors do therefore not consume any power in the unlocked state. 
     The bumping preventing arrangement may further comprise a control system, the control system comprising at least one data processing device and at least one memory having a computer program stored thereon, the computer program comprising program code which, when executed by the at least one data processing device, causes the at least one data processing device to perform the steps of evaluating an authorization request; and commanding each switch to open in response to a granted evaluation of the authorization request. The computer program may further comprise program code which, when executed by the at least one data processing device, causes the at least one data processing device to perform, or command performance of, various steps as described herein. 
     The control system may further comprise a receiving unit, such as an antenna, for receiving the authorization request. The control system may be configured to determine whether or not authorization should be granted based on the authorization request. If access is granted, e.g. if a valid credential is presented, each switch is commanded to open. 
     The bumping preventing arrangement may further comprise a printed circuit board, PCB. The control system may be provided on the PCB. 
     According to a further aspect, there is provided a lock device comprising a bumping preventing arrangement according to the present disclosure. The lock device may comprise an input member and an output member. The output member may be prevented from being moved by movement of the input member when the transfer member is in the locked position. Conversely, the output member may be allowed to be moved by movement of the input member when the transfer member is in the unlocked position. 
     The lock device may be an energy harvesting lock device. To this end, the lock device may further comprise an electric generator arranged to generate electric energy from movement of the input member. The energy harvesting lock device may not comprise a battery. 
     According to a further aspect, there is provided a method of controlling a lock device, the method comprising providing a lock device according to the present disclosure; and opening each switch in response to a granted authorization request from a user. If the authorization request is not granted or if no authorization request is received, the each switch remains closed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details, advantages and aspects of the present disclosure will become apparent from the following embodiments taken in conjunction with the drawings, wherein: 
         FIG.  1   : schematically represents a side view of a bumping preventing arrangement where a transfer member is in a locked position and a plurality of switches are in locked states; 
         FIG.  2   : schematically represents a top view of the bumping preventing arrangement in  FIG.  1   ; 
         FIG.  3   : schematically represents a side view of the bumping preventing arrangement where the transfer member is in an unlocked position and the switches are in unlocked states; 
         FIG.  4   : schematically represents a top view of the bumping preventing arrangement in  FIG.  3   ; 
         FIG.  5   : schematically represents a side view of a key cylinder lock where a plurality of driver pins are in locked positions and the switches are in locked states; 
         FIG.  6   : schematically represents a side view of the key cylinder lock in  FIG.  5    where the driver pins are in unlocked positions and the switches are in unlocked states; 
         FIG.  7   : schematically represents a side view of a further lock device where a blocking member is in a locked position and the switches are in locked states; 
         FIG.  8   : schematically represents a side view of the lock device in  FIG.  7    where the blocking member is in an unlocked position and the switches are in unlocked states; 
         FIG.  9   : schematically represents a front view of a further lock device where a coupling member is in a locked position and the switches are in locked states; and 
         FIG.  10   : schematically represents a front view of the lock device in  FIG.  9    where the coupling member is in an unlocked position and the switches are in unlocked states. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, a bumping preventing arrangement for a lock device, a lock device comprising a bumping preventing arrangement, and a method of controlling a lock device, will be described. The same or similar reference numerals will be used to denote the same or similar structural features. 
       FIG.  1    schematically represents a side view of a bumping preventing arrangement  10  and  FIG.  2    schematically represents a top view of the bumping preventing arrangement  10  in  FIG.  1   . With collective reference to  FIGS.  1  and  2   , the bumping preventing arrangement  10  comprises a transfer member  12 . In this example, the transfer member  12  is constituted by a magnet  14 . The magnet  14  of this example is a permanent magnet. 
     In  FIGS.  1  and  2   , the transfer member  12  is positioned in a locked position  16 . The transfer member  12  is movable from the locked position  16  along an actuation axis  18 . 
     The bumping preventing arrangement  10  further comprises a plurality of electric conductors  20  and a plurality of switches  22 . In this specific example, the bumping preventing arrangement  10  comprises six electric conductors  20  and six switches  22 . Each electric conductor  20  is associated with one of the switches  22  and each switch  22  is associated with one of the electric conductors  20 . Each pair of electric conductor  20  and associated switch  22  encloses the actuation axis  18 . 
     Each electric conductor  20  is arranged in a plane perpendicular to the actuation axis  18  and is shaped as a washer. Each washer comprises a cut-out where the associated switch  22  is positioned. As shown in  FIG.  1   , the electric conductors  20  are arranged in a stack extending parallel with the actuation axis  18 . The electric conductors  20  thereby form a tube enclosing the magnet  14 . The electric conductors  20  may be made of copper or another material of high electrical conductivity. The electric conductors  20  may be electrically isolated from each others. 
     In  FIGS.  1  and  2   , each individual switch  22  is in a locked state  24 . In the locked states  24 , each switch  22  is closed such that an electric circuit or current loop comprising the associated electric conductor  20  is closed. Each switch  22  is arranged to selectively close and open the associated electric circuit. 
     The switches  22  are here exemplified as field effect transistors of the depletion type, i.e. normally closed (on). Thereby, the switches  22  do not consume any power in the locked states  24 . 
     The bumping preventing arrangement  10  further comprises a control system  26 . The control system  26  of this example comprises a data processing device  28 , a memory  3 o and an antenna  32 . The memory  3 o has a computer program stored thereon. The computer program comprises program code which, when executed by the data processing device  28 , causes the data processing device  28  to evaluate an authorization request received by the antenna  32 , and to command each switch  22  to open in response to a granted evaluation request. The authorization request may for example be received by the antenna  32  via Bluetooth Low Energy, BLE. Components of the control system  26  may be arranged on a common PCB. 
     When the switches  22  are in the locked states  24  to short the electric circuits and the transfer member  12  is attempted to be moved from the locked position  16 , eddy currents are created in electric conductors  20  by the moving/changing magnetic field of the magnet  14 . The eddy currents generate a magnetic force on the magnet  14  acting against the movement of the transfer member  12 . In this way, bumping of the transfer member  12  away from the locked position  16  can be prevented. 
       FIG.  3    schematically represents a side view of the bumping preventing arrangement  10  and  FIG.  4    schematically represents a top view of the bumping preventing arrangement  10  in  FIG.  3   . In  FIGS.  3  and  4   , the switches  22  are in unlocked states  34 , e.g. after a user has presented a valid credential. In the unlocked state  34 , each switch  22  may consume less than 10 μA, such as less than 2 μA. 
     When the switches  22  are in the unlocked states  34 , each electric circuit around the magnet  14  is open. Consequently, no eddy currents are induced in the electric conductors  20  by movement of the magnet  14  and the magnet  14  is therefore not subjected to any magnetic force from such eddy currents. The transfer member  12  can thereby be moved from the locked position  16  to an unlocked position  36 . The switches  22  are thus selectively closed and opened in order to turn on and off, respectively, the eddy currents and the consequential braking magnetic field. 
       FIG.  5    schematically represents a side view of a key cylinder lock  38 . The key cylinder lock  38  comprises an outer casing  40  and a plug  42  rotatably arranged in the outer casing  40 . The key cylinder lock  38  further comprises key pins  44 , driver pins  46  and compression springs  48 . Each driver pin  46  is constituted by a cylindrical magnet  14 . 
     Each spring  48  forces the associated driver pin  46  along an actuation axis  18  into the locked position  16 . The springs  48  are examples of elastic elements. The plug  42  is one example of an output member. 
     The key cylinder lock  38  further comprises a bumping preventing arrangement  10  of the same type as in  FIGS.  1 - 4   . Thus, each driver pin  46  is enclosed by a plurality of (four in this example) electric circuits, each formed by an electric conductor  20  and an associated switch  22 . Each driver pin  46  is thus one example of a transfer member. As shown in  FIG.  5   , the bumping preventing arrangement  10  is miniaturized to fit inside the outer casing  40 . Also the control system  26  is arranged inside the outer casing  40 . The control system  26  controls the switching of all switches  22  associated with the driver pins  46 . 
     In  FIG.  5   , the driver pins  46  are in locked positions  16  and the switches  22  are in locked states  24 . Each driver pin  46  thereby directly blocks a rotational force applied to the plug  42 . Should the bumping preventing arrangement  10  not comprise the electric conductors  20 , the driver pins  46  would be possible to bump against the compression of the springs  48  by external forces and/or vibrations on the key cylinder lock  38 , or with a bump key, to obtain a short unblocked state of the driver pins  46 . The key cylinder lock  38  would then be possible to open without authorization. However, by means of the electric conductors  20  and the closing of the switches  22  to close a plurality of electric circuits, eddy currents will be generated by movement of the magnets  14  and the key cylinder lock  38  is therefore much harder or impossible to open using bumping techniques. 
     In order to bump a driver pin  46  from the locked position  16  to the unlocked position  36 , both the force of the spring  48  and the magnetic force generated by eddy currents induced in the electric circuits need to be overcome. A sum of these forces constitutes an unauthorized force hill. Moreover, insertion of a key into the plug  42  will be rather heavy when the electric circuits are closed. 
       FIG.  6    schematically represents a side view of the key cylinder lock  38  in  FIG.  5   . In  FIG.  6   , a valid credential has been presented and the control system  26  has thereby commanded the switches  22  to switch from the locked states  24  to the unlocked states  34 . 
     When the switches  22  are in the unlocked states  34 , each electric circuit around the respective magnets  14  is open. Consequently, no eddy currents are induced in the electric conductors  20  by movement of the magnets  14  and the magnets  14  are therefore not subjected to any magnetic force from such eddy currents. The driver pins  46  can thereby be moved from the locked position  16  to the unlocked position  36  against the forces of the respective spring  48 . The force needed for this movement constitutes an authorized force hill, which is lower than the unauthorized force hill. 
     As shown in  FIG.  6   , a key  50  is inserted into the plug  42 . The key  50  is one example of an input member. The insertion of the key  50  causes the key pins  44  to move, which in turn causes the driver pins  46  to move from the locked position  16  to the unlocked position  36  along the respective actuation axis  18 . The interface between each pair of key pin  44  and driver pin  46  is now aligned with the interface between the plug  42  and the outer casing  40 . The plug  42  can thereby be rotated by rotation of the key  50  to open the key cylinder lock  38 . 
       FIG.  7    schematically represents a side view of a further lock device  52 . The lock device  52  comprises a handle  54  and a latch bolt  56 . The handle  54  is a further example of an input member and the latch bolt  56  is a further example of an output member. In this specific example, the handle  54  is arranged to rotate and the latch bolt  56  is arranged to move linearly. 
     The lock device  52  further comprises a transmission  58 . The transmission  58  is configured to transmit a movement of the handle  54  to a movement of the latch bolt  56 . To this end, the transmission  58  may for example comprise gear wheels and/or a linkage. 
     The lock device  52  further comprises an electromechanical actuator  60 . The actuator  6 o comprises an actuator pin  62 . The actuator  6 o can move the actuator pin  62  linearly. The actuator  6 o is controlled by the control system  26 . 
     The lock device  52  further comprises a blocking member  64  and a spring  48 . The spring  48  is arranged between the actuator pin  62  and the blocking member  64 . The blocking member  64  is one example of a transfer member. The blocking member  64  is constituted by a magnet  14 , here a cylindrical magnet. 
     The lock device  52  further comprises a bumping preventing arrangement  10  of the same type as in  FIGS.  1 - 6   . The bumping preventing arrangement  10  comprises the blocking member  64  constituted by the magnet  14 , a plurality of electric conductors  20 , a plurality of switches  22 , the spring  48  and the control system  26 . The blocking member  64  is enclosed by a plurality of electric circuits, each formed by one of the electric conductors  20  and one of the switches  22 . 
     The lock device  52  may be an energy harvesting lock device. In this case, the control system  26  and the actuator  6 o are powered by electric energy harvested by mechanical movement of the handle  54 . 
     In  FIG.  7   , the blocking member  64  is in the locked position  16 . In the locked position  16 , the blocking member  64  is seated in an aperture  66  in the latch bolt  56 . The latch bolt  56  is thereby blocked from moving. The spring  48  forces the blocking member  64  into the locked position  16  seated in the aperture  66 . 
     In  FIG.  7   , the switches  22  are in locked states  24 . Should the bumping preventing arrangement  10  not comprise the electric conductors  20 , the blocking member  64  would be possible to bump against the compression of the spring  48  by external forces and/or vibrations on the lock device  52  to obtain a short unblocked state of the blocking member  64 . The lock device  52  would then be possible to open without authorization. However, by means of the electric conductors  20  and the closing of the switches  22  to close a plurality of electric circuits, eddy currents will be generated by movement of the magnet  14  and the lock device  52  is therefore much harder or impossible to open using bumping techniques. In order to bump the blocking member  64  from the locked position  16  to the unlocked position  36  when the actuator pin  62  is stationary, both the force of the spring  48  and the magnetic force generated by eddy currents induced in the electric circuits need to be overcome. 
       FIG.  8    schematically represents a side view of the lock device  52  in  FIG.  7   . In  FIG.  8   , a valid credential has been presented and the control system  26  has thereby commanded the switches  22  to switch from the locked states  24  to the unlocked states  34 . 
     When the switches  22  are in the unlocked states  34 , each electric circuit around the magnet  14  is open. Consequently, no eddy currents are induced in the electric conductors  20  by movement of the magnet  14  and the magnet  14  is therefore not subjected to any magnetic force from such eddy currents. Simultaneously with, or after, the switches  22  are switched to the unlocked states  34 , the control system  26  commands the actuator  6 o to move the actuator pin  62 . As shown in  FIG.  8   , the actuator pin  62  is retracted. This causes the blocking member  64  to be moved from the locked position  16  to the unlocked position  36  along the actuation axis  18 . In the unlocked position  36 , the blocking member  64  is retracted completely out from the aperture  66 . 
     The retracting movement of the actuator pin  62  does not need to overcome the force of the spring  48 . In fact, since the spring  48  is compressed when the blocking member  64  is in the locked position  16 , the spring  48  initially assists the retraction of the actuator pin  62 . Thus, a very low authorized force hill is obtained. 
     In  FIGS.  7  and  8   , the blocking member  64  blocks relative movement between the handle  54  and the latch bolt  56  in the locked position  16 , and unblocks relative movement between the handle  54  and the latch bolt  56  in the unlocked position  36 . In the unlocked position  36  of the blocking member  64  in  FIG.  8   , a rotation of the handle  54  is transferred to a linear movement of the latch bolt  56 . The user can now turn the handle  54  to retract the latch bolt  56  to open the lock device  52 . 
       FIG.  9    schematically represents a front view of a further lock device  68 . The lock device  68  comprises a knob  70  and a locking member  72 . The knob  70  is a further example of an input member and the locking member  72  is a further example of an output member. In this specific example, each of the knob  70  and the locking member  72  is arranged to rotate about a common rotation axis. 
     The lock device  68  further comprises an electromechanical actuator  60  having an actuator pin  62 . The actuator  6 o and the actuator pin  62  are of the same type as in  FIGS.  7  and  8   . 
     The lock device  68  further comprises a coupling member  74  and a spring  48 . The spring  48  is arranged between the actuator pin  62  and the coupling member  74 . The coupling member  74  is a further example of a transfer member. The coupling member  74  is constituted by a magnet  14 , here a cylindrical magnet. 
     The lock device  68  further comprises a bumping preventing arrangement  10 . The bumping preventing arrangement  10  comprises the coupling member  74  constituted by the magnet  14 , a plurality of electric conductors  20 , a plurality of switches  22 , the spring  48  and the control system  26 . The coupling member  74  is enclosed by a plurality of electric circuits, each formed by one of the electric conductors  20  and one of the switches  22 . It should be emphasized that the lock device  68  in  FIG.  9    is merely schematically illustrated. In particular, the bumping preventing arrangement  10  and the actuator  6 o may be arranged inside the knob  70 . 
     The lock device  68  may be an energy harvesting lock device. In this case, the control system  26  and the actuator  6 o are powered by electric energy harvested by rotation of the knob  70 . 
     In  FIG.  9   , the coupling member  74  is in the locked position  16 . In the locked position  16 , the coupling member  74  is retracted from an aperture  66  in the locking member  72 . In the locked position  16  of the coupling member  74 , a rotation of the knob  70  is not transmitted to a rotation of the locking member  72 . The coupling member  74  functions as a clutch. In  FIG.  9   , the clutch is open. 
     In  FIG.  9   , the switches  22  are in locked states  24 . Should the bumping preventing arrangement  10  not comprise the electric conductors  20 , the coupling member  74  would be possible to bump against the expansion of the spring  48  by external forces and/or vibrations on the lock device  68  to obtain a short coupled state of the coupling member  74 . The lock device  68  would then be possible to open without authorization. However, by means of the electric conductors  20  and the closing of the switches  22  to close a plurality of electric circuits, eddy currents will be generated by movement of the magnet  14  and the lock device  68  is therefore much harder or impossible to open using bumping techniques. In order to bump the coupling member  74  from the locked position  16  to the unlocked position  36  when the actuator pin  62  is stationary, both the force of the spring  48  and the magnetic force generated by eddy currents induced in the electric circuits need to be overcome. 
       FIG.  10    schematically represents a front view of the lock device  68  in  FIG.  9   . In  FIG.  10   , a valid credential has been presented and the control system  26  has thereby commanded the switches  22  to switch from the locked states  24  to the unlocked states  34 . 
     When the switches  22  are in the unlocked states  34 , each electric circuit around the magnet  14  is open. Consequently, no eddy currents are induced in the electric conductors  20  by movement of the magnet  14  and the magnet  14  is therefore not subjected to any magnetic force from such eddy currents. Simultaneously with, or after, the switches  22  are switched to the unlocked states  34 , the control system  26  commands the actuator  6 o to move the actuator pin  62 . As shown in  FIG.  10   , the actuator pin  62  is extended. This causes the coupling member  74  to be moved from the locked position  16  to the unlocked position  36  along the actuation axis  18 . In the unlocked position  36 , the coupling member  74  is seated in the aperture  66  in the locking member  72 . The extending movement of the actuator pin  62  does not need to overcome the force of the spring  48 . In  FIG.  10   , the clutch is closed. 
     In  FIGS.  9  and  10   , the coupling member  74  decouples the knob  70  from the locking member  72  in the locked position  16 , and couples the knob  70  to the locking member  72  in the unlocked position  36 . Thus, in the unlocked position  36  of the coupling member  74 , the knob  70  and the locking member  72  can be rotated in common to unlock the lock device  68 . Although the bumping preventing arrangement  10  comprising a coupling member  74  is exemplified together with the lock device  68  comprising the knob  70  in  FIGS.  9  and  10   , the bumping preventing arrangement  10  comprising a coupling member  74  can be used with other types of lock devices not necessarily comprising a knob. 
     While the present disclosure has been described with reference to exemplary embodiments, it will be appreciated that the present invention is not limited to what has been described above. For example, it will be appreciated that the dimensions of the parts may be varied as needed. Accordingly, it is intended that the present invention may be limited only by the scope of the claims appended hereto.