WO2011030112A1

WO2011030112A1 - A device for limiting movement

Info

Publication number: WO2011030112A1
Application number: PCT/GB2010/001719
Authority: WO
Inventors: Yaroslay Tenzer; Fernando Maria Rodriguez Y Baena; Brian Lawrence Davies
Original assignee: Imperial Innovations Limited
Priority date: 2009-09-10
Filing date: 2010-09-10
Publication date: 2011-03-17
Also published as: GB0915894D0

Abstract

A programmable limiting device for use in mechanical interfaces such as human- machine that when disengaged operates as a free moving mechanism, with the stopper (5) moving with the platform (2) in a standby position, but when engaged is switchable from free-motion to one-way by binding the stopper (5) to an outer fixed surface (3), prohibiting movement of the stopper and thus prohibition the movement of the platform (2) in the direction of the stopper, but allowing for movement of the platform in the other direction, away from the stopper, and when the platform is moved away the stopper is disengaged, according to an algorithm, and pulled to the platform into the standby position using an elastic type material, whereby allowing switchable programmable mechanical limitation. The programmable brake or programmable limiting device is particularly well suited for use in a mechanical human-machine interface.

Description

A DEVICE FOR LIMITING MOVEMENT

Background

This invention relates to a device for limiting movement. In embodiments, it relates to a programmable mechanism for limiting and for permitting motion of a programmable braking mechanism. In embodiments, it also relates to a device for limiting movement for use in medical applications, such as medical robots.

In arrangements in which one mechanical component moves relative to another, it can be desirable to provide a braking mechanism which can prevent motion in one direction, whilst still allowing motion in other directions.

A conventional brake may be unsuited to the situation described above, because such a brake usually limits, or totally prevents, motion in all directions. An example of this is a rotational mechanism in which a conventional brake will allow free rotation or, when applied, no rotation in either rotational direction. A toothed wheel, together with a sprung-loaded ratchet and pawl, may be used in order to limit the rotation in one direction whilst allowing a free rotation in the alternate direction. A typical example of this is in the free-wheel of a bicycle, which allows free rotation in one direction whilst preventing rotation in the other.

There are four separate conditions, or stages, which require control of motion. For rotational motion these are; free movement in both directions, only clockwise motion, only anticlockwise motion, and no movement at all. It is possible to build a configurable or programmable brake which allows programmed rotation in both directions, one direction or neither direction. Such brakes find useful application in medical technology in which they can be used to limit the motion of medical robots, such as by limiting the range of motion of a medical instrument held by the robot to within limits of a predefined surgical plan. In this way, it is possible to control motion of the instrument such that it reaches a target position, follows a particular trajectory or remains inside a preferred region. An example of such an arrangement is the Passive Arm with Dynamic Constraints (PADyC) system, developed at least partly by Laboratoire TIMC-IMAG of La Tranche, France. This arrangement uses a pair of freewheels and a pair of motors. The pair of freewheels are placed to allow a rotation in opposite directions when each is powered by a motor. When either motor is not powered, rotation in that direction is prevented. Whilst this particular mechanism gives the capability of a programmable brake, it is a complex mechanism which is not robust and is prone to wear.

There is therefore a need to overcome the above drawbacks with existing arrangements for providing such selective braking and/or motion control in such applications.

Summary

In general terms, at least certain embodiments of the invention provide a simple mechanism which comprises a programmable limiting device, which can be applied to either a linear or a rotating mechanism. In a preferred embodiment, a brake unit is positioned on either side of a moving part, (e.g., a platform), in the direction of the axis of motion. The brakes are placed so that they can remain in contact with the platform by being held in place by an elastic unit (e.g., a spring). The brakes can be disengaged from the platform against the action of the elastic unit, by the use of a powered control system. The position of the brakes may be monitored using sensors. A mechanical arrangement can be created such that a brake would be pulled and thus deactivated when the platform moves away from the brake

According to a first aspect of this invention, there is provided a device for limiting movement comprising a stopper, support structure and a body whose motion is to be limited, the stopper unit supported on the support structure for movement relative thereto, and the body arranged for movement relative to the support structure, wherein the stopper is operable to engage the body so as to resist relative movement therebetween, the support structure blocking movement of the stopper in one direction of movement of the body, thereby resisting movement of the body in that direction.

The at least resisting may comprise stopping movement of the body.

The body to be braked may be embodied by a surface. The support structure may be embodied by a platform.

According to a second aspect of the invention, there is provided a programmable brake unit comprising:

(a) a surface so that the following parts would move relative to it,

(b) a platform, which is free to move relative to the said surface,

(c) a stopper unit positioned contiguously to the said platform, said stopper arranged to be actuated into frictional engagement with the said surface thus preventing movement of the said platform in the direction of the said actuated-stopper.

(d) an elastic element fixed to and between the said platform and the said stopper whereby urging the stopper unit to the said platform,

(e) a position sensor sensing directly or indirectly the movement of the said platform,

(f) a control unit to receive the position from the said sensor and control the actuation of the said stopper, whereby when the said stopper is inactive the said platform is free to move, and whereby actuating the said stopper will cause the said stopper to engage with the said surface so that movement of the said platform in the direction of the said stopper is prevented, and whereby the movement of the said stopper in the opposite direction is not affected and, as a result of the movement of the said platform away from the said actuated stopper would stretch the said elastic element and whereby the motion of the said platform is sensed by the said sensor and so that the said stopper may be deactivated by the said control unit and this will end the stopper's engagement and cause the stopper to be pulled to the said platform by the said elastic element, whereby the said stopper may be actuated again as the movement speed of the said platform comes to zero to prevent any movement of the said platform in the direction of the said stopper.

Optionally, two said stoppers are implemented and the said platform is sandwiched between them so that movement of the said platform can be restricted in both directions on a linear track.

Optionally, four said stoppers are used and located on all the sides if the said platform is squared so that movement of the said platform can be restricted in four directions on a plane.

Optionally, the actuation of the said stopper is provided by means such as electromagnetic, pneumatic or hydraulic power.

Optionally, the said elastic element is provided by a spring or any other energy storing mechanical element.

Optionally, the said motion sensor is replaced by a contact sensor between the said platform and the said stopper.

Optionally, the said stopper can have variable resistance to the movement relative to the said surface when actuated, thus allowing greater flexibility on the restrictions which can be programmed.

According to a third aspect of the invention, there is provided a programmable brake unit comprising:

(a) a body,

(b) a shaft, which is free to rotate relative to the said body, (c) a linkage mounted to the said shaft so that the said linkage is pivoted when the said shaft is rotated,

(d) a stopper unit positioned contiguously on the said linkage, said stopper is arranged to be actuated into frictional engagement with the said body, thereby preventing pivoting of the said linkage in the direction of the actuated said stopper.

(e) an elastic element fixed to and between the said linkage and the said stopper arranged to urge the stopper unit to the said linkage,

(f) a position sensor sensing directly or indirectly the rotation of the said shaft,

(g) a control unit to receive the position from the said sensor and control the actuation of the said stopper, whereby when the said stopper is being not activated so the said linkage and the said shaft are free to rotate, and whereby actuating the said stopper will cause the said stopper to engage with the said body and so that the pivoting of the said linkage in the direction of the said stopper is prevented, end whereby the pivoting of the said linkage in the opposite direction is not affected and, as a result of the pivoting of the said linkage away from the said actuated stopper and thus stretch the said elastic element, and whereby the rotation of the said shaft is sensed by the said sensor and so that the said stopper may be deactivated by the said control unit and this will end the stoppers engagement and cause the stopper to be pulled to the said link by the said elastic element, whereby the said stopper may be actuated again as the rotation speed of the said shaft comes to zero, to prevent any pivoting of the said linkage in the direction of the said stopper.

Optionally, two said stoppers are implemented and the said link is sandwiched between them so that pivoting of the said linkage can be restricted in both directions.

Optionally, the said shaft and the said linkage is built as one part. Optionally, the actuation of the said stopper is provided means such as electromagnetic, pneumatic or hydraulic.

Optionally, the said shaft rotation sensor is replaced by a contact sensor between the said linkage and the said stopper.

Optionally, the said stopper can have variable resistance to the movement relative to the said body when actuated, thus allowing additional restriction flexibility.

The or each stopper may comprise a stopper element and braking means.

The device may comprise sensing means operable to sense relative movement between the support structure and the or each stopper and, upon sensing relative movement other than in the direction blocked by the stopper, causing the stopper to disengage the body.

According to a fourth aspect of this invention, there is provided a device for selectively resisting rotation in each of two rotational directions, the apparatus comprising: a shaft arranged to rotate relative to a housing; a first stopper rotatable relative to the shaft and engagable by the shaft to be rotated thereby and therewith in one of the rotational directions whilst allowing rotation relative to the shaft in the respective other direction; a second stopper rotatable relative to the shaft and engagable by the shaft to be rotated thereby and therewith in the second of the rotational directions whilst allowing rotation relative to the shaft in the respective other direction; biasing means to bias each stopper into engagement with the shaft for rotation thereby and therewith; and braking means for selectively braking each of the stoppers relative to the housing, thereby selectively resisting rotation of the shaft in each of the two rotational directions.

The shaft may engage one or both stoppers by means of an abutment coupled to, or forming part of, that shaft that is arranged to abut a respective abutment coupled to, or forming part of each stopper. The abutting may be in a substantially tangential direction with respect to the axis of the shaft. The device may be arranged with the shaft abutment positioned circumferentially between the two stopper abutments. The biasing means may be arranged to bias each stopper abutment into abutment with the shaft abutment. The biasing means may be a resiliently extendible member extending between and coupled to each of the stopper. The biasing means may extend between each of the stopper abutments. It may extend though an aperture in the shaft abutment.

The or each stopper may comprise a surface in a radial plane extending at least partly around the shaft. The surface may be an annular disc. The braking means may be arranged to engage that surface. The braking means may be an electromagnet arranged to act on the surface and, optionally, draw the surface into face-to-face engagement with a surface of the electromagnet, thereby stopping rotation of the stopper relative to the braking means. The braking means may be fixed relative to the housing. At least part of thte stopper may be axially moveable into contact with the braking means when the braking means is operated to brake the stopper.

The device may comprise sensing means arranged to sense movement of the shaft relative to the housing. The device may include control means responsive to the sensing means sensing movement of the shaft relative to the housing in the first rotatable direction to operate the braking means such that it releases the second stopper to rotate, and responsive to the sensing means sensing movement of the shaft relative to the housing in the second rotatable direction to operate the braking means such that it releases the first stopper to rotate.

According to a fifth aspect of this invention, there is provided a method of operating a device as defined in any other aspect, the method including the steps of. a) operating the device to engage one of the stoppers such that motion in a first direction is braked; b) upon detecting motion in a direction opposite to the first direction operating the device such that the one stopper is disengaged and motion in that opposite direction is not braked.

In step (a) operating the device may include operating the braking means to engage the one stopper. In step (b) operating the device may include operating the braking means to disengage the one stopper.

In a sixth aspect of this invention there is provided a programmable brake apparatus for a vehicle, the apparatus comprising a device as defined in any other aspect and arranged to be coupled to the drivetrain of the vehicle and operable to selectively hinder or prevent movement of the vehicle in the forward and/or backward direction. The device may be arranged to operate to prevent movement of the vehicle in the backward direction and allow movement in the forward direction only when the vehicle is at, or coming to, rest; and may be arranged to operate to allow both forward and backward movement once forward movement or motion has been sensed. In a seventh aspect of this invention, there is provided a user-input device for use as part of a graphical-user interface, the user-input device comprising a device as defined in any other aspect and arranged to limit movement of at least part of the user-input device in correspondence with a cursor of the interface reaching the limit of an area of a display of the interface. Optional features of one aspect of the invention may be optional features of each other aspect of the invention.

Brief Description of the Drawings

A preferred embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic side view of a programmable brake presented in a linear type mechanism;

Figure 2 is a schematic side view of a programmable brake according to the in a revolute type mechanism; Figure 3 is a transverse section taken on the line A-A of FIG.2;

Figure 4 is a perspective view of an alternative programmable brake;

Figure 5 A is a perspective view of certain components of the alternative brake, those components shown spaced apart for clarity;

Figure 5B is the perspective view of Figure 5A, with the components fitted together for use and with certain of them coupled by a spring; and

Figures 6A and 6B are schematic views of the components of Figures 5 A and 5B showing how the arrangement of those components limits relative movement

therebetween and guards against over-stretching the spring.

Detailed Description of Example Embodiments

An example of programmable device for limiting movement that embodies the present invention is shown generally on FIGS. l , 2, 3 . Referring to the FIG1 ; A platform 2 is connected to a handle 1 , stands on support wheels 4 and thus is free to move over the surface 3. Two stoppers 5 are located on the opposite sides of the platform 2 and are held against the platform 2 by preloaded springs 6. The springs 6 are held, by means which are not shown, on each side to the stoppers 5.

The two stoppers 5, in the example, are implemented on electro-mechanical actuation where the stoppers 5 can be friction engaged against the surface 3 which, in this example, is made from a ferrite material (e.g. steel). The stoppers 5, are electro-magnets and can be independently in the "on" or "off status. In the "on" status, a stopper 5 is actuated (i.e. magnetized) by running a current through it, which would engage it against the surface 3, which would hold the actuated stopper 5 in place relative to the surface 3, as in this example, by means of friction, and thus block the movement of the platform 2 in the direction of the actuated stopper 5. In the "off status, no current is passing through the stopper 5 coil, thus it is not magnetized and is free to slide on the surface 3 without blocking the movement of the platform 2. Although the shown embodiment utilizes stoppers 5 on of the electro-magnetic type, those skilled in the art would appreciate that the stoppers could be of any other type or shape. A stopper 5 could be implemented on hydraulic or pneumatic technology, for example. The motion of the platform 2 should be sensed along the actuation of the stoppers 5 and accurately controlled in a manner known per se by digital control means such as a process computer, not shown.

In the present embodiment, the programmable brake mechanism can limit the linear motion of the platform 2 into one of four states; free motion, only-to-the-left, only- to-the-right and locked (i.e. no motion allowed). For the "free motion" state, both stoppers 5 are "off (i.e. not actuated) and they are free to move along the platform 2 as one unit. The state of "only-to-the-right motion" is achieved by turning "on" the stopper 5 which is on the left side of the platform 2 (i.e. left-stopper) as on FIG. 1 ; this would instantaneously engage the left-stopper 5 into frictional engagement with the cam surface 3 and lock its movement with respect to the surface and thus prevent the motion of the platform 2 in the direction of the actuated stopper. In this case, the platform 2 is still free to move in the right direction, away from the actuated left-stopper 5, and if it does, the movement is sensed by a control system via a motion sensor, and as the platform 2 is moving away from the actuated left-stopper 5, it can be deactivated, according to a control logic. After deactivation, the left-stopper 5 will be pulled mechanically by the loaded-spring 6 to the standby position where it is held against the body of the platform 2. The left-stopper 5 in its standby position on the linkage 4, can be actuated again to prevent the motion to the left of the platform 2, and it should be done according to a control algorithm. The only-to-the-left restriction is achieved in a similar manner to the only-to-the-right restriction, this time by actuating the stopper 5 on the opposite side (i.e. right-stopper 5 is the one on the right of the platform 2 as on FIG. l ). When locked status is required, then both right and left stoppers 5 should be switched "on", thus preventing the motion of the platform 2 to the right and to the left.

As a matter of example, the motion or position of the platform 2 can be sensed as shown on FIG 1 by the sensor 7. The embodiment can also be implemented without the sensor 7; for example movement of the platform 2 away from an actuated stopper can also be detected by a touch sensor 8 as shown on FIG 1 . This configuration without motion sensor may be applicable in emergency engaging mechanisms, for example. Also, the above configuration was described initializing springs as an elastic but the invention is not only limited to this solution and any elastic material can be used, such as rubber.

The following detailed description illustrates the invention by way of example and not by way of limitation. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. For example, various methods of fixing the housing and effecting movement of the actuator can be conceived. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. Many applications for the programmable limiting device may be used, such as for example, human computer interfaces, emergency limiting mechanisms, door opening systems, robot to robot interfaces, haptic devices and the like. These are merely illustrative.

An example of the previously described embodiment in a rotary implementation is shown on FIG 2-3. A linkage 9, mounted to the shaft 1 0 and secured using a bolt 1 1 and o-ring 12. This allows linkage 9 to rotate freely relative to linkage 13. The angular position of the linkage 9 relative to the linkage 13 is sensed by a sensor 14. Two stoppers 15 are located on two sides of the linkage 9 and held against linkage 9 by a loaded-spring 16. The spring 16 is held, by means which are not shown, on each end to the stoppers 15. In this particular example, the spring 16 is pre-loaded and passing freely through a hole in the linkage 9 and thus is not attached to the linkage 9. This design is used to show an embodiment where fewer components are used while providing simple pre-loading of the spring 16, compared to the linear mechanism which was described above, where two springs were used.

The two stoppers 5, in the example, are implemented with electro-mechanical actuation and consist of a friction disk 17, made from a ferrite material (e.g. steel), and secured to the linkage 9 using bolts 18. The stoppers 1 5, are electro-magnets and designed in a U shape with a wire winded around, not shown. The stoppers 15 can be independently in the "on" or "off status. In the "on" status, a stopper is actuated (i.e. magnetized) by running a current through the coil, this would engage it against the surface of the disk 17, which would hold the stopper in place relative to the surface of the disk 17, as in this example, by means of friction, and thus block the pivoting of the linkage 9 in the direction of the actuated stopper. In the "off status, no current is passing through the coil of a stopper, thus it is not magnetized and free to slide on the surface of the disk 17 along the movement of the linkage 9 without blocking it. Although the shown embodiment utilizes stoppers 15 as an electro-magnetic stopper, those skilled in the art would appreciate that the actuator could be of any other type or shape. The stopper 1 could be implemented on hydraulic or pneumatic technology, for example. The position of the shaft 10 should be sensed along the actuation of the stoppers 15 and accurately controlled in a manner known per se by digital control means such as a process computer, not shown.

The disclosed earlier programmable brake mechanism (FIG 2-3) can limit the rotation of the shaft 10 into one of the four statuses; (a) free rotation, (b) only-clockwise, (c) only-anti-clockwise and (d) locked (i.e. no rotation allowed). For the free status (a), both stoppers 1 are "off (i.e. not actuated) and they are free to move with linkage 9 as one unit. The status (b) - only-clockwise rotation is achieved by turning "on" the stopper 1 5 which is on the left side of the linkage 9 (i.e. left-stopper) as on FIG. 1 , this would instantaneously engage the left-stopper 15 into frictional engagement with the cam surface of the friction disk 17 and lock its surface relative movement and thus prevent the rotation of the linkage 9 in the direction of the actuated stopper, and prevent rotation of the shaft 10 in the anti-clockwise direction accordingly. In this case, the linkage 9 can still free to rotate in the clockwise direction, away from the actuated stopper, and if it does, its position is sensed by the control system via the position sensor 14, and as the linkage 9 is moving away from the actuated left-stopper 15, the stopper can be deactivated, according to a control logic. After the deactivation, the left-stopper will be pulled mechanically by the preloaded-spring 16 to the standby position where it is held against the body of the linkage 9. The left-stopper 15 in its standby position can be actuated again to prevent the anti-clockwise rotation of the linkage 9, and it should be done according to a control algorithm. The status (c) - only-anti-clockwise restriction is achieved in a similar matter described above, this time by actuating the stopper 15 on the right side of the linkage 9 (right-stopper 15) as on FIG 2-3. When status (d) - locked is required, then the right and the left stoppers 15 should be switched "on", thus preventing clockwise and anti-clockwise rotation of the shaft 7 and linkage 4 accordingly.

In this example the mechanism can also be implemented without the position sensor 9, as described in the linear example earlier, by embedding contact sensors between the linkage 4 and the stoppers 5.

A further embodiment is shown in Figure 4. In this embodiment, a programmable brake unit comprises a shaft 101 and a linkage 102, which are joined with a screw and are free to rotate as one unit relative to the body 103. The linkage is held between two stoppers 104, and positioned contiguously to them. Each stopper unit consists of the stopper part and a miniature commercial electromagnetic brake. Electromagnetic brakes were chosen for this embodiment because they provide high reaction torque per unit mass, are simple to operate and are cheap when compared to other brake types. The miniature brake consists of an armature plate 105 and a stator 106. The plate is free to rotate relative to the shaft while the stator is fixed to the body. The armature plates are connected to the stoppers through leaf springs (not shown), thus the rotational force is fully transmitted while a small axial motion is permitted. Some axial motion is required to allow movement (l mm gap) of the armature plate toward the stator during activation, due to the magnetic field resulting from electric current running inside the brake coil. This movement causes frictional engagement between the armature plate and the stator, preventing further rotation of the plate. The armature plate will be pulled back by the leaf springs when the brake is switched off. The cover plates 107 are designed to hold the parts together, house low-friction needle bearings to support the shaft and allow mounting for the encoder 108 which senses the rotation of the shaft. A spring, not shown in Figure 4 but visible in Figure 5B, is fixed to the two stoppers and passes through the linkage freely. The spring is preloaded, which puts initial force on the stoppers and keeps them in a "standby position", flush on either side of the linkage itself.

Finally, a safety mechanism to prevent spring overstretching is implemented as part of the stoppers assembly. This is shown in Figure 6. With reference to Figure 6, a "play mechanism" keeps the motion of the linkage within hard limits: in the event of one stopper being activated, movement away from the stopper is not restricted till the safety gap is reached, after which point the linkage collades with the fixed stopper, preventing further motion.

Turning now to operation, as described above, the programmable brake unit has a number of possible configuration modes and a control algorithm is required to operate the brake and switch between them. The brake shaft can be switched into one of the following configuration modes: no restriction (MA), fully-locked (M\) or part-locked (M2/M ), see Table I below. Brake Stopper Stopper Resulting Reaction torque

Mode A B angular

Table I

POSSI B LE LOCK I NG MODES FOR THE PROGRAMMA BLE B RA KE.

TR - TH E R ES ULTING R EACTION TORQUE, ΤΒ - THE MA XIMUM B RA K E FRICTION TORQUE, T_S - THE REACTION TORQUE PRODUCED B Y TH E

PRELOADED SPRING.

No restriction is achieved by switching stoppers A and B OFF and fully-locked is achieved by switching both stoppers ON (as in Fig. 1 ). The part-locked uni-directional configuration can be achieved by switching stopper A ON and B OFF (or vice versa). Once in the part-locked situation, correct brake operation requires reconfiguration of the stoppers to maintain the restriction while enabling motion in the unconstrained direction, which can be achieved by applying one of the following control schemes:

Velocity scheme: This restricts the rotation of the shaft in one direction but allows motion in the opposite direction, similar to a "ratchet" mechanism. In this mode, the control algorithm monitors the velocity of the shaft and activates the stoppers when the shaft velocity is zero to restrict rotation in the undesired direction, then switches them off when rotation in the allowed direction is detected. The operational mode of the brake is a function of the required angular velocity restriction ω_# and the monitored shaft angular velocity ω (clockwise rotation is positive), and can be summarized as follows:

Ml : ω < 0, ω_Β > 0

M4 : ω > 0, ω_Β > 0

3 : ω > 0, ω_β < 0

Μ 4 : ω < 0, ω_Β < 0 The advantage of this control scheme is that rotation of the shaft in the undesired direction is restricted while the shaft is free to turn in the opposite direction. The disadvantage is that reactivation of the brake may occur during the stopping transient, when the shaft acceleration is above a critical value, at which point the linkage would be stopped by the safety mechanism, as explained above. This can be resolved by applying a time delay before reactivation.

Position scheme: This restricts the rotation of the shaft when the shaft angle becomes larger or smaller than a predefined value. In this mode, the control algorithm monitors the shaft angle Φ and activates the relevant stopper once it crosses the restricted angle _R. In mathematical form:

The advantage of this scheme is that it restricts the rotation of the shaft within an area by only monitoring the rotation angle of the shaft. However, were shaft rotation to be fast enough to cause a penetration error (i.e. stopping to occur slightly within the restricted area due to e.g. finite sampling time), a small movement away from the activated stopper may not be sufficient to trigger a release of the brake. To overcome this limitation, both the position and velocity of the shaft are monitored in the present embodiment, as described in the following section.

Advanced position scheme: This restricts the rotation of the shaft when the shaft angle becomes larger or smaller than a predefined value and uses the velocity of the shaft for deactivation purposes. This logic can be summarized using the following equations:

In this scheme, by monitoring the shaft velocity, the controller would disengage the stoppers when the shaft turns in the direction of the unrestricted zone, irrespective of whether a penetration error has occurred.

Various applications of the arrangements described hereinabove are envisaged, these applications amounting to further embodiments.

In one group of applications, a programmable brake unit such as that described above with reference to Figures 4 is coupled to an electric motor such that one end of the shaft 101 of the brake unit is coupled to the output shaft of the motor to rotate therewith and the other end of the shaft 101 of the brake unit is coupled to provide drive to the application. In such an arrangement, the brake unit can be operated to hinder or prevent movement of the output shaft of the motor, in either or both directions, when the motor is not being powered.

For example, such an arrangement would be useful in an electric window mechanism for a car: when the motor is powered to either open or close the window, the brake unit is operated such that the motor is free to rotate and hence such that the window can be opened or closed (as the case may be); when the motor is not powered, the brake unit is operated such the motor shaft is prevented from rotating and such that the window is prevented from opening under its own weight.

In another example, such an arrangement would be useful in an electric or hybrid- electric vehicle. In such a vehicle, the programmable brake unit could be used to prevent the vehicle rolling backwards down a sloping road surface during the interval between the footbrake being disengaged and before the accelerator is pressed and the electric motor that powers the vehicle being effectively operated. It will be understood that in such an arrangement, the programmable brake unit would be operated as, or when, the vehicle comes to a stop, for example under the action of the vehicle's footbrake, and operated such that movement in a forward direction only is permitted by the

programmable brake unit. When the footbrake is disengaged, the effect of the

programmable brake unit would, as will be understood from the description above, be to prevent the vehicle rolling backwards. When the accelerator is pressed as the vehicle begins to move forwards, this would be sensed by the programmable brake unit and the brake unit would then be disengaged in the manner described hereinabove.

In another group of applications, the programmable brake unit can be used to provide feedback to a user in a man-machine interface. For example, the programmable brake unit could be incorporated into a computer mouse, coupled to the scroll wheel thereof and operated such that, for example, when a user scrolls to the bottom of a screen, the programmable brake unit operates to prevent the scroll wheel being moved any further in a downwards direction. This provides feedback to the user, through the mouse, that he or she has reached the bottom of the screen. The programmable brake unit would of course still allow the scroll wheel to be moved in an upwards direction, and would disengage, in the manner described hereinabove, upon sensing such movement to allow once more movement in both directions. The programmable brake unit could be operable in a corresponding manner to provide feedback when a user scrolls to the top of the screen.

In other applications, different forms of brake may be substituted for the electromagnetic brake 104 of the programmable brake unit described above with reference to Figures 4 to 6. For example, brakes may be used that allow rotation of the stoppers 104 relative to the body 103 to be slowed as well as stopped. An appropriate brake for such use may be a hydraulic brake. Such an arrangement may form part of exercise equipment in which a wound cable is coupled to the shaft 101 and the programmable brake unit operable to vary the resistance to the cable being unwound as part of an exercise routine.

Claims

CLAIMS:

1 . A device for limiting movement, the device comprising a stopper, support structure and a body whose movement is to be limited, the stopper supported on the support structure for movement relative thereto, and the body arranged for movement relative to the support structure, wherein the stopper is operable to engage the body so as to resist relative movement therebetween, the support structure blocking movement of the stopper in one direction of movement of the body, thereby resisting movement of the body in that direction.

2. A device for limiting movement according to claim 1 , wherein movement of the stopper in another direction of movement of the body is not blocked.

3. A device for limiting movement according to claim 1 or claim 2, and comprising two stoppers, each supported on the support structure for movement relative thereto, and each operable to engage the body so as to resist relative movement between the stoppers and the body, the support structure blocking movement of a first one of the stoppers in a first direction of movement of the body, thereby resisting movement of the body in that first direction; and the support structure blocking movement of the second one of the stoppers in a second direction of movement of the body, thereby resisting movement of the body in that second direction.

4. A device for limiting movement according to claim 3, wherein the first direction and the second direction are opposite directions, such as, for example, opposite linear directions or opposite rotational directions.

5. A device for limiting movement according to claim 3 or claim 4, wherein the first stopper is not blocked from movement in the second direction and the second stopper is not blocked from movement in the first direction.

6. A device for limiting movement according to any preceding claim and further comprising biasing means to bias the or each stopper into a position in which it is blocked by the support structure from movement in at least one respective direction of movement of the body; and optionally in with it is not blocked from movement in at least one other respective direction of movement of the body.

7. A device according to any preceding claim and comprising control means arranged to selectively engage the first and/or second stopper with the body.

8. A device according to any preceding claim wherein the body is mounted on the support structure.

9. A device according to any preceding claim and comprising sensing means operable to sense relative movement between the support structure and the or each stopper and, upon sensing relative movement other than in the direction blocked by the stopper, causing the stopper to disengage the body.

10. A device according to any preceding claim, wherein the support structure comprises a rotatable shaft, the body comprises a housing and the movement that is to be limited is relative rotational movement between the shaft and the housing, the device further comprising two stoppers, each comprising a stopper element and braking means, wherein: a first one of the stopper elements is rotatable relative to the shaft and engagable by the shaft to be rotated thereby and therewith in one of two rotational directions whilst allowing rotation relative to the shaft in the respective other direction; a second one of the stopper elements is rotatable relative to the shaft and engagable by the shaft to be rotated thereby and therewith in the second of the rotational directions whilst allowing rotation relative to the shaft in the respective other direction; wherein the device further comprises biasing means to bias each element into engagement with the shaft for rotation thereby and therewith; and wherein the braking means are operable to selectively brake the respective stopper element relative to the housing, thereby selectively resisting rotation of the shaft relative to the housing in a respective one of the two rotational directions.

1 1 . A programmable brake unit comprising:

(g) a surface so that the following parts would move relative to it,

(h) a platform, which is free to move relative to the said surface,

(i) a stopper unit positioned contiguously to the said platform, thereby when the said stopper actuated into frictional engagement with the said surface thus preventing movement of the said platform in the direction of the said actuated-stopper.

(j) an elastic element fixed to and between the said platform and the said stopper whereby urging the stopper unit to the said platform,

(k) a position sensor sensing directly or indirectly the movement of the said platform,

(1) a control unit to receive the position from the said sensor and control the actuation of the said stopper. whereby when the said stopper is being not activated so the said platform is free to move, and whereby actuating the said stopper will cause the said stopper to engage with the said surface and so that the movement of the said platform in the direction of the said stopper is prevented, end whereby the movement of the said stopper in the opposite direction is not affected and, as a result of the movement of the said platform away from the said actuated stopper would stretch the said elastic element, and whereby the motion of the said platform is sensed by the said sensor and so that the said stopper may be deactivated by the said control unit and this will end the stoppers engagement and cause the stopper to be pulled to the said platform by the said elastic element, whereby the said stopper may be actuated again as the movement speed of the said platform comes to zero, to prevent any movement of the said platform in the direction of the said stopper,

12. A programmable brake unit according to claim 9, in which two said stoppers are implemented and the said platform is sandwiched between them so that movement of the said platform can be restricted in both directions on a linear track.

13. A programmable brake unit according to claim 9, in which four said stoppers are used and located on all the sides if the said platform is squared so that movement of the said platform can be restricted in four directions on a plane motion.

14. A programmable brake unit according to claim 9, in which the actuation of the said stopper is provided means such as electromagnetic, pneumatic or hydraulic.

15. A programmable brake unit according to claim 9, in which the said elastic element is provided by a spring or any other energy storing mechanical element.

16. A programmable brake unit according to any preceding claim, in which the said motion sensor is replaced by a contact sensor between the said platform and the said stopper.

17. A programmable brake unit according to claims 9 to 14, in which the said stopper can have variable resistance to the movement relative to the said surface when actuated, thus allowing additional restriction flexibility.

18. A programmable brake unit comprising:

(h) a body,

(i) a shaft, which is free to rotate relative to the said body, j) a linkage mounted to the said shaft so that the said linkage is pivoted when the said shaft is rotated, (k) a stopper unit positioned contiguously on the said linkage, thereby when the said stopper actuated into frictional engagement with the said body thus preventing pivoting of the said linkage in the direction of the actuated said stopper.

(1) an elastic element fixed to and between the said linkage and the said stopper whereby urging the stopper unit to the said linkage,

(m) a position sensor sensing directly or indirectly the rotation of the said shaft,

(n) a control unit to receive the position from the said sensor and control the actuation of the said stopper. whereby when the said stopper is being not activated so the said linkage and the said shaft are free to rotate, and whereby actuating the said stopper will cause the said stopper to engage with the said body and so that the pivoting of the said linkage in the direction of the said stopper is prevented, end whereby the pivoting of the said linkage in the opposite direction is not affected and, as a result of the pivoting of the said linkage away from the said actuated stopper and thus stretch the said elastic element, and whereby the rotation of the said shaft is sensed by the said sensor and so that the said stopper may be deactivated by the said control unit and this will end the stoppers engagement and cause the stopper to be pulled to the said link by the said elastic element, whereby the said stopper may be actuated again as the rotation speed of the said shaft comes to zero, to prevent any pivoting of the said linkage in the direction of the said stopper.

19. A programmable brake unit according to claim 16, in which two said stoppers are implemented and the said link is sandwiched between them so that pivoting of the said linkage can be restricted in both directions.

20. A programmable brake unit according to claim 16, in which the said shaft and the said linkage is built as one part.

21. A programmable brake unit according to claim 16, in which the actuation of the said stopper is provided means such as electromagnetic, pneumatic or hydraulic.

22. A programmable brake unit according to claim 16, in which the said elastic element is provided by a spring or any other energy storing mechanical element.

23. A programmable brake unit according to any preceding claim, in which the said shaft rotation sensor is replaced by a contact sensor between the said linkage and the said stopper.

24. A programmable brake unit according to claims 14 to 21, in which the said stopper can have variable resistance to the movement relative to the said body when actuated, thus allowing additional restriction flexibility.

25. A method of operating a device or a programmable brake according to any preceding claim, the method including the steps of: a) operating the device to engage one of the stoppers such that motion in a first direction is braked; b) upon detecting motion in a direction opposite to the first direction operating the device such that the one stopper is disengaged and motion in that opposite direction is not braked.