A METHOD AND A DRIVE ASSEMBLY FOR OPERATING AND LOCKING COMPONENT MEMBERS OF ELECTRICALLY OPERATED PROSTHESES, MANIPULATORS AND LIKE DEVICES

Abstract: A drive unit for electrically driven prostheses, manipulators and the like, for example, the gripping members of an artificial arm or industrial robot, comprises an electrical drive motor (2) having an output shaft which drives an active component, for example a gripping means, via a transmission arrangement (4). The output shaft (7a) of a brake-motor (7) has arranged thereon a sleeve provided with a part having a right-hand screw thread and a part having a left-hand screw thread in engagement with brake means such as shoes (8, 9) which upon activation of the brake-motor engage a brake disk (6a) connected to the output shaft (2a) of the drive motor. The brake-motor is activated upon completion of the movement of the drive motor and therewith locks the active component in the position to which it has been moved without the occurrence of play.

Description: A method and a drive assembly for operating and locking component members of electrically operated prostheses, manipulators and like devices Field of Invention The present invention relates to a method of operating and locking component members of electrically operated prostheses, manipulators and like devices, such as the gripping elements of artificial arms and robots in which there is used a drive motor from which movement is transferred to said component member via transmission means for the purpose of effecting movement of said member. The invention also relates to a drive assembly for use when carrying out the method. Prostheses are often operated with the aid of so- called myo-signals, which involve the placing of electrodes in the region of the muscles to be used in effecting a given movement of the prosthesis. Upon activation of the muscle there is generated an electric signal which is captured by the electrode and utilised to activate the prosthesis drive unit. Various types of active components in orthosis/ prosthesis for upper and lower extremities are controlled with the aid of myo-signals. Hand hook and elbow consti¬ tute examples of such active components. The invention can also be applied, however, to various kinds of manipulators and like devices, for example robotic gripping means, with which control signals other than myo-signals are used. Background Art Various kinds of prostheses drive systems are known to the art. For example, there is described in Austrian Patent Specification No. 338,410 (Viennatone) a gear mechanism for an orthosis, prosthesis or like device in which drive movement is effected with the aid of a left-hand and a right-hand thread. DE-A-24 26 787 (Forschungsinstitut fϋr Orthopadie-Technik) describes a safety device for an artificial hand with which there is used a separate latching means for holding the fingers of the prosthesis in their closed position. One serious disadvantage with previously known prostheses of this and similar kinds in which a drive motor is controlled to produce movement in the artificial component is that it is not possible to obtain distinct positioning of the active component. The cause hereof is related to the intrinsic inertia of the system, which prevents the component from being stopped in precisely the correct position. A further, related disadvantage is that it is not possible to eliminate play in the known prosthesis. Neither is it possible as a rule to readily prize or force a prosthesis which has inadvertently -locked, this possibility being of extreme importance with most types of prostheses. As will be understood when a prosthesis locks in a certain position and cannot be readily prized, free, the attempts made to force the prosthesis may result in serious damage and injury. Another disadvantage encountered with the majority of hitherto known prostheses is that in order to function satisfactorily they must be manufactured to extremely accurate tolerances. Object of the Invention Accordingly one object of the invention is to provide a method of the-aforesaid kind which avoids the aforementioned disadvantages encountered with known drive systems and which enables the active elements of the prosthesis to be positioned accurately without losing, for example, the gripping power of such elements as a result of play in the prosthesis or the like. A further object is to provide a drive system of the aforesaid kind which enables the active component to be readily prized free or forced even when in a locked position. Another, important object is to provide a drive system for prostheses, manipulators and like devices which can be controlled electronically in a simple and reliable fashion and which can thereby be adapted more readily to the varying requirements demanded in certain contexts, for example, to different patient categories and the environment in which a robot is to work. A further object is to provide an operationally reliable drive and control system which can be manufactured without requiring accurate manufacturing tolerances in respect of the different components of the device. Brief Disclosure of the Invention These and other objects are fulfilled by a method according to the invention which in its widest aspects is characterized by in addition to the drive motor also using a brake-motor and activating said brake-motor during the final stage of movement for locking said component member in the position to which it has been moved, or subsequent to the completion of said movement. The use in accordance with the invention of a separate brake-motor which produces precise locking of the active component in an adopted position enables the active component to be positioned or oriented in a distinct and play-free fashion. The brake-motor also enables the active component member to be forced free when so required. The separate electric motors for effecting the respective driving and locking movements means that the arrangement as a whole can be given a simple and robust form, which in turn results in a reliable function without requiring manufacturing tolerances. Normally the drive movement is obtained through a series-motor, and consequently the applied current will increase when movement of the active component meets with resistance, for example, when said component grips an object. In a preferred embodiment of the invention this fact is utilised to guide the brake-motor, by arranging for said motor to be activated when the strength of the current supplied to the drive motor exceeds a given value. Alternatively, a brake-motor start signal can be transmitted when the movement of the active component ceases or begins to cease, for example, when gripping an object. In one particular application of the invention for guiding and controlling prostheses in which myo- signals are used in a known manner to control movement of the drive motor, such myo-signals are also used to control the brake-motor. This affords particular advantages when the brake-motor is to be activated to release the active component from a locked position, i.e. the brake- motor is caused to rotate in a direction opposite to the rotational direction in which the locked state was achieved. The invention also relates to a drive assembly for operating electrically operated prostheses, manipulators and the like, for example the gripping elements of artificial arms and robots, the drive assembly including an electric drivemotor having an output shaft, a trans- mission means for transmitting movement of the output shaft to a drive shaft associated with an active component member, for example a gripping instrument, said drive unit being characterized by an electrically operated brake- motor having an output shaft which co-acts with brake means arranged to lock the active component in an adopted position by engagement with an element operatively connected to the drive-motor output shaft, and in that control means are provided for activating the brake- motor in the latter stages of the movement of said active component or subsequent to the completion of said movement. In the case of an embodiment preferred in practice the brake-motor output shaft carries a sleeve having a part provided with a right-hand screw thread in self- braking engagement with one brake means such as a shoe, and a part provided with a left-hand screw thread in self-braking engagement with another brake means such as a shoe. This provides a mechanically simple and reliable arrangement capable of rapidly applying powerful braking forces. The self-braking or irreversible features of the screw threaded sleeve parts means that the braking force will be maintained despite interruption of the drive current to the brake-motor immediately the brake means have been applied, thereby minimising the current consumed by the drive and brake units. One problem with the described arrangement, however, is that the torque generated by the brake-motor is normally not sufficient to release the brake means such as shoes when reversing the direction of rotation. This problem is solved, however, with a preferred embodiment of the invention by providing on the brake- motor shaft an eccentric abutment element which when rotating the brake-motor shaft in the opposite direction moves through a dead space corresponding to approximately half of a revolution and then exerts an impact force on an element associated with the aforesaid shaft sleeve. This impact force is sufficient to break the self-braking effect, whereafter the brake means can be moved to their release position without difficulty. In accordance with another embodiment of the invention the drive-motor output shaft has arranged concentrically thereon a brake drum having a brake disk against the brake shoes engage. Despite its simplicity in design, a disk brake of this kind is highly effective. Furthermore, the brake drum shaft may partially enclose the drive motor, which in practice means that the two motors, namely the drive motor and the brake- motor, are positioned close to one another, thereby utilising the space available in the best possible manner, this space normally being restricted in a prosthesis of the kind in question. In other words the invention provides a particularly compact drive and brake assembly. In order to provide for effective control of both drive and brake-motors, the control means may include a sequence part having two or more derivation units for applying and releasing the brake at a desired moment in time, and one or more delay circuits arranged to prevent movement of the drive motor before the brake has been released and to prevent play before the -brake has engaged. Derivation units and delay circuits of the afore¬ said kind constitute simple and inexpensive electronic components, which can be used to advantage in a drive and brake assembly according to the invention. In addition to prostheses a drive and brake assembly according to the invention can also be used to advantage in many other contexts, for exampl , with various types of manipulator, such as robots and like devices. In this case the control signals used to activate the two motors are normally produced from a different source, insomuch as myo-signals are not used to control said motors. The invention will now be described in more detail with reference to an embodiment thereof illustrated in the accompanying drawings. 1 Brief description of the Drawings Figure 1 is a cross-sectional view of a drive assembly or unit according to the invention for use in conjunction, for example, with an artificial arm or han .. Figure 2 is a sectional view taken on the line II-II in Figure 1. Figure 3 is an end view of part of the drive unit illustrated in Figure 2. Figure 4 illustrates schematically an artificial hand having rigid three-point engagement and incorporating a drive unit according to the invention. Figure 5 is a side view of the artificial hand illustrated in Figure 4. Figure 6 is a block schematic illustrating an example of electronic components for a drive unit accord¬ ing to the invention. Figure 7 is a diagram illustrating examples of control signals used for controlling the drive unit. Description of a Preferred Embodiment Figures 1-3 illustrate a drive assembly or unit 1 capable of being used, for example, in an electrically operated artificial terminal device such as a hand or a an industrial robot. The drive unit includes an electric motor 2 having an output shaft 2a. The drive motor may be of a more or less conventional kind and is driven by a six volt battery. The output shaft 2a carries a gear belt drive 2b comprising a belt 3 which extends over a belt wheel 4b on an input shaft 4a of a planet gear box 4. The output shaft 4c carries a gear belt drive 4d incorporating a gear belt 5. Arranged concentrically on the output shaft 2a of the electric motor is a drum 6 which embraces part of the drive motor 2. Arranged centrally on the drum 6 peripherally therearound is a radially extending brake disk 6a. Located beneath the drive motor 2 is a brake- motor 7, the output shaft 7a of which carries a shaft sleeve 7b having a part provided with a left-hand screw thread and a part provided with a right-hand screw thread. Each of these sleeve parts is in self-sustaining engage¬ ment with a respective brake shoe 8 and 9 arranged to engage the brake disk 6a on the drum 6 upon rotation of the brake-motor in a first direction. As will be seen from Figure 3, also arranged on the brake-motor shaft 7a is an eccentric abutment or hammer means 7c which when the shaft 7a is rotated in the reverse direction, to release the brake shoes 8, 9, travels through a dead space corresponding to approxima¬ tely one half of a revolution and then exerts an impact force against an element 7b' mounted on the shaft sleeve 7b. Figures 4 and 5 illustrate an electrical hand prosthesis 10 having a rigid three-point grip. The gear belt 5 on the output shaft 4c of the gearbox 4 extends over a gear wheel or sprocket wheel 11 associated with the movable finger 13 of the prosthesis. This arrangement enables the finger 13 to be moved into engagement with a movably connected thumb 14 via a link 15. Upon completion of the movement of the finger 13 towards the thumb 14 - which takes place subsequent to activating the drive motor 2 - the brake-motor 7 is activated causing the brake shoes 8, 9 to move rapidly towards one another and engage the brake disk 6a on the drum 6, thereby accurately locking the finger 13 and the thumb 14 in their adopted positions in the absence of any play. Both the brake-motor 7 and the drive motor 2 are then immediately deactivated, the locking engagement being maintained through the self-sustaining effect provided by the screw engagement between the brake shoes 8 and 9, respectively, and the corresponding screw- threaded part of the shaft sleeve 7b. When wishing to release the finger grip, the brake-motor is activated for movement in the opposite direction - which can be effected with the use of myo- impulses - whereupon the eccentric hammer element 7a illustrated in Figure 3 exerts the aforesaid impact force on the sleeve part 7b 1 . " Subsequent to releasing the brake shoes 8, 9 from the brake disk 6a the drive motor 2 is activated in the opposite direction, to reverse the movement of the finger 13 and the thumb 14. As will be seen from the block diagram illustrated in Figure 6 the control means includes a sequence part comprising four derivation units for detecting the initial and final stages of a gripping movement. The diagram shown in Figure 7 illustrates these four signals under B. The function of these signals is to release and to apply the brake at the correct moment in time. As a rule the brake shall be opened prior to the drive motor 2 obtaining a movement signal when the movable component is activated and the brake shall be applied when a negative derivative of the myo-signal is detected. The current supply to the brake-motor constitutes an amplification of the time derivative of the myo-signal. As will be seen from the block diagram in Figure , 6, the drive motor 2 incorporates delay circuits which are effective to prevent movement before the brake has been deactivated and to prevent play before the brake has been activated. When wishing to grip an object with the aid of the prosthesis the patient stretches (contracts) the muscle on the upper or lower side of either arm. This muscle contraction gives rise to a myo-signal, which activates the drive motor. When the patient senses that the prosthesis grips around the object (i.e. the- power is built-up) , he relaxes the aforesaid muscle causing a short pulse to be sent to the brake motor. Thus, the current applied to the brake-motor constitutes an amplification of the time derivative of the myo-signal. The brake shoes engage the brake disk so that the grip achieved by the prosthesis is free from play. The current to the drive motor is not interrupted until the short . current pulse to the brake-motor terminates. The control electronics incorporates a final stage for the drive motor and a final stage for the brake- motor. The final stage of the drive motor is suitably supplemented with a so-called battery saving circuit, which prevents unnecessary current consumption upon contraction of a muscle. The battery saving circuit thus ensures that the drive motor is never activated in excess of a pre-determined time period, for example 1.5 seconds. The various active components of the circuits, including associated capacitors, are suitably miniatu- rised in practice, and preferably even more discrete. This type of circuit is normally designated a hybrid circuit. For the sake of completeness it should be mentioned that the current applied to the drive motor is an amplification of the myo-signal with a given time delay. A myo-signal always corresponds to a muscle contraction, this contraction generating a positive or a negative myo-signal, depending upon whether said contraction involves a muscle on the upper or the lower side of the arm, which in turn delivers current for driving the motor in one or the other direction. As an alternative to the embodiment described above the brake disk can be provided with a number of holes (not shown) and instead of using brake shoes engaging the disk a pin member (not shown) can be brought to enter one of the holes to accomplish braking. Said pin member is then operated by the brake-motor via suitable means such as screw threads. Industrial application The aforedescribed drive assembly or unit provided with a brake-motor can be applied in many other connections, for example, with various types of manipulator, such as industrial robots and like devices. The principle utilised to activate and de-activate the two motors is therewith substantially the same, even though the actual guide signals can be produced in different ways, depending upon the environment or circumstances.

Claims: Claims 1. A method of operating and locking components of electrically operated prostheses, manipulators and the like, for example, the gripping means of an artificial arm or a robot, in which there is used a drive motor from which movement is transmitted to said component via transmitting means for the purpose of effecting movement of said member, c h a r a c t e r i z e d by further using a brake-motor which is activated during the final s-tage of the movement for locking the component in the position to which it is moved, or subsequent to completing said movement. 2. A method according to Claim 1, c h a r a c t e¬ r i z e d by activating the brake-motor when the strength of the current applied to the drive motor exceeds a pre- determined value. 3. A method according to Claim 1 or 2 for operating prostheses in which myo-signals are used to control movement of the drive motor, c h a r a c t e r i z e d by also utilising myo-signals to control the brake-motor. 4. A drive assembly for electrically operated prostheses, manipulators and the like, for example, the gripping elements of an artificial arm or robot, said drive assembly comprising an electrically driven motor (2) having an output shaft (2a) , a transmission means (4) for transmitting movement of the output shaft (2a) to a drive shaft of an active component, for example a gripping means (13) c h a c r a σ t e r i z e d by an electrically operated brake-motor (7) having an output shaft (7a) which co-acts with brake means (8, 9) adapted to lock the active component (13) in an adopted position by engagement with a member (6a) operatively connected to the output shaft (2a) of the drive motor; and by control means adapted to activate the brake-motor in the final stage of movement of said active component or upon completion of said movement. 5. A drive assembly according to Claim 4, c h a r a c- t e r i z e d in that the output shaft (7a) of the brake- motor has arranged thereon a sleeve (7b) having a first part provided with a right-hand screw thread in self- sustaining engagement with one brake means such as a shoe (e.g. 8) and a second part provided with a left-hand screw thread in self-sustaining engagement with another brake means such as a shoe (e.g. 9) . 6. A drive assembly according to Claim 5, c h a r a c¬ t e r i z e d in that the output shaft (7a) of the brake- motor (7) has arranged thereon an eccentric abutment element (7c) which when reversing the direction of rotation of said shaft for releasing the brake shoes (8, 9) is arranged to travel through dead space corresponding to approximately one half of a revolution and to then exert an impact force on a part (7b') associated with the shaft sleeve (7b) . 7. A drive assembly according to any one of Claims 4-6, c h a r a c t e r i z e d in that the output shaft (2a) of the drive motor (2) has arranged thereon a brake disk (6a) which is concentrical to the brake drum (6) and against which the brake means (8, 9) engage. 8. A drive assembly according to Claim 7, c h a r a c¬ t e r i z e d in that the brake drum (6) embraces part of the drive motor (2) . 9. A drive assembly according to any one of Claims 4-8, c h a r a c t e r i z e d in that the control means comprises a sequence part having two or more deriving units for releasing and applying the brake at a desired moment in time, and one or more delay circuits for pre¬ venting movement of the drive motor before the brake has been released and to prevent play from occurring prior to the brake engaging.

Inventors: HOLMQVIST TORBJOERN, PERSSON ULF, HOLMQVIST, TORBJOERN, PERSSON, ULF
Applicants: SVENSK HANDIKAPPTEKNIK, S. H. SVENSK HANDIKAPPTEKNIK AB
Application year: 1985
Main classification: A61F2
IPC codes: A61F2, B25J9, B25J13, B25J15, B25J19, H02K7