Abstract:
A power switching mechanism for selectively connecting a robotic system having two-degrees-of-freedom power input to a robot tool having a plurality of actuators. The two-degrees-of-freedom power input comprises a translation power input and a power shaft rotation input. The switching mechanism comprises an axially displaceable connector mounted to the power shaft rotation input for rotating therewith. An indexing mechanism is connected to the power shaft rotation input and is axially movable sequentially between a neutral position and an actuator engaging position for each actuator. The axially displaceable connector engages any one of the actuators in response to movement of the axial translation of the two-degrees-of-freedom power input.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a Continuation in Part of patent application Ser. No. 09/579,493, dated May 30, 2000, by Applicants, the subject matter of which is incorporated herewith by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates to a power switching mechanism for use in robotic applications and, more specifically, for selectively connecting a robotic system to a robot tool.  
         BACKGROUND OF THE INVENTION  
         [0003]    Many different types and forms of gripping mechanisms are known, providing a variety of functions and uses. Some gripping mechanisms are designed for specific tasks, they are simple, robust, easy to manufacture and lead to simple control schemes. However, they are not flexible and a new gripping mechanism must be designed for each given task. These gripping mechanisms have only a few degrees of freedom and are widely used in industry. Other gripping mechanisms are more flexible and can perform several different tasks. However, they are difficult to manufacture, lead to complex control schemes, include several actuators and can provide only small gripping forces. These gripping mechanisms have several degrees of freedom.  
           [0004]    Finally, other gripping mechanisms have an architecture which combines the latter two cases, taking advantage of both through the concept of underactuation. Their design is based on a large number of degrees of freedom but with a reduced number of actuators. Indeed, underactuated gripping mechanisms are defined as those which have fewer actuators than the degree of freedom. This leads to flexible gripping mechanisms without the complexity associated with a large number of actuators.  
           [0005]    Underactuation can be achieved using different structural mechanisms. A typical example is described in the Applicants&#39; U.S. Pat. No. 5,762,390, issued on Jun. 9, 1998. A mechanical gripper, described in this patent, has three fingers and three phalanges per finger. The three pivotable phalanges are actuated by one actuator in a flexible and versatile gripping action of three degrees of freedom. The fingers are robust and can provide large gripping forces and perform power grasps and pinch grasps. An additional mechanism is provided to maintain the last phalanx orthogonal to the palm in order to allow the gripper to perform pinch grasps on objects of different sizes. The mechanical gripper including the limited number of actuators permits the fingers to bend independently so that, by actuating some of the actuators and not actuating others, different co-operative bending relationships are achieved.  
           [0006]    In addition to the underactuation between the phalanges of a finger, it is also possible to obtain underactuation between the fingers of a gripping mechanism. This will further decrease the number of actuators while maintaining the same number of degree of freedom. This principle has been disclosed for the actuation of many fingers, for example, in U.S. Pat. No. 5,378,033 to Guo et al. and in the literature, see, for example, the article by G. Guo, X. Qian and W. A. Gruver, “A SINGLE-DOF MULTI-FUNCTION PROSTHETIC HAND MECHANISM WITH AN AUTOMATICALLY VARIABLE SPEED TRANSMISSION”, published in the proceedings of the ASME mechanism conference, Phoenix, Vol. DE-45, pp. 149-154, 1992, and the article by M. Rakik entitled “MULTI-FINGERED ROBOT HAND WITH SELF-ADAPTABILITY”, published in Robotics and Computer-Integrated Manufacturing, Vol. 5, No.2-3, pp. 269-276, 1989. In these references, each of the fingers has only one degree of freedom, i.e., the motion of the phalanges is coupled. The combination of the underactuation of the phalanges of a finger and the fingers of a hand is disclosed in the Applicant&#39;s United States Patent. The underactuation between the fingers is performed with the help of a one-input/multi-output differential. The concept of this differential has been introduced in the Applicant&#39;s United States Patent using a lever for two outputs.  
           [0007]    It is also possible to orient the fingers with respect to one another (i.e., motion about an axis perpendicular to the palm of the gripping mechanism) with only one actuator by coupling their orientation. This is possible through the use of four-bar mechanisms that connect the base of the fingers. This decreases the number of degrees of the actuation and freedom of the system. This type of coupling has already been suggested in the Applicant&#39;s United States Patent and is provided by gears in U.S. Pat. No. 3,901,547 to Skinner II, and by grooves in the Guo et al. patent.  
           [0008]    In order to achieve this underactuation between the fingers in a differential gripping mechanism, the force of the actuator is to be distributed between the fingers. If a finger grasps an object, the actuator will continue its motion and the other fingers will continue to close with the help of the differential mechanism. Nevertheless, this principle associated with a differential mechanism sometimes limits the performance of the gripping mechanism especially in pinch grasps. It may be desirable, for example, to use only two fingers to perform a pinch grasp and prevent the remainder of the fingers from closing which may potentially disturb the grasp. This is not a problem with a gripping mechanism having multiple actuators because each finger is controllably actuated independently.  
           [0009]    Therefore, there exists a need for improved gripping mechanisms which are underactuated between fingers using differential mechanisms and adapted to deactivate predetermined fingers in a closing action when it is desired.  
           [0010]    It is also desirable to self-lock the fingers when a gripping mechanism grasps an object. It is especially important when a differential mechanism is used for underactuation between the fingers. An external force acting on one of the fingers may cause a displacement not only of the finger receiving the force but also of the remainder of the fingers because all the fingers are associated with the differential mechanism. A lever differential mechanism as described in the prior art is not able to provide the finger self-locking function. Therefore, there exists a need for an actuation system for gripping mechanisms underactuated between fingers, which provides a finger self-locking function.  
         SUMMARY OF THE INVENTION  
         [0011]    It is an object of the present invention to provide a power switching mechanism for connecting a robot system having plural degrees of freedom to a robot tool having plural actuators.  
           [0012]    Therefore, in accordance with the present invention, there is provided a power switching mechanism for selectively connecting a robotic system having a two-degrees-of-freedom power input to a robot tool having a plurality of actuators, with said two-degrees-of-freedom power input comprising a translation power input and a power shaft rotation input, said switching mechanism comprising:  
           [0013]    an axially displaceable connector mounted to said power shaft rotation input for rotating therewith;  
           [0014]    an indexing mechanism connected to said power shaft rotation input and axially movable sequentially between a neutral position and an actuator engaging position for each said actuator;  
           [0015]    wherein the axially displaceable connector engages any one of said actuators in response to movement of the axial translation of the two-degree of freedom power input. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    Having thus described the general nature of the present invention, reference will now be made to the preferred embodiments of the invention by way of examples and the accompanying drawings, in which:  
         [0017]    [0017]FIG. 1 is a perspective view of the gripping mechanism incorporating another embodiment of the invention, which is a passive tool without actuators;  
         [0018]    [0018]FIG. 2 is a partially sectional perspective view of the embodiment in FIG. 1, showing a switching mechanism used for selectively coupling the passive tool with an external driving apparatus;  
         [0019]    [0019]FIG. 3 is a perspective view of a Geneva mechanism connected to the orienting mechanism and used in the embodiment in FIG. 1; and  
         [0020]    [0020]FIG. 4 is a schematic view of an unwrapped pattern for an indexing ring of the switching mechanism. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    In a preferred embodiment as shown in FIGS. 1 and 2, a gripping mechanism is a passive tool generally shown at  200  and is adapted to be attached and actuated by an external apparatus (not shown). This apparatus can rotate and advance a socket that operates the passive tool, i.e., the gripping mechanism. Therefore, the two motors and the mechanisms that typically drive a differential  26  and an orientation transmission  30  are replaced by an interface, which comprise a power switching mechanism  204  and a Geneva mechanism  202 .  
         [0022]    The external driving apparatus generally includes a socket that is able to rotate and advance. Therefore, two degrees of actuation are available. The rotation of the socket can provide a large torque and power, and can rotate in both directions. The advance of the socket provides a smaller force and it is compliant.  
         [0023]    In FIG. 2, the opening/closing and orientation of the fingers of the gripping mechanism are performed by the socket torque. The switching of the power of the socket torque from the open orientation and vice versa is performed by the socket advance with the help of an indexing mechanism. The power of the socket torque is transmitted to a shaft  208  via a male connector  210  which engages the socket of the external driving apparatus (not shown). The power of the shaft  208  is transmitted to the socket  92  or the socket  228  through a male connector  212 . The shaft  208  is free to rotate and translate in the hole of the plate  84 . An indexing ring  214  is free to rotate but fixed in translation on the shaft  208 . Indexing pins  216  are attached to a housing  206  of the switching mechanism  204  and are inserted in the grooves of the indexing ring  214 . A compression spring  218  is inserted on the shaft  208 , between the plate  84  and a shoulder (not shown) on the shaft  208 . The indexing mechanism works as follows. The compression spring  218  pushes to keep the shaft  208  towards the bottom position in which the indexing ring  214  is also towards the bottom position, and the indexing pins  216 , are inserted in the grooves of the indexing ring  214  at positions  220 . The motion of the indexing ring  214  is guided by the indexing pins  216  via the grooves in the indexing ring  214 . When the driving apparatus socket pushes on the shaft  208  via the male connector  210 , the shaft  208  advances against spring  218 . This advance is stopped by the indexing pins  216  that are at position  222  in the grooves of the indexing ring  214 . At position  222 , the male connector  212  is inserted in socket  228 . Then, if the driving apparatus socket torque is activated, the Geneva mechanism  202 , therefore, the orienting mechanism  30  (see FIG. 3) will be activated. If the driving apparatus socket releases its pushing action, the compression spring  218  will push the shaft  208  towards the bottom position until the indexing pins  216  are at position  224  in the grooves of the indexing ring  214 . As best illustrated in FIG. 2, the male connector  212  is in a neutral position when the indexing pins are in the slots  220  or  224 . If the driving apparatus socket pushes again on the shaft  208  via the male connector  210 , the shaft  208  advances against spring  218 . This advance is stopped by the indexing pins  216  that are at position  226  in the grooves of the indexing ring  214 . At position  226 , the male connector  212  is inserted in the socket  92 . Then, if the driving apparatus socket torque is activated, the opening and closing mechanism which is the differential  26  of the gripping mechanism is activated. If the driving apparatus socket releases its pushing action, the spring  218  will push the shaft  208  towards its bottom position until the indexing pins  216  are at position  220  in the grooves of the indexing ring to close the cycle. To switch between the two tasks, this cycle is infinitely repeated. The sockets  92  and  228  and the male connector  212  are machined for easy insertion.  
         [0024]    A Geneva mechanism  202 , as shown in FIG. 3, is used to drive an orientation shaft  164  in order to obtain predetermined self-locked orientations of the fingers of the gripping mechanism  20 . The shaft  230 , the driver  232 , the pin  234  and the locking disc  236  are attached to form the input portion. The shaft  230  is pivotally attached by its ends to the plate  84  and  88  (see FIG. 1). The input is provided via the socket  228  of the shaft  230 . When the Geneva mechanism  202  is in a moving phase, the pin  234  of the driver  232  is in one of four slots  240  of a Geneva wheel  238 . During this phase, the driver  232  moves the Geneva wheel  238  by 90 degrees. When the Geneva mechanism  202  is in a dwell phase, the Geneva wheel  238  is locked by the locking disc  236 , while the entire input portion of the Geneva mechanism  202  is free to rotate. During this phase, the fingers  22  are locked in their orientation.  
         [0025]    In this preferred embodiment, the fingers are oriented in four predetermined positions, separated by thirty degrees each. Therefore, the ratio between either one of the finger gears  172  and  174  and the input gear  166  is 3:1, so that the predetermined positions of the two rotatable fingers are zero degrees, thirty degrees, 60 degrees and 90 degrees. To restrain the orientation of the fingers in these four positions, one of the slots  240  of the Geneva wheel  238  is filled to stop the rotation of the Geneva wheel  238  and the orientation shaft  164 . This mechanism allows self-locking of the fingers even if they are not driven, allows positioning errors of the driver  232 , and allows free motion of the driver  232  during the dwell phase, which is useful for the switching mechanism  204 .  
         [0026]    The power switching mechanism  204  illustrated in FIGS. 1 and 2 provides three output positions to its male connector  212 , which are used by the gripping mechanism  200  as a neutral position, a position for actuating the orienting mechanism  30 , and a position for actuating the opening/closing mechanism. It is pointed out that the male connector  212  is not required to have a neutral position.  
         [0027]    Variation may be made without changes in the features presented in this embodiment. The power of the socket torque, for example, could come from an internal motor and the socket advance and switching mechanism could be replaced by an internal solenoid. Therefore, a gripping mechanism internally powered by a main motor and a solenoid is obtained. Although the passive tool  200  illustrated is a gripping mechanism, it is obvious that it may be any of a plurality of robotic tools for various purposes. For instance, the power switching mechanism  204  may be used in combination with different motorized tools to form an end effector. The tools could be a screwdriver with different heads, grippers for various objects, drills, saws, etc. The power switching mechanism  204  may transmit the input torque to one of the tools.  
         [0028]    It has also been thought to use the power switching mechanism  204  with a manipulator with N degrees of freedom, which could have an input torque transmitted to one of the N joints by the power switching mechanism  204 , for instance, an X-Y-Z positioning table with three axes to be driven one at a time, wherein the power switching mechanism could transmit the input torque to one of the three axes. In these cases, the manipulator would be intended for use in applications where speed of execution is not critical, since the joints would be activated one at a time.  
         [0029]    Other examples of applications for the power switching mechanism  204  are a knob turning device and a multi-ratio gearbox. The knob turning device could consist of a grasping unit for grasping the knob and a turning unit for turning it. In the multi-ratio gearbox application, the gearbox could have many inputs and one output. Depending on the chosen input, the output would have a different ratio. The power switching mechanism  204  could transmit the input torque to one of the inputs of the gearbox.  
         [0030]    The above-described power switching mechanism  204  with two outputs (considering that the neutral position is not used as an output position) can be generalized for multiple outputs. In the two-output version described above, the grooves  222  and  226  of the indexing ring  214  allow two different activated positions. Additional grooves with different lengths may allow more activated positions, provided that the passive tool receiving the outputs from the power switching mechanism  204  has corresponding additional sockets adapted for receiving the male connector  212 .  
         [0031]    Referring to FIG. 4, an unwrapped groove pattern having three output positions and a neutral position is shown as could be applied to the indexing ring  214 . Grooves  222  and  226  each pair up for receiving the indexing pins  216  in the first and second output positions, and grooves  227  pair up for the third output position, whereas grooves  220 ,  224  and  225  define the neutral position. Different sequences of activated positions can be generated, such as the sequence of the pattern of FIG. 4: position  1 , neutral, position  2 , neutral, position  3 , neutral, position  1 , neutral, etc.  
         [0032]    Changes and modifications to the above-described embodiments of the invention may be made without departing from the spirit or scope of the invention, which are intended to be limited solely by the scope of the appended claims.