Handling: hand and hoist-line implements – Grapple – Pivoted jaws
Reexamination Certificate
2000-05-30
2003-01-14
Batson, Victor (Department: 3671)
Handling: hand and hoist-line implements
Grapple
Pivoted jaws
C901S031000
Reexamination Certificate
active
06505870
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a gripping mechanism for use in robotic application and, more particularly, to an actuation system for actuating an underactuated gripping mechanism in which the number of actuators required is smaller than the number of degrees of freedom of the gripping mechanism.
BACKGROUND OF THE INVENTION
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.
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.
Underactuation can be achieved using different structural mechanisms. A typical example is described in the Applicants'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 relationship are achieved.
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 proceeding 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'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's United States Patent using a lever for two outputs.
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'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.
In order to achieve this underactuation between the fingers in a 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.
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.
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 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
It is an object of the present invention to provide an actuation system for a gripping mechanism underactuated between a plurality of fingers, using a differential mechanism which is adapted to deactivate predetermined fingers in close/open actions when desired, while actuating the remainder of the fingers in the action.
It is another object of the present invention to provide an actuation system for a gripping mechanism underactuated between a plurality of fingers, using a differential mechanism which is adapted to provide a finger self-locking function in close/open actions.
In one particular embodiment, it is an object of the invention to provide an actuator system for a self-adaptive gripping mechanism with at least ten degrees of freedom which requires two actuations with respect to two co-ordinates that are the force or position of the closing of the fingers and orientation of the fingers, the two co-ordinate being related to improve the performance of the gripping mechanism.
It is a further object of the present invention to provide an actuation system for an underactuated gripping mechanism, which includes an orienting mechanism to rotate the fingers and allows self-locking of the fingers in predetermined orientations and allows, to a certain extent, for more imprecise actuation input for orientation when the fingers are locked in the predetermined orientations.
In general terms, an actuation system for a gripping mechanism underactuated between fingers thereof is provided with a differential mechanism and an orienting mechanism to actuate the fingers in close/open actions and orientation actions respectively, the differential mechanism being adapted to deactivate predetermined fingers in an close/open action when desired.
In more particular terms, an actuation system is provided for a gripping mechanism underactuated between a plurality of fingers at least two of which are rotatable for orientation, each fing
Gosselin Clement
Laliberte Thierry
Anglehart James
Batson Victor
Renault Ogilvy
Universite Laval
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