Handling: hand and hoist-line implements – Grapple
Reexamination Certificate
2000-05-11
2002-06-04
Walsh, Donald P. (Department: 3653)
Handling: hand and hoist-line implements
Grapple
Reexamination Certificate
active
06398280
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to mechanisms for grasping microcomponents, and in specific to a complementary gripper and handle for grasping microcomponents.
BACKGROUND
Extraordinary advances are being made in micromechanical devices and microelectronic devices. Further, advances are being made in MicroElectroMechanical System (“MEMS”) devices, which comprise integrated micromechanical and microelectronic devices. The terms “microcomponent” and “microdevice” will be used herein generically to encompass microelectronic components, micromechanical components, as well as MEMs components. A need exists in the prior art for a suitable mechanism for picking and placing microcomponents. For example, a need exists for some type of “gripper” device that is capable of grasping a microcomponent and maintaining a rigid grasp of the microcomponent while placing the microcomponent in a desired position. For instance, such a gripper device may be included as part of a robotic device, such as a robotic arm, to allow the robotic device to perform pick and place operations with microcomponents. Such pick and place operations may be performed, for example, in assembling/arranging individual microcomponents into larger systems.
Various types of “gripper” mechanisms are well known for large scale components. For example, mechanisms such as tweezers, clamps, robotic hands, and a variety of other types of gripping mechanisms are well known and commonly used for gripping large scale components. However, such gripping mechanisms for large scale components are generally difficult to implement on such a small scale as necessary for gripping microcomponents. That is, many large scale gripping mechanisms are unacceptable and are not easily adaptable for use in gripping microcomponents.
Turning to
FIG. 1
, an example of utilizing a gripper to perform pick-and-place operations for a microcomponent is illustrated. Starting in block
10
, a gripper
102
is shown, which may be utilized to pick up a microcomponent
104
and attempt to place microcomponent
104
in a desired (or “target”) location
106
. In block
20
, the gripper
102
approaches the microcomponent
104
in an attempt to position itself to grasp microcomponent
104
. Due to the sticking effects present with such small-scale components (as discussed in more detail hereafter), microcomponent
104
may be attracted to the gripper
102
as the gripper
102
makes its approach toward microcomponent
104
. Accordingly, as shown in block
20
, such attraction may result in difficulty in the gripper
102
obtaining a firm grasp on the microcomponent
104
. Block
30
illustrates gripper
102
having grasped microcomponent
104
, and gripper
102
has picked up microcomponent
104
. Thereafter, the gripper
102
may reposition the microcomponent
104
, and place the microcomponent
104
on the desired location
106
, as shown in block
40
. Gripper
102
may then release the microcomponent
104
, as shown in block
50
. As further shown in block
50
, however, releasing the microcomponent
104
may be difficult due to the sticking effects present with such small-scale components. Thus, microcomponent
104
may adhere to gripper
102
. as the gripper
102
attempts to release the microcomponent
104
, resulting in the microcomponent
104
being misaligned (or “incorrectly positioned”) respective to the target location
106
.
As
FIG. 1
demonstrates, while such pick-and-place operations initially appear to be relatively simple, when working with microcomponents, such pick and place operations are very complex. In the micro world, the relative importance of the forces that operate is very different from that in the macro world. For example, gravity is usually negligible, while surface adhesion and electrostatic forces dominate. (See e.g.,
A survey of sticking effects for micro parts handling
, by R. S. Fearing, IEEE/RSJ Int. Workshop on Intelligent Robots and Systems, 1995
; Hexsil tweezers for teleoperated microassembly
, by C. G. Keller and R. T. Howe, IEEE Micro Electro Mechanical Systems Workshop, 1997, pp. 72-77
; Microassembly Technologies for MEMS
, by Micheal B. Cohn, Karl F. Böhringer, J. Mark Noworolski, Angad Singh, Chris G. Keller, Ken Y. Goldberg, and Roger T. Howe; and
Handbook of Industrial Robotics
, by Shimon Y. Nof, chapter 5). Due to scaling effects, forces that are insignificant at the macro scale become dominant at the micro scale (and vice versa). For example, when parts to be handled are less than one millimeter in size, adhesive forces between a gripper and an object can be significant compared to gravitational forces. These adhesive forces arise primarily from surface tension, van der Waals, and electrostatic attractions and can be a fundamental limitation to handling of microcomponents. While it is possible to fabricate miniature versions of conventional robot grippers in the prior art, overcoming adhesion effects for such small-scale components has been a recognized problem.
Often in attempting to place a microcomponent in a desired location, the component will “stick” or adhere to the placing mechanism due to the aforementioned surface adhesion forces present in microassembly, making it very difficult to place the component in a desired location. (See e.g.,
Microfabricated High Aspect Ratio Silicon Flexures
, Chris Keller, 1998). For example, small-scale “tweezers” (or other types of “grippers”) may be used to perform such pick-and-place operations of microcomponents, and often such a component will adhere to the tweezers rather than the desired target location, making placing the component very difficult. It has been recognized in the prior art that to grip microcomponents and then attach them to the workpiece in the desired orientation, it is essential that a hierarchy of adhesive forces be established. For instance, electrostatic forces due to surface charges or ions in the ambient must be minimized. Adhesion of the micropart to the unclamped gripper surfaces (with zero applied force) should be less than the adhesion of the micropart to the substrate, to allow precise positioning of the part in the gripper.
Accordingly, unconventional approaches have been proposed for performing the pick-and-place operations. For example, Arai and Fukada have built manipulators with heated micro holes. See
A new pick up and release method by heating for micromanipulation
, by F. Arai and T. Fukada, IEEE Micro Electro Mechanical Systems Workshop, 1997, pp. 383-388). When the holes cool, they act as suction cups whose lower pressure holds appropriately shaped objects in place. Heating of the cavities increases the pressure and causes the objects to detach from the manipulator. Alternatively, some type of external adhesive (e.g., a type of liquid “glue”) may be utilized to enable the microcomponent to be placed in a desired location. That is, an external adhesive may be required to overcome the adhesive force between the component and the placing mechanism (e.g., tweezers). For example, the target spot on the workpiece may have a surface coating that provides sufficiently strong adhesion to exceed that between the microcomponent and the unclamped gripper.
With the advances being made in microcomponents, various attempts at developing a suitable gripper mechanism for performing pick-and-place operations have been proposed in the prior art. (See e.g.,
Handbook of industrial Robotics
, by Shimon Y. Nof, chapter 5). However, gripper mechanisms of the prior art are problematic in that they typically do not allow for a microcomponent to be accurately positioned. One factor that commonly decreases the accuracy in the placement of a microcomponent by prior art grippers is the above-described sticking effects between the gripper and the microcomponent.
Prior art grippers commonly rely on frictional forces between the gripper and the component for performing pick-and-place operations. For example, a small-scale pair of tweezers may be utilized to squeeze against the outer edges of a component, thereby grasping the compo
Parker Eric G.
Skidmore George D.
Beauchaine Mark J.
Fulbright & Jaworski L.L.P.
Walsh Donald P.
Zyvex Corporation
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