Geometrical instruments – Gauge – Collocating
Reexamination Certificate
2003-04-14
2004-08-03
Fulton, Christopher W. (Department: 2859)
Geometrical instruments
Gauge
Collocating
C033S533000, C033S644000
Reexamination Certificate
active
06769194
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device for positioning components with high precision. In particular, the present invention relates to a parallel kinematic manipulator capable of positioning components with nanometer tolerances.
BACKGROUND OF THE INVENTION
The precise positioning of components is increasingly important. For instance, optical communications systems require that the ends of optical fibers be precisely aligned with mating components or fibers to ensure minimal transmission losses. The precision alignment of components is also important in connection with the manufacture of semiconductor devices, and with devices having miniaturized components and/or fine tolerance requirements. As yet another example, precision surgery applications, including remote surgery, require the ability to precisely control the position and movement of instruments. However, previous attempts at providing for the precise positioning of a component or instrument have been incapable of providing high resolution positioning. In particular, previous attempts at providing devices capable of precisely positioning components and instruments have been incapable of providing a desired number of degrees of freedom in combination with a desired positioning tolerance.
Manipulators or positioners capable of providing a number of degrees of freedom are available. One such type of device is a manipulator having stacked stages. An example of a manipulator
100
incorporating stacked stages is illustrated in FIG.
1
. The manipulator
100
includes first
104
, second
108
and third
112
linear stages for providing linear movement of the mobile plate or tool plate
116
relative to the base plate
120
. In particular, the linear stages
104
,
108
and
112
provide movement of the mobile plate
116
with respect to the base plate
120
along the x, y and z axes. In addition, a first
124
and second
128
rotational stage are provided to rotate the mobile plate
116
with respect to two separate axes. The combination of three linear stages
104
,
108
and
112
and two rotational stages
124
and
128
provides a manipulator
100
having five degrees of freedom.
Although the manipulator
100
is capable of providing five different movements for positioning a component or instrument interconnected to the mobile plate
116
, the resolution or step size with which such positioning can be accomplished is limited. In particular, manipulators having stacked stages, such as the manipulator
100
illustrated in
FIG. 1
, suffer from additive positioning errors. Specifically, there are sine and cosine position errors associated with each movement, in addition to linear (or rotational) position errors. Errors associated with each stage can contribute additively to an overall positioning error associated with the manipulator. As a result, even if great efforts are made to accurately control the position of each stage, the overall positioning error remains relatively high. For example, if each linear actuator has an error of 50 nm, the overall positioning error of the manipulator is likely to be at least 150 nm. Adding in errors associated with the rotational stages, and sine and cosine errors, a high quality, 5 degree of freedom manipulator
100
having stacked stages is likely to have 250 nm or more of position error.
Parallel mechanisms provide a manipulator structure that avoids additive errors. In a parallel mechanism, such as the parallel mechanism
200
illustrated in
FIG. 2
, a base plate
204
is interconnected to a mobile plate
208
by a plurality of kinematic links
212
. In the parallel mechanism
200
illustrated in
FIG. 2
, six kinematic links
212
a
-
f
are provided. As a result, the parallel mechanism manipulator
200
, also known as a hexapod, is capable of moving the mobile plate (tool plate)
208
with six degrees of freedom (x, y, z, &PHgr;, &thgr;, &psgr;). Because the position error of a parallel mechanism is not additive, higher positioning tolerances are possible than with a stacked stage type device (e.g., manipulator
100
in FIG.
1
). For example, if positioning resolutions of 50 nm are available with respect to each kinematic link, a parallel mechanism type manipulator such as the manipulator
200
illustrated in
FIG. 2
might be capable of positioning the mobile plate
208
with a resolution that is also about equal to 50 nm. Although such resolution is acceptable in many cases, it is still too high for may applications, particularly aligning fiber optic cables. At the same time, it is also desirable to provide actuators capable of operating at high velocities, for example, to speed up production processes. Typical actuators include servo motors, linear motors and inch worm type ceramic actuators.
Servo motor type actuators may suffer from backlash associated with the screw-type jacking mechanisms often used to effect changes in the length of the kinematic link. In addition, servo and linear motor type actuators suffer from dithering, which involves high frequency, small amplitude movements of the motor as it searches for the correct position. Such dithering can result in vibrations that can interfere with intended positioning operations, even when changes in the lengths of the kinematic links are not being effected.
Inch worm-type piezoelectric motors generally include a pair of ceramic rings capable of selectively engaging a rod running through the rings. In particular, the ceramic rings can be electrically excited in such a way as to controllable move the rod with respect to the rings. Although such devices are capable of providing small changes in the length of a kinematic chain, they suffer from inaccuracies due to hysteresis. Therefore, it is difficult to accurately control the length of a kinematic chain utilizing an inch worm-type piezoelectric actuator. The operation of such devices is also relatively slow. In addition, the operation of inch worm-type piezoelectric actuators creates vibrations that can interfere with the intended positioning operations.
Therefore, there is a need for a method and apparatus capable of providing for the precise positioning of a component or instrument. In particular, there is a need for a method and apparatus for providing a manipulator capable of positioning a component or instrument with high repeatability, resolution, and speed, without dither.
SUMMARY OF THE INVENTION
In accordance with the present invention, a parallel kinematic micromanipulator is disclosed. Also disclosed is a method for precisely positioning a component or instrument. The method and apparatus of the present invention allows for the positioning of components and instruments with extremely high repeatability and allows multiple degrees of freedom in the movement of a component or instrument.
The inventor of the present invention has recognized that higher positioning resolutions than are available using prior art manipulators would require kinematic links capable of having their lengths controlled with greater precision. Furthermore, the inventor of the present invention has recognized that the inaccuracies encountered with respect to the position of individual kinematic links are in large part due to the inaccuracies inherent to the actuators used to control the length of the kinematic links. Such actuators have included servo motors, linear motors, and inch worm-type ceramic actuators. In contrast, the present invention comprises linear piezoelectric actuator assemblies capable of providing movement with resolutions that have not been available in connection with conventional manipulators. As can be appreciated by one of skill in the art, piezoelectric actuators take advantage of the piezoelectric effect exhibited by certain crystals, in which the application of an electric field causes the crystal to expand or contract in certain directions. Furthermore, the linear piezoelectric actuator assemblies utilized in connection with the present invention are capable of providing motion that is substantially continuous, as opposed to the intermi
Duft Setter Ollila & Bornsen LLC
Fulton Christopher W.
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