Work holders – Relatively movable jaws – Means to actuate jaw
Reexamination Certificate
1999-04-09
2001-05-15
Watson, Robert C. (Department: 3723)
Work holders
Relatively movable jaws
Means to actuate jaw
Reexamination Certificate
active
06231037
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a cassette clamp for a microtome.
2. Description of the Related Art
Before specimens can be cut using a microtome, the specimens must be made stable. To do this, they are embedded in paraffin, for example. This embedding in paraffin is usually done in so-called plastic cassettes, as are described in DE-43 33 118-A1, for example. To cut them, the embedded specimens are placed, together with the cassettes, in the clamp of a microtome.
A clamp which can hold cassettes of this type is known from U.S. Pat. No. 3,802,691. The clamp has a base part with fixed limit stops and forms, together with a movable clamping jaw, a holder for a cassette. Compression springs are provided between the clamping jaw and the base part. The first end of a pivotally mounted tie rod is connected to the clamping jaw via a thread, while its other end is connected to an eccentric. The clamping jaw can be adjusted slightly via the thread of the tie rod, so that the holder can be adapted to different cassette sizes.
A similarly constructed specimen clamp for a microtome is known from DE-36 07 766-C1. In this clamp, the tie rod is designed as a spindle on which the movable clamping jaw runs for the purpose of adjusting the holder size. In this case, the specimen is also clamped via an eccentric.
A quick-action chuck system for microtomes with a chuck head is known from DE-30 40 217-C2, in which the specimen can be clamped between four fingers forming a holder. The fingers are secured with cam followers, which are connected to one another by springs. The holder can be opened and closed via a pivot lever for the purpose of receiving the specimen.
A cassette clamp for a microtome is known, for example, from the publication “LEICA RM 2145” from Leica Instruments GmbH, July 1997. The cassette clamp has a base part with fixed limit stops as a support for the paraffin cassette. Provided opposite these limit stops there is a clamping jaw which is mounted on the base part so as to pivot about an axis. The clamping jaw is pre-stressed via a tension spring and thus presses against the inserted cassette. Also arranged on the clamping jaw there is a lever via which the clamping jaw can be moved about its pivot axis into a cassette-exchange position counter to the spring force.
In these known cassette clamps, two hands are needed to change cassettes. One hand is used to move the lever into the cassette-exchange position and to hold it there counter to the spring force. The cassette is then either removed or inserted using the other hand. When holding the lever in the cassette-exchange position, force has to be applied, so that there is a danger of slipping and injuring oneself on the cutting knife.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to simplify the cassette exchange in the specimen holder of a microtome and in so doing to minimize the force applied.
A pivot lever, according to preferred embodiments of the present invention, locks in the cassette-exchange position and therefore no longer needs to be held. The pivot lever is connected to a spring and is mounted on the base part via a pivot axis provided between the first and second ends of the spring. The pivot lever forms, together with the spring, a tilting clamp mechanism. By simply inserting the cassette into this opened holder, the tilting clamp mechanism is activated and the cassette is held in the holder between the limit stops and the clamping jaw. The clamp is opened by moving the pivot lever across a pressure point. Thereafter, the pivot lever is moved onward into the cassette-exchange position by the spring.
The spring according to preferred embodiments of the present invention performs a an over-center function wherein the magnitude of the spring bias changes at different pivotal positions of the pivot lever with respect to the base portion. The spring bias is relatively smaller when the pivot lever is in the cassette-clamping and cassette-exchange positions, and the spring bias is relatively larger in a transitional center position between the cassette-clamping and cassette-exchange positions. According to most preferred embodiments of the present invention, the transitional center position occurs when the longitudinal axis of the spring intersects the pivot axis of the pivot lever. Thus, the pivot lever according to preferred embodiments of the present invention tends to remain in one of the cassette-clamping and cassette-exchange positions, and tends to resist crossing the transitional center position between the cassette-clamping and cassette-exchange positions.
The objects of the present invention are achieved by a clamp for holding a specimen cassette with respect to a microtome. The clamp comprises a base including at least one fixed limit stop adapted for restraining the specimen cassette; a lever pivotally mounted with respect to the base, the lever pivoting on an axis; a jaw adapted for clamping the specimen cassette with respect to the at least one fixed limit stop, the lever supporting the jaw for movement around the axis; and a spring extending from a first end engaging the base to a second end engaging the lever, the spring exerting a biasing force on the lever and the base. Wherein the biasing force reaches a maximum when the axis intersects a line between the first and second ends.
The objects of the present invention are also achieved by a cassette clamp for a microtome cassette. The cassette clamp comprises a base part having at least one fixed limit stop adapted for receiving the cassette, at least one pivotally mounted clamping jaw, and a spring; the limit stops and the clamping jaw being adapted for clamping the cassette therebetween by spring force, the clamping jaw being connected to a pivot lever and being able to move counter to the spring force from a cassette-clamping position into a cassette-exchange position via the pivot lever, wherein a first end of the spring engages the base part and a second end of the spring engages the pivot lever, the pivot lever being mounted on the base part via a pivot axis arranged between the first end of the spring and the second end of the spring, wherein the pivot lever and the spring form a tilting clamp mechanism adapted to be activated by installing the cassette in the cassette-exchange position.
REFERENCES:
patent: 1745379 (1930-02-01), Perry
patent: 2053699 (1936-09-01), Coates
patent: 3552733 (1971-01-01), Pickett
patent: 3802691 (1974-04-01), White
patent: 4695046 (1987-09-01), Berleth
patent: 5188347 (1993-02-01), Hunnell et al.
patent: 5673905 (1997-10-01), Kiene
patent: 30 40 217 (1980-10-01), None
patent: 36 07 766 (1986-03-01), None
patent: 43 33 118 (1993-03-01), None
“LEICA RM 2145”; Leica Instruments GmbH; Jul. 1997; pp. 1-6.
Foley & Lardner
Leica Microsystems Nussloch GmbH
Watson Robert C.
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