Measuring and testing – Dynamometers – Responsive to force
Reexamination Certificate
1999-07-28
2002-03-12
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to force
C073S862530
Reexamination Certificate
active
06354159
ABSTRACT:
REFERENCE TO RELATED APPLICATION
This application is a companion to the Bonino, et al., U.S. application Ser. No. 09/111,574 filed Jul. 8, 1998, and assigned to the same assignee as the present invention.
FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION
The present invention concerns an overload protector for a force-measuring device, in particular a balance, comprising a load receiver that has two parts, the first of which serves to introduce the force to be measured into the force-measuring device. The second part, which serves to transfer the force to be measured to a measuring transducer, is connected to the first part in an arrangement resembling a parallelogram by two parallel guide members whose lengthwise direction runs transverse to the direction of the force introduction. The parallel guide members are rigid relative to their longitudinal direction and elastically flexible in the transverse direction. Formed on the first part and the second part, respectively, the overload protector has a first and a second engagement area by which the first part and the second part can be brought into an engagement that blocks their displacement relative to each other in the direction of the force introduction. The overload protector further comprises a pre-tensioned elastic element urging the two parts into spring-loaded contact opposing the force to be measured that is introduced into the first part.
The purpose of overload protectors of this kind, particularly in sensitive balances, is to protect the measuring transducer and the parts that serve to transfer the force to be measured to the measuring transducer against being overloaded by forces that significantly exceed those that occur at the specified nominal capacity load of the balance. Harmful force effects of this kind occur, for example, when through incorrect operation of the balance the load to be weighed is put on the weighing pan in an unduly abrupt manner. In this case, the instantaneous force acting on the load receiver will exceed the nominal capacity force. Even if a stationary stop is provided to limit the amount of travel of the load receiver in the direction of force introduction, the load receiver is nevertheless subjected to an excessive amount of acceleration up to the point where the motion comes to rest at the stationary stop. This gives rise to inertial forces of a corresponding magnitude in the measuring transducer as well as in the parts that serve to transmit the force to be measured; and/or it will cause transient peaks of tensile and compressive stress in the pivots and couplings, which the balance is not equipped to withstand, being designed for a given capacity load.
DESCRIPTION OF RELATED ARTS
In a known overload protector provided in a balance as described above at the outset (DE 28 30 345 C3), the two guide members of the overload protector are formed in a triangular or trapezoidal shape out of flat material stock and are attached with clamping bolts to the second part at the longer base side of the triangle or trapeze and to the first part at the opposing corner or shorter side of the triangle or trapeze, respectively. For the purpose of attaching the guide members, the second part on the side facing away from the first part is equipped with a console located at a distance from the second part and extending in the transverse direction relative to the two guide members. The main portion of the second part that supports the console extends through the material-free interior area of the triangle or trapeze that is delimited by the sheet material portions that form the guide members running along the sides of the triangle or trapeze that extend between the two parts. This geometry of the overload protector requires a relatively large amount of space. In addition, the cost of assembling the first part and the second part and the guide members with the clamping bolts is relatively high.
On the other hand, a particularly space-saving arrangement is known for a monolithic design (DE 41 19 734 A1) of the parts that serve to introduce and transfer the force to be measured to the measuring transducer. However, this does not include an overload protector for the load receiver.
SUMMARY OF THE INVENTION
The object of the present invention is to create an overload protector of the kind described above at the outset, combining an exceptionally space-saving design with a low assembly cost.
According to the invention, the solution for this problem is to design the two parts and the two guide members as integrally connected material portions of a monolithic material block in which the guide members are separated from each other by a material-free space that traverses the material block.
Because the two parts of the load receiver are connected through the guide members into a single integral part, the assembly labor for the inventive overload protector is reduced to the operation of inserting the pre-tensioned elastic element that urges the two parts into spring-loaded contact against each other. Furthermore, the volume taken up inside the material block by the material-free space separating the two parts and the two guide members from each other can be kept small and, consequently, the amount of space required for the overload protector will also be small. Economical manufacturing processes are available for forming the material-free space including, e.g., milling, drilling or spark erosion as well as a combination of these processes. Primarily the last-mentioned, spark erosion, proves to be particularly well suited.
As long as the pre-tensioned elastic element urges the two parts into spring-loaded contact against each other, the first part and the second part are rigidly coupled to each other, and the force introduced into the first part is transmitted by the second part and directed to the measuring transducer. On the other hand, if the force introduced into the first part exceeds the contact force corresponding to the pre-tension of the elastic element, the first part will be displaced and set into motion relative to the second part up to the point where the first part comes to rest against a stationary stop. However, the portion of the inertial forces that exceeds the amount of the pre-tension is not transmitted to the second part. Thus, the harmful inertial forces are prevented from reaching the measuring transducer and those other parts of the force-measuring device that serve to transmit the force. In this, the amount of pre-tension of the elastic element is selected in the appropriate magnitude to maintain the spring-loaded contact of the two parts up to the nominal capacity load of the balance.
In a further development of the invention, a practical solution is offered wherein the first engagement area is formed by a first shoulder in the material portion making up the first part and the second engagement area is formed by a second shoulder in the material portion making up the second part. Each of the shoulders projects towards the respective opposite material portion. The first shoulder has a free surface facing towards the first guide member, i.e., against the direction of the force to be measured, and the second shoulder has a free surface facing towards the second guide member, i.e., in the same direction as the force to be measured. The material portions forming the first part and the second part are pressed against each other at the free surfaces by the pre-tensioned elastic element. Given that on the one hand, the free surface of the shoulder of the second part faces in the direction of the force introduction, i.e., the surface vector of this free surface has the same direction as the force introduction, and on the other hand, the free surface of the shoulder of the first part faces in the direction against the force introduction, i.e., the surface vector of this free surface has the opposite direction of the force introduction, the force acting on the first part will have the tendency to separate the free surface of the shoulder of the first part from the free surface of the shoulder of the sec
Burkhard Hans-Rudolf
Schneider Ferdinand
Laubscher, Sr. Lawrence E.
Mettler-Toledo GmbH
Noori Max
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