Expansible chamber devices – With separate biasing means for working member – Fluid spring
Reexamination Certificate
1999-10-19
2001-09-04
Ryznic, John E. (Department: 3745)
Expansible chamber devices
With separate biasing means for working member
Fluid spring
Reexamination Certificate
active
06283011
ABSTRACT:
The present invention relates to a cylinder with an elastic device for returning a working piston unit to a neutral position, this piston unit being attached to a working rod and mounted in at least one working chamber so that it slides between a rest position and a working position, said neutral position being between these two positions or coinciding with the rest position.
The operating part of this cylinder may be hydraulic or pneumatic, depending on the applications in which it is used and the amount of working force to be produced. The working rod may be connected to any type of tool, for example a clamp with arms or jaws articulated at X or at C and provided with electrodes for resistance spot-welding. With this type of welding, the workpieces to be welded may be fixed relative to the ground whilst the welding clamp is carried by the operator.
A welding clamp of this type is described in French patent application No. 98.08752 filed in the name of this applicant, for example, to which reference may be made for further details. In principle, the electrodes are clamped onto the workpieces to be welded, which corresponds to the working position mentioned above, following an initial approach pass of the tool which is in effect a wide-open position in readiness for the first assembly to be performed (wide-open position which can be regarded as corresponding to the rest position mentioned above) and a positioning of the tool to a neutral position, for example an intermediate position, in readiness for subsequent assemblies. In practice, the constraints inherent in the welding range make it necessary to operate with a three-position cylinder enabling the jaw to be opened wide (so-called “rest position”), particularly when engaging and retracting the arms of the tools relative to the workpieces to be welded, closing down to a neutral or intermediate point as the arms approach the point to be welded and closure applied by a high force during the welding cycle (so-called “working” position). In order to save time during the welding cycle, the neutral or intermediate position must be such that it can be used as a small opening to avoid having to fully re-open the clamp.
Furthermore, a known approach to ensuring that the working piston unit is returned to a neutral or intermediate position in such cylinders is to subject this piston to the antagonistic forces of one or two return springs.
The disadvantage of a mechanical return design of this type is that the welding force is dependent on the number of pistons mounted, their sections and the return coefficient of the springs back to the neutral or intermediate position. The higher the return coefficients, the higher the positioning speed at the neutral or intermediate point but the lower the clamping force and the lower the opening speed and vice versa.
Furthermore, if a clamp with a multi-stage cylinder is used, a higher number of and more complex control members and associated logics are needed the greater the number and complexity of the chambers to be pressurised or exhausted, which means more control cables, a more complex control logic and a heavier clamp, thereby rendering this tool useless as a portable unit.
The objective of this invention is to eliminate the disadvantages of the prior art and to this end, a cylinder as proposed by the invention, of the type defined above, is characterised in that the elastic device for returning said working piston to a neutral or intermediate position is of the pneumatic type and operates an auxiliary piston unit with a relatively small section, slidably mounted in an auxiliary chamber which is pneumatically supplied independently of that which operates said working piston unit.
Advantageously, said elastic device has at least one auxiliary piston unit connected to said working piston unit and slidably mounted in an auxiliary chamber, this auxiliary piston unit being designed to be displaced inside said auxiliary chamber in one direction or the other by said working piston unit when the latter is displaced between its rest position and its working position or vice versa, and to elastically compress a gas inside said auxiliary chamber so as to be able to return said working piston unit elastically into said neutral or intermediate position.
As will be seen below, the invention may be used with a “working piston unit” comprising one or more working pistons, depending on the working force required during clamping. If, for example, there are two working pistons, the “auxiliary piston unit” of the elastic device will have one or more auxiliary pistons, located between the two working pistons, and designed to return these latter to a neutral position or intermediate small opening between the wide-open position and the clamped position of a welding clamp.
REFERENCES:
patent: 380375 (1888-04-01), Williams et al.
patent: 1786474 (1930-12-01), Bickel
patent: 2092580 (1937-09-01), Kelley
patent: 3672402 (1972-06-01), Bloemer
patent: 3752161 (1973-08-01), Bent
patent: 3834276 (1974-09-01), Gournelle
patent: 4226167 (1980-10-01), Lew
patent: 5125326 (1992-06-01), Sacona
patent: 2 673 983 (1992-09-01), None
patent: 2 721 359 (1995-12-01), None
patent: 3330 (2000-04-01), None
Aro
Piper Marbury Rudnick & Wolfe
Ryznic John E.
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