Electrical resistors – Mechanically variable – Movable contact electrically adjustable over length of...
Reexamination Certificate
2000-07-17
2001-09-04
Easthom, Karl D. (Department: 2832)
Electrical resistors
Mechanically variable
Movable contact electrically adjustable over length of...
C338S047000, C338S099000
Reexamination Certificate
active
06285276
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to a control device for an industrial truck, in particular the hitch of a towbar-guided industrial truck, with a circuit element for the generation of a multi-stage electrical control signal.
Control devices for industrial trucks are equipped with control elements for the actuation of the various functions of the industrial truck, such as operation of the truck or an associated lifting apparatus. Depending on the function to be controlled, the control elements have circuit elements for the generation of actuation/deactuation control signals in the form of multi-stage or stepless control signals. Multi-stage or stepless control signals are used in particular to control the speed of travel of the industrial truck or to control the speed of raising and lowering a load-carrying device.
Signal generators of the prior art for the generation of multi-stage control signals entail significant effort and expense in terms of design and construction and consist mostly of a plurality of mechanical and electrical components that are subject to wear. A signal generator of the prior art to be used on an industrial truck for the generation of a stepless control signal is described in DE-GM 94 17 201, for example. The circuit element described in that document is realized in the form of a membrane potentiometer and has a resistance track attached to a flexible pin, by means of which it is possible to generate a control signal which is proportional to the distance the control element is moved. The electrical and mechanical components of this signal generator of the prior art are complex and expensive to design and manufacture.
Therefore, it is an object of the invention to make available a control device with a simple, low-wear circuit element for the generation of a stepped control signal.
SUMMARY OF THE INVENTION
The invention teaches that this object can be accomplished by means of a circuit element that has at least one contact membrane. The contact membrane can be connected with at least one of a plurality of contact points adjacent to the contact membrane by a pressure force exerted on the contact membrane. The contact points are connected by electrical resistors. The electrically conducting contact membrane is pressed by means of the pressure force on at least one of the contact points which is located on a circuit board, whereby an electrical connection is created between the contact membrane and the contact point. A specified contact point can be connected with the contact membrane as a function of the point at which the pressure force is applied. This location is defined by the operator who controls the position of the circuit element. Because the various contact points are connected to one another by means of resistors, the total resistance of the circuit element can be defined in specified stages by the operator.
In one advantageous embodiment of the invention, the electrical resistors are connected in series, whereby each connecting line between two resistors is connected with a contact point. The resistors are therefore connected in a series circuit. The contact membrane is connected to a specified connecting line between two resistors as a function of the site at which the pressure force is applied.
It is particularly advantageous if each of the resistors connected in series has the same resistance value. It thereby becomes possible to keep the number of different components to a minimum.
A different type of advantage can be achieved if the resistors connected in series have different resistance values. The differences from one resistor to the next that result over the entire switching range of the circuit element are therefore different. For example, if the circuit element is used to control the speed of travel, the differences between resistances in the switching range can be graduated in smaller intervals for a low speed of travel than in the switching range for a high speed of travel. This measure results in a precision control capability in the low speed range.
The contact points are preferably all located on one circuit board. In one advantageous refinement of the invention, the contact points can be connected by means of the contact membrane with an additional contact area which is located on the same circuit board. Located on the circuit board is a contact area that is connected with a specified contact point by means of the contact membrane in the manner described above. All of the connections for lines leading outward from the circuit element can thus be located directly on the circuit board. The contact membrane preferably does not have any connections for electrical lines.
It is preferable if there is a first movable slider, by means of which the pressure force can be applied to the contact membrane. The movable slider is movable over the contact membrane when the circuit element is actuated, as a result of which the location at which the slider presses on the contact membrane changes. No electric current thereby flows through the slider, so that there is practically no wear of the slider.
It is likewise preferable if there is a second slider that exerts a pressure force on the contact membrane, as a result of which the contact membrane can be connected with the contact area.
It is particularly advantageous if the movement of the first slider is mechanically coupled to the movement of the second slider. The movement of the sliders over the contact surface in the same direction is thus guaranteed. It consequently becomes possible to prevent undesirable fluctuations in the total resistance of the circuit element.
There are particular advantages if the pressure force of the slider on the contact membrane can be generated by means of a spring force, such as a coil or leaf spring pressing downwardly on the sliders, whereby the magnitude of the pressure force is independent of the position of the slider on the contact membrane. The pressure force of the slider should thereby be adjusted so that an electrical connection between the contact membrane with the contact area or the respective contact area is guaranteed, and so that at the same time there is no mechanical wear of the signal generator.
In one particularly appropriate refinement of the invention, at least some of the contact points have different dimensions in the direction of movement of the slider. As a result of the different widths of the contact points, the required actuation distance of the circuit element between two switching stages can be of different lengths. For example, if the circuit element is used to control the speed of travel, the widths of the contact points in the switching range for low speeds of travel can be wider than in the switching range for a high speed of travel. This measure makes possible a precision control capability in the slow speed range.
It is particularly advantageous if the circuit element can be used to generate a two-channel control signal. A two-channel capability of the control signal achieves a significant increase in safety, in particular on a circuit element used to control a lifting device.
In an additional embodiment of the invention, there is at least one additional contact point that does not have any connection to the other contact points that are connected to one another by means of resistors. This additional contact point is only connected to the contact membrane when the circuit element is in the neutral position. The neutral position can thereby be detected by means of a separate electrical circuit, which achieves a two-channel capability of the circuit element.
REFERENCES:
patent: 3418850 (1968-12-01), Goddin
patent: 4333068 (1982-06-01), Kishel
patent: 4421269 (1983-12-01), Ts'ao
patent: 4739184 (1988-04-01), Onesti
patent: 5302936 (1994-04-01), Yaniger
patent: 5334967 (1994-08-01), Paszkiewicz
patent: 5554965 (1996-09-01), Sundberg
patent: 3624166 (1988-01-01), None
patent: 4328824 (1995-03-01), None
patent: 0894763 (1998-07-01), None
Bruder Frederic
Maller Pierre
Nedele Hartmut
Schöller Eugen
Weber Edgar
Easthom Karl D.
Lee Kyung S.
Still & Saxby S.A.R.L.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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