Machine element or mechanism – Control lever and linkage systems – Multiple controlled elements
Reexamination Certificate
1999-07-26
2001-05-08
Herrmann, Allan D. (Department: 3682)
Machine element or mechanism
Control lever and linkage systems
Multiple controlled elements
C267S150000
Reexamination Certificate
active
06227066
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a self-centering “joystick” input device capable of supporting multiple compound torque profiles for returning the joystick to the center position. Joystick input devices are well known in the art, and have been employed in a wide range of applications, from aircraft control to video game inputs. Joysticks may be provided to supply directional input information related to a single rotational axis, or to multiple axes. More sophisticated joystick instruments may provide magnitude data as well.
In operation, an operator will manually displace the joystick relative to one or more of its rotational axes in order to issue directional commands to other equipment. Sensors within the joystick will sense the angular displacement of the joystick and develop input signals accordingly, which may be transmitted to the equipment to be controlled. The sensors and the signals they produce may operate electronically, hydraulically, or otherwise.
In many applications it is desirable that the joystick return to a center or neutral position after it has been released by the operator. Many joysticks are designed to be displaced about two perpendicular axes, so that directional information may be detected through 360°. Thus, in order to return the joystick to a center position on both axes, many designs have required two or more springs to provide a centering force relative to each axis. Some designs, for example that disclosed in U.S. Pat. No. 4,124,787 require two springs per axis. A problem with multiple spring designs is their complexity and higher cost. Also, most multiple spring designs include a significant amount of backlash around the center position. Backlash around the center position allows the joystick to be displaced by a small amount without developing an adequate restoring force to return the joystick to center. Thus, prior art instruments often include a slight wobble around the center position that can lead to inaccurate input measurements. The backlash problem is especially troublesome in applications where a high degree of accuracy and sensitivity is required.
A number of single spring designs have been developed in order to simplify the design of self-centering joysticks and reduce backlash. U.S. Pat. Nos. 4,479,038 and 5,724,068, for example, each employ a single spring to bias a thrust plate, or force plate, against a restoring member which is attached to the joystick itself. These designs prove simpler, and improve backlash around the center position, however, they are limited to providing a uniform restoring torque that is substantially equal in all directions.
In some applications it is desirable that the restoring torque for returning the joystick to the center position be greater in some directions than it is in others. Further, it may also be desired that the torque profile have a step such that the restoring torque is significantly increased if the joystick is displaced beyond a certain amount. Prior art joystick designs include no provisions for such multiple compound force profiles.
SUMMARY OF THE INVENTION
In light of the background given above, a primary object of the present invention is to provide a self centering joystick that may be angularly displaced relative to at least one axis and automatically and accurately returned to a center position.
A further object of the invention is to provide a self-centering joystick having compound torque profiles wherein a restoring torque for returning the joystick to the center position varies significantly depending on the angular displacement of the joystick.
Yet another object of the present invention is to provide a self-centering joystick having multiple torque profiles, compound or otherwise, provided by a single biasing spring.
These objects, as well as others that will become apparent upon reading the detailed description of the preferred embodiment are accomplished by the Self-Centering Joystick as herein disclosed.
The present invention provides a centering device for returning an angularly displaceable joystick to a center position, and retaining the joystick in the center position until it is acted upon by an external force. The centering device provides multiple compound torque profiles for restoring the joystick to the centered position. The compound force profiles are such that as the joystick is angularly displaced, the magnitude of the restoring torque is dependent on the direction and angular distance that the joystick is displaced. Furthermore, the multiple compound torque profiles are provided by a single biasing spring.
The joystick-centering device of the present invention includes a support fixture which supports the joystick. The support fixture includes a mounting bracket which supports the joystick above the base of the fixture. A restoring plate is attached to a lower end of an elongate member that comprises the joystick itself, and the restoring plate is pivotally mounted to the mounting bracket. The self-centering joystick mechanism of the present invention may be employed on a joystick rotatable about a single axis or multiple axes. In a preferred embodiment the restoring plate is mounted within a two axis gimbal which allows the joystick to be rotated independently about two perpendicular axes.
A lower surface of the restoring plate is formed of a plurality of adjacent planar segments or facets. Included among the plurality of facets are a center facet and angularly displaced lateral facets abutting the center facet. The junction between the lateral facets and the center facet form distinct straight primary contact lines between the adjacent facets. The center facet is positioned such that pairs of primary contact lines are laterally offset an equal distance from each axis. Secondary lateral facets are formed adjacent the lateral facets. The secondary lateral facets abut the lateral facets to form secondary contact lines. The secondary contact lines are offset further from their associated axes than are the parallel primary contact lines.
A force plate is disposed between the base of the fixture and the restoring plate. A compression spring is compressed between the base and the force plate to bias the force plate against the multi-faceted lower surface of the restoring plate. The compressed spring provides a restoring force which biases the force plate against the restoring plate. When the joystick is in the center position, the center facet abuts the surface of the force plate, parallel thereto. The centering force applied by the force plate is evenly distributed against the center facet such that no net torque is transmitted to the joystick. However, when the joystick is displaced by a relatively small angle about a first axis, the centering force is concentrated against only one of the primary contact lines surrounding the center position facet. When the joystick is displaced further, the centering force is applied against one of the secondary contact lines. Because the secondary contact lines are located further from the first axis than are the primary contact lines, a first relatively smaller centering torque is developed when the centering force acts against one of the primary contact lines, and a second relatively larger centering torque is developed when the centering force is acting against one of the said secondary contact lines.
The arrangement of the lateral and secondary facets, and the subsequent formation of primary and secondary contact lines, may be repeated for each axis of rotation of the joystick. Thus, multiple compound torque profiles may be provided for centering the joystick about each axis. Furthermore, such multiple compound force profiles are provided by a single biasing spring compressed between the support fixture base and the force plate, providing a significantly less complex multi-axis self centering joystick than has heretofore been available in the art.
REFERENCES:
patent: 2383554 (1945-08-01), Krickler
patent: 2896034 (1959-07-01), Nolden et al.
patent: 3308675 (1967-03-01), Jonsson
patent: 3434
Herrmann Allan D.
Laff, Whitesel & Saret, Ltd.
MPC Products Corporation
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