1. Field of the Invention
This invention relates to an adjustable joint for coupling two segments of a positionable arm. More specifically, this invention relates to a joint for coupling two segments forming a positionable arm that can be fixedly positioned and repeatedly repositioned.
2. Description of Related Art
Various types of positionable arms are known. These arms typically use motors or mechanical friction caused by, for example, the tightening of screws or bolts, to maintain the orientation of the arm. Such arms may include a plurality of arm segments connected by adjustable joints, thereby providing multiple degrees of freedom with which to arrange the arm. Positionable arms can be used in any number of applications, such as where a workpiece or tool is attached to the end of the positionable arm and the user must reposition the tool periodically during use. In such an application, it is important that the arm, when positioned, fixedly retain that position during use, while still allowing for relatively easy repositioning when desired.
Positionable arms which maintain their positions using friction created between arm members by tightening screws are disadvantageous because in order to reposition the tool, the frictional retaining force must be overcome by the repositioning force applied by the user. This type of apparatus is impractical where the tool being suspended is sufficiently heavy that the downward force caused by the weight of the tool is roughly equivalent to or greater than the force that is applied by the user. Thus, the necessary amount of friction required to prevent movement of the heavily-weighted arm interferes with the user""s ability to easily reposition the tool. Accordingly, there is a need for a positionable arm which can fixedly maintain a position while under load, but is easily repositionable by hand.
In accordance with the present invention, an adjustable joint is provided, comprising a first member having an inner surface and an end portion defining a first connector opening, a piston having a first end and a second end, a chamber within the first member defined by the first end of said piston and the inner surface of the first member, a rotatable connector received in the first hollow member between the second end of said piston and the end portion of the first hollow member such that an increased pressure in the chamber urges the piston towards the first connector opening, thereby clamping the rotatable connector between the first connector opening and the second end of said piston, and a pressurized fluid source in fluid communication with the chamber.
A spring may be provided in the chamber, said spring providing a force against said piston such that said piston presses against said rotatable connector, thereby providing a frictional resistance to rotation of said rotatable connector.
In accordance with another aspect of the present invention, a method for locking and unlocking a joint is provided. This method comprises providing a first member having an inner surface and an end portion defining a first connector opening, a piston in said first member, said piston having a first end and a second end, said first end of said piston and said inner surface of said first hollow member defining a chamber, joining said first member with a second member using a rotatable connector, arranging said rotatable connector in said first member between said second end of said piston and said end portion of said first member, increasing a fluid pressure in said chamber, said increased fluid pressure urging said piston towards said first connector opening, thereby clamping said rotatable connector between said first connector opening and said second end of said piston, and decreasing said fluid pressure in said chamber, thereby decreasing the clamping applied to said rotatable connector by said first connector opening and said second end of said piston.