Abstract:
A positionable arm composed of multiple member segments connected by an adjustable joint which may be fixedly positioned and repeatedly repositioned. The first member includes an end portion defining a first connector opening and an inner surface defining a chamber. A slideable piston provided in the first member includes a first end and a second end, the first end being adjacent the chamber and creating a seal along the inner surface of the first member. A rotatable connector is received in the first member between the second end of said piston and the end portion of the first member, and a second member is attached to the rotatable connector. To position the arm, a pressurized fluid source supplies compressed air to the chamber, which presses the piston against the rotatable connector, fixedly clamping the connector between the piston and the end portion of the first chamber.

Description:
BACKGROUND 
     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&#39;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. 
     SUMMARY 
     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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a positionable arm in accordance with an embodiment of the present invention. 
     FIG. 2 shows a cross-section of a joint member in the positionable arm of FIG.  1 . 
     FIG. 3 shows another embodiment of a joint member in accordance with the present invention. 
     Use of the same reference symbols in different figures indicates similar or identical items. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with an embodiment of the present invention, a positionable arm  100  is shown in FIG.  1 . Arm  100  is mounted to ceiling  102  through ceiling mount portion  104 , and hangs downward therefrom to suspend workpiece  106 . Arm  100  may be mounted in any orientation, such as from a vertical wall, or may rest on the floor in the workspace area. First joint  108  connects ceiling mount  104  to first arm segment  110 , first arm segment  110  is connected to second arm segment  114  through second joint  112 , and second arm segment  114  is connected to tool mount  118  through third joint  116 . The joints and arm segments can be made of various type of materials, including metals, such as aluminum alloys or steel. Each arm segment  110 ,  114  could be made in any length and any size, depending on the application. 
     A pressurized fluid source  120  feeds pressurized fluid through tube  122  to first joint  108 , second joint  112 , and third joint  116 . It will be understood that the term “fluid” refers to both liquid and gaseous fluids. In the embodiment illustrated in FIG. 1; pressurized fluid source  120  is a compressed air generator, and ambient air is used as the pressurized fluid which is provided in tube  122 . Although FIG. 1 shows an externally mounted tube  122 , it is also possible to incorporate tube  122  in the interior of arm  100  as will be described below. 
     FIG. 2 is a cross-sectional view of joint  112 . Hollow member  130  contains rotatable connector  134  and includes a head plate  128 , which defines first connector opening  132 . Rotatable connector  134  protrudes through first connector opening  132  to attach to second arm segment  114 . Hollow member  130  has an inner surface  136 , which defines an interior region containing slideable piston  138 . Piston  138  has a first end  140  and a second end  142 . First end  140  of piston  138 , inner surface  136 , and back wall  168  define a chamber  146 . First gasket  152  provides a seal around first end  140  and second gasket  154  provides a seal around second end  142 , thereby enabling piston  138  to slide laterally within hollow member  130  while providing an airtight seal for chamber  146 . 
     Second end  142  defines a second connector opening  144 , which abuts rotatable connector  134 . First connector opening  132  of hollow member  130  abuts an opposite side of connector  134 . Thus, rotatable connector  134  is positioned between first connector opening  132  and second connector opening  144  of piston  138 , being held securely in place by the two connector openings  132 ,  144 . In another embodiment, second end  142  is solid and has a contour which matches the shape of connector  134 , thereby increasing the contact area between second end  142  and connector  134 . 
     Spring  148  is provided within chamber  146  in a compressed state such that spring  148  provides a constant pressure against piston  138 , pressing piston  138  against connector  134 . Tube  122  feeds pressurized fluid into chamber  146  and interior  150  of piston  138  through valves (not shown). Release valves (not shown) are also provided in chamber  146  and interior  150  of piston  138  to enable depressurization of these two regions. 
     The operation of joint  112  is as follows. The bias provided by compressed spring  148  exerts a constant force on piston  138 , pressing second connection opening  144  of piston  138  against connector  134 . This pressure creates a frictional resistance between the rim of second connector opening  144  and connector  134  and between the rim of first connector opening  132  and connector  134 , thereby opposing rotation of connector  134 . Connector gaskets  156 ,  158  may also be provided on first and second connector openings  132 ,  144  to either increase or decrease the rotational resistance. 
     In order to fix joint  112  in a particular orientation, pressurized fluid is provided from source  120  into chamber  146 . Controls  160  provided on tool mount  118  control the valves leading to chamber  146 , thereby controlling the flow of fluid into and out of chamber  146 . The increased pressure within chamber  146  combines with the force applied by spring  148  to press the second end  142  of piston  138  against connector  134 , clamping connector  134  firmly between second connector opening  144  and first connector opening  132 . The amount of rotational resistance created by this clamping depends upon a number of factors, such as the fluid pressure within chamber  146 , the preset compression of spring  148 , the effectiveness of the seal around piston  138  in preventing fluid leaks, and the coefficient of friction between the connector openings  132 ,  144  and connector  134 . The coefficient of friction depends upon the materials used for these features and the contact surface area of openings  132 ,  144  with connector  134 . Numerous materials can be used for these components, such as an O-ring made of rubber or plastic. 
     Each arm segment  110 ,  114  could be made in any length and any size, depending on the application. The size of the arm segments  110 ,  114  and the weight of the workpiece  106  can affect the internal pressures necessary to maintain the arm  100  in a stationary position. In one embodiment, each arm segment  110 ,  114  is approximately 100 cm long, workpiece  106  weighs approximately 20 kg, and the pressure within chamber  146  is 50 kg/cm 2 . 
     To reposition joint  112 , some of the fluid within chamber  146  is released, equalizing the pressure between chamber  146  and the region  126  between head plate  128  and second end  142 , and thereby decreasing the pressure against piston  138 . The force from spring  148  continues to be applied against piston  138  to maintain some clamping force against connector  134 . This clamping force created by spring  148  provides a default rotational resistance in joint  112 , which provides sufficient rigidity to the arm structure to enable accurate repositioning when arm  100  is heavily loaded. Without this default resistance, the user would receive no assistance in supporting the weight of arm  100  together with the weight of the workpiece  106  at the end of arm  100 . Where arm  100  and workpiece  106  are significantly heavy, the user may not be able to support the weight, or may have to struggle to support the weight while attempting to reposition arm  100 . Thus, the default resistance provided by spring  148  is selected based on the desired application. Some pressure differential between chamber  146  and region  126  may be maintained to increase the default rotational resistance. 
     According to another aspect of the present invention, the user may wish to adjust the rotational resistance of joint  112  to a level of resistance lower than the default resistance provided by spring  148 . In such a situation, fluid passes from pressurized fluid source  120  into interior portion  150  of piston  138 , increasing the pressure within interior portion  150  to a level greater than that of chamber  146  and region  126 . This increased pressure within interior portion  150  creates a pressure against the portion of connector  134  received in second connector opening  144 . This drives piston  138  away from connector  134 , opposing the force applied by spring  148 . Thus, as the pressure within interior portion  150  is increased, the rotational resistance of joint  112  decreases. 
     Connector  134  may be provided in the shape of a cylinder or a sphere. When connector  134  is spherical, openings  132 ,  144  are formed in a circular shape and joint  112  is capable of movement and rotation in any direction. Alternatively, when connector  134  is cylindrical, openings  132 ,  144  are rectangular, and the direction of movement for joint  112  is limited to rotation about the axis of cylindrical connector  134 . A bearing  162  may also be provided to allow rotation of joint  112  about the longitudinal axis of first arm segment  110 , thus enabling greater range of movement for cylindrical connectors. 
     First joint  108  and third joint  116  are similar to joint  112 , as discussed above. Each joint  108 ,  112 ,  116  receives pressurized air from pressurized fluid source  120  through externally-mounted tube  122 . In one embodiment, controls  160  on tool mount  118  include independent controls for the valves and air flow into each joint  108 ,  112 ,  116 , enabling the user to adjust the resistance and reposition each joint independently of the others. Alternatively, controls  160  may simply control all of the collective internal air pressures within joints  108 ,  112 ,  116 . In another embodiment, the mechanical pressurized fluid source  120  illustrated in FIG. 1 is replaced with a manually-operated hand pump located on tool mount  118 . 
     Another embodiment of an adjustable joint  212  in accordance with the present invention is illustrated in FIG.  3 . Here, first arm segment  210  is joined to second arm segment  214  through joint  212 . First arm segment  210  is hollow with an interior surface  236  which contains piston  238 . A first end  240  of piston  238 , interior surface  236 , and back wall  268  define chamber  246 . Springs  248  in chamber  246  apply a force on piston  238 , urging it in the direction of connector  234  and clamping connector  234  between first connector opening  232  in head plate  228  and second connector opening  244  in second end  242  of piston  238 . First gasket  252 , second gasket  254 , and connector gasket  256  provide seals between various moving parts within joint  112 . 
     The operation of adjustable joint  212  is similar to that of joint  112 , except that unlike tube  122 , the tubes which feed pressurized fluid to joint  212  are located on the interior of the arm. First tube  270  is connected to a pressurized fluid source and provides compressed air through opening  272  in back wall  268  into chamber  246 . Second tube  274  is also connected to a pressurized fluid source and carries compressed air through opening  276  in back wall  268  and opening  278  in first end  240  into the interior portion  250  of piston  238 . Finally, third tube  280  travels compressed air through opening  282  in back wall  268 , opening  284  in first end  240 , and through opening  286  in connector  234  to provide compressed air from the pressurized fluid source into joints that are located farther along the positionable arm. Where multiple fluid sources are needed downstream of joint  212 , tube  280  may comprise a bundle of tubes. Valves (not shown) may also be provided at openings  272 ,  276 ,  278 ,  282 ,  284 , and  286  to control the airflow to the various regions of the positionable arm. 
     Although the invention has been described with reference to particular embodiments, the description is only an example of the invention&#39;s application and should not be taken as a limitation. In particular, even though much of preceding discussion was aimed at adjustable mechanical arms, alternative embodiments of this invention may be used wherever positionable joints are use. Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention as defined by the following claims.