Abstract:
A retractable support arm structure, which is applied between a base and a steering mechanism of a LCD stand includes an upright arm having a hollow part, an telescopic arm having one end inserted into the hollow part, and a spring member located between the upright arm and the telescopic arm to store a upwardly extending potential energy and several friction members therebetween are used to maintain the balance. The upright arm and the telescopic arm are constituted by square tube made by seamless corner bar.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention provides an improvement on China Patent Utility No. ZL 03 2 03726.0, entitled “Rack for LCD Monitor”. 
   2. Description of the Related Art 
     FIGS. 1 and 2  show a rack for LCD monitor according to China Patent Utility No. ZL 03 2 03726.0. This rack is adapted to support a LCD monitor or LCD TV, allowing adjustment of the elevation and angle of the LCD monitor or LCD TV. According to this design, the rack comprises a base ( 10 ′), which has a horizontally extended area that can be positioned on a flat surface positively, an upright tube ( 11 ′) vertically upwardly extended from the base ( 10 ′) at the top, a telescopic arm ( 12 ′) inserted into the upright tube ( 11 ′), a resilient means ( 13 ′) that imparts an upward force to the telescopic arm ( 12 ′) relative to the upright tube ( 11 ′), a holder frame ( 20 ′) fixedly provided at the free end of the telescopic arm ( 12 ′), a first steering member ( 21 ′) pivotally connected to the holder frame ( 20 ′) by a Z-axis pivot, a second steering member ( 22 ′) pivotally connected to the holder frame ( 20 ′) by a pair of X-X axis pivot and turnable in direction perpendicular to the first steering member ( 21 ′), and a third steering member ( 23 ′) pivotally connected to the front side of the second steering member ( 22 ′) by a Y-axis pivot and adapted to bearing the load and freely rotatable relative to the second steering member ( 22 ′). In  FIG. 1 , the resilient means ( 13 ′) is an air cylinder ( 13 ′) provided within a space at the center of said telescopic arm ( 12 ′), having a cylindrical casing ( 131 ′) with its one end connected to the free end of the telescopic arm ( 12 ′), a piston ( 133 ′) axially movably supported in the cylindrical casing ( 131 ′), and a piston rod ( 132 ′) for driving the piston ( 133 ′) being fixedly fastened to the base ( 10 ′). When the telescopic arm ( 12 ′) is lowered, the air cylinder ( 13 ′) imparts a resisting force to the telescopic arm ( 12 ′). According to this design, the capacity of the air cylinder ( 13 ′) is determined in such a way that the resisting force of the air cylinder ( 13 ′) is slightly larger than the load at the third steering member ( 23 ′), and the pressure difference between the resisting force of the air cylinder ( 13 ′) and the load is set up by the friction force between the telescopic arm ( 12 ′) and the upright tube ( 11 ′). Therefore, the telescopic arm ( 12 ′) can be freely moved up and down relative to the upright tube ( 11 ′) and then positioned in the desired position. According to the embodiment shown in  FIG. 2 , the resilient means ( 13 ′) is a spring ( 13 ″) which achieves the same effect. 
   SUMMARY OF THE INVENTION 
   The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a retractable support tube structure, which is easy to adjust, inexpensive to manufacture, and durable in use. 
   To achieve these and other objects of the present invention, the retractable support arm structure is connected between a base and a steering mechanism to support a load at the steering mechanism, comprising an upright tube, which has a bottom end fixedly fastened to the base, a top end, and a longitudinal receiving space extending through the top end and bottom end; an telescopic arm, which has a bottom end inserted into the longitudinal receiving space of the upright tube and a top end connected to said steering mechanism; a first friction member, which is capped on the top end of the upright tube and disposed in contact with the periphery of the telescopic arm; a second friction member, which is capped on the bottom end of the telescopic arm and disposed in contact with the inside wall of the upright tube; and a spring member, which has a top fastened to the upright tube inside the longitudinal receiving space and a bottom end coiled up to form a helical spring portion that is to stop against the second friction member. 
   The upright tubes and the telescopic arms can be directly obtained from commercial available seamless rectangular stainless or aluminum alloy tubes for the advantage of low cost. Comparing to seamed tubes, seamless tubes have higher structural strength. Therefore, the upright tubes and the telescopic arms are durable against friction. 
   According to the present invention, the spring member is mounted inside the upright tube and preserves a potential energy against the load carried on the steering mechanism at the telescopic arm. The weight of the load at the steering mechanism is slightly smaller than the resisting force of the spring member. The force difference between the spring member and the load is balanced by the force exerted by the first friction member and the second friction member. The first friction member imparts a friction resistance to the outside wall of the telescopic arm, while the second friction member imparts a friction resistance to the inside wall of the upright tube. Therefore, the telescopic arm can be freely adjusted relative to the upright tube in well-controlled manner to reach balanced state at any point and thereby firmly positioned at any position to hold the LCD monitor or LCD TV at the desired elevation. This retractable support tube structure is simple, and uses only a limited number of component parts. Therefore, the manufacturing cost of the retractable support tube structure is low. Further, the adjustment of the retractable support tube structure is also simple and requires less effort. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic sectional view of a rack for LCD monitor according to the prior art of China Patent Utility No. ZL 03 2 03726.0. 
       FIG. 2  is another schematic sectional view of an alternate form of the rack for LCD monitor according to the prior art China Patent Utility No. ZL 03 2 03726.0. 
       FIG. 3  is an exploded perspective view of a retractable support tube structure according to the present invention. 
       FIG. 4  is an exploded elevational view in cross-section of the retractable support tube structure according to the present invention shown in  FIG. 3 . 
       FIG. 4   a  is an elevational perspective view of the second friction member for the retractable support tube structure according to the present invention. 
       FIG. 4   b  is an elevational perspective view of the spring member for the retractable support tube structure according to the present invention. 
       FIG. 4   c  is an elevational perspective view of the first friction member for the retractable support tube structure according to the present invention. 
       FIG. 5  is a schematic sectional drawing of the retractable support tube structure, showing the telescopic arm moved upwards relative to the upright tube according to the present invention. 
       FIG. 6  is a schematic sectional drawing of the retractable support tube structure, showing the telescopic arm moved downwards relative to the upright tube according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A retractable support tube structure according to the present invention is designed for use in a rack and connected between the base and a steering mechanism for supporting a LCD monitor or LCD TV, allowing adjustment of the height, direction and angle of the supported LCD monitor or LCD TV. 
   Referring to  FIG. 3  and  FIGS. 4˜4   c , the retractable support tube structure, referenced by  1 , comprises an upright tube  10 , a first friction member  20 , an telescopic tube  30 , a second friction member  40 , and a spring member  50 . 
   The upright tube  10  is a seamless rectangular tube that can be made out of metal, such as stainless steel or aluminum alloy, or nonmetal material such as plastics or FRP etc. The upright tube  10  has a bottom end  10   a  fixedly fastened to a base (not shown), a top end  10   b  in vertical alignment with the bottom end  10   a , a longitudinal receiving space  11  extending through the top end  10   a  and the bottom end  10   b , two hook holes  12  formed in the peripheral wall thereof at two opposite sides near the top end  10   b , and two protruding inward stop portions  14  integrally formed with the peripheral wall at two opposite sides and respectively projecting into the longitudinal receiving space  11  adjacent to the bottom end  10   a , and an inside hook  13  formed integrally with the peripheral wall at one side inside the longitudinal receiving space  11  and adjacent to the top end  10   b.    
   The first friction member  20  (see  FIG. 4   c ) is capped on the top end  10   b  of the upright tube  10 , having an outer race  20   a , an inner race  20   b , a coupling groove  21  defined between the outer race  20   a  and the inner race  20   b  and coupled to the top end  10   b  of the upright tube  10 , a plurality of friction pads  201  respectively fixedly fastened to the outer surface of the inner race  20   b  and suspending inside the longitudinal receiving space  11  of the upright tube  10  and extending along the four peripheral sides of the rectangular upright tube  10 , and two hook portions  22  respectively formed integral with the outer race  20   a  at two opposite sides and respectively hooked in the hook holes  12  of the upright tube  10 . 
   The telescopic arm  30  is a seamless rectangular tube that can be made out of metal, such as stainless steel or aluminum alloy, or nonmetal material such as plastics or FRP etc. The telescopic arm  30  has a bottom end  30   a , a top end  30   b  mounted with a steering mechanism (not shown), a longitudinal open chamber  31  extending through the bottom end  30   a  and the top end  30   b , and two hook holes  32  formed in the peripheral wall thereof at two opposite sides near the top end  30   a.    
   The second friction member  40  (see  FIG. 4   a ) is capped on the bottom end  30   a  of the telescopic arm  30 , having an outer race  40   a , an inner race  40   b , a coupling groove  41  defined between the outer race  40   a  and the inner race  40   b  and coupled to the bottom end  30   a  of the telescopic tube  30 , a plurality of friction pads  401  respectively fixedly fastened to the outer surface of the inner race  40   b  and suspending inside the longitudinal open chamber  31  of the telescopic arm  30  and extending along the four peripheral sides of telescopic arm  10 , and two hook portions  42  respectively formed integral with the outer race  40   a  at two opposite sides and respectively hooked in the hook holes  32  of the telescopic arm  30 . The second friction member  40  further has a bottom wall  43 , and two arched abutting portions  44  downwardly protruding from the bottom wall  43 . 
   The spring member  50  (see  FIG. 4   b ) is mounted inside the longitudinal receiving space  11  of the upright tube  10 , having one end provided with a hook hole  52  that is engaged with the corresponding hook  13  inside the longitudinal receiving space  11  of the upright tube  10  and the other end coiled up to form a helical spring portion  51  which preserves a potential energy. The arched abutting portions  44  of the second friction member  40  are pressed on the outer diameter of the helical spring portion  51 . 
   Referring to  FIGS. 5 and 6 , the telescopic arm  30  is inserted into the longitudinal receiving space  11  of the upright tube  10 . Further, the upright tube  10  has a plurality of threaded holes  16  spaced around the bottom end  10   a  for fastening to a base (not shown). The telescopic arm  30  has a plurality of threaded holes  36  spaced around the top end  30   b  for fastening to a steering mechanism (not shown) of load. When installed, the telescopic arm  30  can be moved in and out of the upright tube  10  and stopped in the desired position so that the retractable tube structure can be adjusted steplessly to the desired length (height). Further, the resisting (spring) force of the spring member  50  is determined by the load to be carried on the steering mechanism, i.e., the resisting (spring) force of the resilient member  50  is made slightly larger than the load, and the force difference exists therebetween. Further, the friction pads  201  of the first friction member  20  that are disposed at the top end of the upright tube  10  are stopped against the outside wall of the telescopic arm  30 , and the friction pads  401  of the second friction member  40  that are disposed at the bottom end of the telescopic arm  30  are stopped against the inside wall of the upright tube  10 , thereby holding the telescopic arm  30  in the upright tube  10  in balance state. When adjusting the elevation of the load (LCD monitor or LCD TV), pull the load vertically upwards in the arrow direction shown in  FIG. 5  to move the telescopic arm  30  upwards relative to the upright tube  10 . When released the hand from the load at this time, the telescopic arm  30  is held firmly to the upright tube  10  in the adjusted position. On the contrary, when pressing the load vertically downwards in the arrow direction showed in  FIG. 6  to move the telescopic arm  30  downward relative to the upright tube  10 . When released the hand from the load at this time, the telescopic arm  30  is held firmly to the upright tube  10  in the adjusted position. 
   Although a preferred embodiment of the invention has been described in detail for illustrative purposes, various modifications and enhancements can be made without departing from the spirit and scope of the invention.