referring to the drawings and particularly to fig1 , one form of the seating unit of the present invention is there shown and generally designated by the numeral 18 . seating unit 18 , here depicted as an airplane seat , comprises a back portion 18 a , a seat portion 18 b and vertical side structure 20 of the character illustrated in fig2 and 3 of the drawings . connected to one side 20 a of the side structure 20 is the linear locking device of the apparatus , here shown as a friction brake mechanism 24 ( fig2 a , 3 and 6 ). connected to the opposite side 20 b of the side structure is a linear bearing 26 ( fig2 , 3 , 4 and 4 a ). in a manner presently to be described , a vertically adjustable armrest 28 is operably interconnected with the friction brake mechanism 24 and with the linear bearing 26 . with this construction , vertical motion of the armrest is controlled by linear bearing 26 , while position control of the armrest is provided by the friction brake mechanism 24 . the linear locking device , or brake mechanism 24 , which is readily commercially available from several sources , including the p . l . porter company of burbank , calif ., comprises a hollow housing 30 and an elongated , vertically extending rod 32 that is slidably mounted within the housing . the brake mechanism 24 here comprises first and second coiled springs 33 a and 33 b that are tightly wound on the rod 32 and are fixed against axial movement relative to the housing ( fig6 ). a release collar 34 is provided for acting upon the springs , thereby relaxing their grip on the rod 32 and allowing vertical movement of the housing 30 along the rod 32 . as will be discussed in greater detail hereinafter , release collar 34 forms a part of the novel release mechanism of the invention for partially unwinding the springs so that the housing 30 , along with the armrest 28 can be vertically adjusted . it is to be noted that if the rod is pushed before the springs are unwound , the springs will grip the rod even more tightly to prevent vertical movement of the housing 30 and the armrest 28 . uniquely , brake mechanism 24 has one maximum stroke setting that can lock at any position within the travel range of the housing and has positive locking capabilities in both directions . as indicated in fig6 , the distal ends of the coiled springs 33 a and 33 b are fixed within the housing 30 . thus , when the release mechanism is actuated causing a force to be exerted on the actuating lever 34 a of the collar 34 , the distal ends of the springs cannot be moved about the axis of the rod and the force imparted to the springs by the collar 34 will cause them to unwind and release their grip on the rod . however , when the actuating force on the lever 34 a is released , the springs will immediately return to their gripping positions on the rod . in the present form of the invention , the release mechanism also includes a release cable system 34 b , the operation of which causes an operating force to be exerted on the actuating lever 34 a of the collar 34 . the details of the construction and operation of the release cable system 34 b will presently be described . for a more complete understanding of the construction and operation of the brake mechanism , the p . l . porter company should be contacted . alternatively , reference should be made to u . s . pat . no . 3 , 874 , 480 issued to porter et al , and entitled friction brake mechanism . u . s . pat . no . 3 , 874 , 480 is hereby incorporated by reference as though fully set forth herein . linear bearing 26 is a conventional type of linear motion device that allows motion and positioning along a linear axis . while various types of linear bearings are suitable for the present application , a linear bearing manufactured and sold by iko nippon thompson co . ltd . of tokyo , japan has proven satisfactory . as best seen by referring to fig2 of the drawings , linear bearing 26 here comprises a vertical slide member 36 and a carriage 38 that is connected to slide member 36 for vertical movement along a pair of spaced - apart tracks 36 a and 36 b between an upraised position shown by the solid lines in fig3 and a lowered position shown by the dotted lines in fig3 . vertical slide member 36 is interconnected with the vertical side structure 22 by a plurality of spaced - apart threaded connector bolts 40 ( fig2 ), while carriage 38 is interconnected with the adjustable armrest by means four spaced - apart threaded connector bolts 42 . also connected to vertical side structure 22 is biasing means for continuously urging armrest 28 toward its upraised position . this biasing means is here provided in the form of a conventional , commercially available reel - type torsion spring assembly 44 that includes a reel housing 44 a , a torsion spring 44 b mounted within the housing and elongated , retractable , reel cable 46 having a first end 46 a interconnected with the torsion spring 44 b and a second end 46 b connected to side structure 22 by means of a suitable cable anchor 48 ( fig2 ). as best seen in fig2 of the drawings , reel cable 46 is entrained over an idler pulley 50 that is rotatably connected to side structure 22 and also forms a part of the biasing means of the invention . in use , the armrest 28 is maintained in the upper , normal operating position shown in fig1 by the previously described biasing means . when it is desired to move the armrest into a lowered position a downward pressure is exerted on a pushbutton 53 that is mounted on the upper portion of the armrest ( fig1 ). pushbutton 53 , which , along with release collar 34 , forms apart of the release mechanism of the invention , is operably associated with a conventional release cable mechanism 55 that is carried within the armrest 28 and also forms a part of the release mechanism of the invention . as indicated in fig2 a of the drawings , the distal end 55 a of the internal cable of the release cable mechanism 55 is received with a release housing 57 that also forms a part of the release mechanism 34 . also received with release housing 57 , in a manner indicated by the dotted lines and fig2 a , is the release lever 34 a of the collar 34 . with this construction , the force exerted on the cable of the release cable mechanism 55 by exerting a downward pressure on the pushbutton 53 will , in a manner well understood by those skilled in the art , cause the cable to exert pressure on the release lever 34 a causing it to move into the release position . as the release lever moves into the release position , the coiled springs 33 a and 33 b will be caused to unwind and release their grip on the rod 32 . with the release lever in the release position , a downward force exerted on the armrest will cause the armrest to move freely downwardly . however , as previously discussed , if pressure on the pushbutton is removed , the release lever 34 a will return to its locking position causing the torsion springs 33 a and 33 b to once again securely grip rod 32 and thereby prevent further downward movement of the armrest . during the downward movement of the armrest , the reel cable 46 will be wound about the drum of the torsion spring assembly 44 so that , with the armrest in a downward position , a pressure exerted on the pushbutton will exert pressure on the release lever 34 a causing it to move into the release position and thereby permit the armrest to automatically return to its upraised position due to the urging of the torsion spring 44 a of the torsion spring assembly 44 . having now described the invention in detail in accordance with the requirements of the patent statutes , those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions . such changes and modifications may be made without departing from the scope and spirit of the invention , as set forth in the following claims .
a vertically adjustable armrest that is suitable for use in connection with various types of passenger vehicles , including commercial aircraft . the armrest includes a slide mechanism for permitting easy height adjustment of the armrest and also includes a locking mechanism for securely locking the headrest in the desired elevated position . the armrest moves in a smooth vertical motion and is continuously biased toward an upraised position . vertical adjustment of the armrest is accomplished by pushing a push button located in the upper portion of the armrest .