fig1 a and 1b are perspective views from different sides of an embodiment of a practitioner stool 100 . the stool 100 has a seat back assembly 102 , which extends from a seat assembly 104 . the seat back assembly 102 and the seat assembly 104 are supported by the leg assembly 106 . as shown , the leg assembly 106 has a center support from which multiple legs with casters extend . the seat assembly 104 includes a seat 108 shaped to support a practitioner in a seated position . the seat back assembly 102 is adjustable to change a height of a seat back 110 coupled to its upper end . at a lower end , the seat back assembly 102 has a support 112 ( also referred to as a support member ) that is connected to a rear area of the seat assembly 104 . fig2 a is an exploded perspective view of an embodiment of the seat back assembly 102 , which is also referred to herein as a height adjust mechanism . as shown in fig2 , the support 112 in the illustrated implementation has a lower end 114 and an opposite upper end 116 . the lower end 114 can have apertures 118 for receiving fasteners 120 to secure the support 112 in place . in the illustrated implementation , there are optional spacers 122 through which the fasteners 120 are threaded . the lower end 114 can be angled as shown to suit the particular configuration , or it may have another suitable shape . as is described in more detail below , a movable portion , or movable height adjusting assembly , is movable relative to the support 112 which is stationary ( unless provided with an optional tilt capability , as is described below ). the support 112 includes at least one generally upright guiding feature , such as one or more guide grooves or slots . in the illustrated implementation , the support 112 includes a pair of parallel through slots 124 configured to be positioned generally vertically when assembled . the support 112 is constructed to have a robust configuration that does not yield . in some implementations , the support 112 is machined from solid bar stock steel . the slots 124 receive guide members , which in the illustrated implementation are the respective guide members 126 extending from an inner surface 127 of an outer cover 150 . each guide member 126 has a lateral width shaped to be slidingly received in one of the slots 124 , respectively , and a substantial length so as to ensure that the movable assembly can be extended and retracted smoothly without excess play . the guide members 126 are secured in the respective slots 124 by a plate 134 on an inner side , which is secured by fasteners 136 that extend through apertures 135 and are received in threaded holes or bores 137 in the guide members 126 . in the illustrated implementation , there are two fasteners 136 securing the left side of the clamp plate 134 to a left guide member 126 . there are also two fasteners 136 securing a right side of the clamp plate 134 to a right guide member 126 , but the right side of the clamp plate 134 has a cut - out or opening 142 shaped to receive an actuator 140 accessible from an exterior surface of the seat back assembly 102 ( see , e . g ., fig1 ) that the user can depress or otherwise manually actuate to allow the user to adjust the position of the seat back 110 , i . e ., to move it upward or downward . in some implementations , the actuator 140 is a pushbutton actuator . fig2 b is a perspective view of the seat back assembly 102 from a rear side with a portion of the outer cover 150 cut away to show the interaction of the guide members 126 in the slots 124 and an engagement member 144 . as illustrated , a distal end 145 of the engagement member 144 is positioned into one of a series of spaced recesses 147 formed in the support 112 , such as by being spring - biased in a direction towards the support 112 . the spaced recesses 147 define a height adjustment range for the seatback 110 . in the illustrated implementation , the engagement member 144 is attached at its lower end to the inner surface 127 with fasteners 146 ( fig2 a ). when the actuator 140 is depressed with sufficient force , a projection 149 on the actuator contacts the engagement member 144 and moves the distal end 145 away from the support 112 and out of engagement with the recess 147 . while the distal end is disengaged , the user can adjust the height of the seat back 110 by grasping the movable assembly ( formed by the outer cover 150 , a mating inner cover 152 and the other associated components coupled thereto ) and sliding it upward or downward relative to the support 112 to a new position . conveniently , the user can reach behind with a right hand , depress the actuator 140 with a thumb , and at the same time use the other four fingers to grasp and move the movable subassembly . thus , it is possible to adjust the height of the seat back using one hand , which is advantageous , particularly in working environments where frequent changes in seating positions are desirable . as shown in fig1 b and 2b , the actuator 140 can be positioned against the inner cover 152 with a mount 150 held in place to permit the actuator to pivot when depressed . as shown in fig2 a , optional wear pads 130 , 132 can be assembled in contact with the outer and inner surfaces of the support 112 . the wear pads , which can made of a nylon plastic or other similar material , can be provided to make components of the movable subassembly slide more freely relative to the support 112 and to minimize wear from repeated use . when the actuator 140 is in its at rest position , the engagement between the distal end 145 and the selected one of the recesses 147 provides sufficient force to keep the seatback 110 in place and prevent unwanted movement . of course , other suitable arrangements to provide suitable engagement and / or clamping forces can be used . the height range and adjustment increment are set to accommodate users of a wide range of heights and sizes , as well as to accommodate users &# 39 ; different positions on the stool , including a regular seated position and other positions a practitioner might adopt while working that would cause the practitioner to contact some portion of the seat back assembly 102 . as shown in fig2 a , a lower cover 154 can be provided , and it can be secured in place , such as to the outer cover 150 as shown , with fasteners 156 . the outer cover 150 can be formed of extruded aluminum or another suitable material . the inner cover 152 and the lower cover 154 can be formed of injection molded plastic , such as an injection molded polyester and polycarbonate blend , or another suitable material . the inner cover 152 may have a tab 159 or other feature to assist in aligning it with the outer cover 150 . as can be seen in fig1 a , 1b , 2b , 3a - 3c , the seat back assembly 102 ( as well as the related assembly 102 ′ discussed below ) has an exterior configuration that features few surfaces that are generally smooth , few if any sharp corners and substantial generally planar areas . as a result , the actuator 140 can be situated as shown on a forward surface of the assembly adjacent a seat practitioner &# 39 ; s back . this positioning has been found to allow the practitioner to reach back , such as with his or her right hand , to locate the actuator without needing to view it , and to depress it while grasping the surrounding structure , i . e , the relatively smooth and uninterrupted surfaces of the inner cover 152 and the outer cover 150 . in addition , the smooth surfaces of the seat back assembly that are relatively free of interruptions allow for the stool to be cleaned effectively and easily , which is a necessary requirement for the dental operatory environment . although described as a height adjustment mechanism for adjusting the height of the seat back 110 , the same components can be configured for other adjusting functions . for example , as shown in fig7 for an assistant &# 39 ; s stool 300 , the same assembly as the seat back assembly 102 can be implemented as a torso bar assembly 102 ′ to allow a height of a torso bar 302 to be adjusted upward or downward relative to the seat 108 . this allows an assistant or other occupant to adjust the torso bar 302 for a proper height relative to the assistant &# 39 ; s size and current activity , which may require leaning over the torso bar 302 to access a patient &# 39 ; s oral cavity . the assistant &# 39 ; s stool 300 is generally similar to the stool 100 , which allows common components to be used interchangeably . as illustrated , the stool 300 is fitted with an optional , rotatable foot rest 304 that is useful to support the user &# 39 ; s feet when the stool 300 is used at greater heights . according to another implementation as shown in fig3 a - 6d , a stool 200 has adjustable armrests , such as a right armrest assembly 160 for supporting a right armrest 162 and a left armrest assembly 164 for supporting a left armrest 166 ( for convenience , “ left ” and “ right ” as used herein refer the seated occupant &# 39 ; s left and right ). the armrest assemblies 160 , 164 are capable of multiple movements to allow the armrests 162 , 166 to be independently positioned in a wide variety of positions . referring to the front side elevation view of fig3 a , the armrests 162 , 166 are shown in a regular width position . fig6 a is a plan view of the chair 200 with the armrests 162 , 166 in the regular width position . in fig3 b , the armrests 162 , 166 have been moved to a wide position by adjusting each respective armrest assembly 160 , 164 relative to an armrest base 158 , as is described in detail below . fig6 b is a plan view of the chair 200 with the armrests 162 , 166 in the wide position . in fig3 c , the armrests 162 , 166 have been rotated inwardly to a narrow , elbow support position in which the user can conveniently place his or her elbows on the armrests 162 , 166 . fig6 d is a plan view of the chair 200 with the armrests 162 , 166 rotated to the elbow support position . fig6 c is a plan view of the chair 200 with the armrests 162 , 166 rotated to a spread position , which can be used to move the armrests out of the way for the user &# 39 ; s specific activities , as well as ingress and / or egress . fig4 is an exploded perspective view of the armrest assembly 160 , the armrest assembly 164 and the armrest base 158 , showing the components that allow the relative movements necessary to permit the armrests 160 , 166 to be positioned in a wide range of positions . fig5 is a sectioned elevation view of the armrest assembly 160 for the right side showing the components in an assembled state . referring to fig4 and 5 , the armrest assembly 160 has an adjustment knob 172 a with a shaft that extends through a slot 184 a in a support member 170 a that supports the armrest 162 and through an aligned opening 186 a in the armrest base 158 . the distal end of the shaft is received in a pivot hub 190 a . a backer plate 197 a is secured to a lower side of the armrest base with fasteners 198 a . there is a friction adjustment screw 196 a with a threaded end extending outwardly through the backer plate 197 a that receives a nut 199 a for adjusting the amount of friction experienced during movements . if necessary , the friction adjustment screw 196 a can be held in place while the nut 199 a is rotated by inserting an appropriate tool in a slot or recess provided at an end 201 a of the friction screw 196 a . in the illustrated implementation , there is a series of components positioned between the adjustment knob 172 a and the armrest base 158 , namely a thrust washer 174 a , a thrust bearing 176 a , a thrust washer 178 a , a low friction ( e . g ., nylon plastic ) washer 180 a and another low friction ( e . g ., nylon plastic ) washer 182 a . similarly , there are similar components in the assembly below the armrest base 158 , including a friction washer 188 a positioned over the pivot hub 190 a , and a friction isolation bearing stack comprising a thrust washer 192 a , a thrust bearing 194 a and a thrust washer 195 a positioned between the pivot hub 190 a and the friction adjustment screw 196 a . a slight gap is maintained between the support member 170 a and the armrest base 158 . the bearings , hub , washers and friction components provide for smooth pivoting and an adjustable degree of friction to prevent unintended rotation of the armrests . desirably , a range of friction is possible , including sufficient friction to keep the armrests in position after only incidental contact , but allowing the armrest to be moved freely , without manipulation of other components , when pushed or pulled . this provides users with a positive fee for how components of the stool move relative to each other . the adjustment knob 172 a can be tightened to keep the armrest 162 at any desired position . the armrest assembly 164 is a mirror image of the armrest assembly 160 . a yoke 185 and fasteners 187 are used to secure the arm base 158 to part of the chair , such as , e . g ., a shaft of the chair . the stool can include one or more manual controls , e . g ., the levers ( or paddles ) 201 , 203 and / or 205 , to allow the user to adjust the positions of portions of the stool . for example , the leg assembly 106 that supports the seat 108 may include a gas cylinder controllable with the lever 201 to assist the user in raising or lowering the seat 108 to a desired height . as another example , the lever 203 may be configured to actuate a tilt adjust mechanism to permit the seat 108 and back 110 to be angled in unison under tension ( such as when a seated user leans against it them ), to change the tension and / or to lock the seat 108 and back 110 in place and prevent any tilting . the lever 205 may be configured to permit the back 110 to be reclined relative to the seat 108 . commonly assigned and concurrently filed applications entitled “ seat assembly for task - oriented seating ” ( u . s . patent application no . not yet assigned ) and “ height adjusting mechanism and stool for dental practitioner ” ( u . s . patent application no . not yet assigned ) are incorporated herein by reference . in view of the many possible embodiments to which the disclosed principles may be applied , it should be recognized that the illustrated embodiments are only preferred examples and should not be taken as limiting the scope of protection . rather , the scope of protection is defined by the following claims . we therefore claim all that comes within the scope of these claims .
an adjustable armrest assembly for a stool or chair comprises an armrest base , an armrest support member and an adjustment assembly . the armrest base is connectible to the stool or chair and has a first opening . the armrest support member has a first end with a second opening . the first end is positionable with the second opening aligned with the first opening . the armrest support member has a second end opposite the first end and extending distally to support an armrest . an adjustment assembly is positionable to extend through the second opening and the first opening to define a pivot axis and an adjustable pivot connection between the support member and the base . the assembly is movable within at least one of the first opening and the second opening to laterally reposition the pivot axis . a variable friction member applies a selected degree of resistance to the adjustable pivot connection .