for purposes of description herein , the terms “ rear ,” “ front ,” “ vertical ,” “ horizontal ,” and derivatives thereof shall relate to the invention as oriented in fig1 . however , it is to be understood that the invention may assume various alternative orientations , except where expressly specified to the contrary . it is also to be understood that the specific devices illustrated in the attached drawings , and described below are simply exemplary embodiments of the invented concepts . hence , specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting . the present seating unit 10 includes a seat structure 12 and a base 14 ( fig2 , 8 and 10 ). the seat structure 12 and base 14 are connected by a base to seat mounting assembly . the base to seat mounting assembly includes a base mounting assembly and a seat mounting bracket , both discussed in detail below . optionally , the seating unit 10 may include a tablet assembly 16 ( fig1 , 5 - 7 and 9 ). referring to fig1 - 15 , the tablet assembly 16 includes a tablet mounting assembly 18 , a support arm 20 attached to the mounting assembly at a first end 22 , a pivot assembly 24 engaging the support arm at a second end 26 , and a tablet 28 attached to the pivot assembly . the mounting assembly 18 attaches to the seating unit 10 between and in - line with the seat structure 12 and base 14 . referring to fig1 - 15 and 27 - 30 , the mounting assembly 18 includes a mounting collar 30 attached to the support arm first end 22 , a bushing 32 or 32 a press fit into a bottom 34 of the mounting collar , and a pivot cover 36 nested over a top 38 of the mounting collar and the support arm 20 . the pivot cover 36 preferably is constructed of plastic material and includes a channel 40 , a mousehole - shaped opening 42 and stop surfaces 44 and 46 . the pivot cover 36 conceals stops and prevents pinch points when the stops engage . the mousehole - shaped opening 42 ensures that stop surfaces 44 and 46 contact the pivot cover 36 instead of the first end 22 of the support arm 20 . where the pivot cover 36 includes plastic , the mouse hole - shaped opening 42 replaces noisy metal - to - metal contact with a quieter metal - to - plastic contact condition . the tablet assembly 16 may turn freely on the base 14 through 360 degrees of rotation . however , rotation of the support arm 20 is constrained relative to the seat structure 12 to prevent the tablet 28 from contacting the seat structure . the support arm 20 can rotate approximately 110 degrees relative to the seat structure 12 . specifically , movement of the support arm 20 relative to the seat structure 12 is restricted by stop surfaces 44 and 46 contacting stops on the seat structure . rotation of the tablet assembly 16 relative to the seat structure 12 is illustrated in fig2 c and 23c . contact and friction between the tablet assembly 16 and the seat structure 12 are designed such that if a seated user swivels the seat structure relative to the base 14 , but does not touch the tablet assembly 16 , the tablet 28 will remain stationary relative to the base , until a stop is reached , at which point the tablet assembly will begin moving along with the seat structure . the stops prevent contact between the tablet assembly and the seat structure which may damage both over time . the pivot assembly 24 connects the tablet 28 to the support arm 20 and allows the tablet to rotate horizontally on the second end 26 of the support arm . referring to fig1 - 19 , the pivot assembly 24 includes a tablet mount 48 secured to a bottom 50 of the tablet 28 , a bushing 52 press fit into the second end 26 of the support arm 20 , and an inner tube 54 . the tablet mount 48 includes a connecting portion 56 having a central passage 58 and a depression 60 . the depression 60 includes edges 62 and 64 which form stops . the bushing 52 includes a central throughbore 66 , and a top annular flange 68 . a top surface 70 of the annular flange 68 includes a rib 72 with bent ends 74 and 76 which form stop surfaces which restrict the relative motion of the tablet 28 on the support arm 20 . typically , rib 72 is made of a plastic material , so bent ends 74 and 76 replace hard , noisy metal - to - metal contact with a quieter metal - toplastic contact condition . the top flange 68 also includes a cutout 78 positioned parallel to the rib 72 . the second end 26 of the support arm 20 includes a projection 80 corresponding to the cutout 78 . the shapes of the rib 72 , cutout 78 and projection 80 correspond to each other and may be linear , angled or arcuate . however , in a preferred embodiment , the shapes of the rib 72 , cutout 78 and projection 80 are arcuate . to assemble the pivot assembly 24 , the bushing 52 is press fit into the second end 26 of the support arm 20 with the projection 80 passing through the cutout 78 such that the rib 72 and projection are adjacent to each other . a lower end 82 of the inner tube 54 is inserted and secured in the bushing throughbore 66 , and an upper end 84 of the inner tube 54 is inserted and secured in the tablet mount passage 58 . when the inner tube 54 is inserted into the passage 58 of the tablet mount connecting portion 56 , the top surface 70 of the annular flange 68 abuts a bottom 86 of the connecting portion and the rib 72 and projection 80 reside in the depression 60 . when assembled , the bottom 86 of the connecting portion 56 and the annular flange 68 work together to conceal the stops where edge 64 contacts bent end 76 and edge 62 contacts bent end 74 , thereby preventing pinch points . rotation of the tablet 28 relative to the support arm 20 is illustrated in fig2 a and b through 25 a and b . horizontal rotation of the tablet 28 is restricted to prevent the tablet 28 from contacting the seat structure 12 , to allow a user to comfortably sit on and exit from the chair , and to ensure adequate stability of the seating unit 10 . regarding stability , horizontal outward rotation of the tablet 28 is restricted to prevent tipping of the chair . when the tablet 28 is rotated outward and an object is placed on the tablet , the weight of the object , w obj , produces a moment , m obj , that can tip the seating unit 10 over if the center of the tablet extends beyond the base of the seating unit . the value of moment m obj is equal to the weight of the object , w obj , multiplied by the shortest horizontal distance , l obj , between the center of the weight , w obj , and the axis of rotation , where the axis of rotation is a line drawn through the centerlines of two casters 162 nearest to the object . for the seating unit 10 to be stable , m obj must be less than or equal to a counterbalancing moment , m su , formed by the weight of the seating unit , w su , multiplied by the shortest horizontal distance l su from the seating unit &# 39 ; s center of mass to the axis of rotation . this is expressed mathematically as m obj ≦ m su or ( w obj * l obj ) s ( w su * l su ). in a preferred embodiment , maximum outward rotation of the tablet 28 relative to the support arm 20 is restricted to an angle where the tablet 28 does not tip when an object weighing up to 25 pounds is placed onto the center of the tablet ( le ., w obj ≦ 25 pounds ). specifically , maximum outward rotation of the tablet 28 is restricted to approximately 60 degrees by bent end 74 contacting edge 62 ( fig2 a , 20b , 23a , 23b ) to prevent the seating unit 10 from tipping . also , in a preferred embodiment , maximum inward rotation of the tablet 28 relative to the support arm 20 is restricted to approximately 60 degrees by bent edge 76 contacting edge 64 ( fig2 a , 22b , 25a , 25b to prevent the tablet from contacting the seat structure 12 . the tablet 28 is illustrated in fig1 and includes a tray base 88 attached to the tablet mount 48 and a skin 90 attached to the tray base . the tray base 88 is typically constructed of a strong structural material such as glass - filled nylon . the skin 90 can be molded from a wide variety of materials , such as acrylonitrile butadiene styrene ( a8s ) or other plastic materials . optionally , an insert 92 may be molded into the skin 90 . suitable inserts 92 may be constructed of a high pressure laminate ( hpl ) or thermoplastic polyurethane ( tpu ). to prevent rattling and to dampen sound resonating through the tray base 88 , an intermediate layer 94 may be positioned between the tray base and skin 90 . typically , the intermediate layer 94 includes a nonwoven sheet . a thin layer of soft cellular foam or damping foil may also be used as the intermediate layer . the seat structure 12 rotates freely on the base 14 through 360 degrees of rotation and includes a backrest 96 , a seat 98 , armrests 100 and a seat mounting bracket 102 ( fig1 , 13 , 26 and 28 ). typically , the backrest , seat and armrests are formed as a one - piece shell . alternatively , the backrest , seat and armrests may be separate . the backrest and seat may also include upholstery . the armrests 100 extend upwardly and outwardly from a lower portion 104 of the backrest 96 to form a valley 106 between the armrest and the backrest . a backpack , purse , bag , or other article having a strap can be hung on an armrest 100 by placing the strap into the valley 106 and around the armrest . the article supported by the armrest is available for easy access by a seated user . referring to fig1 and 28 , an underside 108 of the seat 98 includes multiple protrusions 110 molded into and integral with the seat . the protrusions 110 include an over - molded boss insert 112 having a central aperture 114 . although the seat 98 may include any number of protrusions 110 , preferably , there are four protrusions . attached to protrusions 110 is the mounting bracket 102 for connecting the seat structure 12 to the base 14 and optionally to a tablet assembly 16 . the mounting bracket 102 can be any shape , but preferably the bracket is x - shaped and includes an aperture 116 near an end 118 of each leg 120 of the x . the mounting bracket 102 can be attached to the seat 98 by passing a fastener 122 through the aperture 116 in the leg 120 and into a corresponding aperture 114 in a protrusion 110 . alternatively , the mounting bracket 102 may be attached to the seat 98 using an adhesive or rivets . the mounting bracket 102 also includes a central female connector 124 and an annular rib 126 surrounding the female connector . as illustrated in fig1 , 13 and 26 , the height of the annular rib 126 is not uniform , but rather includes a first portion 128 having a greater height than a second portion 130 . the first and second portions 128 , 130 are connected by angled portions 132 and 134 . angled portions 132 , 134 form stop surfaces which restrict movement of the tablet assembly 16 relative to the seat structure 12 . in particular , movement of the support arm 20 toward the rear of the seat structure 12 is restricted by stop surface 44 contacting angled portion 132 . likewise , movement of the support arm 20 toward the front of the seating structure 12 is restricted by stop surface 46 contacting angled portion 134 . ( see fig2 c and 23c ). referring to fig9 and 27 - 30 , for a seating unit 10 including a pedestal base , the mounting bracket 102 may also include a lever 136 . the lever 136 is used to activate an actuator button 138 of a vertically adjustable gas cylinder 140 . the base 14 includes a base support 142 and a base mounting assembly 144 ( fig1 ). as illustrated in fig1 - 6 , 11 , 12 and 31 - 34 , the base support 142 may have three or more legs 146 . in an alternative embodiment , the base support may include a pedestal with radially extending legs 148 , such as a five - star pedestal ( fig7 - 10 and 27 - 30 ). referring to fig3 and 32 , in one embodiment , the seating unit 10 includes a base 14 having a tripod base support 150 . the tripod base support 150 includes a top 152 attached to a bottom pan 154 . the pan 154 can be used to store a backpack , purse , bag , or other article . the top 152 includes three curved legs 146 extending from a central hub 156 and attached to a bottom ring 158 . a seated user can also use the pan 154 or bottom ring 158 as a footrest . preferably , the bottom ring 158 is attached to legs 146 to minimize cost and maximize structural integrity of base 150 . however , in an alternative embodiment , the bottom ring 158 may be attached to the bottom pan 154 . the bottom ring 158 includes a plurality of pintle mounts 160 for mounting casters 162 or glides . in a preferred embodiment , the legs 146 and pintle mounts 160 are positioned equidistantly around the bottom ring 158 ( see fig3 and 34 ). flanking the pintle mounts 160 are fastening bosses 164 . the bottom pan 154 can be any shape , but preferably is circular . the pan 154 typically includes a series of holes 166 . the series of holes 166 permits air flow through the pan 154 and allows liquids from stored articles or shoes which may accumulate to drain . typically , the series of holes 166 is arranged in a circular pattern of small holes , however , any other pattern or hole size can be used . the bottom pan 154 also includes a plurality of apertures 168 located equidistantly adjacent a periphery 170 of the pan . the plurality of apertures 168 includes a central opening with a smaller hole on each side of the central opening . the position of the apertures 168 corresponds to the position of the pintle mounts 160 and fastening bosses 164 . to assemble the base 14 including a tripod base support 150 , the top 152 is positioned over the bottom pan 154 with the pintle mounts 160 extending through the central hole of apertures 168 . fasteners 172 pass through the two smaller holes of apertures 168 and engage the fastening bosses 164 to secure the pan to the top 152 . optionally , the top 152 and bottom pan 154 may include clips ( not shown ) positioned between pintle mounts 160 and casters 162 , respectively . the top clips are releasably engaged to the bottom clips . the clips help maintain contact between the top 152 and bottom pan 152 and prevent gaps between them . casters 162 or glides are inserted into the pintle mounts 160 . as the seating unit 10 moves around , articles stored on the pan 154 remain with the seating unit and are available for access by a seated user . typically , the tripod base support 150 includes six pintle mounts 160 and casters 162 , although more pintle mounts and casters can be used . as noted above , in a preferred embodiment , the pintle mounts 160 and legs 146 are positioned equidistantly around the bottom ring 158 of the top 152 . when the tripod base support 150 includes six pintle mounts 160 , each pintle mount is positioned approximately 60 degrees from adjacent mounts and each leg 146 is positioned approximately 120 degrees from adjacent legs . to maximize stability of the seating unit 10 and minimize deflection of the base pan 154 , the pintle mounts 160 and casters 162 are offset from the legs 146 . it has been discovered that when at least some of the pintle mounts 160 and casters 162 line up with the legs 146 , the structural integrity of the base 150 and the stability of the seating unit 10 is compromised . specifically , where the pintle mounts 160 and casters 162 are in - line with the legs 146 , a user sitting on the seating unit 10 applies a load which is transferred to the casters below the legs . however , almost no load is transferred to the remaining casters . an uneven load distribution can cause pintles and casters to break . also , the in - line configuration may also compromise the stability of the seating unit and create potential safety issues for a seated user . for example , if a user turns the seating unit 10 such that one of the legs 146 faces straight forward and an open section faces backward , and then leans back , the user can rock with the seating unit pivoting on the two rear legs . the rear portions of the pan 154 and bottom ring 158 flex excessively and the front casters 162 lift off the ground , causing the seated user to tip backwards . offset casters 162 and legs 146 address both of these issues by distributing loads and stresses evenly among all casters and reducing the ability of a user to flex the pan 154 and bottom ring 158 when leaning backwards . this is true whether the pintle mounts 160 and casters 162 are positioned equidistantly around the bottom ring 158 or not . however , it has been discovered that preferably the number of casters 162 is 2x , where x is the number of legs 146 , and the distance between a midpoint 174 of where the leg attaches to the bottom ring 158 ( le ., half the width , w , of the bottom of the leg ) and adjacent casters is ttd / 4x , where d is the diameter of the pan 154 . in other words , the distance from an edge of a leg 146 to the nearest adjacent caster is ttd / 4x − w / 2 . the base mounting assembly 144 components vary depending on the type of base support . the base mounting assembly 144 for a tripod base support 150 is illustrated in fig1 - 15 . in this embodiment , the base mounting assembly 144 includes a cup 176 with a flange 178 at a top end 180 , a bushing 182 press fit into the cup , and a base tube 184 . the cup 176 is inserted into the central hub 156 and the flange 178 is secured to the base top 152 . a bottom end 186 of the base tube 184 is inserted through the bushing 182 and into the cup 176 . the bushing 182 and bottom end 186 of the base tube 184 are secured to a bottom 188 of the cup 176 with a fastener and a series of washers and thrust bearings 190 . typically , the fastener is a mechanical fastener such as a shoulder bolt . referring to fig1 , to assemble the seating unit 10 including a base 14 having a tripod base support 150 and a tablet assembly 16 , a top end 192 of the base tube 184 is inserted through the tablet mounting assembly 18 and mateably engages the female connector 124 of the seat mounting bracket 102 . in this configuration , a bottom portion 194 of the tablet mounting assembly 18 resides in the base cup 176 , and the annular rib 126 of the seat mounting bracket 102 resides in the channel 40 of the tablet mounting assembly pivot cover 36 . referring to fig7 - 10 , in an alternative embodiment , the seating unit 10 includes a base 14 having a pedestal base support 196 . one example of a suitable pedestal base support is a five - star pedestal base support having a vertically adjustable gas cylinder 140 and radially extending legs 148 . typically , the gas cylinder 140 is tapered and includes a top activated actuator button 138 . the base mounting assembly 144 for a pedestal base support 196 including a tapered gas cylinder 140 is illustrated in fig2 - 30 . in this embodiment , the base mounting assembly 144 includes a receiver 198 having a top 200 and a bottom 202 , and a button extender 206 . the receiver 198 is generally cylindrical and includes a tapered male connector 208 at the top 200 . the receiver 198 also includes an internal taper 210 and an outer flange 212 at the bottom 202 . the tapered gas cylinder 140 is accepted into the internal taper 210 and the button extender 206 is inserted into the male connector 208 . referring to fig3 , to assemble the seating unit 10 including a pedestal base support 196 and a tablet assembly 16 , receiver 198 of the base mounting assembly is inserted into the bushing 32 a of the tablet assembly 16 such that the bottom 34 of the mounting collar is supported by the receiver flange 212 and bushing , and the receiver extends through the pivot cover 36 . in this configuration , the male connector 208 including the button extender 206 of the receiver 198 extends past the top of the bushing 32 a and mateably engages the seat mounting bracket 102 female connector 124 , and the annular rib 126 of the seat mounting bracket resides in the channel 40 of the tablet mounting assembly pivot cover 36 . the button extender 206 abuts the lever 136 . to vertically adjust the height of the seating unit 10 , a user engages the lever 136 which depresses the button extender 206 . in turn , the button extender 206 depresses the gas cylinder actuator button 138 to provide vertical adjustment of the seating unit . advantageously , the height of the tablet assembly is adjustable in tandem with the seat structure 12 when the gas cylinder 140 is activated . for a seating unit 10 having either a tripod base support 150 or pedestal base support 196 , the pivot assembly 24 and base mounting assembly 144 advantageously cooperate to allow a seated user to pull the tablet 28 closer , or push it farther away , maintaining the front edge of the tablet perpendicular to the centerline of the seat , with minimal side - to - side displacement of the tablet . this cooperation between the pivot assembly 24 and base mounting assembly 144 allows users of various sizes to comfortably use the tablet 28 . as illustrated in fig2 , 8 and 10 , the seating unit 10 may be assembled without a tablet assembly 16 . in particular , to assemble the seating unit 10 including a base 14 having a tripod base support 150 , the base tube 184 is inserted into the seat mounting bracket 102 , with the top end 192 mateably engaging the female connector 124 . similarly , to assemble the seating unit 10 including a base 14 having a pedestal base support 196 , the receiver 198 is inserted into the seat mounting bracket 102 , with the male connector 208 including the button extender 206 mateably engaging the female connector 124 . a seating unit 10 not including a tablet assembly 16 may also include an aesthetic cover positioned between the base mounting assembly 144 and seat mounting bracket 102 . alternatively , a seating unit 10 without a tablet assembly 16 may be constructed by omitting the receiver 198 , the button extender 206 and any aesthetic covers . the tapered top of the gas cylinder 140 would mateably engage the female connector 124 of the mounting bracket 102 , and the lever 136 would directly activate top activator button 138 . the seating unit 10 is easy to ship in a ready - to - assemble form with the seat structure 12 , base 14 and optional tablet assembly 16 separate . this saves space and reduces packaging costs , while minimizing final assembly labor and complexity . final assembly of the seating unit 10 is accomplished by optionally placing the tablet assembly 16 onto the base 14 and then placing the seat structure 12 onto the base and applying downward pressure . the final assembly processes disclosed above require no tools or small parts or hardware items which can be lost .
a seating assembly comprising a seat structure including a seat member having an undersurface and a seat edge , a mounting bracket mounted to the undersurface of the seat member , a base including a central hub and a plurality of leg members , the mounting bracket mounted to the base and spaced above the central hub , a first vertical axis passing through the central hub , a base tube mounted to and extending upward along the first vertical axis from the central hub , a mounting collar mounted to the base tube for rotation about the first vertical axis , the mounting collar positioned proximate the mounting bracket and located at least in part located between the mounting bracket and the central hub , a support arm having first and second ends , the first end mounted to the mounting collar for rotation therewith about the vertical axis , the support arm extending radially outward from the mounting collar along the undersurface of the seat member and upward to the second end and a tablet member mounted to the second end .