with reference to fig1 a there is shown , in isometric projection , an office chair 1 of the prior art having a seat 2 connected to a feet assembly 3 via a central pillar 4 . feet assembly 3 is designed to provide stability to office chair 1 , and as shown , includes a plurality of radially protruding feet 5 a - e , each of which has a caster 6 a - e thereon , to allow the chair to be easily moved along the floor , in all directions . central pillar 4 often includes a piston ( not shown ) allowing vertical height adjustment , and providing a pneumatic cushion which makes the office chair more comfortable . furthermore , the seat is often able to rotate around central pillar 4 , allowing a person seated in office chair 1 to swivel himself without moving feet 5 a - e with respect to the floor . sometimes , in addition to allowing a swiveling rotational movement and a vertical height displacement , office chair 1 additionally has a lilt mechanism allowing the seat to be tilted with respect to the central pillar and the feet assembly . office chair 1 includes a backrest 7 , but does not include armrests and is fairly compact . the office chair of the type shown in fig1 a is commonly used by secretaries and typists , and is sometimes referred to as a “ typist &# 39 ; s chair .” typist chairs are usually padded to some extent , with cheap upholstery , and are usually somewhat limited in the positioning features available . with reference to fig1 b there is shown , in isometric projection , a second office chair 1 ′ of the prior art consisting of a seat 2 ′ and back 7 ′, feet assembly 3 ′ including a plurality of radially protruding feet 5 a - e and casters 6 a - e connected to the seat 2 ′ via a central pillar 4 ′, as with the first office chair mutatis mutandis . office , chair 1 ′ is fairly massive as compared to office chair 1 , and is sometimes referred to as an “ executive chair ”. the executive type of office chair 1 ′ may include further features such as armrests 8 l , 8 r , for example . executive type office chairs 1 ′ are usually well padded and upholstered in leather . sometimes , they include vibration and massage systems . generally , executive type office chair 1 ′ is designed to allow an executive to sit comfortably at his / her desk for extensive periods . in the descriptions hereinbelow , reference to office chair 1 and to any of its components is meant to include office chair 1 ′ and its components , as well as any office chair with similar components . office chair 1 is widely used by users operating a computer . although laptop type computers can briefly be operated when positioned on the user &# 39 ; s knees , for longer term operation , and when using a desktop type computer / computer terminal , the user is required to sit at a table or desk . the tabletop of a conventional table is typically 90 cm above floor level . although computer desks sometimes have keyboard trays about 85 cm above floor level , tables are fairly limited in that they rigidly define the height of the keyboard and screen . also , tables and desks typically occupy a lot of floorspace . referring to fig2 , 4 , and 5 there is shown in isometric projection , side view , front elevation , and from above , respectively , an embodiment of the present invention comprising an appendage for retrofitting office chair 1 around central column below seats 2 and above feet assembly 3 thereof . appendage 100 essentially consists of a monitor support structure 10 a seat connector 12 and a chassis 14 . seat connector 12 connects to any standard type office chair 1 as known in the art around central column 4 thereof . the chassis 14 consists of at least one tubular , elongated support rail 44 , bent into an arcuate form , and preferably of a pair of such rails 44 , 48 arranged as parallel , two rails 44 , 48 being held at a constant separation by the monitor support structure 10 and by seat connector 12 attached thereto . typically , at least one further spacer element 22 is also provided . seat connector 12 consists of a bracket 20 having a hole therethrough 36 through which central column 4 passes . there is preferably provided a locking means 40 for locking bracket 20 onto the central column . rails 44 , 48 pass through corresponding holes 28 , 26 in bracket 20 , allowing rails 44 , 48 to be attached to bracket 12 , and thus to central column 4 of the office chair ( not shown in its entirety ) thereby . monitor support structure 10 may consist of a monitor support tray 54 having holes thereon 56 , 58 through which ends of rails 44 , 48 pass . attached to tray 54 are pairs of grooved auxiliary rollers 60 , 70 which engage rail 48 , above and below tray 54 respectively , and corresponding rollers 62 , 72 which engage rail 44 , above and below tray 54 respectively . rollers 62 , 72 , 60 , 70 engage rails 44 , 48 and allow the positioning of monitor tray 54 with respect to bracket 20 , and thus positioning of a monitor thereon ( not shown ) with respect to the user seated in the office chair . for accurate positioning of tray 54 with respect to the user ( not shown ), monitor support structure 10 includes a rail clamp 50 and piston device 64 . it will be appreciated however , that other means for varying the position and / or angle of tray 54 with respect to chassis 14 , and thus the monitor position with respect to the user may be substituted , as alternative embodiments of the present invention . as shown , attached to rails 44 , 48 of the chassis 14 , are foot pedals 30 , 32 , and around rails 44 , 48 , behind the bracket 20 are a pair of helical springs 34 , 38 held in position by retaining elements 66 , 68 , respectively . the user , sitting on seat 2 may rest his feet on pedals 32 , 34 and exert a force thereon , thereby causing chassis 14 to move forwards in bracket 20 , increasing separation of a monitor on tray 54 from the user . when the force is relieved compressed helical springs 34 , 38 will tend to return chassis 14 to its original position . strictly speaking , of course , only one foot pedal is required , however providing a pair of foot pedals 30 , 32 makes the appendage of the embodiment of the present invention comfortably used by enabling the user to use either his right or left foot . having described embodiments , many variations will now present themselves to those skilled in the art , all of which providing the essential feature of the invention , that is , an appendage that is retrofittable to an office chair , that converts the chair into a computer workplace , allowing a user to work at a computer without requiring a laptop type computer or a desktop type computer and a desk . other trays for keyboard and mouse may be attached to chassis 14 , or all interfaces between operator and computer may be operated on monitor support tray 54 . it will be appreciated that the invention is not limited to what has been described hereinabove merely by way of example . rather , the invention is limited solely by the claims which follow , wherein the word ‘ comprise ’, and variations thereof , such as ‘ comprising ’, ‘ comprised ’ and the like , indicate that the listed component or steps are included , but not necessary to the exclusion of other components or steps not specifically listed .
an appendage that is retrofittable to an office chair for converting the office chair into a computer workplace ; the office chair being characterized by comprising a seat supported by a central column , having a feet assembly attached thereto ; wherein the appendage comprises : a chassis coupled to a seat connector , and a monitor supporting structure ; the seat connector for facilitating connection of said chassis to said central column of said office chair , and the monitor support structure for supporting a computer monitor thereon .