fig1 depicts an exemplary dental chair 10 in accordance with the principles of the present disclosure . the dental chair 10 comprises a patient support 12 including a seat section 14 and a back section 16 that is movable relative to the seat section 14 from a generally inclined position that facilitates maintaining a patient in a seated position , and a generally reclined position that supports a patient in a supine position . the dental chair 10 further includes a base 18 and a lift assembly 20 coupled to the base 18 for moving the patient support 12 from a raised position , as depicted in fig1 and 2a , to a lowered position , as depicted in 2 b . the dental chair 10 may further include a headrest 22 coupled to the back section 16 of the patient support 12 to facilitate supporting a patient &# 39 ; s head while the patient is in the chair 10 . with continued reference to fig2 a , and referring further to fig3 a , 3 b , 4 , and 5 , the lift assembly 20 comprises a lift arm 30 having a first end 32 pivotally coupled to the base 18 , and a second end 34 pivotally coupled to a seat mount assembly 36 . the patient support 12 is operatively coupled to the seat mount assembly 36 for movement with the lift arm 30 . with particular reference to fig4 , the lift arm 30 of the embodiment shown comprises a frame having first and second side members 38 , 40 extending longitudinally between the first and second ends 32 , 34 of the lift arm 30 . the lift arm 30 may further include horizontal or diagonal cross members , or other structure , between the first and second side members 38 , 40 to provide strength and rigidity to the frame . in the embodiment shown , the lift arm 30 is formed as a casting . it will be appreciated , however , that the lift arm 30 may alternatively be machined , welded , forged , or formed by various other methods or combinations of methods . at the first end 32 of the lift arm 30 , the first and second side members 38 , 40 define respective first and second clevis arms 42 , 44 for securing the first end 32 of the lift arm 30 to an axle 46 supported on the base 18 . first and second spaced apart flanges 48 , 50 extend generally vertically upwardly from the first end 52 of the base 18 to form support structure for the axle 46 . the axle 46 supported by the first and second flanges 48 , 50 defines a pivot axis 54 for the lift arm 30 about the first end 52 of the base 18 . similarly , the first and second side members 38 , 40 of the lift arm 30 define first and second clevis members 56 , 58 at the second end 34 of the lift arm 30 for pivotally supporting the seat mount assembly 36 . in the embodiment shown , the first and second clevis members 56 , 58 are coupled to trunnions 59 extending from opposite sides of the seat mount assembly 36 . as the lift arm 30 is pivoted about the axle 46 to raise and lower the patient support 12 , the seat mount assembly 36 may pivot about the second end 34 of the lift arm 30 to maintain the seat section 14 and the back section 16 in a desired orientation relative to horizontal . because the pivot axis 54 of the lift arm 30 is located at the first end 52 of the base 18 , components of the dental chair 10 for raising and lowering the lift arm 30 , or otherwise controlling operation of the dental chair 10 , are located behind the pivot axis 54 instead of being positioned forward of the pivot axis 54 as is typical of conventional dental chairs . this configuration provides a compact construction that reduces the overall footprint of the base 18 while allowing for a generally longer lift arm 30 compared to conventional dental chairs . the longer lift arm 30 provides a greater vertical rise of the patient support 12 while minimizing fore and aft movement of the patient support 12 during raising and lowering . referring to fig3 a , 3 b , and 4 , the lift assembly 20 further includes an actuator 60 coupled between the base 18 and the lift arm 30 to facilitate moving the lift arm 30 about the pivot axis 54 , thereby raising and lowering the patient support 12 . in the embodiment shown , the actuator 60 comprises a hydraulic cylinder including a housing 62 and a piston rod 64 extendable from the housing 62 . the housing 62 is pivotally coupled to the base 18 and the distal end of the rod 64 is pivotally coupled to the lift arm 30 by respective pin connections 66 , 68 , whereby the lift arm 30 is moved from a lowered position , depicted in fig3 b , to a raised position , depicted in fig3 a , as the piston rod 64 is actuated to extend from the housing 62 . to achieve a compact configuration of the dental chair 10 , the actuator 60 is positioned relative to the base 18 and the lift arm 30 at a location offset from a longitudinal centerline 70 of the lift arm 30 and in a direction toward the second side member 40 of the lift arm 30 , as depicted in fig4 . the dental chair 10 further includes a pump 72 operatively coupled to the actuator 60 by a hydraulic line 74 and appropriate fittings . the pump 72 is operable to provide pressurized fluid to the hydraulic cylinder so that the piston rod 64 is moved in and out of the housing 62 to raise and lower the lift arm 30 , as described above . as depicted in fig4 and 5 , the pump 72 is positioned on the base 18 at a location between the first and second side members 38 , 40 of the lift arm 30 and behind the axle 46 . while the actuator 60 of the lift assembly 20 has been shown and described herein as a hydraulic cylinder moved by pressurized fluid from a pump 72 , it will be appreciated that the actuator may alternatively comprise a pneumatic cylinder , an electric motor , or various other linear or rotary actuators suitable for moving the lift arm about the pivot axis . the lift assembly 20 further includes a generally elongate linkage member 80 coupled between the base 18 and the seat mount assembly 36 at the second end 34 of the lift arm 30 . in the embodiment shown , the first end 82 of the linkage member 80 is pinned to a boss 84 on the base 18 and positioned between the first and second flanges 48 , 50 . a second end 86 of the linkage member 80 is pivotally coupled to the seat mount assembly 36 by a pin 88 spaced from the pivotal connection between the seat mount assembly 36 and the first and second clevis members 56 , 58 at the second end 34 of the lift arm 30 . the lift arm 30 and linkage member 80 therefore define a linkage assembly , together with the seat mount assembly 36 and the base 18 , whereby the orientation of the seat mount assembly 36 is controlled as the lift arm 30 is moved from the lowered position , depicted in fig3 b , to the raised positioned , depicted in fig3 a . the linkage member 30 also facilitates supporting the load of the patient support 12 on the second end 36 of the lift arm 30 . the weight of the patient support 12 , including a patient supported on the patient support 12 , tends to unevenly load the second end 34 of the lift arm 30 as a result of the actuator 60 being offset from the longitudinal centerline 70 of the lift arm 30 . this uneven loading tends to deflect the first side member 38 of the lift arm 30 more than the second side member 40 of the lift arm 30 . to accommodate the uneven loading of the lift arm 30 , the lift assembly 20 further includes a load bearing panel 90 , or skin , secured to the lift arm 30 . in the embodiment shown , the panel 90 comprises 0 . 120 - inch thick steel sheet secured to the lift arm 30 by bolts 92 installed into threaded apertures 94 in the lift arm 30 . it will be recognized that panel 90 may alternatively be secured to lift arm 30 by other methods . as a non - limiting example , one or more bolts 92 may be replaced by dowel pins ( not shown ) extending from the lift arm 30 and adapted to engage corresponding apertures in the panel 90 . the connection of the panel 90 to the lift arm 30 provides a monocoque construction whereby the panel 90 is loaded to resist twisting of the lift arm 30 under the weight of the chair . the dental chair 10 may further include a control 100 mounted to the lift arm 30 . in the embodiment shown , the control 100 is positioned centrally between the first and second side members 38 , 40 , although it will be appreciated that the control may alternatively be mounted at various other locations on the lift arm 30 , or at various locations on the dental chair 10 . the control 100 is operatively coupled to the pump 72 and the actuator 60 and is configured to control operation of the dental chair 10 as described herein . the lift assembly 20 may further include front and back cover panels 102 , 104 over the lift arm 30 , and cover panels 106 , 108 on the base 18 to conceal the components of the dental chair 10 and to provide an aesthetically pleasing appearance . while the present invention has been illustrated by the description of exemplary embodiments thereof , and while the embodiments have been described in considerable detail , they are not intended to restrict or in any way limit the scope of the appended claims to such detail . additional advantages and modifications will readily appear to those skilled in the art . the various features disclosed herein may be used alone or in any desired combination . the invention in its broader aspects is therefore not limited to the specific details , representative apparatus and method and illustrative examples shown and described . accordingly , departures may be made from such details without departing from the scope or spirit of the general inventive concept .
a dental chair for supporting a patient during examination and the performance of procedures on the patient includes a patient support having a seat and a back , a base adapted to engage a floor surface , and a lift arm . the lift arm has a first end pivotally coupled to support structure at a first , terminal end of the base for rotation about a pivot axis defined by the support structure . a second end of the lift arm is coupled to the patient support .