Dental patients chair with a parallelogram supporting arm
United States Patent 1191 1111 3,874,728 Weiland Apr. 1, 1975 DENTAL PATIENTS CHAIR WITH A- 3.162.150 12/1964 Armstrong l08/l47 PARALLELOGRAM SUPPORTING ARM 3.554.598 l/l97l Durkin 248/421 [75] Inventor: Rolf-Jurgen Weiland,  
  L t th. G a zenbachfFur erm my Primary E.\&#39;am1&#39;nerCasm1r A. Nunberg Asslgneei Slemens Aktlengesenschafh Attorney. Agent, or F irm-Richards &amp; Geier Erlangen, Germany [22] Filed: Oct. 17, 1973 [21] Appl. No.: 407,179  
 . ABSTRACT [30] Foreign Application Priority Data 06[ Gcrmam, Q1808 A dental patients chair with a parallelogram supporting arm having one end linked to a base and another 52 us. c1. 297 330, 248 421 end Carrying the Seat of Chair and f i51i Int. Cl A47c 1/(i2 A470 i/oe device for the height Of the Chm The of 34 &#39;;47. vention is particularly characterized in that the adjustbw 5 ing device is a spindle drive actuated by electromotor u and engaging the supporting arm preferably between [56] References Cited two diagonally opposed link axes of the arm ends.  
  UNITED STATES PATENTS 2.526.248 10/1950 Luketa 297/330 10 Claims, 7 Drawing Figures PATENTED APR 1 I975 sumlqfz DENTAL PATIENTS CHAIR WITH A PARALLELOGRAM SUPPORTING ARM This invention relates to a dental patients chair with a parallelogram supporting arm having one end linked to a base and another end carrying the seat of the chair and with an adjusting device for the height shifting of the chair.  
  Various treating methods and different sizes of patients make it necessary to be able to change the seat carrying upper part of a dental treating chair in relation to its height within wide limits. Particularly when the patients are of large size and the treating person is sitting, it is necessary to be able to bring the chair into a particularly deep position. Carrying arms having the shape of parallelograms were found particularly suitable for this purpose since they can bring a chair into a deep position which is actually limited only by the height of the parallelogram arm which is quite small as compared to other height adjusting devices suitable for these purposes. Another advantage of the parallelogram carrying arm is that its linking to the base requires little space, so that there is sufficient freedom for the feet of the treating person. Hydraulic lifting devices (piston-cylinder arrangements) have been used for the height adjustment of the parallelogram arm of such patients chairs, since they can raise the weight of the heavy upper chair part along with the patient at most inconvenient lever arrangements in the deepest end position (pressure forces in the size of more than one thousand kilopond). Furthermore, they are so small that it is possible to provide them in a sufficiently narrow parallelogram carrier. (A widening of parallelogram arms would make difficult an easy movement of the doctor to the chair or the patient and would affect his work). However, it is necessary to accept the drawback of these hydraulic devices consisting in that devices cannot be obtained which are sufficiently oil tight. It was found that in the course of years these leakage losses dirty the lower chair portions and the floor of the treating room. Chair parts dirtied by oil can be cleaned only with considerable expense and loss of time which cannot be compensated.  
  An object of the present invention is to provide a dental patients chair of the described type which can produce the high pressure forces required for adjusting the chair without it being necessary to substantially increase the size of the parallelogram arm, which can be operated more simply and which cannot produce dirt by oil through oil leakage. Another object is the dimi nution of costs of making the chair.  
  Other objects of the present invention will become apparent in the course of the following specification.  
  In the accomplishment of the objectives of the present invention it was found desirable to provide as the adjusting device a spindle drive actuated by electromotor and engaging the parallelogram supporting arm preferably between two diagonally opposed link axes of the arm ends.  
  The use of the spindle drive not only eliminates the above-mentioned drawbacks of known devices but also has the advantage that substantially fewer structural parts are necessary. Furthermore, the transporting and the mounting are simplified since there are no more dependent drives for shifting the back and adjusting the seat by means of the parallelogram arm, as is the case in known chairs. There it was necessary to apply pressure upon oil transmitted by an oil pump located in the base in addition to the hydraulic circuit for the carrying arm, also in the hydraulic circuit of the raising device for moving the back, which is located in the upper part of the chair.  
  In accordance with an advantageous embodiment of the present invention it is suggested that the spindle drive should be a roller screw drive, preferably a ball spindle drive. It is advantageous to switch a self-locking drive in front of the roller screw drive since this eliminates the use of more expensive means for locking the driving motor when standing still. The driving motor can be arranged in or outside of the parallelogram carrying arm. Since the parallelogram carrying arm due to its box-like structure constitutes a hollow body with good resonance properties which could strengthen the noises of the motor, it is advantageous to arrange the motor outside of the parallelogram carrying arm. This also eliminates sound absorbing provisions which are difficult to attain. The advantageous arrangement of the driving motor arranged outside the supporting arm has the further advantage that the motor is easier to reach (for exchange of brushes. belts etc.).  
  The connection of the spindle or spindle nut to the diagonally extending link axes of the supporting arm is not absolutely necessary but is advantageous since it avoid undesirable bending forces which could affect parallelogram rods.  
  Within the scope of the present invention it is possible to select the location of the spindle and spindle nut upon the upper or the lower link axis. However, it is advantageous to connect the drive to the link axis located at the side of the base, since this provides a comparatively short distance for transmitting the rotary movement of the motor to the spindle.  
  The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawings showing by way of example only, preferred embodiments of the inventive idea.  
 In the drawings:  
 FIG. 1 is a perspective view of a dental chair.  
 FIG. 2 is a perspective view of the base of the chair.  
  FIG. 3 is a partial perspective view of a different chair base.  
  FIG. 4 is a partial perspective view showing the para]- lelogram carrying arm of FIG. 1 in its lowermost position.  
 FIG. 5 is a partial top view of the same carrying arm.  
  FIG. 6 is a partial sectional view showing the axial bearing of the arm.  
  FIG. 7 is a partial sectional view showing the spindle drive of the arm.  
  FIG. 1 shows a dental patients chair having a base 1 to which the parallelogram carrying arm 2 is connected. A support 3 is arranged at the free end of the arm and carries the chair upper part consisting substantially of the back 4 and the seat 5. The back 4 can be inclined about the axis 6 relatively to the seat 5 and the seat 5 can be tipped relatively to the carrier 3 about an axis also extending transversely to the longitudinal axis of the chair which is not shown in the drawing. The three adjusting movements, namely, the inclination of the back, the tipping of the seat and the height adjustment of the upper part of the chair are actuated by means of the parallelogram carrying arm by actuating members 7 to 9 provided upon the back 4. The actuating members 7 to 9 are located upon the upper part of the back 4 and are so arranged that they can be operated from the back surface of the back as well as from its upper side. The back is made very thin so as to provide a sufficient freedom of foot movement for the seated person in the lower chair position when the back is substantially vertical. In order to avoid extending parts the actuating members 7 to 9 are embedded in the chair back.  
  The base 1 consists substantially of a bottom part 11 upon the front portion of which on opposite sides are provided two vertical side pieces 12, 13 in which the parallelogram arm 2 is swingably mounted. The side pieces l2, 13 are covered by removable covering sheets 17, 18. The parallelogram 2 can be moved from the illustrated position into a deep position in which the arm extends substantially horizontally (FIG. 4). In the back part ofthe bottom 11 there is a stepping plate 14 which is swingably mounted and which cooperates with switching members in the base 11 in such manner that when the plate 14 is stepped on the drive for moving the parallelogram 2 is switched off. This arrangement serves for the safety ofthe operator if by mistake an object (foot of the operator or chair) reaches into the moving range of the carrier 3 or the parallelogram carrier 2 during the downward movement of the chair.  
  The base 1 consists of a welded structure formed by a plate 15 which can be fixed to the floor, a box-shaped cover 16 and side pieces 12, 13 welded on both sides of the part 16 to the plate 15. Each of the side pieces 12, 13 consists of two half shells 19, 20 welded to each other and held by space supports 21. The half shells are made of sheet metal (drawn or pressed part). Bushings supporting the bearing axles 22 and 24 ofthe parallelogram arm are welded in the half shells 19, 20. The cover 16 is made ofa sheet plate by suitable cutting and edge forming. Within the box which is thus formed there are provided sheet profiles 26 which are welded both to the cover 16 and to the plate 15 and extend parallel to the longitudinal sides of the base plate. The sheet profiles are also produced in a bending process. At its rear end the cover 16 has a recess which forms with the base plate 16 an open box 27 containing two switches 28 as well as different electrical connecting parts 29. The switches 28 are actuated by the stepping plate 14 shown in FIG. 1.  
  FIG. 3 shows a different construction of a welded base for supporting the parallelogram carrying arm 2. Here the basic part is constituted by a base plate 30 and welded four edged hollow profile rods 31, 32. The hollow profile rods 31, 32 provide a safe frame free from windings. Upon the frame is provided a sheet covering 33. The side pieces for supporting the parallelogram carrying arm consist of struts 34 to 37 which are welded together also from hollow profile rods.  
  The two welded constructions are technically very easy to manufacture, they have a low transportation weight and are very suitable for receiving side loads. The last-described construction is particularly easy to produce without a great use of special tools.  
  FIG. 4 shows the parallelogram carrying arm 2 swingably connected to the base 1 in its lowermost position. The drawing shows the parallelogram carrying arm partly in section for better illustration of its adjusting means. The parallelogram arm 2 consists substantially of two halves 40 and 41, whereby the upper half 40 is swingably connected on the one hand by an axle 22 to the side pieces 12, 13 and on the other hand is connected by an axle 23 to the carrier 3. The lower carrying arm half 41 is also connected to the side pieces 12, 13 by an axle 24 and is mounted in the carrier 3 by an axle 25. The movement of the parallelogram arm 2 and thus of the carrier 3 for the upper part 4, 5 of the chair, takes place by an electromechanical drive consisting of an electromotor 39, a drive 46 and a ball revolving spindle 47. The motor 39 is mounted upon the base plate 15 outside of the box-shaped parallelogram carrying arm 2. The power transmission from the motor takes place by a V-belt 48 and a roller 49 and from there through a further V-belt 50 to the driving shaft 51 of a worm gear to which the rotary spindle 58 of the spindle drive 47 is connected on the side away from the drive. The motor is fixed to a holding device 52 adjustably connected to the base plate 15 for tensioning the V-belt 48. The V-belt 48 can receive the necessary belt tension by a tensioning screw 53.  
  The drive 46 is connected by a pin 45 flanged thereto to the axle 24. The spindle nut 54 is connected to the axle 23, so that the spindle drive engages between the diagonal axles 23, 24 of the parallelogram rectangle 22 to 25. For easier accessibility the motor 39 is covered by a removable cover 57.  
  FIG. 5 shows the parallelogram carrying arm in top view, some parts of the arm and coverings being also sectioned. The roller 49 is a part of an intermediate shaft which can be easily removed from the axle bearing 24 for the replacement of the V-belts 48 and 50. Details of the axle bearing 24 are shown in FIG. 6.  
  The lower half4l of the parallelogram carrying arm 2 is supported on the one hand by a bolt 62 and a sliding bearing 63 in the side piece 13 and on the other hand by a further bolt 64 and a further sliding bearing 65 in the side piece 12. The intermediate shaft 60 is rotatably mounted by two ball bearings 66, 67 upon a plug axle 68 serving as a bearing axle. An inner six edge screw is used as the plug axle, which engages on the one hand with its head ajoint of the bearing part 62 and on the other hand is screwed into the bearing bolt 64. The two bearing bolts 62, 64 are protected against rotation by radially directed screws 69, 70. When the plug axles 68 are screwed into the bearing bolt 64, the inner rings of the ball bearings 66, 67 are pressed against the front surfaces of the bearing bolts 62 and 64, so that the bearings of the intermediate shaft are tensioned.  
  The removal of the intermediate shaft 60 for exchanging a V-belt takes place by unscrewing the plug axle 68 by a few turnings out of the bolt 64. Then the fixing screw 70 is released and the bearing bolt 64 is easily pressed outwardly by a light hitting upon the head of the axle 68. The outer movement of the bearing 64 relatively to the bolt 62 releases the bearing tension. After the axle 68 has been completely screwed out, the intermediate roller 60 can be removed.  
  FIG. 7 shows partly in longitudinal section the spindle drive 47 engaging on the one hand the axle bearing 24 (at the bearing bolt 64) and on the other hand the spindle drive 47 engaging the axle bearing 23. The drive 46 which is in general use, is screwed to a flange of the bolt 45. The sectional view of FIG. 7 shows the inner structure of the spindle nut 54. The spindle nut 54 is transversely separated at the location 71 into a part 72 containing the rotary ball part and a part 74 receiving a switch 73 and connected with the axle bearing 23. Both parts 72 and 74 are screwed together by three circumferentially located screws 75 while leaving a small axial play 76. Since in normal conditions the entire spindle drive is loaded solely by pressure, the three screws 75 serve only to transmit the action transmitted from the driving spindle 58 to the spindle nuts 72, 74. If, however, the driving spindle is subjected to pull. then the two parts 72 and 74 are raised from each other. When the two parts are separated. the switch 73 fixed to the part 74 is switched on. since the actuating pin 76 is raised from its support 77 (part of 72). The switch 73 is included in the circuit of the driving motor 39, so that when the switch is actuated the motor stops immediately.  
  The spindle 58 has a rise of about l2 mm. In its screw threads within the range of the part 72 are located balls 78 which are placed next to each other as an endless chain. When the spindle is rotated the balls move in the screw thread passages. During one direction of rotation of the spindle the balls leave the screw thread passages at the location 79 and run into a channel 80 of the part 72, where they move out of the opening 81 and move back into the screw thread passages of the spindle. The movement of the balls is reversed in the opposite direction of rotation.  
 I claim:  
  1. A dental patients chair. comprising a base, a seat. a parallelogram carrying arm having one end connected with said base and the other end carrying said seat, the ends of said arm having diagonally opposed axles, and a device for height shifting of the seat, said device comprising an electrically driven spindle drive engaging said arm between said axles. said spindle drive comprising a motor, a rotary spindle driven by said motor, a bearing for the spindle connected with one of said axles and a screw nut engaging said spindle and connected with that end of the arm having the other one of said axles.  
  2. A chair according to claim 1, wherein said bearing for the spindle is connected with the one axle which is connected with said base and wherein said driving motor for the spindle is located outside of said arm on said base.  
  3. A chair according to claim 2, having an intermidiate shaft connected with said motor and transmitting the drive of said motor to said spindle.  
  4. A chair according to claim 3, having an axle supporting said intermidiate shaft, the last-mentioned axle being in alignment with said one axle.  
  5. A chair according to claim 4, wherein the lastmentioned axle and said one axle form a continuous axle bearing.  
  6. A chair according to claim 4, wherein said intermediate shaft is removable from said one axle.  
  7. A chair according to claim 6, comprising a plug axle and two opposed bearings for said one axle and supporting said plug axle. said intermediate shaft being rotatably mounted upon said plug axle.  
  8. A chair according to claim 7, wherein said opposed bearings are axially movable and. wherein said plug axle is a clamping screw for connecting the bean ings of said one axle with the bearings of said intermediate shaft.  
  9. A chair according to claim 8. wherein said spindle drive comprises a safety switch operable when sub jected to tension for interrupting the circuit of said driving motor.  
  10. A chair according to claim 9, wherein said spindle has transversely separated non-rotary portions, means interconnecting said portions when subjected to rotary moment and separating said portions when sub jected to pull, said safety switch being located between said portions.