Improvements in dental and other chairs, and in lifting and lowering apparatus applicable to the same / [Thomas Harry Gardner].

  • Gardner, Thomas Harry.
Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: Improvements in dental and other chairs, and in lifting and lowering apparatus applicable to the same / [Thomas Harry Gardner]. Source: Wellcome Collection.

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    N° 14,508 A.D. 1892 Date of Application, 11th Aug., 1892 Complete Specification Left, 9th May, 1893—Accepted, 24th June, 1893 PROVISIONAL SPEOIFJ CATION. Improvements in Dental and other Chairs, and in Lifting’ and Lowering* Apparatus applicable to the same. We, Thomas Harry Gardner and Edward Gardner both of Hadfield Street, Cornbrook, Manchester, Engineers, do hereby declare the nature of this invention to be as follows :— In the dental chair to which the invention is applicable, there is a fixed chair 5 standard ; an intermediate moving part sliding on the fixed standard up and down ; and an upper moving part sliding upon the intermediate part and carrying the chair seat. These three parts are so geared by racks and pinions that for every increment of rise given to the intermediate part, the upper part rises a corresponding increment 10 in relation to the intermediate part. Consequently in relation to the fixed standard the upper moving part rises and falls twice as fast as the intermediate moving part. The improved lifting apparatus is arranged as follows :—On a spindle mounted on the intermediate part and carrying pinions gearing into racks on the other parts 15 is fixed a silent clutch worked by a tread lever so that as the lever is depressed the spindle is turned and so raises the chair. One end of a controlling arm is fixed loosely on the spindle, the other end is slotted and rides loosely on a pin fixed on the upper moving part of the chair. In the periphery of the clutch case which also is loose upon the spindle is fixed a projection which normally is held by a spiral 20 spring hard down on a similar projection on the controlling arm. The tread lever and the controlling arm project on opposite sides of the spindle and when the extremity of the controlling arm is raised by its connection with the upper moving part, the extremity of the tread lever is depressed. Thus the tread lever is arranged to stand ready for use with its foot end always at the same distance from 25 the ground. The silent clutch consists of a disc rigidly connected with the spindle and is enclosed in the clutch case. The case at one part of its circumference is slotted through to the inside and receives a tongue which is pivotted in the case. The tread lever is attached by a joint to the tongue and when the tongue is depressed 30 by the lever it presses on the disc. One end of a helical spring connects a boss on the clutch case with the tread lever. When the tread lever is depressed the tongue presses against the periphery of the disc causing sufficient friction to carry the disc and spindle round. When the tread lever is lifted by the spring the tongue ceases to touch the disc 35 thus leaving the chair free to be lowered. The lowering is effected by improved lowering apparatus. A spindle is provided and is geared with the spindle before referred to. This spindle through a worm drives an axis and the worm is so proportioned that it will just turn and permit the load to descend unless restrained. Upon the axis there is 40 a flanged disc and concentric with this is a stationary disc, the flange and the stationary disc being in the same plane. Two levers are pivotted to the flanged disc. The levers at the pivot ends are so shaped as to embrace a portion of the periphery of the disc in such a manner that one or other end of the arc of embrace on the levers presses- on to the disc rim 45 according as the lever arms are pulled away from or pressed towards the centre a spring on each lever presses the levers towards the axis and they act after the manner of a brake sufficiently to prevent the axis from revolving under the load.