Patent GB-400691-A (GB)
Title: Improvements relating to microtomes
IPC: G01N1/06
Filed: 1932-05-11
Abstract: 400,691. Microtomes. ALLDRIDGE, R. S., 100, Bayham Street, Camden Town, London. May 11, 1932, No. 13597. [Class 97 (i).] The feeding movement of the object in a microtome is effected by a ratchet mechanism actuated by an eccentric cam the throw of which is made adjustable to vary the thickness of the section, this cam imparting simple harmonic motion to the pawl to minimize the risk of overthrow. The feed screw (or feed nut) is connected to the ratchet wheel by a clutch which is automatically disengaged at a certain stage of the feed movement. An improved form of clamp for the object is also described. The Figures show a rotary microtome in which the object support 2 is carried by a disc 4 secured to a spindle 6 mounted by bearings 8 in a sleeve 12 carried by pillars 14. The sleeve 12 is provided at its end nearer the disc 4 with a threaded socket 50, eccentric to the axis of the spindle, into which is screwed a sleeve 52 on which is formed a cam surface 54 in the form of a circle eccentric to the sleeve, the amount of this eccentricity being equal to that of the socket 50 in relation to the sleeve 12, so that by rotating the sleeve 52 the throw of the cam 54 can be varied from zero to its maximum. A lever 72 pivoted to the disc 4 has a follower 74 engaging the cam, and the free end of this lever is formed as a pawl actuating the feed ratchet wheel 68. The feed screw 56 and its nut 58 are mounted in a sleeve 60 extending from the disc 4, the screw having an enlarged extension 62 which can slide within the sleeve but is prevented from rotation by a key 64. A knurled disc 86 secured to the nut 58 is connected to the ratchet wheel 68 bv a clutch 84 comprising a split spring-pressed tumbler, and the screw 56 is provided with a disc 88 adapted, when the screw is nearing the forward limit of its travel, to operate the tumbler and free the disc 86 from the ratchet wheel. The screw is run back by turning the disc 86, and to prevent jamming during this operation the nut 58 and extension 62 are provided with stop pins 90 which abut against each other just before these parts would come into contact, and prevent further rotation of the nut. To enable the pawl to be disengaged from the ratchet during the running back, the pawl arm 79 is pivoted to the lever 72 at 81, a tail 83 on the arm being pressed upwards by a spring 85, carrying a plate 87 having a notch 89 into which the tail 83 fits when the arm is drawn away from the ratchet wheel. The object clamp comprises a square stem 13 on the stage 11 fitting into a hole passing through a ball 15 having four radial slits 17 three of which do not extend to the back of the ball while the fourth (the upper one in Figs. 5 and 7) extends right through. The forward end of the extension 62 has a spherical seating for the ball and is externally threaded to receive a clamping nut 19. The knife 28, Fig. 1, is carried by a clamp 18 adjustably supported on the base 16 and having two pairs of jaws 20 (only one shown) each of which is provided with two screws 22, 24 for adjusting the cutting angle of the knife, the screw 24 having a collar 26 engaging behind the knife, and the screw 22 bearing on the knife to push it forwards.