902,231. Shearing. KOPPERS CO. Inc. Dec. 23, 1958 [Dec. 27, 1957], No. 41536/58. Class 83 (4). [Also in Groups VIII, XXXV and XXXVII] Apparatus for cutting sheet material into equal lengths by means of rotary shears C comprises an adjustable ratio transmission 16 which determines the length of sheet being cut by determining the time which elapses between consecutive meetings of blades 14. The peripheral speed of the blades is made equal to the linear speed of the sheet at the time of cutting by means of differential mechanism Y having a ring gear 24 which is rotated to add to or subtract from the angular velocity of the blades as is required for the particular length of material to be severed. Linkage mechanism for the gear 24 comprises crank-shaft 33 with rollers engaging slots in slidable yoke members 38L, 38R, to which are attached rocking arms 42L, 42R. Fulcrum members 44L, 44R, for the rocking arms are journalled in block 46 which is moved relatively to base 48 by screws 46s. Racks 52L, 52R are engaged by the rocking arms and have teeth engaging pinions 53L, 53R. Thus, the motion of yoke member 38L is transmitted to the ring gear 24, the amplitude of the rack motion being determined by the position of block 46, and the blades being arranged to meet when the rocking arm 42L is perpendicular to the longitudinal axes of rack 52L and yoke 38L. A differential unit X has a ring gear 24X engageable with ring gear 24 and a flywheel 60 mounted on its output shaft so as to counterbalance the reaction torques on gears 20, 31. A flywheel similarly counter-balances the reaction torques on the linkage mechanism 38L-56L. A coarse-adjusting motor 61 and a fine-adjusting motor 62 are provided for adjusting the ratio between the speeds of the input and output shafts of the transmission 16, and the control-shaft 21 changes this ratio as well as adjusting the position of the fulcrum block 46. A main drive motor 101 drives the shaft 6 and the control system for the motors 61, 62 is rendered ineffective until the main motor has reached a predetermined speed. The length of sheet to be cut is set by selector 136 coupled to potentiometer 128, and length-sensing means comprise tachometer generators 111, 112, driven by the shafts 9 and 19, respectively. An error voltage developed across potentiometers 128, 132, is amplified in amplifier 148 and applied to the coil 160 of meter 162. Contacts 164, 165, or 173, 174 are closed if the length being cut is shorter or longer than the desired value. A damping circuit comprises feed-back resistor 183 and coupling transformer 154. Engagement of contacts 164, 165, energizes relay 169, whereupon relay 237 closes the contactor 93 to operate motor 62 for re-adjusting the position of the fulcrum block 46 and the variable speed drive 16 to decrease the speed of shaft 19. When substantially the correct length of sheet is being cut, the error voltage becomes zero and the contacts 164, 165 are disengaged. Similarly, when contacts 173, 174 are closed, relay 176 is energized, whereupon relay 284 closes contactor 92 and the motor 62 is operated in the opposite direction until substantial balance is restored. The energizing circuits for the contactors 92, 93, comprise contacts of relays 120, 127, which are controlled by limit switches associated with the fulcrum block 46. Should the above automatic adjustments be stopped and the length of sheet being cut is not exactly the length set on selector 136, the pointer of meter 162 will be off-centre. Manual pushbuttons 270, 310, may then be actuated selectively to turn the motor 62 in either direction until exact balance is restored. Interlocks are provided so that only one motor 61 or 62 can be energized at any time. A new length of sheet to be cut may be selected, while the blades are cutting the length previously selected, by moving the switch 201 to close contacts 403 whereby operation of motor 62 is prevented. If the selector 136 is rotated to select a new length longer than the previous length, an error voltage is developed across potentiometers 128, 132, and is applied to meter 162 for closure of contacts 164, 165. Depression of push-button 450 opens clutch 261 and energizes contactor 95 for operating motor 61 and lighting lamp 504 until the error voltage is removed. When the contacts 164, 165 are opened, a brake 480 is applied for a short period after the motor 61 is deenergized. During operation of the motor 61, the damping circuit including the resistor 183 is short-circuited to decrease the response-time of the amplifier 148. Similar operation is effected if the selected length is shorter than that obtaining. Indicator lamps 605, 611, show if the sheet is " too short " or " too long," these lamps flashing if the fulcrum block 46 reaches its limits of travel in either direction. In another embodiment, one tachometer generator is coupled to the output shaft of the transmission 16, and another is coupled directly to the sheet passing to the cutters. Specification 805,318 is referred to.