| 摘要 |
<p>1,084,455. Drilling. NORTH AMERICAN AVIATION Inc. Feb. 8, 1965, No. 5384/65. Heading B3C. [Also in Division G3] In a control system for a drill, rotational speed is automatically increased and decreased with decrease and increase in measured torque load on the tool and feed rate is automatically increased and decreased with increase and decrease in rotational speed. In Fig. 8, a drill spindle is rotated by an electric motor 18 and the torque is maintained constant during drilling by a system (see Division G3) automatically controlling the speed of motor 18 in dependence on signals from electrical transducers 28 detecting twist, and hence torque, in a replaceable torsion bar 20 transmitting the drive. A disc 60 perforated with holes and controlling the light transmitted to a number of photocells, produces signals of different frequencies, one of which is selected by a push-button unit to control stepping motors 46A, 46B driving a lead screw 44 to feed the drill into the work at a speed related to the rotary speed of the drill. Should the drill become clogged or worn, undue decrease in speed due to the increase in torque is detected by a tachometer or the photo-cells to cause operation of an hydraulic ram 202 to withdraw the drill from the work, whereupon it speeds up and clears itself by centrifugal action. Motors 46A, 46B are also reversed for a short period so that when, immediately afterwards, the drill is reinserted, it is not initially forced to the bottom of the hole. If the fall in speed is due to wear, the drill is withdrawn and reinserted repeatedly without effect, but this draws the attention of an operator who replaces the drill. A limit switch operates to withdraw the drill when a desired drilling depth has been attained. An electromagnetic clutch 210 may be engaged instead of clutch 212 to speed up the initial advance and final withdrawal of the drill.</p> |
