| 摘要 |
1297199 Machinery safety device E SICK 28 April 1970 [13 May 1969] 20271/70 Heading F2J [Also in Division G1] The operation of a plurality of relays is checked by connecting one change over contact from each in a chain so arranged that all the contacts have to change in order to energize a test relay. The invention is described as embodied in a machine tool control system incorporating, as a safety precaution, obstruction detection means for inhibiting operation of the machine when an obstruction, e.g. an operator, is detected in the workpiece region. The obstruction detection means (not shown) controls two relays A, B Fig. 1 so that when no obstruction is detected only the first is on (A, B) = (1, 0), and when an obstruction is detected only the second is on (A, B) = (0, 1). The correct inverse operations of these two relays A and B is checked by a slow-to-release relay C, which, having been initially energized by the detection of no obstruction (A, B) = (1, 0), remains energized providing relays A and B operate inversely, i.e. C = AB+ABC. A machine tool operation is initiated by closing a switch E to the position shown, but providing that no obstruction is being detected at that time (A, B) = (1, 0), then nothing further occurs. An obstruction is then simulated by means not shown (A, B) = (0, 1), whereupon providing relays A and B are correctly operating inversely, C = 1, and power is applied to a slow-to-release relay D = ABC + ABD. Relay D however is also slow to pick up, so that a transitional state in which relays A and B indicate an obstruction (A, B) = (0, 1), and relay D has not picked up, D = 0, occurs. This conjunction of events causes a relay G, Fig. 2, to be energized until the eventual pick-up of relay D, and this momentary energization of relay G constitutes a check on relays A, B, C and D. If relay G does not pick-up then the tool is turned off. Relay D having picked up, simulated obstruction is removed, relays A and B revert to their no obstruction states (A, B) = (1, 0) and a relay F = ABCD, Fig. 2, is energized starting the operation of the tool. If during operation of the tool an obstruction is detected (A, B) = (0, 1) the operation of the tool is inhibited, since relay F drops out, until the obstruction is removed. When the operation of the tool is complete the switch E opens and relays D and F drop out. |
