READ-ONLY SEQUENCE CONTROL SYSTEM

Abstract: A read-only sequence control system comprises a control unit having an EPROM and a plurality of relays responsive to data outputs of the EPROM for controlling a machine. The system has a first sensor for detecting an entrance of work in the machine and a second sensor for detecting discharge of the entered work. When the second sensor does not detect the work at an end of working cycle, the control unit operates to stop the machine.

Description: The present invention relates to a read-only sequence control system as set forth in the preamble part of claim 1. From WO81/02937, a read-only sequence control system is known which is composed of compact standardized units, including a read-only sequence controller, which comprises memory means, an output-relay unit which is controlled by data stored in the memory and externally applied addresses. The control system further comprises a step checking device and a read-out clock pulse controller for generating clock pulses of a given period. The pulse controller controls the output operation of the read-only sequence controller and stops delivering clock pulses according to an emergency signal from the step checking device. The system can be efficiently adapted for any control system by combining a plurality of units. From EP-A-0020764, a sequence control system, and in particular, a programmable logic controller, is known with which data programming and its modification can be performed. The sequence control system comprises memory means which are operated by a user designated keyboard switch for generating clock pulses. A logic control circuit, which is responsive to the clock pulses, provides addressing signals for the memory means which outputs the programming parallel-output data. The above-described sequence controllers, however, are very complexly constructed and, accordingly, their operation requires a great amount of knowledge of the operation. Furthermore, the controllers of the prior art consume storage space and are quite expensive in production costs. It is, accordingly, the object of the present invention to provide a read-only sequence control system which is compact in size and simple in structure at low cost. The object is solved by a sequence control system comprising the features of patent claim 1. Preferred embodiments are subject matters of the subclaims. These and other objects and features of the present invention will become more apparent from the following description with reference to the accompanying drawings, which show: Fig. 1 shows a plan view of a read-only sequence control system according to the present invention; Fig. 2 shows a side view of the control system; Fig. 3 shows a circuit of a control unit of the present invention; and Fig. 4 shows a schematic view showing an example of an automatic manufacturing system employed with sequence control systems of the present invention. Referring to Figs. 1 and 2, a read-only sequence control system of the present invention comprises a read clock pulse control unit 1 having a supply source and an output relay unit 2 mounted on the clock pulse control unit 1. The output relay unit 2 comprises a board detachably secured to the control unit 1. Relays 3 constructed with eight relays are mounted on the board. Terminal units 4 and 5 are disposed adjacent to the relay unit 2. The terminal unit 4 has eight terminals for four relays and the terminal unit 5 has ten terminals for other four relays and for on alternating current power supply. An EPROM 6 is detachably fixed to a connector 7. Numeral 8 is a transistor array, and 9 is a connector for the clock pulse control unit 1 and the output relay unit 2. A display 10 employed with an LED is provided for displaying operation for each relay. On the read clock pulse control unit 1, a power switch 11, fuse 12, pilot lamp 13 with an LED, preset code switch 14, abnormality display 15 with an LED, reset switch 16, starting switch 17, and input terminals 18 are provided. The preset code switch 14 displays digits of two figures for one cycle time and is adapted to select a necessary cycle time. If the unit time for the digits is 0.1 second, digits "32" of preset code switch 14 shown in Fig. 1 means that a cycle time of 3.2 seconds is provided. The cycle time of the preset code switch can be set to a time between 0.1 and 9.9 seconds. It is possible to provide a unit time for the cycle time between 1 second and 1 minute by changing a frequency divider in the preset code switch 14. Accordingly, the cycle time can be set between 1 second and 99 minutes. Referring to Fig. 3 showing a circuit of the control system, the cycle time is set to 3.2 seconds by the preset code switch 14. When power switch 11 and reset switch 16 are depressed , the Vcc is obtained by a switching regulator 19, and a system supply voltage is applied to an initial reset circuit 20 to reset each of a number of flip-flops. When the supply voltage is applied, a second flip-flop 22 is reset through an inverter 21, a third flip-flop 24 is reset through a 3-input NAND gate 23, a fifth flip-flop 26 is reset throguh a 2-input NAND gate 25, a fourth flip-flop 28 is reset through a 2-input NAND gate 27, and a first flip-flop 30 is reset through a 2-input NAND gate 29. When the second flip-flop 22 is reset, a transistor 31 is turned off causing the output to go to 1. The output is applied to a NAND gate 23 and to an external control line 33 through an input and output terminal 32. When the third flip-flop 24 is reset, the output at a 1 level is applied to a CI input of a presettable down counter 35 through a 2-input NAND gate 34, so that the presettable down counter stops producing clock pulses. When the fifth flip-flop 26 is reset, an output at a 0 level is applied to a 2-input NAND gate 36 as an abnormality signal output gate. When the fourth flip-flop 28 is reset, a 1 output inverted through the transistor array 8 is applied to a OE of the EPROM 6, so that the EPROM 6 stops producing the data. When a work passes a first sensor 37 which is provided near an inlet of a manufacturing machine, a signal having a 0 level is produced to set the first flip-flop 30 through a first input terminal 38, chattering preventing circuit 39, and inverter 40. A one-shot pulse "1" appears at the output of a one-shot pulse generating circuit 41. This one-shot pulse "1" is applied A. to a reset R of a binary counter 42 and a reset R of a clock pulse generating circuit 43 to reset them to the zero states, respectively, and to inputs PE of presettable down counters 35 and 46 through an inverter 44 and a 2-input NAND gate 45 to preset the digit "32" of preset code switch 14 in counters 35 and 46, respectively. B. to a set S of the fourth flip-flop 28, the output Q thereof is applied to the OE of the EPROM 6 through one of transistor arrays 8 and the EPROM turns to the output state, and to a set S of the third flip-flop 24 to set to produce an output 1 which is applied to the CI of the presettable down counter 35 through the 2-input NAND gate 34 to produce clock pulses. The output of the clock pulse generating circuit 43 provided with a crystal oscillator is 1000 Hz, as clock pulses. The clock pulses are applied to clock lines C of the presettable down counters 35 and 46, respectively. Preset lines P1, P2, P3 and P4 of the presettable down counters are connected to BCD lines of preset code switch 14. Each time one clock pulse is applied to the presettable counter 35, the preset count therein decreases by one. When 32 clock pulses are applied to the presettable counters, both inputs of a 2-input NOR gate 47 go to a "0". Thus, the 2-input NOR gate 47 produces one read clock pulse. On the other hand, when the output of the 2-input NOR gate 47 goes to "1", a 2-input NAND gate 51 causes to produce "0" when an inverter 52 produces output "1" by a negative going clock input. Thus, PE of each presettable counter is applied with a pulse "1" through the 2-input NAND gate 45. At the same time, the "32" of the preset code switch is preset again in the presettable down counters. Thus, every time 32 clock pulses are applied to presettable counters, one read clock pulse is generated from the gate 47. The read clock pulse is applied to the clock line C of the binary counter 42 through an inverter 48. Accordingly, the binary counter 42 produces outputs through address lines Q0 to Q6, so that the outputs are applied to the address in the EPROM 6 through transistor arrays 8 and connector 9. Time of one cycle is decided by the number of read clock pulses. Operation in the case of 100 read clock pulses in one cycle will be explained hereinafter. In order to produce the one-cycle end signal upon 100 read clock pulses, address lines Q2, Q5 and Q6 of the binary counter 42 are selected as the inputs of a 3-input NAND gate 49. Since the binary number of "100" is 1100100, when the 100 read clock pulses are applied to the input of the binary counter 42, outputs on the address lines Q2, Q5 and Q6 go to "1" and the 3-input NAND gate 49 produces a one-cycle end signal "0". On the other hand, the EPROM 6 produces a data signal in response to the address signals, so that respective actuators of the machine are operated through relay unit 2. When one cycle ends, the fourth flip-flop 28 is reset through the 2-input NAND gate 27, so that the EPROM 6 stops producing the output. The third flip-flop 24 is reset through 3-input NAND gate 23. The presettable down counters 35, 46 stop producing the output. Thus, each of actuators of the machine stops. The fifth flip-flop 26 is set through an inverter 50. A first input of abnormality signal output gate of 2-input NAND gate 36 is changed to "1". When the work after the manufacturing process passes a second sensor 53 provided on an outlet of the machine, a signal having a 0 level is applied to a second input terminal 54. The fifth flip-flop 26 is reset through a chattering preventing circuit 55 and 2-input NAND gate 25 to change the first input signal of abnormality signal output gate of 2-input NAND gate 36 into a "0". Further, the first flip-flop 30 is reset by the output of the 2-input NAND gate 29. Then, the first flip-flop 30 is set when the first sensor 37 produces a signal, thereby restarting the operations of the control system and actuators of the machine. The operations of actuators are kept unless an abnormality occurs. When a signal from the second sensor 53 is not applied to the control unit at the end of the one cycle operation, the first input signal of abnormality signal output gate of 2-input NAND gate 36 is kept to "1", and first flip-flop 30 is not reset. Accordingly, the first flip-flop 30 is not set even if the signal from the first sensor 37 is applied. A 1 signal from the inverter 40 is applied to a second input of the abnormality signal output gate 36. Since output of the gate 36 goes to "1", the second flip-flop 22 is set. The transistor 31 is turned on to operate the abnormality display 15 to emit a light. The output 0 of transistor 31 is applied to the 3-input NAND gate 23 to reset third flip-flop 24, so that the signal at the 1 level is applied to CI of counter 35 through the gate 34. Thus, the output of the clock pulse stops and the machine stops. Referring to Fig. 4 showing an automatic system consisting of three read-only sequence controllers a , b and c , each of sequence controllers a , b , c , is adapted to control manufacturing machines A, B and C, respectively. (Hereinafter it is assumed that the sequence controllers are called sequencers.) A first machine A, as a known parts-feeder is provided for automatically lining up works at predetermined positions and this operation is repeated. When predetermined numbers of works are lined up, the first sensor 37 of the sequencer a detects it to produce an output signal. The output signal is applied to the first input terminal 38 through a delay circuit 57. Thus, the sequencer a starts to operate the machine A which operates to feed works and stops at one cycle end. However, the sequencer a is restarted by a signal from the second sensor 53 provided on the outlet of the parts-feeder A. The work is fed to the next machine B at regular intervals. When the work passes the first sensor 37 of the machine B, the machine B starts by the signal from the sensor 37. Thus, in the same manner, machines A, B, C are sequentially operated. A first product is discharged from the machine C at a third cycle end and thereafter the product is discharged at every cycle end. If an abnormality occurs in the machine C, the work stops on the way of the process. The second sensor 53 does not produce the signal. A stop signal is produced in accordance with the signal of the first sensor 37 of the sequencer c , so that sequencers b and a , as well as sequencer c , are stopped through the control line 33. As the abnormality display 15 emits the light, inspection and repair of the machine C are done. Thereafter, the reset switch 16 of the sequencer c is depressed and the start switch 17 is depressed, so that sequencers restart operation at the same time. The process of work at the next machine must be finished before the next work from the previous machine passes the first sensor of the next machine. Accordingly, the cycle time is determined on the basis of a first sequencer. For example, the cycle time of the sequencer a is at 3.2 seconds, sequencer b is set at 2.8 seconds, and sequencer c at 2.4 seconds.

Claims: A read-only sequence control system for controlling the operation of a machine having a memory (6), a control unit including a clock pulse generating circuit (43) for producing clock pulses, a presettable counter (35,46) for counting the clock pulses and for producing a read clock pulse at every preset count, a binary counter (42) for counting the read clock pulse and for producing outputs for addressing the memory (6), so that the memory produces data outputs to turn on relays for operating the machine, and a control circuit for controlling the start and stop operations of the counters (35,46), the control system comprising: first circuit means (25,26) for producing an abnormality signal; second circuit means (22,23,24,34) responsive to the abnormality signal for producing a stop signal for the presettable counter; and first gate means (34) responsive to a count end signal of the binary counter (42) for producing a stop signal for the presettable counter, characterized in that there is further provided: a first sensor (37) detecting a feed of a work into the machine and producing a feed signal; a first flip-flop (30) responsive to the feed signal for generating control signals for the clock pulse generating circuit (43), the presettable counter (35), and the binary counter (42); a second sensor (53) detecting a discharge of the feed work and for producing a discharge signal; and that the first circuit means (25,26) are responsive to a non-existence of the discharge signal for generating a control signal for a second gate means (36) to produce the abnormality signal. Sequence control system according to claim 1, wherein the control circuit further includes a second flip-flop (28) responsive to the count end signal for producing a control signal for the memory (6). Sequence control system according to claims 1 or 2, wherein the first circuit means (25,26) includes third gate means (25) responsive to the discharge signal for operating a third flip-flop (26) for generating an output signal which is applied to the second gate means (36). Sequence control system according to one of claims 1 to 3, wherein the second gate means (36) is further responsive to the feed signal from the first sensor (37) to produce the abnormality signal. Sequence control system according to one of claims 1 to 4, further comprising a terminal (32) for connecting another control system so as to apply the output signal of the second circuit means (22) to the other control system.

Inventors: KUZE, YOSHIKAZU
Applicants: KUZE, YOSHIKAZU
Application year: 1987
Main classification: G05B19
IPC codes: G05B19