NUMERICAL CONTROL METHOD

Abstract: A method of numerically controlling a numerical control system is provided with a numerical control (NC) unit for numerically controlling a machine tool, or the like, and a programmable controller (PC) unit. When an interrupted machining operation is resumed, the NC unit (1) executes a machining program from the start thereof to a predeter­ mined block from which the operation is to be restarted, without any distribution operation. During the execution, data in the machining program concerning M, S, T functions is successively transferred to the PC unit (2) and is stored therein. During this time, the PC unit (2) does not deliver this data to the machine side. After the completion of the search as far as the predetermined block, the machining is resumed. This time, however, the M, S, T functions have already been automatically set in the PC unit (2) so that the conditions are the same as those at the interruption of the machining. It is therefore possible to smoothly resume the machining from the machining resumption point.

Description: This invention relates to a numerical control method and, more particularly, to a numerical control method wherein operation is simple at resumption of machining. If, during the machining of a workpiece by a machine tool controlled by a numerical control unit, a tool should break or a power failure occur and result in suspension of the machining operation, the conventional practice is to take the following counter-measures and then resume machining: (1) The numerical control unit stores, in advance, a machining resumption starting point. For example, the starting point is set on a digital switch or stored in a non-volatile memory. (2) To resume machining, the operator manipulates an NC operator's panel to restore a table or tool to the machine origin. (3) After restoration to the origin is performed, the operator positions the table or tool at the machining starting point by using machining starting point information stored in the non-volatile memory or set on the digital switch. (4) After positioning at the machining starting point is performed, the operator returns numerical control command data to the beginning. (5) The operator then causes the numerical control unit to search a program from the beginning of the numerical control command data to the position at which machining was suspended. At this time, M-, S-and T-function instructions are not delivered to a programmable controller unit (PC) and these functions are not performed on the PC or machine side. (6) After (5) is carried out, the operator observes the M-, S- and T-function data that prevailed at the suspension of machining, which data are displayed on a display of the numerical control unit, manually sets these data in the PC and resumes machining. Thus, at the resumption of machining, the conventional numerical control unit is caused to search the program from the beginning of the numerical control command data to the position at which machining was suspended. In doing so, however, the numerical control unit does not perform a distribution operation. Since arithmetic functions are suspended on the PC side, the PC does not know what the M-, S- and T-function data that prevailed at suspension of machining are. Consequently, when the program arrives at the state for resumption of machining, the states of the M-, S- and T-functions are displayed on the display unit and these are set in the PC while being verified visually by the operator. Thus, in resuming machining, operator intervention is a necessity in the prior art. This not only results in a troublesome machining restart operation but is also inconvenient in that unexpected accidents occur when the operator mistakes the states of the M-, S- and T-functions and sets them in the PC. In the published prior art, PATENTS ABSTRACTS OF JAPAN, vol 8, no 31 (P-253)[1468], 9th February 1984, discloses a numerical control method according to the precharacterising part of attached claim 1, which does not involve a programmable controller unit An object of the present invention is to provide a numerical control method whereby, when machining is suspended and then resumed, execution is restarted from any block of a machining program and machining is continued under conditions exactly the same as those that prevailed when the program was run from the beginning, this being accomplished in a short period of time and without requiring much skill. Another object of the present invention is to provide a numerical control method whereby machining is capable of being resumed without manually inputting the states of M-, S- and T-functions in a PC. According to the present invention there is provided a numerical control method, for a machine tool, performed by a numerical control system comprising a numerical control unit for executing numerical control of the machine tool on the basis of a machining program comprising a series of data blocks, wherein when execution of the machining program is suspended during normal machining, the machining program is returned to the beginning and then run up by the numerical control unit to a prescribed data block necessary for resuming machining, characterised in that a programmable controller unit is provided for executing sequence control of the machine tool on the basis of a control signal from the numerical control unit, and while the machining program is being run up to said prescribed data block the programmable controller unit is operated based on data transmitted by the numerical control unit without the programmable controller unit outputting signals to the machine side, whereby when machining is resumed the conditions in the programmable controller unit are the same as those which prevailed immediately before machining was suspended, these conditions including the states of auxiliary M-, spindle S- and tool T-functions. By providing the numerical control method of the present invention, when machining is resumed following restoration after suspension of machining caused by breakage of a tool or a power failure, it is possible for machining to be resumed under exactly the same conditions that prevailed at suspension. Brief Description of the Drawings Fig. 1 is a block diagram of a numerical control system for practicing a numerical control method of the present invention, Fig. 2 is a block diagram of a numerical control unit in Fig. 1, and Fig. 3 is a flowchart illustrating the general features of a numerical control method according to the present invention. To explain the present invention in greater detail, a preferred version of the invention will now be described in conjunction with the accompanying drawings. Fig. 1 is a block diagram of a numerical control system for practicing a numerical control method of the present invention. In the Figure, numeral 1 denotes a numerical control (NC) unit, which will now be described in detail with reference to Fig. 2. The NC unit 1 is composed of a central processor (CPU) 11 for executing processing on the basis of a machining command program, mentioned below, or a control program, a working memory 12, a control memory 13 for storing the control program, a data memory 14, a random-access memory (RAM) 16 for storing machining command data read in via a tape reader 18 from a tape 17 bearing punched machining commands, an interface 15 connected to an NC operator's panel 4, mentioned below, and a data bus 19 interconnecting the foregoing units. Returning to Fig. 1, numeral 2 denotes a programmable controller unit (PC) of a construction similar to that of a microcomputer and having a memory for storing a sequence program, a processor for executing processing based on the sequence program stored in the memory, and a memory for storing various data. The programmable controller unit performs an exchange of control signals with the NC unit 1 and executes sequence control in accordance with commands from the NC unit 1. Numeral 3 denotes an input/output circuit connected to the PC unit 2 and to a machine operator's panel 5, a magnetics circuit 6, and an apparatus 7 for an auxiliary (M) function, a spindle speed (S) function, and a tool (T) function. Numeral 8 denotes a velocity control unit for executing control based on a velocity command from the NC unit 1 in such a manner that the velocity of a feed motor 9 follows up the commanded velocity. A control method for resuming machining after machining is suspended in the foregoing numerical control system will now be described in conjunction with the flowchart of Fig. 3. (1) First, when a tool breaks or a power failure occurs during the machining of a workpiece, the NC unit 1 senses the event, suspends the machining of the workpiece and, by way of example, causes a display unit provided on the NC operators' panel 4 to display the fact that an accident has occurred, or issues a warning by means of an alarm (step 1). (2) The position at which machining is suspended is sensed. This generally is performed by the operator. The operator observes the position indication and records the coordinates of the position at which operation stops (step 2). (3) Next, by using the operator's panel 4, the operator indicates the appropriate program block position for resuming machining in accordance with the sensed position, whereupon the NC unit 1 restores the workpiece and/or tool to this resumption block position (step 3). In this case, the block position to which restoration is made is decided in the following manner, with reference being had to the program stored in the RAM 16 of Fig. 2, by way of example. In a case such as one in which machining of the workpiece is suspended at a block having program number N0052, the operator restores the machining status of the workpiece to program number N0051 or N0050 upon first examining a program list displayed on the display unit of the NC operator's panel 4. That is, once the position at which machining of the workpiece has been suspended is sensed, restoration is made to the optimum position, which depends upon the status that prevails. (4) Next, on the basis of the indicated block suitable for resumption of machining, the NC unit 1 sets up search flags from the beginning of the machining program to the block at which machining is to be resumed (step 4). (5) The NC unit 1 sends a search status signal to the PC unit 2 from the beginning of the machining program to the block at which machining is to be resumed, the search flags having been set up here in step (4), and causes the PC unit 2 to execute a search of the machining program (step 5). In case of a move command encountered in the searching of the machining program, the commanded distribution is not performed on the machine side, but coordinate system setting solely for updating position, an auxiliary (M) function, spindle speed (S) function and tool (T) function are executed. Dwell, however, is neglected. In case of an M-, S- or T-function block encountered in the searching of the machining program (step 6), the NC unit 1 sequentially stores these data in the memory of the PC unit 2 to update the memory (step 7). However, the PC unit 2 does not send M-, S- and T-function commands to the machine side when the search of the machining program is being executed. (6) When the search from the beginning of the machining program to the machining resumption block is completed (step 8), namely in response to an OFF signal during the search, the NC unit 1 causes the PC unit 2 to execute the stored M-, S- and T-functions (step 9). In this way the M-, S- and T- functions can be set to conditions the same as those that prevailed when the program was run in the ordinary manner. (7) Next, the NC unit executes numerical control on the basis of the machining program starting from the machining resumption block, thereby to resume machining of the workpiece (step 10). From this point onward, the numerical control system continues ordinary operation. In step 3, it is permissible for the program block position suitable for resuming machining to be located several blocks before the machining suspension position or at the machining suspension position. Though the present invention has been described based on the illustrated embodiment, the invention is not limited to the illustrated embodiment but can be modified in various ways without departing from the scope of the claims. As set forth above, the present invention enables machining to be resumed automatically under conditions exactly the same as those that prevailed when the machining program was run from the beginning, even in a case where machining is resumed from any block of the machining program. Accordingly, the present invention is particularly useful when used in a numerical control system of a machine tool capable of performing sophisticated machining.

Claims: A numerical control method, for a machine tool, performed by a numerical control system comprising a numerical control unit (1) for executing numerical control of the machine tool on the basis of a machining program comprising a series of data blocks, wherein when execution of the machining program is suspended during normal machining, the machining program is returned to the beginning and then run up by the numerical control unit to a prescribed data block necessary for resuming machining, characterised in that a programmable controller unit (2) is provided for executing sequence control of the machine tool on the basis of a control signal from the numerical control unit (1), and while the machining program is being run up to said prescribed data block the programmable controller unit (2) is operated based on data transmitted by the numerical control unit (1) without the programmable controller unit (2) outputting signals to the machine side, whereby when machining is resumed the conditions in the programmable controller unit (2) are the same as those which prevailed immediately before machining was suspended, these conditions including the states of auxiliary (M)-, spindle (S)- and tool (T)-functions. The numerical control method according to claim 1, characterised in that the prescribed position of the machining program necessary for resuming machining is a data block which prevailed when machining was suspended. The numerical control method according to claim 1, characterised in that the prescribed position of the machining program necessary for resuming machining is a data block prior to a data block which prevailed when machining was suspended.

Inventors: KIYA, NOBUYUKI YOKOKAWACHO-JUTAKU 13 - 106, YOSHINO, MOTOAKI HAITSU-FUKUJU B-205
Applicants: FANUC LTD.
Application year: 1985
Main classification: G05B19
IPC codes: B23Q15, G05B19