STOP CONTROLLER OF CUTTING TOOL

Abstract: A stop controller of a cutting tool which performs emergency stopping of a cutting tool during a cycle operation and returns the cutting tool to a cycle start position according to the present invention is provided with memory means (A, B) for storing a sequence operation program for returning the cutting tool to the cycle start position in accordance with a stop position at each stage of the cycle operation, discrimination means (3) for discriminating the step of the cycle operation at the time of stop, and program control means (2) for calling the sequence operation program in the memory means from the cycle program in accordance with the stop position corresponding to the discriminated cycle operation. The stop controller can return automatically the cutting tools through an optimum route using a sequence program for retreat in accordance with the operation interruption state at the time of emergency stop.

Description: This invention relates to a cutting tool stop-control apparatus for controlling the stopping of a cutting tool for example when executing a hole drilling operation by a machining center or milling machine, and particularly, but not exclusively, when executing a back-boring operation. In order to machine a workpiece by an ordinary CNC machine tool, a program for controlling the movement of a tool in dependence upon the contents of machining is created and the machine tool is run in an NC mode based on the program. When an abnormal condition such as tool breakage occurs on the side of the machine tool, the numerical control apparatus is capable of interrupting cycle operation, which is based upon the cycle program in the process of being run. On the side of the machine tool, the cutting tool is brought to an emergency stop, after which the tool is changed. In order to resume the prescribed operation applied to the workpiece, it is required that the tool be withdrawn to the cycle starting point. With a numerical control apparatus of this kind, generally a method is adopted in which the tool is returned to the cycle starting point while the path of withdrawal is read out as the reverse of the same path traversed. For example, if operation is suspended when a program is being executed in a machining mode having a complicated path, as in the case of a back-boring cycle, the operation for withdrawing the tool to the cycle starting point is a major undertaking. In the prior art, therefore, operation from this time onward is switched over to manual to make the tool change. This is disadvantageous in that the efficiency of operation declines. The present invention has been devised in order to solve the foregoing problems and its object is to provide a cutting tool stop-control apparatus in which, even if a stop request is generated in a machining mode having a complicated path, as in the case of a back-boring cycle for example, a machine tool can be automatically commanded to perform a post-stop continuation operation corresponding to the operation being executed. This contrasts with the prior art method of tool withdrawal disclosed in US-A-3 496 805, wherein a back-boring machining operation is controlled by data sets in a punched strip. If the tool breaks during machining, it is withdrawn from the workpiece to its starting point, under the control of auxiliary data sets in the punched strip or in another punched strip. During withdrawal, no further use is made of the data in the data sets defining the machining operation. According to the present invention there is provided a cutting tool stop-control apparatus for bringing a cutting tool to an emergency stop during cycle operation based on a commanded cycle program, and restoring said tool to a cycle starting position, comprising: a first memory means storing the commanded cycle program for controlling the cutting tool, the commanded cycle program comprising a plurality of operation steps one after another in sequence; a second memory means storing continuance programs for returning the cutting tool to the cycle starting position in dependence upon the emergency stop position of the cutting tool in said plurality of operation steps of the commanded cycle program; discriminating means for discriminating the cycle operation step prevailing at the time of an emergency stop; and program control means for calling a continuance program from the corresponding memory in dependence upon the cycle operation step discriminated by the discriminating means as prevailing at the time of an emergency stop, the called continuance program being operable to advance the commanded cycle program from the discriminated, prevailing cycle operation to a subsequent cycle operation in the commanded cycle program, such that when an emergency stop is applied the prevailing operation step will be halted immediately and the cutting tool will be returned to the cycle starting position by the continuance program corresponding to that prevailing operation step, through an optimum sequence of a subsequent one or ones of the operation steps of the commanded cycle program. Accordingly, the cutting tool stop-control apparatus of the invention is such that if tool breakage occurs during cycle operation, the operation is not merely suspended automatically. Rather, in accordance with the continuance program conforming to the actual conditions that prevail at the suspension of operation, the tool is withdrawn to the cycle starting point along the optimum path and operation following the tool change is resumed automatically. In accordance with the invention, there can be provided a cutting tool stop-control apparatus for tool control having a complicated machining path, as in the case of a back-boring cycle, in which a tool change is possible upon controlling a spindle to move it to the cycle starting position in reliable fashion. Accordingly, the apparatus is useful in that a machine tool employing a self-restoration system can have its automatic operation controlled in an efficient manner. Brief Description of the Drawings Fig. 1 is a block diagram illustrating an embodiment of the invention, Fig. 2 is a sectional view illustrating an example of workpiece machining, Fig. 3 is a view for describing the operation of a back-boring cycle, Fig. 4 is a view illustrating a machining control operation based on a back-boring cycle, and Fig. 5 is a flowchart illustrating the contents of a continuance program. An embodiment of the present invention will now be described in detail with reference to the drawings. Fig. 1 is a block diagram illustrating an example of the construction of a numerical control apparatus for controlling the NC operation of a machine tool 1. A CPU 2 is equipped with a memory A storing a program for controlling the machine tool 1, and a memory B storing a continuance program for returning a tool to a cycle starting position in dependence upon the tool stopping position at each stage of cycle operation. Connected to the CPU are a discriminating circuit 3 which discriminates the content of cycle operation when the operation of the machine tool 1 is suspended, and an operator's panel 4 for external control, such as the setting of modes. Fig. 2 is a sectional view illustrating an example of a workpiece 5 machined by the machine tool 1. The workpiece 5 has its interior cut away to a diameter greater than that of an initial hole 6 formed by a separate machining process. Back-boring machining entails inserting a tool into the workpiece from above the initial hole 6, shifting the rotational axis of the tool over the range of the diameter of the initial hole 6 and then applying cutting machining a prescribed distance thereabove. The back-boring cycle is set by 15 steps serving as one series of operations, which will be described next. Fig. 3 is a view for describing the operation of the back-boring cycle. The following cycle is applied to a numerical control apparatus in a data format regarding machining in the following canned cycle: G87X - Y - Z - R - Q - P - F - L - ; In other words, in accordance with the foregoing a tool 7 is positioned at a drilling point P₁ designated by hole position data X, Y, after which the spindle is stopped at a fixed rotational position and then shifted, in a direction opposite that of the tool nose, in conformity with the hole 6 formed in the workpiece. Thereafter, the tool is positioned at the hole bottom (point R) in the rapid-traverse mode, at which position the tool is returned the abovementioned shift amount and the spindle is rotated in the forward direction from point P₂ to perform cutting. Machining in the positive direction along the Z axis arrives at position P₃ corresponding to point Z, dwell is then applied and the spindle is stopped at the fixed rotational position, after which the tool is again shifted in a direction opposite the tool nose. In this way the tool 7 is extracted in the Z direction from the initial hole position and shift is cancelled, thereby restoring the tool to the drilling position P₁, which is the initial cycle starting point. Processing then proceeds to the operation of the next block. Fig. 4 is a view illustrating the machining control cycle based on the back-boring cycle. During execution of a cycle program (step a), the numerical control apparatus applies an emergency stop in response to an alarm from the machine tool side, thereby stopping the machine tool (step b). At this time, the cycle program being executed is suspended and, at the same time, the stopped state of the machine tool is discriminated. If the stopped state is due to generation of the alarm (step c), a predetermined continuance program is called in dependence upon the program execution state at this time (step d). The tool 7 is then returned to the starting point of the back-boring cycle at an optimum operating sequence (step e). Fig. 5 is a flowchart illustrating the contents of the continuance program in a case where a stop request is received during execution of each operation for every one of operation steps S₂ - S14 of the abovementioned back-boring cycle. In each case, if there is a stop request while the particular operation is being executed, the operation is halted and the continuation operation is executed in accordance with the arrows at the left sides of the blocks indicating the operation steps S₂ - S₁₄, whereby the tool is returned to the cycle starting point. In other words, if axial movement is in effect, this movement is decelerated and stopped. If a dwell is being executed, this is suspended. If an M function is being executed, the program proceeds to the step designated after the operation specified by the M function ends. Thus, in a case where an emergency stop is applied, the prevailing operation is halted immediately and the tool can be returned to the starting point of the back-boring cycle by the continuance program through an optimum sequence conforming to the stopped state. Accordingly, all steps for subsequently executing tool change and performing the back-boring cycle again or for proceeding to a new machining cycle can be resumed automatically. The cutting tool stop-control apparatus of the present invention is useful in that a machine tool employing a self-restoration system can have its automatic operation controlled in an efficient manner.

Claims: A cutting tool stop-control apparatus for bringing a cutting tool (7) to an emergency stop during cycle operation based on a commanded cycle program, and restoring said tool (7) to a cycle starting position, comprising a first memory means (A) storing the commanded cycle program for controlling the cutting tool (7), the commanded cycle program comprising a plurality of operation steps (S₂ to S₁₅) one after another in sequence; a second memory means (B) storing continuance programs for returning the cutting tool (7) to the cycle starting position in dependence upon the emergency stop position of the cutting tool (7) in said plurality of operation steps (S₂ to S₁₅) of the commanded cycle program; and program control means (2) for calling a continuance program from the corresponding memory (B) in dependence upon the prevailing cycle operation step; characterised in that said apparatus further comprises: discriminating means (3) for discriminating the cycle operation step prevailing at the time of an emergency stop; and in that the called continuance program is operable to advance the commanded cycle program from the discriminated, prevailing cycle operation to a subsequent cycle operation in the commanded cycle program, such that when an emergency stop is applied, the prevailing operation step will be halted immediately and the cutting tool (7) will be returned to the cycle starting position by the appropriate continuance program through a sequence of a subsequent one or ones of the operation steps (S₂ to S₁₅) of the commanded cycle program. A cutting tool stop-control apparatus according to claim 1, wherein the commanded cycle program commands back-boring machining for the cutting tool.

Inventors: KAWAMURA HIDEAKI, MATSUURA SYUJI, SASAKI TAKAO ESUTETO-HACHIOJI, KAWAMURA, HIDEAKI, MATSUURA, SYUJI, SASAKI, TAKAO ESUTETO-HACHIOJI 2-502
Applicants: FANUC LTD, FANUC LTD.
Application year: 1988
Main classification: G05B19
IPC codes: B23Q1, G05B19