Machine tool numerical controller with a trouble stop function

Abstract: A numerical controller for a grinding machine is com­ posed of a central processing unit (CPU), which is program­ med to read out a numerical control program block by block from a memory device and to control a pulse generation circuit to generate pulses of such number and frequency as to determine by the read-out data block, for supply to feed servomechanisms of the grinding machine. The CPU is also programmed to execute a trouble identification routine and a trouble processing routine at predetermined time intervals. The trouble identification routine enables the CPU to identify the kinds of troubles occurring in the grinding machine to assort the troubles into a number of trouble modes. The trouble processing routine enables the CPU to operate so that a movable member of the grinding machine is immedi­ ately stopped or, for preventing the actual position of the movable member from differing from a present position thereof stored in the memory device, slowly stopped de­ pending upon the kind of a trouble presently occurring in the grinding machine.

Description: The present invention relates to a machine control apparatus according to the features indicated in the preamble of claim 1. The present invention starts from a prior art as it is known from EP-A3-0 121 212. This document discloses a machine control apparatus for controlling the movement of at least one movable member, i.e. the grinding wheel, of a machine tool in the form of a grinding machine in accordance with a numerical control program. In order to avoid a damage of the grinding wheel caused by a sudden overload stop control means are provided which stop the grinding wheel, wherein the actual operating conditions thereof are monitored by a speed sensor. In case the speed sensor detects a situation dangerous for the grinding wheel by outputting a signal indicating a serious trouble, a trouble processing means stops the grinding wheel. Because of the aforementioned stopping of the grinding wheel, a damage can surely be avoided. Due to the rapid stopping of the machine tool, however, the position of the machine tool deviates from its correct position, so that, in order to restart the machine, the operator has to move the machine tool in the correct position corresponding to the position before the occurrence of the trouble. Otherwise the numerical control program would be unable to restart the machine control. This reposition is obviously very tiresome and time-consuming. In vol. 6 of the "Zeitschrift für wirtschaftliche Fertigung", 1983 pages 272 to 275 a flexible numerical control is described. Such control is used to achieve a more complex functional variety and a resulting increase of productivity without the development of an own, adapted numerical control. In addition to the evaluation of limit switch signals for the position control the special treatment of faults for instance in the case of a tool failure or wear is disclosed. It is provided to free the tool upon detection of a corresponding fault message, and to resume the production after the insertion of a spare tool. Document DE 26 40 257 C2 discloses the mode of function of a process computer controlled machining center. The program flow used for the operation of the machining center or a machining head activated thereby is controlled in accordance with various anomalous operating conditions by respective subroutines. When an occurring anomalous condition cannot be eliminated by the program flow, the execution of the respective operation is stopped. Therefore, the object of the present invention is to improve a machine control apparatus according to the preamble of claim 1 in such a way that the restart of the machine tool is an easy as possible. According to the present invention this object is obtained by the advantageous measures indicated in the characterizing portion of claim 1. Hence, according to the present invention, the sensing means comprises a plurality of trouble sensors arranged at various parts of said machine tool, wherein the stop control means is adapted to stop the movable member in a first stop mode, in which the movable member is stopped as fast as possible, and in a second stop mode, in which the movable member is stopped slowly in such a way that its respective actual position is prevented to differ from a position stored in the numerical control program. Due to this advantageous measures the trouble processing means is able to determine by way of output signals of the trouble sensors the kind of trouble occurring and to operate the stop control means so as to perform either the first or the second stop mode depending on the kind of trouble determined. According to the present invention, after a machine stop due to a trouble condition, the position of the machine tool only deviates from its nominal position stored then when the trouble is very serious. In all other cases the machine keeps the correct position because of the slow reduction of speed. As a consequence, in most cases the operator only has to press a restart button in order to begin a new and correct operation of the machine. "Regelungstechnische Praxis" discloses some principles for realizing a cost-effective CNC software. In "Electronic" a process for stopping an electric motor irrespective of the signals of a numerical control system is shown. Various other objects, features and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of a preferred embodiment when considered in connection with the accompanying drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and in which: Figure 1 is a block diagram of a machine control apparatus according to the present invention, also showing a schematic plan view of a grinding machine; Figure 2 is a flow chart of a numerical control data read-out routine executed by a central processing unit shown in Figure 1; Figure 3 is a flow chart of a pulse distribution routine executed by the central processing unit; Figure 4 is a flow chart of a trouble identification routine executed by the central processing unit; Figure 5 is a flow chart of a trouble processing routine executed by the central processing unit; Figure 6 is a flow chart of an emergency stop processing executed by a programmable sequence controller shown in Figure 1; Figure 7 is a flow chart of an immediate return processing executed by the programmable sequence controller; and Figure 8 is a flow chart of an immediate stop processing executed by the programmable sequence controller. Referring now to the drawings and particularly to Figure 1 thereof, a numerical control machine tool to which the present invention is applied is shown as a numerical control grinding machine having a bed 10, on which a work table 11 and a wheel head 12 are guided for sliding movements in Z and X-axis directions perpendicular to each other and are drivingly connected to servomotors 15, 16 through feed screws 13, 14, respectively. The work table 11 carries thereon a work head 17 and a foot stock 18 for rotatably carrying opposite ends of a workpiece W to be ground. Movements of the work table 11 and the wheel head 12 are given by controlling command pulses supplied from a numerical controller 20 to the servomotors 15, 16, so that the workpiece W can be ground to have a desired shape and dimension. The numerical controller 20 for controlling movements of the work table 11 and the wheel head 12 is computerized and is composed of a central processing unit (hereafter referred to as "CPU") 21, a memory 22, interfaces 23, 24, and a pulse generation circuit 25. The interface 23 is connected to a data input device 26, while the interface 24 is connected to a programmable sequence controller 30. The pulse generation circuit 25 is connected to drive units 27 and 28 for respectively driving the servomotors 15, 16. The memory 22 stores, in addition to a numerical control (NC) program, a number of system control programs which include a base routine (not shown), an NC data read-out routine NDRR shown in Figure 2 and a pulse distribution routine PGR shown in Figure 3 for performing a pulse distribution function and the like in accordance with the numerical control program so as to effect feed control of the grinding machine. The read-out routine NDRR is executed in response to an interruption signal which is generated at a predetermined time interval for enabling the CPU 21 to read out the NC program block by block and to calculate feed amounts based upon each read-out NC data block. The distribution routine PGR enables the CPU 21 to calculate the number of pulses which are to be generated within a unit time period and a distribution rate at which the number of pulses are to be distributed, based upon the calculated feed amounts and the calculated feed rate and then, to set the number of pulses and the distribution rate in the pulse generation circuit 25, so that the same performs a pulse distribution operation in a condition so determined. The routine PGR is repeatedly executed by the CPU 21 each time the same receives a distribution completion signal from the pulse generation circuit 25. The above-noted base routine causes the CPU 21 to execute the NC data read-out routine NDRR when a machining start command is given or when any of the work table 11 and the wheel head 12 reaches each objective point thereof designated by a previously read-out NC data block. With the starting of the routine NDRR, step 60 is executed to ascertain whether such an objective point has been reached or not. The occurrence of any trouble which is classified into trouble modes 1-5 as described later in detail is ascertained in step 61. Unless such any trouble has occurred and the NC program end is ascertained in step 62, step 63 is reached wherein an initial or successive NC data block is read out from the memory 22. If such any trouble has occurred or the NC program end is ascertained, on the other hand, return is made to the base routine to prevent a successive NC data block from being read out. Feed amount data and feed rate data designated by the read-out NC data block are set in registers (not shown) defined in a parameter storage area of the memory 22 in step 64, and a processing is executed in step 65 to trigger the subsequent execution of the pulse distribution routine PGR before the returning to the base routine. As a result, the base routine then directs the CPU 21 to execute the pulse distribution routine PGR. In this case, since it is ascertained in step 70 that an objective point designated by the read-out NC data block has not been reached yet, the CPU 20 advances its processing through steps 71 and 72 described later in detail to step 74, wherein the number of pulses to be distributed within a unit time period and the pulse distribution rate are calculated to be set in the pulse generation circuit 25. Step 75 is then executed to renew the remaining feed amount to the objective point and present positions of the work table 11 and the wheel head 12. A pulse distribution command is then given to the pulse generation circuit 25 in step 76 before return is made to the base routine. Consequently, the circuit 25 distributes feed pulses to one or both of the drive units 27, 28 at the feed rate or frequency set therein, whereby the work table 11 and the wheel head 12 are relatively moved. When completing the distribution of pulses of the number designated by the CPU 21, the pulse generation circuit 25 issues a pulse distribution completion signal, in response to which the CPU 20 executes the pulse distribution routine 70 again. This causes the pulse generation circuit 25 to distribute pulses for another unit time period. The routine PGR is repeatedly executed in this manner, and when it is ascertained in step 70 that the objective point has been reached, the CPU 21 returns to the base routine to then execute the routine NDRR for successive NC data block. The memory 22 further stores therein a trouble identification program or routine ACCR shown in Figure 4 and a trouble processing program or routine APR shown in Figure 5. The CPU 21 identifies and processes several kinds of troubles in accordance with these routines. The sequence controller 30 is responsible to a number of trouble processing commands applied from the numerical controller 20. Sequence programs shown in Figures 6-8 are stored in a program memory (not shown) of the sequence controller 30 for enabling the same to selectively process different kinds of troubles. Description will be made hereafter with respect to the trouble identification and processing operations performed by the CPU 21 and the sequence controller 30. Occurrences of troubles in the automatic operation are checked at a predetermined time interval in accordance with the trouble identification routine ACCR. For detections of such troubles, as shown in Figure 1, the grinding machine is provided with sensors 31, 32 (e.g., limit switches) which are responsive to excessive movements or overruns of the work table 11 and the wheel head 12, and the drive units; 27, 28 incorporate therein sensors 33, 34 for detecting overloads on the servomotors 15, 16. Signals from the sensors 31, 32 are input to the sequence controller 30 by way of a terminal box 35 of the grinding machine, and signals from the sensors 33, 34 are also input to the sequence controller 30. Thus, the CPU 22 is enabled to detect any of the above-noted troubles in response to an interruption from the sequence controller 30. Further, the sequence controller 30 is programmed to apply, in response to various output signals or data from the CPU 20, various machine control signals to the terminal box 35 and commands to circuit breakers 37, 38 incorporated in the drive units 27, 28, as will be described later. With the starting of the routine ACCR shown in Figure 4, the occurrences of troubles on the feed servomechanisms (i.e., the drive units 27, 28 and the servomotors 15, 16), the CPU 21, axis overrun, etc. are selectively detected in any of steps 40a-40d, and an error code which is assigned to the kind of any detected trouble is set in an error code register (not shown) provided in the memory 22 in steps 41a-41d. In step 42a following steps 41a and 41b and in step 42b following steps 41c and 41d, an error mode register (not shown) formed in the memory 22 is set with a trouble mode information which represents the emergency of a processing against a trouble occurring. MODE 1 Trouble needing emergency stop of whole system MODE 2 Trouble needing reverse feed subsequent to immediate feed stop MODE 3 Trouble needing immediate feed stop MODE 4 Trouble needing slow-down feed prior to feed stop MODE 5 Trouble needing feed stop right before execution of successive NC data block MODE 6 Trouble needing display of trouble The troubles modes used in this particular embodiment includes MODES 1-6, as noted in the above Table 1. Of these modes, MODES 1-3 represent troubles which need the immediate stop of any feed movement, MODES 4 and 5 represent troubles which need a slow-down feed prior to a feed stop, and MODE 6 represents a trouble which needs the display of the trouble only. The trouble processing routine APR shown in Figure 5 is executed at a predetermined time interval. The CPU 21 executes step 51 and those successive thereto when ascertaining in step 50 that trouble mode information has been set in the error code register ECR. That is, processings in steps 51 and 52 are executed to read out an error code, e.g., 1501, 1505, 4001 or 4002 as seen in Figure 4, from the error code register ECR and then, to display it on a display screen (not shown) of the data input device 26. It is ascertained in steps 53-55 whether the trouble occurring is of any of MODES 1-3. If the trouble occurring is of MODE 1, a command for emergency stop of the whole system is output to the sequence controller 30 in step 56. If it is of MODE 2, a command for an immediate reverse feed is applied to the sequence controller 30 in step 57. Further, if it is of MODE 3, step 58 is reached to deliver a command for immediate feed stop to the sequence controller 30. Further, if the trouble occurring is of any of MODES 1-3, such is detected in step 71 of the pulse distribution routine PGR shown in Figure 3, and this causes the processings in steps 74-76 for pulse distribution to be bypassed. Consequently, when any trouble of MODES 1-3 occurs, the pulse distribution operation is immediately terminated without executing a slow-down feed processing. On the other hand, the sequence controller 30, when given the emergency stop command, executes the processings shown in Figure 6, wherein an automatic operation mode is cancelled in step 81 after the break of electric power to the feed servomechanism as well as to a pump unit (not shown) constituting a hydraulic control system of the grinding machine. Further, the sequence controller 30, when given the immediate return command, cancels the automatic operation mode in step 82 of Figure 7 and then, instructs in step 83 the CPU 21 to execute a program (not shown) that is stored in the memory 22 of the numerical controller 20 for reverse feed of a predetermined amount. Further, as shown in Figure 8, the sequence controller 30 cancels the automatic operation mode in response to the immediate feed stop command given thereto. With the numerical controller 20 and the sequence controller 30 operated in the above-described manner, the occurrence of the MODE 1 trouble results in the immediate stop of pulse distribution, the break of electric power to the drive units 27, 28 as well as to the pump unit, and the cancellation of the automatic operation mode. The occurrence of the MODE 2 trouble results not only in the immediate stop of the pulse distribution followed by the cancellation of the automatic operation mode, but also in the execution by the numerical controller 20 of the reverse feed program, whereby the wheel head 12 is reversely moved a predetermined amount. Troubles which directly concern the movement of the wheel head 12 are treated as the MODE 2 trouble. Therefore, when the MODE 2 trouble occurs during the machining of the workpiece W, the wheel head 12 is stopped, with any stress of the workpiece W being removed and with the grinding wheel G being away from the workpiece W, thereby ensuring safety. Further, the occurrence of the MODE 3 trouble results in the immediate stop of the pulse distribution followed by the cancellation of the automatic operation mode. However, when a trouble occurring is of MODES 4-6, no command is applied to the sequence controller 30 as understood from Figure 5, and a processing against the trouble is carried out only at the side of the numerical controller 20. More specifically, the occurrence of the MODE 4 trouble is detected in step 72 of the pulse distribution routine PGR shown in Figure 3, and a processing is executed in step 73 to set a predetermined slow-down feed amount as the remaining feed amount. Accordingly, a slow-down feed processing is executed in step 74, whereby the feed rate of the movable member (table 11 or wheel head 12) is gradually decreased to stop the movable member when the remaining feed amount is reduced to zero. Upon the remaining feed amount becoming zero, the CPU 21 of the numerical controller 20 judges in step 70 that the movable member has reached an objective point. This permits the CPU 21 to subsequently execute the NC data read-out routine NDRR, whereby the occurrence of the MODE 4 trouble is ascertained in step 61 to direct the CPU 21 for the base routine. Since steps 62-65 is thus bypassed, no successive NC data block is read out. Consequently, the processings of the CPU 21 according to the NC program is discontinued upon completion of the slow-down feed. In the case of the MODE 5 trouble, the pulse distribution presently executed is continued, and the occurrence of the trouble is detected when the processing in step 61 of the NC data read-out routine NDRR is executed, to prevent the read-out of a successive NC data block so as to thereby keep the stopped status. That is, the occurrence of the MODE 5 trouble permits feed control to be continued until the pulse distribution according to the NC data block presently executed is completed, whereby the feed control of a movable member is discontinued upon completion of a slow-down feed. As described above, at the occurrence of any of the MODE 4 and 5 troubles, the feed control of the movable member is discontinued after a slow-down feed. Accordingly, when the machining is resumed after the removal of any cause of the trouble, it is unnecessary to return the movable members (table 11 and the wheel head 12) to original positions thereof, thereby reducing manipulations necessary for resumption of the machining operation.

Claims: A machine control apparatus (20) for controlling the movement of at least one movable member (11, 12) of a machine tool (10) in accordance with a numerical control programm, said control apparatus comprising: stop control means (21, 56-58) for stopping said at least one movable member (11, 12) ; a plurality of trouble sensors (31-34) , arranged at various parts of said machine tool (10) , for monitoring operating conditions of said machine tool (10) ; and trouble processing means (21, ACCR, APR) responsive to output signals of said plurality of trouble sensors (31-34) for operating said stop control means (21, 56-58) when said output signal is indicating a serious trouble of said operating conditions, characterized in that A) said stop control means (21, 56-58) is adapted to stop said at least one movable member (11, 12) in a first stop mode ( MODE 3 ) in which said at least one moveable member (11, 12) is stopped as fast as possible; B) said stop control means (21, 56-58) is adapted to stop said at least one movable member (11, 12) in a second stop mode (MODE 4) , in which said at least one movable member (11, 12) is stopped slowly in such a way that its actual position is prevented from differing from a nominal position variable, which is stored in said machine control apparatus (20) and which is used to indicate the present position of said at least one movable member (11, 12) , wherein a predetermined slow-down feed amount is set as a remaining feed amount and the feed of the respective movable member (11, 12) is discontinued when the respective movable member (11, 12) has been fed by said predetermined slow-down feed amount; C) said trouble processing means (21, ACCR, APR) determines by way of said output signals of said trouble sensors (31-34) the kind of trouble occurring and operates said stop control means (21, 56-58) to perform one of said stop modes depending on the kind of trouble determined. A machine control apparatus according to claim 1, characterized in that said stop control means (21, 56-58) is adapted to stop said at least one movable member (11, 12) in a third stop mode (MODE 5) , in which said at least one movable member (11, 12) is stopped in such a way that its actual position is prevented from differing from said nominal position, and in which said at least one movable member (11, 12) can be stopped only when reaching an objective position designated by a presently executed one block of said numerical control program. A machine control apparatus according to claim 1, characterized by means (21, 61) for inhibiting the execution of a subsequent one block of said numerical control program when said at least one movable member (11, 12) is stopped in any one of said stop modes.

Inventors: SAKAKIBARA YASUJI, YONEDA TAKAO, SAKAKIBARA, YASUJI, YONEDA, TAKAO
Applicants: TOYODA MACHINE WORKS LTD, TOYODA KOKI KABUSHIKI KAISHA
Application year: 1986
Main classification: G05B19
IPC codes: G05B19, G05B9