Automatic operating systems of machine tools and method

While machining a workpiece with a tool of a machine tool according to a numerically controlled machining program, when the tool breaks, the workpiece is removed from the machine tool and a new workpiece is substituted. A new program for the new workpiece is selected and a new tool for machining the new workpiece is selected and substituted for the broken tool. Now the new workpiece is machined in accordance with a new program. The workpieces removed from the machine tool are collected, fragments of the broken tools are removed therefrom, and then machined again. A tool magazine containing a plurality of tools is provided. Broken tools are removed from the machine tool and returned to the tool magazine. When all tools in the tool magazine are judged to be broken, new tools of the same type are supplemented. When the tools are worn out similar steps are executed.

BACKGROUND OF THE INVENTION 
This invention relates to an automatic operating system of a machine tool 
and method, more particularly to a system and method of operation for 
exchanging a tool and a workpiece worked thereby when the tool breaks or 
wears. 
In an automatic operating system of a machine tool wherein a plurality of 
different workpieces are machined sequentially over a long time by using 
machine tools including a plurality of machining centers, there are many 
problems to be solved including 
(a) handling of the chips, 
(b) detection of the presence or absence of a workpiece to be supplied, 
that is the detection of a pallet which carries the last workpiece and 
deenergization of the system, 
(c) detection of the abnormal cutting of each machine tool and the 
operation of the control system after the detection, and 
(d) administration of the cutting agent. 
Among these problems, (c) is the most important for performing an automatic 
operation. When abnormal cutting occurs various expedients have been used 
for the purpose of preventing the shut down of the entire system or a 
specific machine tool in which abnormal cutting is detected. 
Suppose now that while a machining center (MC) is machining an opening 
through a workpiece for tapping, a drill for machining the opening breaks. 
Even when the breakage is detected by some detecting means, continued 
machining of the opening by a new drill is not possible because fragments 
of the broken drill remain in the opening. In such a case, it is not 
simple to automatically check whether the fragments of the drill remain in 
the opening or not and to remove the remaining fragments. 
According to another proposed method, the drilling operation is interrupted 
and the workpiece is advanced to another working position without 
completing the drilling operation. Where a plurality of openings for 
tapping are to be formed by the same drill, it is usual to sequentially 
form the openings and then successively form screw threads with a tap. 
Accordingly, when a drill breaks while it is being used to form an opening 
for tapping at a given position (X.sub.j, Y.sub.j, Z.sub.j), a new 
identical drill is used to sequentially form openings at other working 
positions, and then screw threads are formed by using a tap, it is 
necessary to avoid to use the tap at said position (X.sub.j, Y.sub.j, 
Z.sub.j). More particularly, while a working program is being executed, 
when an accidental fault, for example breakage of a tool T.sub.1 occurs at 
a working position (X.sub.j, Y.sub.j, Z.sub.j), to instruct that the 
working by a different tool T.sub.2 at the same position should be 
eliminated while executing a subsequent working program, and to store said 
working position complicates the construction and operation of the control 
system. 
Where K working steps are required to machine a workpiece at a given 
position (X.sub.j, Y.sub.j, Z.sub.j), when the fault occurs in the first 
working step it is necessary to modify an NC (numerically controlled) 
program so as to omit remaining (K-1) working steps at that position, thus 
complicating the NC system. Such modified control is based on the desire 
that even when a portion of the working step is not performed it is 
desirous to perform as far as possible the remaining steps. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an improved system and method 
of automatic operation of a machine tool capable of eliminating the 
difficulties of the prior art system described above. 
Briefly stated, according to this invention when a tool, for example a 
drill, breaks, the machining of a workpiece by the tool is interrupted and 
the workpiece is exchanged with a new workpiece. At the same time a new 
program is selected for machining the new workpiece and the broken tool is 
exchanged with a new tool suitable for machining the new workpiece. Then 
the new workpiece is machined with the new tool. Workpieces which have 
worked by tools until they are judged to be broken are collected at a 
predetermined position and after removal of the fragments of the tools 
remaining in the workpieces they are subjected to remaining machining 
steps. According to this invention, the term "break" not only means actual 
breakage but also a state immediately before breakage since abnormal 
increase in the armature current of a motor for driving the tool or 
increase in the thrust acting upon the tool is used for the judgement. 
Where wear occurs similar procedures are executed. 
According to one aspect of this invention, there is provided an automatic 
operating system of a machine tool havng a spindle on which a tool is 
mounted for machining a workpiece mounted on a machining area of the 
machine tool in accordance with a numerically controlled machining 
program, said system comprising tool storage means containing a plurality 
of tools for use on the machine tool; means for detecting a broken state 
of a tool while it is mounted on the machine tool and machining the 
workpiece; memory means including first and second memory areas 
corresponding to the tools contained in the tool storage means for 
respectively storing a first data which is referred to for judging the 
broken state of the tool on the machine tool, and a second data 
representing that the tool has been judged to be broken in accordance with 
the first data; means for detecting a third data and storing the same in 
the second memory area, the third data being compared with the first data 
during actual cutting operation of the workpiece with the tool mounted on 
the machine tool; means to read out the first and third data from the 
first and second memory areas respectively and to compare the read out 
data with each other for judging the broken state of the tool; means for 
storing the second data in the second memory area of the memory means when 
the tool is judged to be broken; means responsive to the judgement of the 
broken state of the tool for interrupting the machining of the tool; means 
for moving the spindle relative to the workpiece to separate the tool 
therefrom; means for removing the workpiece out the machining area; means 
for mounting a new workpiece on the machining area; means for selecting a 
new machining program for said new workpiece; means for selecting a new 
tool out of said tool storage means and for exchanging said new tool with 
said tool judged to be broken; and means for machining said new workpieces 
with said new tool. 
According to another aspect of this invention there is provided a method of 
automatic operation of a machine tool having a spindle on which a tool is 
mounted for machining a workpiece mounted on a machining area of the 
machine tool in accordance with a numerically controlled machining 
program, said machine tool being combined with tool storage means 
containing a plurality of tools for use on the machine tool, and memory 
means including first and second memory areas corresponding to the tools 
contained in the tool storage means, said method comprising the steps of 
storing a first data which is referred to for judging the broken state of 
the tool on the machine tool and a second data representing that the tool 
has been judged to be broken in accordance with the first data in the 
first and second memory area respectively; detecting a third data which is 
compared with the first data during actual cutting operation of the 
workpiece with the tool mounted on the machine tool; storing the third 
data in the second memory area; reading out the first and third data from 
the first and second memory areas respectively and to compare the read out 
data with each other for judging the broken state of the tool; storing the 
second data in the second memory area when the tool is judged to be 
broken; interrupting the machining of the workpiece by the tool when it is 
judged to be broken; moving the spindle relative to the workpiece to 
separate the tool therefrom; removing the workpiece out of the machining 
area; mounting a new workpiece on the machining area; selecting a new 
machining program for the new workpiece; selecting a new tool out of the 
storage means and exchanging the new tool with the tool judged to be 
broken and machining the new workpiece with the new tool.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The layout of machine tools, a pallet transfer line, etc. which constitute 
the automatic operating system of this invention is shown in FIG. 1. As 
shown, a transfer line 11 is provided at the center to extend in X 
direction, and a plurality of machine tools that is machining centers 
MCl--MCj are installed along the transfer line 11. Respective machining 
centers are provided with NC control devices NC1, NC2, . . . NCj and tool 
magazines MG1, MG2, . . . MGj respectively. Although not shown in FIG. 1, 
as will be described later, each NC control device contains a power 
distribution panel (PDP) including a sequence control device and a 
detecting unit which characterizes the invention. 
At the righthand end of the transfer line 11 is provided a waiting area 12 
for accommodating pallets P on which workpieces to be machined are mounted 
and secured. At the lefthand end of the transfer line 11 is provided an 
area 14 for collecting pallets which carry workpieces whose machinings 
have been interrupted for the reason described below. 
A selfpropelling carriage 16 which carries pallets is mounted on the 
transfer line 11 so that by driving the wheels 17 of the carriage 16 it 
can be moved to any desired position along the transfer line 11. Two 
pallets can be mounted at the same time on a guide 18 supported by a pivot 
pin 19 secured to the carriage to be swingable about the pivot pin 19. A 
transfer bar, not shown, is provided for the guide 18 for loading and 
unloading the pallet P onto and from the guide 18 so that when the 
transfer bar is operated the pallet is moved onto the table of a machining 
center or moved onto the carriage from the table as shown by an arrow a. 
A control device 20 is provided to control various operations including the 
movement of the carriage 16 on the transfer line 11, 90.degree. rotation 
of the guide 18, the advance and retraction of the transfer bar. The 
informations from a pallet transfer control device 21 for these operations 
are applied to signal transmitter-receivers SGP and SGPO located at 
suitable positions along the transfer line 11. The informations are 
supplied to the control device 20 from the transmitter-receivers SGP and 
SGPO through terminals provided on the lower surface of the carriage. 
Transmitter-receivers SGP are provided for respective machining centers 
while the transmitter-receiver SGPO is located at the wating position (at 
the lefthand end of the transfer line 11) of the carriage 16. 
As shown in FIG. 1, a transfer line 11A is provided for supplementing tools 
which are contained in a tool shelf 15 and have been set for operating 
condition. A carriage 16A similar to the carriage 16 is mounted on the 
transfer line 11A to be movable therealong. On the carriage 16A is mounted 
a tool pallet TLP including a tool container 31 adapted to accommodate a 
plurality of tools. As shown in FIGS. 2A and 2B, a tool robot TROBT is 
carried by the tool pallet TLP so as to grasp a tool contained in the tool 
shelf 15 for accommodating the tool in the tool container 31. Furthermore, 
the tool robot operates to put tools contained in the tool container 31 in 
a tool shelf 15A which accommodates defective tools. Tools are arranged in 
the tool shelf 15 such that tools of the same type are grouped so as to 
simplify the positioning of the carriage 16A and the operation of the tool 
robot TROBT. The tool pallet TLP is transferred from carriage 16A onto 
carriage 16 at a position along the transfer line 11A and near the 
transfer line 11 and then moved to the table of any machining center MC by 
the carriage 16. 
Furthermore, the tool robot TROBT operates to mount a desired tool (one or 
more) on the spindle of a given machining center MC and to remove a tool 
which has been judged broken or worn out for accommodating it in the tool 
container 31 on the pallet TLP. The shelf 15A is provided for receiving 
defective tools that have been judged broken or worn out. 
Informations regarding the sequential operation of the tool robot TROBT on 
the transfer line 11A and on the machining center MC are applied to the 
carriage through the transmitter-receiver SGPO from the transfer control 
device 21 together with the informations (instructions) regarding the 
movement of the carriage 16A and stored in a memory device which is also 
provided for the carriage 16A contained in the pallet TLP when the 
carriage 16A is positioned at the position of the transmitter-receiver 
SGPO at the front end of the transfer line 11, that is the waiting 
position of the carriage 16A. Consequently, when the carriage 16A stops at 
a suitable position along the transfer line 11A the tool robot TROBT 
sequentially reads and understands the content of the memory device so as 
to perform a series of operations described above. 
Also when the pallet TLP is moved on the table of a machining center, the 
tool is exchanged between the spindle and the tool magazine according to 
an information stored in the other portion of the memory device. 
It is possible to amplify an information given by the transfer control 
device 21 so as to supplement new tools and collect defective tools to and 
from a plurality of machining centers while the pallet TLP is moved along 
transfer line 11. 
The electric power for operating the self-propelling carriages 16 and 16A 
and the tool robot TROBT is supplied from the central conductors of the 
transfer lines 11 and 11A respectively. Where the system contains an 
electric source the power supply terminals are provided at the waiting 
positions SGPO and SGPOA of the transfer lines 11 and 11A. 
As shown in FIG. 2A, on the righthand half of a pallet TLP is mounted a 
tool container 31 comprising two shelves which contain a total of 14 tools 
in this example. 
The tool robot TROBT is mounted on the upper surface of the lefthand half 
of the pallet TLP and a horizontal arm 33 extends through the supporting 
column 32 of the tool robot to be movable in the forward and rearward 
directions. 
The lower end of the supporting column 32 is mounted on a rotary member 34 
on a base 35 so that a chuck 33a secured to the righthand end of the arm 
33 can be brought to any position about the axis of the supporting column 
32. As diagrammatically shown, the tool robot is controlled by a control 
device 30. 
As shown in FIG. 2B, the tool pallet TLP is movably supported by a guide 
rail of the carriage 16A shown by dot and dash lines. A signal receiver 36 
is mounted on the bottom surface of the base 35 to oppose a signal supply 
member 37 mounted on the upper surface of the carriage 16A to be movable 
in the vertical direction so as to receive the informations regarding the 
movement of the carriage 16A together with informations regarding the 
sequential operation of the tool robot TROBT at the position of 
transmitter-receiver SGPOA shown in FIG. 1. These received informations 
are stored in a memory device in the control device 30. 
FIGS. 3A through 3D show a pallet PL which carries supplementary tools and 
has a shape and function different from those of the pallet shown in FIGS. 
1 and 2. FIG. 3A is a side view showing the pallet PL mounted on the table 
TAB of a machining center MC and carrying a group of supplementary tools 
STLG. 
As shown in FIG. 3B, the supplementary tools STLG are radially supported 
and the tools are brought toward the spindle SPD in the lateral direction 
as shown by an arrow X so as to dismount a tool from the spindle SPD. A 
shaft AX carrying the tools is rotated by a rotary table RTA mounted on 
the pallet PL. 
FIG. 3D shows steps a through c for dismounting a tool T1 from the spindle 
SPD and steps d and e for mounting the other tool T2 on the spindle. 
While in FIG. 3A a rotary table is mounted on the pallet PL, it is also 
possible to rotate the pallet PL by a rotary table provided for the 
machining center MC so as to index a desired tool for the spindle SPD. 
With the construction shown in FIGS. 3A through 3D, the transfer line 11A, 
the tool shelf 15 and the carriage 16A are not necessary. In the case 
shown by FIGS. 3A - 3D, a plurality of pallets PL each carrying a group of 
supplementary tools STLG as shown in FIG. 3A are installed on the front 
side of the transfer line 11 to be moved to a desired machining center MC 
by the carriage 16. 
FIG. 4 is a block diagram showing the flow of principal control 
informations in the automatic operating system of this invention shown in 
FIG. 1. As shown in FIG. 4, the NC devices NCl . . . NCj of respecitve 
machining centers MCl through MCj are coupled with a central computer 41. 
When a workpiece is mounted on a machining center, for example MCj, the 
program data for machining the workpiece are transmitted to the NC device 
NCj from the central computer 41. A signal informing the completion of the 
machining of the workpiece is sent from the NC device NCj to the central 
computer. In addition to the signals described above, signals requiring 
supplement of tools to the machine center MCj and signals informing 
detection of the breakage of a tool while it is used are also exchanged 
between the central computer 41 and the machining center MCj. Also, 
instructions regarding the movement of the carriages 16 and 16A, and 
informations regarding the movement of a pallet P between the waiting area 
12 and the transfer line 11 and between the transfer line 11 and the 
collection area 14, regarding the movement of pallet P along a transfer 
line 11A and regarding the sequential operation of the tool robot TROBT on 
the tool pallet TLP are exchanged between the transfer control device 21 
and the central computer 41. 
As shown by dotted lines wireless may be used to exchange sequence 
informations between the transfer control device 21 and the carriages 16 
and 16A. Transmitter-receivers SGP, SGPO and SGPOA are arranged at stop 
positions of carriages 16 and 16A along the transfer lines 11 and 11A. 
FIG. 5A shows the relationship among any one of the machining centers MC, 
its NC control device, the power distribution panel PDP and the detecting 
unit 51 shown in FIG. 1. The NC device applies command pulses to the 
machining center MC for moving or rotating the table, the saddle rotary 
table, etc. thereof through a line 52, and a feedback pulse is fed back to 
the NC device through a line 53. 
Line 54 supplies a sequence operation instruction signal to the machining 
center MC from a sequencer 58 of the power distribution panel PDP, while 
line 55 supplies sequence completion signals to the NC device from the 
machining center MC. Signal lines 56 and 57 extend between the NC device 
and the sequencer 58. A motor M for driving the spindle of the machining 
center MC is driven by a drive circuit 59. The armature current of the 
motor M is detected by a shunt current detector 60 while the number of 
revolutions of motor M is detected by a tachometer generator TG and fed 
back to the drive circuit 59. The armature current detected by the 
detector 60 is applied to a logical operating unit 51-3 via a line 61, a 
low-pass filter 51-1 of the detecting unit 51 and an analogue-digital 
converter 51-2. The logical operating unit 51-3 is connected to sequencer 
58 through lines 62 and 63 to operate as will be described later with 
reference to the flow charts. 
More particularly, when a drill breaks during its use such breakage is 
detected when data representing the normal cutting condition of the drill 
has been stored in the memory device of the logical operating unit 51-3 
and the data detected during the drilling operation are judged to have a 
relationship normal cutting current&lt;actual cutting current and a signal of 
the judgement is sent to the sequencer 58 and then to the NC device 
whereby the NC device produces an instruction signal to the machining 
center MC to stop its drilling operation and an instruction signal to 
remove the workpiece from the working area of the machining center MC. At 
the same time, the NC device applies a signal to the central computer 41 
to cause the transfer control device 21 to make a request for removing the 
workpiece out of the working area, a request for supplementing the broken 
drill and a request for mounting a new workpiece. 
Lines 62 and 63 constitute interfaces between the sequencer 58 and the 
logical operation unit 51-3. For example, line 63 is supplied with signals 
NC, RESET, ONTC, CYLLE START, MO6 COMPLETE, C.sub.iX, MO5, STP, SSP, SRV 
(see Table 1 below) and line 62 is supplied with signals requesting 
judgement of the tool breakage, wear and supplement of the tools. 
A unit 64 bounded by dot and dash lines represents a computerized numerical 
control CNC wherein the NC device, the sequencer 58 and the logical 
operating unit 51-3 are integrated. 
FIG. 5B shows the front view of the panel of the detecting unit 51. An 
ammeter 98 is mounted on the left upper corner which shows the armature 
current of the spindle driving motor. During the actual cutting with a new 
tool under a DATA-SET mode, when the operator depresses a STORE button by 
noting that the cutting state is normal, the actual cutting current value 
at that time is converted into a digital quantity from an analogue 
quantity and the digital quantity is stored in a memory device to 
correspond to the tool number (ONTC No.) of the tool being utilized at 
that time. 
A clear push button is used to clear the data of the ONTC tool under the 
DATA-SET mode. A lamp FTCNN is lighted when the actual cutting data of a 
tool NN (ONTO NO) are stored. A reset push button RESET is provided for 
all flags except FTCNN, and lamps FBRK and FWEAR are lighted when the tool 
is judged that it has been broken or worn out. Lamps FiNET, FCNST, FCST 
and FNUL are lighted when the normal cutting current value is stored in 
iNET, when the normal cutting operation is commenced, when the cutting 
start is judged, and when the no load current is stored respectively. 
FIG. 6 shows a manner of forming an opening through a workpiece W by 
mounting a drill on the spindle SPD and by rotating the same with a drive 
motor M through a gear train GTR. The armature current of the motor M is 
applied to a detector 72 of the detecting unit 51 including a low pass 
filter and an A-D converter, not shown. Reference character 73 shows a 
memory device having a plurality of memory areas or addresses for storing 
various data for each tool including a current value iNETNN corresponding 
to the normal cutting state of the tool (its number is designated by NN), 
a signal FTCNN which shows that the signal iNETNN has been stored, a 
signal FTBNN representing that the tool NN was judged broken, a signal 
FTWNN representing that the tool was judged worn out, and a signal FCOMNN 
showing that the tool NN is one of the tools of the same type. A temporary 
memory device 73A is provided to receive the current value iNETNN from the 
detector 72 through line L1 and then supplies it to the memory device 73. 
The use of the temporary memory device 73A is convenient where all of the 
normal cutting current values iNETNN of various tools are stored in the 
memory device 73A before the operation of the automatic system. As has 
been described in connection with the pannel shown in FIG. 5B, the value 
of the cutting current iNETNN is stored in the temporary memory device 73A 
when a skilled operator judges that the cutting state is normal by 
observing the ammeter. 
If a numerical data regarding iNETNN of a tool NN were available, it is not 
necessary to detect the actual value of iNETNN by actual cutting test of 
the tool NN used. 
For a number of tools of the same type the same value of iNETNN may be 
stored. Line L2 is used to supply the value iNETNN directly to the memory 
device 73 from the detector 72 without passing through the temporary 
memory device 73A. A comparator 74 having a logical operation performance 
is provided to calculate a value IV in accordance with a value of the 
cutting current iCNSTNN when the tool NN is actually machining the 
workpiece W and then compare the value IV with iNETNN. When the value IV 
is larger than iNETNN by predetermined times, it is judged that the tool 
is broken or worn out. These judgement signals are also applied to the 
memory areas of the memory device 73 which stores data FTWNN, FTBNN, etc. 
The break judgement signal and the wear judgement signal are applied to a 
unit 75 containing the sequencer 58 and the NC device. When the wear 
judgement signal is applied the operation is advanced to step 76 for 
stepwisely decreasing the feed of the tool NN by an instruction from the 
NC device. Where the break judgement signal is applied to unit 75, the 
operation is transferred to step 77 to execute a retract cycle thereby 
separating the tool NN from the workpiece W. Under these conditions, if 
necessary, the rotation of the spindle SPD is stopped. Then the program 
operation is advanced to step 78 to initialize the NC device. At step 79 
the workpiece W is transferred to the transfer line 11 from the table that 
is the working region of the machining center MC. 
At step 80, where a tool that can be substituted for the tool that has been 
judged broken is not stored in the tool magazine of a machining tool, the 
supplemental tool is supplied from the tool shelf before mounting a new 
workpiece on the machining center MC at step 81. At step 82 a substitute 
tool is selected, and at step 83 the working program of the newly mounted 
workpiece is changed to that which the NC device can execute. Step 84 
shows that the machining is to be continued, and at step 80A a judgement 
is made as to whether the tool magazine of the machining center contains a 
tool that can substitute the tool judged worn out or not. Where such tool 
of the same type is not available, a supplement signal thereof is applied 
to the transfer control device 21 through the NC control device NC and the 
central computer 41. However, the supplement of the tool is not performed 
immediately but the tool is put into the tool magazine before the next new 
workpiece is mounted. 
Steps 80 and 80A may be omitted where the tool magazine contains a 
sufficient number of substitute tools as spares. 
FIG. 7 shows the detail of the detector 72 shown in FIG. 6. The detector 72 
comprises a rectifier 92 for driving a spindle driving motor 91, a shunt 
93 connected in series with the armature of motor 91, an isolation circuit 
94, a low-pass filter 95 connected to the output of the isolation circuit 
94, an A/D converter 96 connected to the output of the low-pass filter 95 
and an ammeter 98 connected to the output of the low-pass filter 95 via an 
amplifier 97. The output of the A/D converter 96 comprises 8 to 10 bits 
and utilized as signal iNETNN, for example. 
FIG. 8 shows the memory regions or areas of the memory device 73 shown in 
FIG. 6 and data stored therein corresponding to respective tools NN. In 
FIG. 8, the tool numbers are shown by decimal numbers of two orders. 
Symbol 00 is used to identify the groups of tools of the same type. For 
each tool, the normal cutting current vaue iNETNN is constituted by 8 
bits, signal FTCNN showing that the signal iNETNN is stored by one bit, 
signal FCOMNN by 5 bits and signals FTBNN and FTWNN by one bit 
respectively. Tool numbers 01, 02, 03 and 04 represent tools of the same 
type. In the same manner, 05 and 06 represent the tools of the same group 
(FCOMNN=00010), 07 and 08 mean that FCOMNN=00011, and 09 means that 
FCOMNN=00100. Signals iNETNN for tool numbers 01, 02, 03 and 04 are zero 
and FTCNN=0 of these tool numbers shows that the normal cutting current 
values of tools 01-04 are not stored. 
As the signals iNETNN of tools 05 and 06, the same value 01011001 is stored 
so that signals FTCNN are 1. However, for tool 05, FTBNN=0 and FTWNN=1 
show that a wear judgement has been made. For tool 06, FTBNN=1 and FFWNN=1 
mean that a wear judgement was made during cutting and then break 
judgement was made. For tool 09, iNETNN=10010001 and FTCNN=1 mean that 
either one of the wear and break judgements has not yet been made. 
FIGS. 9 to 17 show flow charts showing the operation of the system 
diagrammatically shown in FIG. 6, and the meanings of various signals are 
shown in Table 1 at the end of the specification. 
Referring first to FIGS. 9A and 9B when a source is connected at step 1 
(hereinafter a step is abbreviated as "ST"), all data of the memory device 
except data iNETNN, FTCNN, FCOMNN, FTBNN and FTWNN and flags (signals 
utilizing F as the first letter) are cleared at ST2. 
Where a start instruction is applied at ST3 the program is advanced to ST4 
at which a judgement is made as to whether the bit state of the data 
SETFiN stored in a data memory device in the comparator 74 if "0" or not. 
The data SETFiN means that a tool NN (termed ONTC TOOL) is mounted on the 
spindle and a signal FTCNN showing that the data SNETNN of the tool has 
been stored in the memory device 73 is "1". 
At ST2, since SETFiN is cleared, the program is advanced to ST5 at which 
the address of the memory device 73 (FIG. 6) storing the tool number NN of 
the tool ONTC TOOL now being mounted on the spindle is searched, thus 
finding out addresses of the data iNETNN, FTCNN, FCDMNN, FTBNN and FTWNN 
corresponding to this tool number. 
Then the program is advanced to ST6 to check whether the mode selection is 
AUTO or DATA SET. In the case of AUTO the execution of the program is 
transferred to a junction A . On the other hand, where the mode is AUTO 
SET, a step group STG1 consisting of ST7 through ST16 is executed. The 
step group STG1 shows one example of setting the data iNETNN in one of the 
data areas of the memory device 73 shown in FIG. 6. 
At ST9 when the spindle is rotating at a speed above a definite value 
(CiX="1") the operator judges the cutting state of the ONTC TOOL Tj by 
reading the ammeter and when the cutting current value is normal he turns 
ON the store push button. 
At ST11, whether the store push button is ON or not is judged. When the 
result is YES, the program is advanced to ST12 where after 0.1 sec., for 
example, the cutting current is sampled 8 times and the mean value IC is 
calculated. Then, at ST13, the mean value IC is stored in the iNETNN 
region of the memory device 73 (at this time NN=j). At the same time, a 
flag FTCNN showing that the data iNETNN has been stored is set to "1". 
Then, at ST14 the data bit of SETFiN is set to "1" and the program is 
returned to a junction S . Where the result of ST9 is NO, that is when 
the speed of the spindle is less than a predetermined value the program is 
advanced to ST10 to judge whether the clear button is ON or not. When the 
result is YES at ST15, "0" is stored as the data bit of data iNETNN and 
FTCNN and then "0" is stored at ST16 as the data bit of SETFiN. Then the 
program is returned to the junction S . When the result of ST10 is NO the 
program is returned directly to the junction S . When ST16 is executed, 
as the data iNETNN is not stored in the memory device 73, steps 
ST4.fwdarw.ST5.fwdarw.ST6 are executed again and this execution loop of 
the program would be repeated until CiX becomes "1" at ST9. When the step 
ST14 is executed the storing of the data iNETNN for tool Tj is completed, 
the execution loop ST7.fwdarw..fwdarw.ST10.fwdarw. S would be repeated 
until the next tool T(J+1) is mounted on the spindle by the MO6 completion 
signal. 
When the result of judgement at ST7 is YES, that is when MO6 is completed 
and the exchange of the next new tool T(j+1) is completed, at ST8 data 
SETFiN is firstly made to "0" so that the data iNETNN (NN=j+1) for the 
next tool T(j+1) would be stored. Thus, cutting is made with the new tool 
T(j+1) and the data iNETNN is stored in a corresponding memory region. The 
same operations are performed for the tools contained in the tool magazine 
of a given machining center. 
The process of executing the program where the judging step ST6 is of a 
mode AUTO will be described hereunder. 
At this time, at ST17 and ST18, the data bits of break judging data FBRK, 
and wear judging data FWEAR stored in the read access memory device (RAM), 
that is the data memory device in the memory device 73 shown in FIG. 6 are 
checked. When the result of either ST17 and ST18 is YES, the program is 
transferred to step group STG2. At ST25, the actual cutting current of the 
tool (ONTC TOOL) mounted on the spindle is judged and when it is judged to 
be equal to the normal cutting current, the data FiNET becomes "1". Then, 
the program proceeds to 4 . At ST25, if FiNET="0", the program is 
transferred to ST26 and when the result of judgement of ST26 is FCNST="1", 
that is the normal cutting state, the program is transferred to 3 . If 
the result of judgement at ST26 is FCNST="0", the program is advanced to 
ST28 and when the result of judgement of this step is FINUL="1" that is a 
case wherein no load current is stored, the program is transferred to 1 . 
Where the result of ST28 is FINUL="0", the program is advanced to ST29 
where judgement is made as to whether the spindle has reached a 
predetermined speed or not. Where CiX="0", that is when the speed of the 
spindle is below the predetermined speed the program is transferred to 
junction S . When the result of ST29 is CiX="1", at ST30 the no load 
current INUL is calculated a definite time (TM1=0.5 sec.) after, which is 
set by a timer TM1 (not shown). At this time, the new tool OTNC TOOL does 
not start cutting. The no load current INUL is obtained by sampling 8 
times the coded armature current Ii and then calculating the mean value 
##EQU1## 
The data INUL is stored in a data memory device (contained in the memory 
device 73, for example). 
At ST31 the data bit of FINUL is set to "1" for the purpose of showing that 
the data INUL has been stored. Thus, the bit ("1" or "0") of this data 
FINUL shows that whether the no load current has been stored or not. 
At ST32 the mean value ICST is calculated 0.1 sec. after which is set by a 
timer TM2 (not shown) by sampling 4 times the armature current at an 
interval of 40 ms. Also the ratio IR1 of ICST to INUL is calculated. 
At the next step a judgement is made as to whether IR1 is equal to or 
larger than a predetermined constant K (K=1.2 for example). If the result 
of judgement at ST33 is NO, the values of ICST and LR1 stored in the data 
memory device of the memory device 73 are made to be "0" respectively. 
When the result of judgement at ST33 is YES, at ST34, the data bit of FCST 
stored in the data memory device is set to "1". This means that the tool 
ONTC TOOL is judged that it has started cutting. 
Turning now to FIG. 10, steps ST36 and ST37 are utilized to judge whether 
the cutting state is normal or not. Thus, after 0.1 sec. predetermined by 
a timer TM3, not shown, the cutting current is sampled 4 times with an 
interval of 40 ms to calculate the mean value ICNST. Thereafter, the 
cutting current is sampled 4 times to calculate the mean value ICNST2, and 
then the ratio IR2 of the mean values is calculated. When the result of 
ST37 shows that the ratio IR2 is larger than a constant K2=0.9 but smaller 
than a constant K3=1.1, the program proceeds to ST38 where it is judged 
that whether FCNST is equal to "1" or not, that is whether the cutting is 
performed under normal state or not. When the result of the judgement at 
ST37 is NO, data ICNST1, ICNST2 and IR2 calculated at step ST36 and have 
been stored in the data memory device are cleared. Then the program 
proceeds to junction 5 . 
Subsequent to ST38, step ST40 is executed. In this step, after 0.1 sec. 
predetermined by timer TM4, not shown, the cutting current is sampled 8 
times to calculate a mean value iNET. Then the ratio IR3 of iNET to INUL 
is calculated. At steps ST41, ST42 and ST43, the values of constants K5 
and K6 which are used in later program steps for judging the wear and 
break of the tool ONTC TOOL are varied in accordance with the value of 
ratio IR3. At step ST44 a judgement is made as to whether iNETNN 
corresponding to the tool ONTC TOOL is stored or not. If the result is 
YES, at step 45 data iNETNN is changed to data iNET. On the other hand, if 
the result is NO, at step ST46, after 0.1 sec. predetermined by a timer 
TM5, not shown, the actual cutting current is sampled 8 times to calculate 
a mean value iNET, and at step ST47 the mean value iNET is substituted for 
data iNETNN and set the data bit of data FTCNN to "1". 
The program steps ST46 and ST47 are executed when the data iNETNN of step 
group STG1 under the DAT SET mode is stored in the data memory region of 
the memory device 73. At ST48, "1" is set as the data bit of the flag 
FiNET which shows that the normal cutting current has been stored. 
Then, the program proceeds to a judging step ST49 shown in FIG. 11. The 
purpose of a program step group STG3 comprising ST49 through ST55 is to 
prevent the sampling of the peak current value under a transient rotating 
condition of the spindle driving motor which occurs when a stop 
instruction (STP="1") is applied to stop the motor and the motor restarts 
after 0.5 sec. 
More particularly, if STP="1" at ST49, at ST51 the data bits of the signals 
SSP1 and SSP2 showing the stop of the spindle are set to "1" respectively. 
If the result of judgement at ST49 is STP="0", at ST50 judgement is made 
as to whether CiX is "1" or not, that is whether the number of revolutions 
of the spindle is normal or not. If the result is NO, the program is 
advanced to ST51. If the result of judgement of ST50 is YES (CiX="1"), at 
ST52 the data bit of data SSP2 is set to "0". 
At ST53 a judgement is made as to whether the data SSP1 is equal to "1" or 
not. When the result is YES, at ST54 a judgement is made as to whether 
data SSP2 is "1" or not. If the result is YES, the program is advanced to 
ST59 to clear the data IV and IR4 which were calculated at ST56. When the 
result of judgement at ST54 is NO, the program advances to ST55 where 
after dwelling for 0.5 sec., signal SSP1 is cleared. Signal SSP1 is set to 
"1" when the spindle stop signal STP becomes "1". Thereafter, when the 
spindle is restarted and reaches a predetermined speed, signal SSP2 is 
made to "0". After dwelling for 0.5 sec, SSP1 is made "1". At ST56, after 
0.1 sec. set by a timer TM6, not shown, the cutting current is sampled 8 
times to calculate a mean value IV and a ratio IR4=(IV/iNET) is also 
calculated. 
Then at ST57, a judgement is made as to whether IR4 lies between constants 
K5 and K6 which are determined at ST42 or ST43 or not. If the result of 
judgement at ST57 is NO, at ST58 a judgement is made as to whether IR4 is 
larger than K6 or not. If the result is NO, at ST59 data IV and IR4 are 
cleared and the program is transferred to junction 5 . When the result of 
ST57 is YES, it means a wear so that at ST60 the FWEAR data bit is set to 
"1", and at ST60, a judgement is made as to whether a tool wear detection 
switch is ON or not. If the switch is ON, at ST64 a wear judging signal is 
applied to the sequencer as shown by dotted lines and the execution of the 
program is transferred to junction 5 . If the result of ST62 is NO, that 
is no wear is detected, the program is transferred from ST62 to junction 
5 . In the same manner, if the result of the judgement at ST58 is YES, 
that is IR4&gt;K6, at ST61 the data bit of FBRK is set to "1". Furthermore, 
if the result of the judgement at ST63 is YES, that is when the tool break 
detection switch is ON, at ST65 a break judgement signal is sent to the 
sequencer as shown by dotted lines. If the result of ST63 is NO, that is 
when the tool break detection switch is OFF, the program is transferred 
directly to the junction 5 . 
Various program steps of the step group STG2 shown in FIG. 9 will now be 
described. 
At ST17 if the tool is judged broken, that is FBRK="1", at ST19 a judgement 
is made as to whether the NC device has been reset or not. If the NC 
device has been reset, all flags and data INUL, ICNST1, ICNST2, iNET, IV, 
IR1, IR2, IR3 and IR4 except iNETNN, FTCNN, FCOMNN, FTBNN, FTWNN are 
cleared at ST20. 
After executing ST3, the program is transferred to junction S . If the 
result of ST19 is NO, that is if the NC device were not reset, the program 
proceeds to junction 5 , and at ST21 a judgement is made as to whether 
MO6 has been completed or not, that is whether exchange of the new tool 
has been completed or not. If the result of ST21 is YES, the data and 
flags are cleared as above described. If the result of ST21 is NO the 
program proceeds to junction A . 
At ST18, if the tool wear judging flag FWEAR is "1", at ST22 a judgement is 
made whether a cycle start is ON (YES) or not. If the result is YES, at 
ST23, flag FWEAR is cleared. Then at ST24, the FEED HOLD is cleared by the 
NC device and the program proceeds to 4 . 
If the result of ST22 is NO, or CYS is not ON the program is transferred to 
ST19. 
FIG. 12 is a flow chart showing the program steps of step group STG2 shown 
in FIG. 9 which are substituted by a computerized NC device. In FIG. 12, 
when the result of ST17 is YES, the program is advanced to ST17-1 where a 
judgement is made whether break judging flag FTBNN is "1" or not. If the 
result is NO, at ST17-2 the flag FTBNN is set to "1". On the other hand, 
if the result is YES, the program is transferred directly to ST17-3 where 
a judgement is made as to whether the bit of BRESET is "1" or not. If the 
result is YES, at ST17-4 break judging flag FBRK="1" is cleared and then 
the program returns to A . If the result of ST13-3 is NO, at ST17-5 a 
judgement is made whether MO6 has been completed or not. When the result 
of ST13-5 is YES, the program is advanced to ST17-7 to clear all data and 
flags other than those pointed out before and program is returned to 
junction S . If the result of ST15-5 is NO, at ST-6 a judgement is made 
as to whether NC device has been reset or not. If the result of ST17-6 is 
YES, the program is transferred to ST17-7, whereas when the result is NO, 
the program proceeds to junction A . 
In the same manner, at ST18 a judgement is made whether the wear judging 
flag FWEAR is "1" or not and when the result is YES, at ST18-1 a judgement 
is made whether flag FTWNN is "1" or not. If the result of ST18-1 is NO, 
at ST18-2 the flag FTWNN is set to "1", whereas when the result is YES, at 
ST18-3 a judgement is made whether WRESET is "1" or not. When the result 
of ST18-3 is YES, at ST18-4 the wear judging flag WEAR is cleared and the 
program proceeds to the junction A . The program also proceeds to the 
junction A when the result of ST18-3 is NO. 
The program steps shown in the flow charts shown in FIGS. 9-12 are executed 
successively in a manner described above. FIG. 13 shows a modification of 
the flow chart shown in FIG. 11. More particularly, while a tool (ONTC 
TOOL) NN is used to work a workpiece, suppose now that it is judged that 
the tool has broken. The flow chart shown in FIG. 13 is constructed such 
that, when a flag FTBNN regarding all tools NN.sub.1 -NN.sub.n belonging 
to a tool group in a tool magazine including the tool NN is "1" before any 
one of the tools in the tool group is designated for use to work a next 
workpiece, a tool supplement instruction is provided to assure at least 
one sound tool NN in the tool group in that tool magazine. 
When the result of judgement of ST62 shown in FIG. 11 is YES, at ST66 a 
judgement is made as to whether the tool break judging flag FTBNN or the 
tool wear judging flag FTWNN of all tools of a tool group in which the 
values of FCOMNN of the tools which have been judged broken are the same. 
When the result of ST66 is YES, it means that there is no sound tool NN in 
the tool magazine and the program proceeds to ST66 where a judgement is 
made as to whether a new tool request flag FNTCAL is "1" or not. If the 
result of ST67 is NO, at ST68, the flag INTCAL is set to "1", whereas when 
the result is YES, an instruction is generated for supplementing a new 
tool NN in the tool magazine to the carriages 16 and 16A, tool pallet TLP 
and tool robot TROBT shown in FIG. 1, via sequencer 58, the ND device, and 
the central computer shown in FIG. 5A. At ST70, a judgement is made 
whether at least one tool has been supplied to the tool magazine to 
supplement the broken tool or not. If the result of ST70 is NO the program 
returns to ST67. 
If the result of ST70 is YES, the break flag of the supplemented tool is 
cleared at ST71 to show that the broken tool has been substituted by a 
sound tool. Where a worn out tool is to be supplemented, steps similar to 
steps 66-72 are executed. For example, at a step corresponding to ST66 a 
judgement is made as to whether the flag FTBNN or FTWNN of a tool of 
FCOMNN is "1" or not. However, when a tool TFW is judged worn out, the 
machining of a workpiece I is still continued instead of exchanging the 
workpiece I with a new workpiece II as in the case where the tool is 
judged to be broken. 
Accordingly, even when the operation of the tool TFW is finished, the 
machining of the workpiece I is not completed so that during the remaining 
machining steps the tool TFW would be selected again. Where there is no 
sound tool having the same type as the tool TFW remaining in the tool 
magazine it would be impossible to continue the machining of the workpiece 
I. Accordingly, it is necessary to remove the workpiece I from the 
machining area of the machining center and to supplement a new tool to the 
tool magazine. Since this procedure is inconvinient, where a tool 
supplement instruction is generated as a result of a wear judgment, 
instead of applying the supplement instruction when the flag FTBNN or 
FTWNN of all tools of FCOMNN becomes "1" as above described, it is more 
advantageous to generate the tool supplement instruction in a case in 
which the flag FTWNN of only one tool in the tool group of FCOMNN is "0". 
FIG. 14 shows a tool selection routine where sequencer 58 receives a tool 
code. Thus, when a tool code is applied, at ST73 the tool code is 
temporarily stored in a spare tool register SPTREG in the data memory 
device. Then at ST74, a judgement is made as to whether the break judging 
flag FTBNN corresponding to a tool designated by the tool code is "1" or 
not. When the result of ST74 is YES, the program advances to ST76, whereas 
when the result is NO the program advances to ST75 where a judgement is 
made as to whether the wear judging flag FTWNN is "1" or not. If the 
result of ST75 is NO, at ST81 the count of register SPTREG is changed to 
the value of TOOL BUFFER (TBR). By the automatic tool exchange, a tool at 
the position of a tool pot in the tool magazine designated by TBR is 
exchanged with the ONTC TOOL mounted on the spindle. On the other hand, 
when the result of ST75 is YES, at ST76 a tool having a lower tool number 
(TNEW) belonging to the same tool group is searched in response to FCOM 
corresponding to a tool NN having a tool number corresponding to the count 
of SPTREG. Then at ST77, the presence of the tool TNEW is checked. When 
the result of ST77 is YES, at ST78 a judgement is made as to whether the 
flag FTBNN or FTWNN or tool TNEW is "1" or not. If the result of ST78 is 
YES, at ST79 one is added to the count of SPTREG and then the program 
proceeds to ST76. If the result of ST78 is NO, at ST80 the bit data of 
TNEW is set in register SPTREG. Then the program is advanced to said step 
ST81. If the result of ST77 is NO, at ST82 a message showing that there is 
not substitute tool is displayed. At ST83, after producing an emergency 
stop instruction, the control system is turned OFF. Tools are supplemented 
as shown in FIG. 13 so as to prevent steps ST82 and ST83 from being 
executed actually. 
The flow chart shown in FIG. 15 shows a sequence of a control signal which 
is supplied to a machining center from an NC device in response to an 
instruction from the step ST65 shown in FIG. 11. AT ST101 a judgement is 
made whether the break judging flag FBRK is "1" or not. When the result is 
YES, the feed of a tool is stopped. After 1 sec., the NC device gives a 
RESET signal at ST103. Then at ST104 a retract instruction along Z axis 
(FIG. 1) is given so as to disengage the tool from the workpiece I. Then, 
at ST105 the workpiece I is moved to the zero position in the machining 
area of the machining center. Then at ST106 the rotary table also is 
returned to the 0.degree. position to wait for transferring the workpiece 
onto the transfer line 11. In the absence of a tool pallet TLP for 
supplementary tools, the next workpiece II is transferred to the pallet 
exchange position of the machining center MC by the carriage. Where a 
pallet carrying supplementary tools arives at first, the pallet exchange 
operation on the carriage 16 is executed in two steps as follows during 
the pallet change cycle (P.C. cycle) of ST107. 
##EQU2## 
At ST108, the NC device causes a new machining program to the new 
workpiece II (in the case of a tape rewind type). In this embodiment, the 
NC device receives the machining program for the new workpiece II from the 
central computer 41. Then at ST109, after 0.1 sec., BRESET is set to "1", 
and after one sec. a cycle start signal is given at ST110 for 0.3 sec. 
When the result of ST101 is NO the previous machining program is continued 
without executing steps 102 through 110. 
FIG. 16 shows a routine when a wear detection signal is applied to an NC 
device from ST64 shown in FIG. 11. 
At ST111 a judgement is made as to whether the tool wear judging flag FTWNN 
is "1" or not. When the result is YES, at ST112 the feed speed of the tool 
NN relative to a workpiece instructed by the program is decreased 10%, for 
example. At ST113 a judgement is made whether the reduced feed speed is 
more than 30% of the value instructed by the program or not. If the result 
is YES, at ST115, WRESET is set to "1" after 0.1 sec. If the result of 
ST113 is NO, the program proceeds to ST114 to continue the machining by 
maintaining the feed speed at 30%. If the result of ST111 is NO, the 
cutting is continued with the feed speed instructed by the program without 
executing the steps 112-115. 
In the flow charts shown in FIG. 9 through FIG. 12 which are executed for 
detecting worn out tools, for the purpose of preventing a tool from being 
judged worn out due to increase in the cutting current caused by chips 
although actually the tool is not worn out, a flow chart corresponding to 
the step group STG4 shown in FIG. 11 and shown in FIG. 18 is to be 
executed. 
Thus, subsequent to ST56, at ST57-1 a judgement is made as to whether a 
flag FWCHK representing the wear detection is "1" or not, and when the 
result is NO, at ST57 the wear detection is made in the same manner as in 
ST57 shown in FIG. 11. When the result of ST57 is YES, the program 
advances to ST60 where FWEAR is set to "1". On the other hand, when the 
result of ST57 is NO, at ST57-2, the flag FWCHK is set to "1". Then, at 
ST58 a tool break is judged. 
When the result of ST57-1 is YES, the program advances directly to break 
judging step ST-58. When the result of step 58 is NO, at ST57-3 a 
judgement is made as to whether the tool ONTC TOOL has separated from the 
workpiece or not. When the tool has separated, at ST 57-4, FWCHK is 
cleared and then the program advances to ST59. When the result of ST57-3 
is NO, the program advances directly to ST59. With the flow chart shown in 
FIG. 17, where a drill is used as the tool to form an opening, when the 
result of the wear judging step 57 is NO, since flag FWCHK is set to "1" 
the opening machining is continued so that even when the cutting current 
increases due to chips, the wear judging step ST57 would not be executed 
and only the break judging step ST58 would be performed. 
Where the opening is deep, it is necessary to frequently withdraw the drill 
out the workpiece to remove the chips and then continue the drilling 
operation. In this case, since at ST57-3 a judgement is made as to whether 
the tool has separated from the workpiece or not, the wear judgement is 
performed again. 
FIG. 18 shows the relationship between cutting current waveforms and the 
signals when a drill and a tap are used as the ONTC TOOL. Where a drill is 
used, a definite time after starting the spindle, the speed of the spindle 
reaches 70% of the instructed value. Then, CiX becomes "1". 0.5 sec. 
after, the no load current INUL is stored. Then cutting is started and the 
cutting start judging flag FCST is set to "1". Thereafter, the normal or 
steady cutting judging flag FCNST is set to "1". Where the value iNETNN 
corresponding to the drill is not stored beforehand, the value of iNETNN 
is measured and stored. Thereafter, iNETNN and IV are compared with each 
other. When IR4 lies between K6 and K5, the drill is judged to be worn out 
whereas when IR4&gt;K6, the drill is judged to be broken. The wear and break 
judgements of the tap are performed in the same manner. When the direction 
of rotation of the tap reverses, STP becomes "1" during which no wear and 
break judgement is made. 
FIGS. 19A and 19B show interfaces between the sequencer 58 and the logical 
operation unit 51-3 shown in FIG. 5A and the contents of respective 
signals are shown in Table 1 below, and FIGS. 20A and 20B show the 
waveforms of actual cutting currents. In this case, a 10 H.sub.z low-pass 
filter was used, the drill had a diameter of 6 mm, the number of 
revolutions of the spindle was 1250 rpm, the feed speed of the drill was 
12.5 mm/min., and 61 perforations were successively formed through a metal 
plate having a thickness of 19 mm. At the 61st working step the drill was 
broken. 
Numerals applied to respective waveforms represent the number of times of 
machining the perforations. As shown in FIG. 20A, up to 20th machining 
step the value of IV is substantially constant, but at the 49th and 50th 
machining steps, the cutting current increases substantially immediately 
before the drill penetrates through the metal plate. At the 60th machining 
step the value of the cutting current exceeds the break judging level, and 
at the 61st machining step, the drill was broken immediately before it 
penetrates through. For this reason, when the drilling operation is 
interrupted by making a tool break judgement at the tool break judging 
level at the 60th machining step shown in FIG. 20B, the 61st perforation 
would not be made so that it would be possible to prevent damage of the 
workpiece caused by the broken drill. 
Regarding the progress of the wear of the 6 mm diameter drill, in a 
condition immediately after assuming the steady cutting state in each of 
the first, second, 19th, 20th, 49th, 50th, 60th and 61st machining steps, 
the extent of wear does not vary appreciably. Actually however, it an be 
noted that the wear proceeds gradually by the fact that the value of the 
cutting current immediately before the drill penetrates through the metal 
plate increases gradually. 
The result of test shows that the number of breaks and the degree of wear 
of the drills depend upon the diameter thereof. For example, drills having 
a diameter of less than 8 mm, the number of breaks is large and the speed 
of wear has a direct influence upon the break. On the other hand, in 
drills having a diameter larger than 12 mm, the break does not occur 
frequently, and only the wear accumulates. 
FIGS. 21A and 21B show cutting current waveforms when perforations are 
successively formed through a metal plate having a thickness of 20 mm with 
a drill having a diameter of 20 mm. In this case, the normal cutting 
current increases gradually. FIGS. 21A and 21B show waveforms 1, 140, 900, 
1600 and 2300 until a wear judging level TWL is reached. Although the 
cutting performance degrades a little, after the 230th drilling operation, 
drilling was possible even when the wear judging level has exceeded. 
Although in the foregoing description, the value of the cutting current of 
the tool was detected by certain type of the torque detecting system in 
which the armature current of the motor for driving the spindle was 
detected through a shunt, it is also possible to use a thrust detecting 
system. In this case, a pressure sensitive element is embedded in the 
bearing member of the spindle and an output signal of the pressure 
sensitive element is passed through an analogue-digital converter. 
According to another method, the armature current of a motor for feeding 
the tool in the Z direction (the axial direction of the spindle.) is used, 
and according to still another method a servo-lag is used. 
FIG. 22 shows the use of a pressure sensitive element. Thus, a member 103 
embedding a pressure sensitive element 102 is abutted under a suitable 
preload against one end of the outer race of the bearing assembly BII 
received in a sleeve 101 for supporting the spindle. The output of the 
pressure sensitive element 102 is amplified and then converted into a 
digital quantity which is used as iNETNN and Ii in the flow charts shown 
in FIGS. 9, 10 and 11. 
FIG. 23 shows a feed drive system in the Z axis direction of a machining 
center MC and is useful to explain the servo-lag method and the method of 
utilizing the armature current of the Z axis feed motor. As shown, an NC 
device applies a motion instruction .DELTA.Z to a register 111 with an 
interval of .DELTA.T. In this case, the register 111 has 6 bit capacity 
and .DELTA.Z=001111 that it has a value of 15 times of the unit movement. 
This value is applied to a servo-amplifier 113 through a digital-analogue 
converter 112. Consequently, a servomotor 114 energized by the output of 
the servo-amplifier 113 moves a load 115 including a spindle in the Z axis 
direction by rotating a feed screw 116 (a direction instruction is not 
shown). A rotary encoder 118 is mounted on the feed screw 116 and the 
output of the rotary encoder 118 is supplied to the register 111 to act as 
a feedback pulse FBP to decrease the count of the register 111. For the 
purpose of stabilizing the operation of the servo-motor 114, the output of 
a tachometer generator 117 is fed back to the servo-amplifier 113. The 
count of the register 111 would not overflow when accumulating the 
instruction .DELTA.Z because although .DELTA.Z is applied at an interval 
of .DELTA.T, the count of the register 111 is constantly decreased by the 
feedback pulse FBP. The count of the register 111 is termed servo-lag and 
constantly supervised by a supervisor 119 in the NC device to adjust the 
interval .DELTA.T so as to prevent the overflow of the register 111. As 
shown, the servo-lag is applied to the sequencer 58 and thence to the 
detecting unit 51. To improve the sensitivity of the detection of such 
system utilizing the servo-lag it is necessary to set to suitable values 
the gain of a control loop comprising servo-amplifier 113, servo-motor 
114, tachometer generator 117 and servo-amplifier 113, and of a control 
loop comprising servo-amplifier, servo-motor 114, rotary encoder 118, 
register 111, D/A converter 112 and servo-amplifier 113. With this 
servo-lag system, it is not necessary to use such special detecting 
circuit and an analogue-digital converter as disclosed in FIG. 7. 
Moreover, since digitallized signal is used, the system can operate 
satisfactorily. 
In the system shown in FIG. 23, a shunt current detector 120 is used for 
detecting the armature current of the Z axis servo-motor 114 and the 
output of the shunt current detector 120 is supplied to the detecting unit 
51. The program proceeds just in the same manner as in FIGS. 9 through 
FIG. 17 except that detected current is the armature current of the Z axis 
feed motor. 
Although the invention has been shown and described in terms of a specific 
embodiment, the invention can be modified as follows. 
1. In the illustrated embodiment, although the armature current of the 
motor for driving the spindle is sampled at the time of cutting and the 
mean value of the sampled values is used, it is possible to use a waveform 
pattern of the armature current over a definite time or to use the quantum 
value of the oscillation waveform of the spindle. 
2. In this invention, tool break is principally taken up for the reason 
that the wear of a tool will finally result in the break. Accordingly, in 
the flow charts shown in FIGS. 9 through FIG. 17, both the wear judgement 
and the break judgement are included, but it will be clear that the 
routine relating to the wear judgement is not always essential. 
3. In this invention, where the tool magazine of a machining center 
contains a sufficient number of substitute tools it is not necessary to 
provide means for supplementing the same. 
4. Instead of supplementing a specific tool a tool magazine as a whole can 
be exchanged. 
5. In the illustrated embodiment, for the purpose of supplementing a tool 
to the tool magazine, an automatic tool exchanging device is provided for 
each machining center MC. More particularly, a pallet carrying supplement 
tools is mounted on a machining center MC for supplying the tools to the 
tool magazine via a table. However, it will be clear that the 
supplementary tools may be supplied directly to the tool magazine without 
the intervention of the table of the machining center. 
6. Although in FIGS. 1 and 4, a control system is shown utilizing the 
central computer 41 associated with an NC device and transfer control 
device for each machining center, it should be understood that the central 
computer 41 is not always necessary. More particularly, the control system 
may be constructed such that the NC device for each machining center MC is 
provided with machining programs for various workpieces, that means is 
provided for identifying a pallet when it is mounted on the table of the 
machining center, and that in response to the operation of said 
identifying means, a machining program is made to correspond to the 
workpiece on the pallet. 
7. Instead of mounting the pallet on a carriage as has been described in 
connection with the illustrated embodiment the pallet may run on a 
conveyor line. 
8. As shown by steps 36, 37 and 38 shown in FIGS. 9, 10 and 11, a 
relationship 
K3&gt;IR2&gt;K2 
was used to judge whether a normal cutting condition has occurred or not, 
but it is also possible to set the flag FCNST to "1" when the feed amount 
of the ONTC TOOL reaches a predetermined value after starting the cutting 
start judgement. 
The invention has the following advantages. 
I. While a machining center MC is machining a workpiece I, when a break of 
an ONTC TOOL is judged, machining of the workpiece I is interrupted 
immediately and the workpiece is removed from the machining area. Then a 
new workpiece II is mounted. Accordingly, it is possible to make simple 
the operation of the system than a prior art system in which the remaining 
machining of the workpiece I is continued after exchanging the broken tool 
with a new one. The workpieces I whose machining has been interrupted are 
stored at a predetermined position so that they can be machined readily. 
II. According to this invention, a memory device is provided for storing 
bit data representing the states (FTBNN, FTWNN and FCOMNN) of respective 
tools stored in a tool magazine, a broken or worn out tool which has been 
judged so (FTBNN="1" or FTWNN="1") will not be mounted on the spindle even 
when it is designated by the program. As a consequence, the workpiece is 
always machined by a sound tool. 
III. Since a tool magazine stores a plurality of tools which are liable to 
break, where a tool is judged broken, another sound tool of the same type 
can be rapidly substituted for the broken tool. 
IV. Where all of the tools of the same type supplied from a tool magazine 
are judged broken, since means is provided for supplementing the tools of 
the same type, it is possible to continuously operate the system, thus 
improving its operating efficiency. 
V. According to this invention, since a wear judgement is made in addition 
to a break judgment of the tool, the tool is possitively judged worn out 
before it is judged to be broken, and since such worn out tool would not 
be used further it is possible to decrease the chance of interrupting the 
machining of the workpiece. 
VI. The data, for example iNETNN and IR4, utilized for judging a break can 
also be used for judging a wear so that it is not necessary to use any 
special detector and routine for judging the wear. 
VII. According to this invention, such ratios as IR1, IR2, IR3 and IR4 are 
used to determine a cutting start and a normal cutting start in a routine 
for judging the break or wear of the tool, so that where the diameter of a 
drill, for example, varies variously it is not necessary to set the 
judging conditions for different diameters. 
VIII. In the system of this invention, the wear judgement is made 
immediately after starting the normal cutting state and when the result of 
such judgement is NO, only the break judgement is made during the 
subsequent cutting operation. This is based on a consideration that the 
wear of the tool does not increase abruptly while machining an opening but 
it increases gradually. Accordingly, even when the cutting current 
increases beyond the wear judging level due to chips which do not wear the 
tool, the system operates such that the wear judgement of the tool is 
prevented and the wear judgement is made only for a tool actually worn 
out. 
IX. In the system of this invention, when a tool is judged worn out, the 
feed speed of the tool is decreased thereby continuing the machining of 
the workpiece without interruption. The degree of decreasing the feed 
speed is made to increase each time a wear judgement is made. Thus, 
decrease in the cutting ability caused by wear is compensated for by the 
decrease in the feed speed of the tool, thus continuing the machining of 
the workpiece by a tool judged worn out until it is replaced by a new 
tool. In other words, even when a tool is judged worn out, it is still 
used continuously until it is judged broken, thus decreasing the chance of 
interruption of the machining. 
X. Since the break judgement is made before the tool actually breaks, the 
chance of damaging the worked surface of the workpiece by the fragments of 
the broken tool can be decreased. 
XI. According to this invention, a tool supplement is instructed before the 
number of the sound tools FTBNN=FTWNN="0" in the tool groups contained in 
the tool magazine reduces to zero so that there is no such disadvantage of 
displacing the workpiece to proceed the tool supplement sequence when 
there is no substitute tool remaining in the tool magazine when a tool 
belonging to that group is judged to be worn out and when a tool of the 
same group is designated as an ONTC TOOL for continuing the machining. 
XII. Since a self-propelling carriage carrying a pallet is provided and 
since a workpiece and supplemental tools can also be mounted on the 
carriage, the transfer of the workpiece and the supplementary tools can be 
made readily. 
TABLE 1 
______________________________________ 
In the table NN represents the tool number. 
Correspond- 
Symbol Meaning of the Symbol ing Step 
______________________________________ 
FTCNN "1" is stored when iNETNN is set. 
ST13 
FTBNN "1" is stored when tool NN is judged 
ST17-2 
broken, and cleared when it is 
ST71 
exchanged with a substitute tool. 
FTWNN becomes "1" when tool NN is judg- 
ST18-2 
ed worn out, and cleared when it 
is exchanged with a substitute 
tool. 
FCOMNN when tool NN is of the same type, 
ST76 
it is set to the same value. 
iNETNN represents the actual cutting cur- 
ST13 
rent value at normal state which 
ST45 
is used as a reference. 
FBRK "1" is stored when the tool breaks. 
ST61 
FWEAR "1" is stored when the tool wears. 
ST60 
FiNET "1" is stored when iNET is set. 
ST48 
FCNST "1" is stored when the normal 
ST38 
cutting state is judged. 
FCST "1" is stored when a cutting 
ST34 
start is judged. 
FiNUL "1" is stored when no load cur- 
ST31 
rent value INUL is set. 
FNTCAL "1" is stored when FTBNNs or 
ST68 
FTWNNs of respective tools hav- 
ing FCOMNN of the same value and 
belonging to the same group of a 
tool magazine become "1", and 
when a substitute tool is re- 
quested. 
FWCHK "1" is stored if wear is not 
ST57-2 
judged when a wear judging step 
is passed once. 
iNET iNETNN is read out (iNETNN .fwdarw. 
ST45 
iNET). 
INUL no load current value. 
ST30 
ICST used to judge cutting start. 
ST32 
mean value of sampled cutting 
current value. 
ICNST1 used to judge normal cutting 
ST36 
state. mean value of sampled 
cutting current value. 
ICNST2 used to judge normal cutting 
ST36 
state. measured immediately af- 
ter ICNST1. 
IR1 ratio ICST/INUL. ST-32 
IR2 ratio ICNST2/ICNST1. ST-36 
IR3 ratio iNET/INUL. ST-40 
IR4 ratio IV/INET. ST-56 
IV current value under actual nor- 
ST56 
mal cutting state. 
Ii armature current measured by a 
ST56 
shunt. 
CiX "1" is stored when the speed of 
ST29 
the spindle reaches 70% of a 
ST50 
predetermined value. 
SSP1 "1" is stored when STP becomes "1" 
ST51 
and cleared 0.5 sec. after CiX has 
ST55 
become "1" when the spindle is re- 
started to rotate and reaches 
normal speed. 
SSP2 "1" is stored when STP becomes "1" 
ST52 
and cleared when CiX becomes "1" 
after restarting the spindle. 
STP spindle stops. ST49 
ONTC "1" is stored when tool NN is be- 
ST5 
ing mounted on the spindle. 
MO6 "1" is stored when tool exchange 
ST7 
(comple- 
has been completed. ST21 
tion) 
BRESET referred to clear FBRK. 
ST17-3 
WRESET referred to clear FWEAR. 
ST18-3 
RESEC represents reset of NC. When this 
ST19 
signal appears, all flags and data 
in the detecting unit except FTCNN 
FCOMNN and iNETNN in the detect- 
ing unit are cleared. 
SETFiN "1" is stored when "1" is stored 
ST14 
for FTCNN regarding a tool NN. 
ST16 
TNEW represents tools belonging FCOMNN 
ST76 
of the tool magazine and sequen- 
tially designated. 
SPTREG represents a register in which the 
ST73 
code of a tool (tool NN) is tem- 
porarily stored when a tool selec- 
tion instruction is given. 
TBR represents a tool buffer which 
ST81 
designates a tool to be exchanged 
in response to the count (tool 
number) of register SPTREG. 
______________________________________