Apparatus for controlling position of a plurality of machining shafts each including a machine tool fitted thereto

Apparatus for controlling the position of a plurality of machining shafts each including a machine tool fitted thereto so as to move each machining shaft up to its given position in response to the kind of machining to be subjected to a work piece. The apparatus comprises a memory for memorizing the position of each of the machining shafts which are different from each other in dependence with the kind of machining to be subjected to the work piece and a central processing unit for reading out data showing the position of each machining shaft from the memory in succession and generating through one servo-amplifier a signal required for moving the machining shaft corresponding to each servometer to its given position.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to apparatus for controlling the position of a 
plurality of machining shafts each including a machine tool fitted thereto 
so as to move these machining shafts to positions where desired machinings 
are subjected to a work piece. 
2. Description of the Prior Art 
In a machine tool having the ability of simultaneously subjecting a 
plurality of different kinds (types) of machinings to one work piece, 
particularly in a wood-working machine, it has been the common practice to 
determine the position of a plurality of machining shafts including 
suitable machine tools for various machinings fitted thereto by moving a 
movable block for supporting each machining shaft up to its given position 
by means of a servomotor. As a result, such kind of apparatus for 
controlling the position of a plurality of machining shafts comprises an 
operating panel for appointing the position of each machining shaft, a 
controller for generating an electric signal corresponding to the position 
thus appointed, and a plurality of servo-amplifiers each generating a 
driving current for driving each servomotor from the output signal 
delivered from the controller. 
Such conventional apparatus must operate so as to appoint the position of 
each machining shaft everytime the desired kind of machining is changed. 
As a result, if use is made of a number of machining shafts, the above 
mentioned operations take a long time and there is a risk of these 
operations being erroneous. 
SUMMARY OF THE INVENTION 
A principal object of the invention, therefore, is to provide apparatus for 
controlling the position of a plurality of machining shafts each including 
a machine tool fitted thereto which can set all of the machining shafts to 
their respective given positions by merely appointing the desired kind of 
machining. 
The control apparatus according to the invention comprises a memory for 
memorizing the positions of all of machining shafts for each kind of 
machining operation, and a central processing unit for supplying data to 
the memory and reading out data from the memory. The central processing 
unit functions to read out from the memory data showing the positions of 
all of the machining shafts for machining operations whose kind is 
appointed by an operating panel. As a result, the kind of the machining 
operations can be changed by merely selecting a new kind of machining 
operation. 
The central processing unit constitutes a closed loop including a 
controller, servo-amplifier, servomotors and signal generators for 
generating signals showing the position of the servomotors. In the closed 
loop, the operation for rotating the servomotor for a given angle is 
effected. The closed loop includes further a selection switch for 
selecting one of a plurality of servomotors in succession. This selection 
switch is controlled by the output signal from the central processing unit 
such that the servomotor corresponding to the position data of the 
machining shaft which is read out from the memory by means of the central 
processing unit is selected. 
In addition, the invention provides a method of controlling the position of 
machining shafts of machine tools which can move the machining shafts up 
to predetermined correct positions. 
Further objects and advantages of the invention will be fully understood 
from the following detailed description with reference to the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a control apparatus according to the invention applied to a 
double-ended tenoner. The tenoner is composed of a table 10 for supporting 
a work piece thereon and a pair of conveyors 12 and 14 arranged on and 
beneath the table 10 and moving the work piece at a given speed in a 
direction shown by an arrow, for example. By the table 10 are supported a 
plurality of machining shafts 16, 18, 20, 22, 24 each including a machine 
tool such as a circular saw, planer or the like selected in accordance 
with the kinds of desired machinings to be subjected to the work piece. 
These machining shafts are controlled by means of a control device 
according to the invention to be described later such that these machining 
shafts are urged against the work piece for the purpose of effecting 
respective given machinings at respective given positions. 
FIG. 2 shows a mechanism for moving each machining shaft to its given 
position. The mechanism shown in FIG. 2 comprises a frame 26 secured to 
the table 10, a shaft 28 rotatably journaled in the frame 26 and provided 
at its peripheral surface with screw threads and a movable block 30 
movably supported by means of the frame 26 and the screw threaded shaft 
28, the movable block 30 being provided with a downwardly extending 
portion 31 having a tapped hole threadedly engaged with the screw threaded 
shaft 28. As a result, if the screw threaded shaft 28 is rotated in one or 
the opposite direction, the movable block 30 is moved for a distance 
corresponding to the rotated angle of the screw threaded shaft 28 in a 
direction corresponding to the rotating direction of the screw threaded 
shaft 28. In order to rotate the screw threaded shaft 28, provision is 
made for a servomotor 32 secured to the frame 26. The movable block 30 
serves to support one of the machining shafts, so that the rotation of the 
servomotor 32 causes the machining shaft to change its position. 
FIG. 3 shows a control device according to the invention including a 
plurality of servomotors 32. The control device shown in FIG. 3 comprises 
n servomotors 32 (n is a positive integer larger than 1) designated by 
M.sub.1, M.sub.2, . . . M.sub.n, respectively. A central processing unit 
(CPU) 40 shown in FIG. 3 functions to receive a signal from an operating 
panel 42 or memory 44 when at least one position of each machining shaft 
must be changed and generates a signal for rotating a selected servomotor 
for a required angle in a required direction. This signal is supplied 
through a controller 46 and switch 48 to a servo-amplifier 50. The 
servo-amplifier 50 functions to receive the signal from the controller 46 
when the switch 48 is closed and supply it through a selection switch 52 
to one of the servomotors M.sub.1 to M.sub.n. As a result, the rotary 
shaft of the selected servomotor is rotated for a required angle in a 
given direction so as to move the machining shaft to its given position. 
In addition, to the servomotors M.sub.1 to M.sub.n are connected signal 
generators G.sub.1 to G.sub.n such as rotary encoders which function to 
detect the position of each rotary shaft and generate a position signal. 
This position signal is supplied through a selection switch 54 to the CPU 
40. The switch 48 is controlled by a control signal delivered from the CPU 
40 such that the switch 48 becomes open or closed in response to the 
control signal. The selection switches 52 and 54 are controlled by a 
control signal delivered from the CPU 40 so as to select one of the 
servomotors M.sub.1 to M.sub.n and hence that signal generator which is 
connected to the servomotor thus selected. 
In the case of starting the position determining operation of each 
machining shaft and hence moving each machining shaft to a given position, 
in the first place the operating panel 42 is operated to select one of the 
machining shafts and then the servomotor is rotated so as to set the 
machine tool fitted on the selected machining shaft to a given position 
for the work piece. Similar position determining operations are effected 
for all of the other machining shafts so as to set all of the machine 
tools to respective positions suitable for effecting a given machining 
operation for the work piece. The position signals delivered from the 
signal generators G.sub.1 to G.sub.n connected to the servomotors M.sub.1 
to M.sub.n, respectively, are supplied to the CPU 40 where the position 
signals are subjected to required processing treatments and then supplied 
to given addresses of the memory 44 and stored in succession. The stored 
signal is used for the purpose of setting up each machining shaft to its 
original position. 
In the preferable embodiment of the invention, the memory 44 is composed of 
a random access memory having a memory capacity which is sufficient to 
memorize the position of each machine tool used at each of a plurality of 
machining operations. The data showing the position of the machine tool at 
each machining operation together with discrimination symbol showing the 
kind of the machining operation are written into the memory 44. 
The following Table 1 shows one example of the pattern of the data written 
into the memory 44. 
TABLE 1 
______________________________________ 
Kind 
of Machining Shaft No. 
operation 1 2 3 4 
(n-1) n 
______________________________________ 
A O O 
O 
B O 
O 
O 
C 
O O 
O 
D O O O 
O 
.vertline. .vertline. .vertline. .vertline. .v 
ertline. .vertline. .vertline. .vertline. 
.vertline. .vertline. .vertline. .vertline. .v 
ertline. .vertline. .vertline. .vertline. 
.vertline. .vertline. .vertline. .vertline. .v 
ertline. .vertline. .vertline. .vertline. 
.vertline. .vertline. .vertline. .vertline. .v 
ertline. .vertline. .vertline. .vertline. 
N 
O O 
O 
______________________________________ 
In the above Table 1, a mark O shows a digital code for showing the 
position of each machining shaft and a mark - shows an absence of such 
digital code. 
In the case of carrying out practical machining operations, the kind of 
operations shown by A, B, C, . . . N in Table 1 is selected by the 
operating panel 42 and a signal produced by such selection operation is 
supplied to the CPU 40. The CPU 40 functions to read out position data for 
each machining shaft with respect to the selected kind of operation from 
the memory 44 and supply the read out position data to the controller 46. 
At the same time, the CPU 40 functions to supply a control signal to the 
switch 48 and selection switches 52, 54 in association with the reading 
out operation of the position data. The selection switches 52, 54 are 
interlocked with each other upon receipt of every control signal so as to 
effect their change-over operations. 
When the CPU 40 is reading out the position data of the machining shaft No. 
1, the selection switch 52 functions to select the servomotor M.sub.1 and 
the selection switch 54 functions to detect the output from the signal 
generator G.sub.1 and supply it to the CPU 40. 
The CPU 40 functions to compare the position signal read out from the 
memory 40 with the position signal delivered from the signal generator 
G.sub.1 and supply a signal having a code corresponding to a code of 
difference, if any, between both the position signals to the controller 
46. The controller 46 functions to detect the code of the difference 
signal delivered from the CPU 40 to produce a positive or negative code 
signal which is supplied through the switch 48 to the servo-amplifier 50. 
The servo-amplifier 50 functions to supply a driving current for rotating 
the rotary shaft of the servomotor M.sub.1 in a direction corresponding to 
the code of the output signal from the controller 46 to the servomotor 
M.sub.1. The servomotor M.sub.1 is rotated in such direction that the 
output signal from the signal generator G.sub.1 approaches to the position 
signal read out from the memory 44 until both signals become equal with 
each other so as to stop the servomotor M.sub.1. If the servomotor M.sub.1 
is stopped, the CPU 40 functions to supply a control signal to the 
selection switch 52 so as to select the servomotor M.sub.2 and signal 
generator G.sub.2 and subsequently read out a position signal of a 
machining shaft No. 2. Under such condition, the position control 
operation for the servomotor M.sub.2 is carried out in the same manner as 
in the case of the servomotor M.sub.1. A similar operation will be carried 
out for the other servomotors M.sub.3 to M.sub.n. 
When the position control operations for all of the servomotors M.sub.1 to 
M.sub.n have been completed, the machining shafts Nos. 1 to n are set up 
to positions suitable for carrying out selected kinds of machining 
operations. This set up operation is automatically repeated everytime a 
particular kind of machining operation is selected. 
The switch 48 inserted between the controller 46 and the servo-amplifier 50 
functions to prevent the signal supplied to the servomotor and the 
position signal supplied to the CPU 40 from being subjected to a bad 
influence by signal disturbance due to chattering or the like produced 
during the change-over operation of the selection switches 52, 54. 
The CPU 40 functions to cut off the signal to be supplied to the controller 
46 prior to generation of the control signal for changing over the 
selection switches 52, 54, and then to supply the control signal to the 
switch 48 so as to make it open. After a lapse of suitable time, for 
example, 0.2 to 0.3 second from the opening of the switch 48, the CPU 40 
functions to supply the control signal to the selection switches 52, 54. 
In addition, the CPU 40 functions to effect the sequence of operations so 
that the switch 48 is closed after the change-over operations of the 
selection switches 52, 54 have been completed, and after a lapse of 
suitable time from the closing of the switch 48 the output from the CPU 40 
is supplied to the controller 46. This sequence of operation of the CPU 40 
causes it to supply no signals therefrom during a time from immediately 
before the start of operating the switch 48 and selection switches 52, 54 
to immediately after the completion of such operation. As a result, the 
CPU 40 can prevent an erroneous operation due to the chattering of these 
switches and also prevent a position error. 
The above mentioned operations of the switch 48 and selection switches 52, 
54 make it possible to exchange the servomotors and signal generators, if 
necessary, in a closed loop including the CPU, controller, servomotors and 
signal generators. That is, even though a number of pairs of servomotors 
and signal generators are used, it is only necessary to use one controller 
and one servo-amplifier. As a result, the apparatus according to the 
invention is simple in construction and less expensive if compared with 
conventional apparatus comprising a number of controllers and 
servo-amplifiers for respective servomotors and signal generators. 
A mechanical play between the rotary shaft of the servomotor and the 
machining shaft will now be considered. Referring again to FIG. 2, the 
angle of the rotary shaft of the servomotor 32 is not precisely reflected 
in the position of the movable block 30, that is, in the position of the 
machining shaft supported by the movable block 30, owing to the play which 
is inevitably present between the screw threaded shaft 28 and the movable 
block 30. 
In order to rapidly move the movable block 30 from one position to the 
other position and to correctly stop it at a desired position, it is 
desirous to control the rotary shaft of the servomotor 32 such that the 
rotary shaft is started by a torque which is sufficiently large to 
overcome the resistance of the screw threaded shaft 28 due to viscosity of 
lubrication oil, that after the starting operation the rotary shaft is 
rotated at a high speed until the movable block 30 approaches to its 
desired stop position, and that at a substantially predetermined stop 
position the rotary shaft is rotated at such low speed that no overshoot 
thereof occurs. 
The invention is also intended to provide a method of controlling the 
position of the machining shaft of a machine tool which can satisfy the 
above mentioned requirements. 
The method of controlling the position of the machine shaft of a machine 
tool according to the invention will now be described with reference to 
FIGS. 4 and 5 which show the case in which the movable block for 
supporting the machining shaft tends to move along the axial direction of 
its driving shaft in one direction. 
FIG. 4 shows the relation between the position and time when the movable 
block is moved in that direction in which the movable block per se tends 
to move (hereinafter referred to as "forward direction"), while FIG. 5 
shows the relation between the position and time when the movable block is 
moved in a backward direction which is opposite to the forward direction 
shown in FIG. 4. 
In FIG. 4, step I shows a time in which the rotary shaft of the servomotor 
is rotated in the backward direction. In this time, after starting the 
rotation of the rotary shaft of the servomotor, the movable block remains 
at its original position until the play between the movable block and the 
rotary shaft becomes zero. Then, the movable block starts to move in the 
backward direction which is opposite to its desired moving direction. This 
movement of the movable block continues until the rotation of the rotary 
shaft becomes stopped and causes the movable block to move from its 
original position P.sub.0 to a position P.sub.1 in that direction which is 
opposite to the desired direction. In step II, subsequent to step I, the 
rotary shaft of the servomotor is rotated in such direction that the 
movable block is moved toward a desired position P.sub.d. After such 
reversal of the rotation of the rotary shaft of the servomotor, the 
movable block remains at the position P.sub.1 until the play between the 
movable block and the rotary shaft becomes zero. Then, the movable block 
rapidly moves toward the position P.sub.d at a speed which is proportional 
to the rotary speed of the rotary shaft of the servomotor. When the 
movable block reaches a position P.sub.2 near the final position P.sub.d, 
step II is completed to begin a subsequent step III. In step III, the 
rotating speed of the rotary shaft of the servomotor is decreased to a 
value that can prevent the overshoot of the rotary shaft due to the 
inertia of the mass of the movable block. As a result, the movable block 
slowly moves from the position P.sub.2 toward the final position P.sub.d 
where the movable block is stopped. 
The desired amount of movement of the movable block is the distance from 
the initial position P.sub.0 to the final position P.sub.d. In practice, 
however, at the beginning of the movement, the movable block moves 
backwardly from the position P.sub.0 to the position P.sub.1. As a result, 
the rotary shaft of the servomotor must be rotated for that angle which is 
required for moving the movable block over a distance which is obtained by 
adding together, in steps II and III, the amount of movement of the 
movable block in step I and the amount of the desired movement of the 
movable block. 
Let the rotary angle of the rotary shaft of the servomotor in the reverse 
direction in the step I be .beta. and the rotary angle of the rotary shaft 
of the servomotor required for absorbing the play between the rotary shaft 
and the movable block be G, then the amount of movement of the movable 
block from the position P.sub.0 to the position P.sub.1 is given by 
-(.beta.-G). In addition, let the rotary angle of the rotary shaft of the 
servomotor required for moving the movable block over a desired distance 
from the position P.sub.0 to the position P.sub.d be xB, then if the 
rotary shaft is rotated for xB in step II, the amount of movement of the 
movable block in step II is given by (xB-G). If the movable block is 
forwardly moved in step III for the rotary angle .beta., the total amount 
of movement of the movable block is given by the following equation (1). 
EQU -(.beta.-G)+(x.beta.-G)+.beta.=x.beta. (1) 
The above equation (1) shows that if the rotary shaft of the servomotor is 
rotated for an angle corresponding to the distance .beta. in the reverse 
direction and then is forwardly rotated for an angle corresponding to the 
distance (xB+.beta.), the play between the rotary shaft and the movable 
block is absorbed, and that the movable block is precisely moved for the 
desired distance xB in the forward direction. It should be noted that if 
the movable block arrives at the desired final position, the play between 
the rotary shaft of the servomotor and the movable block must not function 
to move the movable block in the backward direction. As a result, it is 
possible to hold the movable block at the desired position during the 
machining operation and to make clear the starting point for the 
subsequent movement of the movable block. 
FIG. 5 shows the relation between the position and time when the movable 
block is moved in the backward direction. The case shown in FIG. 5 is 
similar to the case shown in FIG. 4 except that the moving direction of 
the movable block in step II is opposite to that in the case shown in FIG. 
4. The desired amount of movement xC of the movable block is given by the 
following equation (2). 
EQU -(.beta.-G)-xC+(.beta.-G)=-xC (2) 
Both the equations (1) and (2) are satisfied when .beta. is larger than G. 
In wood-working machines in general, the play G has a dimension on the 
order of 0.3 to 0.6 mm. As a result, it is preferable to make the value of 
.beta. larger than the above value of the play G, for example about 2 mm. 
The above mentioned control for the rotary direction, angle and speed of 
the rotary shaft of the servomotor can easily be effected by supplying 
pulses having a desired frequency from the CPU 40 shown in FIG. 3 to the 
controller 46. 
The rotation of the rotary shaft of the servomotor in the backward 
direction at the beginning of the movement of the movable block causes the 
rotary shaft to rotate under substantially no load condition until the 
play G becomes zero. As a result, it is possible to rapidly start the 
rotation of the rotary shaft in a smooth manner. In addition, the movable 
block moves at a low speed in the forward direction in step III 
irrespective of the moving direction thereof in step II, so that it is 
possible to prevent occurrence of the overshoot of the rotary shaft when 
the movable block stops at the desired position P.sub.d. In addition, 
during the movement of the movable block at low speed, it is possible to 
absorb the overshoot of the rotary shaft which has eventually been induced 
in the previous step.