Machine tool with automatic tool change function

In a machine tool with an automatic tool change function, a rotatable tool spindle carries a key engageable with a key-way formed on a tool. A tool change arm, serving as a tool support device, rotatably supports at least one tool to selectively insert and remove the same into and from said tool spindle. When a tool change operation is to be performed, the rotation of the spindle is changed into a predetermined speed suitable for the key-way engagement. An operating device is provided for causing relative movement between the tool change arm and the spindle to insert a tool into the spindle. However, the relative movement thereof is stopped by a stopping device just before the engagement of the key with the key-way. Subsequently, when a first detecting device detects that the key has reached a predetermined angular position, the relative movement of the tool change arm is permitted to thereby make engagement of the key with the key-way. A second detecting device detects the key-engagement and then the tool is clamped in the spindle for a machining operation. After the machining operation, when a third detecting device detects that the key has reached a predetermined angular position, the operating device is operated to move the tool change arm for removing the tool from the spindle.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a machine tool with an automatic tool 
change function, which is capable of making engagement between a key of a 
tool spindle and a key-way of a tool or a tool holder without stopping 
rotation of the spindle. 
2. Description of the Prior Art 
Conventionally, in order to make engagement between a key of a tool spindle 
and a key-way of a tool, the spindle is stopped at a predetermined angular 
position where the key comes into the corresponding position of the 
key-way to thereby permit the tool to be inserted thereinto by a tool 
change arm. 
In order to stop the spindle at such a predetermined angular position, two 
operational steps are required. That is, the spindle is first stopped 
within a predetermined angular range by controlling a spindle drive motor 
and then indexed to the predetermined angular position by a mechanical 
device including, for example, an index plate and an index pin. 
Accordingly, it takes a longer time for stopping the spindle at the 
predetermined angular position, resulting in a longer tool change time. 
Further, the device required for accomplishing the above operation is 
rather expensive. 
In order to solve these disadvantages and perform a tool change operation 
without stopping rotation of a spindle, it has been considered to urge a 
flange portion of a tool toward the key of the rotating spindle to achieve 
the engagement between the key-way of the tool and the key of the spindle 
after relative frictional rotation therebetween. In this method, however, 
the contacting surfaces of the key and the flange portion of the tool are 
necessarily worn due to the sliding contact therebetween and the 
relatively high pressure applied thereto and there is a fear of decreasing 
the final accuracy after a machining operation due to the variation of the 
tool position inserted in the spindle as a result of uncertainty of which 
one of two key-ways is engaged with the key of the spindle. 
Furthermore, even if a tool change operation is performed without stopping 
rotation of the spindle, there is a problem that a large diameter tool 
with a radially projected cutter has to be returned from the spindle to 
the tool magazine with its key-way being maintained at a predetermined 
angular position in order to prevent interference with an adjacent tool in 
the tool magazine. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved machine 
tool with an automatic tool change function wherein a key engagement is 
performed between a key-way of a standard tool and a key of a spindle 
without stopping the rotation of the spindle and without making any 
sliding contact between the key-way and the key. 
Another object of the invention is to provide an improved machine tool with 
an automatic tool change function wherein a key engagement is performed 
between a key-way of a standard tool and a key of a spindle in response to 
a signal generated when the key comes into a predetermined angular 
position relative to the key-way. 
Briefly, according to the present invention, these and other objects are 
achieved by providing a machine tool with an automatic tool change 
function having a tool spindle rotatably supported and capable of 
receiving a tool at one end thereof. A key is fixedly mounted on one end 
of the tool spindle and a key-way is formed on the tool. Tool support 
means are provided for rotatably supporting at least one tool to 
selectively insert and remove the same into and from the tool spindle. 
Control means are responsive to a tool change command for rotating the 
tool spindle at a predetermined speed suitable for the engagement of the 
key with the key-way. Operating means are provided for causing relative 
movement between the tool support means and the tool spindle for a tool 
change operation with the tool spindle being rotated at the predetermined 
speed. Stopping means are provided for stopping the relative movement 
between the tool support means and the tool spindle at a predetermined 
position before the key comes into engagement with the key-way. A first 
detecting means is provided for detecting a first predetermined angular 
position of the key relative to the key-way to thereby generate a first 
signal, and a releasing means is responsive to the first signal for 
permitting the relative movement between the tool support means and the 
spindle. A second detecting means is provided for detecting the engagement 
of the key with the key-way to generate a second signal, and a clamp means 
is responsive to the second signal for clamping the tool inserted into the 
tool spindle. 
In another aspect of the present invention, a third detecting means is 
provided for detecting a predetermined angular position of the key 
relative to the key-way to thereby generate a third signal, and the 
operating means is operated in response to the third signal for causing 
relative movement between the tool support means and the tool spindle to 
remove the tool from the tool spindle.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawings, wherein like reference numerals or 
characters refer to identical or corresponding parts throughout the 
several views, and more particularly to FIG. 1, there is shown a spindle 
head 10 which is guided on guide ways 12 and 12 formed on an upstanding 
column, not shown, for a vertical sliding movement and rotatably supports 
a vertical spindle 11. FIG. 1 shows an upper end position of the spindle 
head 10, where a tool change operation is performed. The reference numeral 
13 indicates a tool change arm having tool grippers at opposite ends 
thereof to serve as a tool support device. The tool change arm 13 is 
movable in a direction parallel to the axis of the spindle 11 and is 
rotatable about a vertical axis. A tool magazine 15 is rotatably supported 
and carries a plurality of tool sockets 16 on the periphery thereof. Each 
tool socket 16 removably supports a tool T and is indexable to a tool 
change position C, where the indexed tool socket 16 is pivotable from a 
horizontal position shown in solid lines to a vertical position shown in 
phantom lines for enabling the tool change arm 13 to change the tools 
between the vertically oriented tool socket 16 and the spindle 11. Each 
tool socket 16 on the tool magazine 15 is provided with a detent pin 16a 
engageable with a key-way 36 formed on each tool T with some play to 
restrict the direction of movement of the key-way 36 of the tool T 
received in the tool socket 16 within a predetermined angular extent. 
Accordingly, a large diameter tool with a radially projected cutter, such 
as a boring cutter, is prevented from interference with an adjacent tool. 
Referring to FIG. 2, showing a detailed construction of the spindle head 
10, the spindle 11 rotatably supported by a housing 20 is formed with a 
tool receiving tapered bore 11a at its lower end and a through bore 11b 
connected to the tapered bore 11a. Within the through bore 11b, there are 
received a snap member 21 engageable with a pull stud 17 extended from one 
end of a tool T received in the tapered bore 11a, a drawing rod 22 
connected at its forward end with the snap member 21 and projecting at its 
rear end from the rear end of the spindle 11, and a set of washer springs 
23 urging the drawing rod 22 in the rearward direction relative to the 
spindle 11, in such a manner as to constitute a clamp device for clamping 
the tool T relative to the spindle 11. In face-to-face relationship with 
the rear end of the drawing rod 22, there is disposed an unclamping 
cylinder 24 whose piston rod 25 rotatably supports an abutting member 26 
at its forward end through a thrust bearing 27. When the drawing rod 22 is 
urged against the springs 23 through the abutting member 26, the tool T in 
the spindle 11 is unclamped. A gear member 28 is secured on the spindle 11 
and is connected through a shiftable transmission gear member 30 and a 
drive gear 29 to an output shaft 32 of a spindle drive motor 31 which is 
mounted on the upper end of the spindle head 10. The drive motor 31 is 
driven at a speed depending upon a rotary speed command applied from a 
numerical control device NC and also at a predetermined low speed in 
response to a tool change command, as described later in more detail. 
To the rear end of the spindle 11 are secured first and second dog members 
33a, 33b at predetermined angular positions, referred to later in detail. 
The first and second dog members 33a, 33b cooperate with first and second 
proximity switches 34a, 34b secured to the housing 20 to generate first 
and second signals indicating the proper timing when a tool T should be 
inserted into and removed from the spindle 11, respectively. On the front 
end of the spindle 11 is mounted a key 35 which is engageable with each 
one of the key-ways 36 formed on a flange portion 37 of a tool T. In order 
to make engagement between the key 35 and the key-way 36 without trouble 
during rotation of the spindle 11, the width l1 of the key 35 is formed to 
be more narrow than the width l2 of the key-way 36 by several millimeters, 
as shown in FIG. 8. 
Referring to FIG. 3, showing a detailed construction of the tool change arm 
13 and a drive device therefor, a support shaft 41 is rotatably and 
axially movably supported by a support body 40. The support shaft 41 has 
secured at its lower end the tool change arm 13 which is formed at its 
opposite ends with a pair of circular tool grippers 13a and 13b symmetric 
with respect to the axis of the support shaft 41 and engageable with the 
flange portion 37 of each tool T. In order to prevent a tool T from 
falling from the tool gripper 13a or 13b, a plunger 43, rotatably 
supporting an engaging roller 42 at its one end, is guided at each end of 
the tool change arm 13 to be movable in a substantially radial direction 
and is urged outwardly by a spring, not shown. This spring is calibrated 
in such a manner that when the tool change arm 13 is rotated to grip or 
release the tools held in the spindle 11 and the tool socket 16 in its 
vertical position, the plunger 43 is moved inwardly to allow such grip or 
release of the tool, and when the tools are held by the tool grippers 13a 
and 13b of the tool change arm 13, the engaging roller 42 is urged toward 
the tool T to prevent the tool from falling but to allow frictional 
rotation of the tool. 
The support shaft 41 is formed at its intermediate portion with a piston 45 
slidably received in a cylinder 44 formed in the support body 40. 
Selective supply of pressurized fluid into upper and lower cylinder 
chambers of the cylinder 44 causes the tool change arm 13 to be vertically 
moved to insert and withdraw the tools T. The support shaft 41 is formed 
at its upper end with an elongated gear 53 being in meshing engagement 
with a rack bar 46. The rack bar 46 is connected through a piston rod 47 
with a piston 49 of a hydraulic cylinder 48 capable of positioning at four 
positions. The piston 49 is slidably received in an inner cylinder 50 
which is, in turn, slidably received in an outer cylinder 51. When the 
inner cylinder 50 is moved relative to the outer cylinder 51 with relative 
movement being restrained between the piston 49 and the inner cylinder 50, 
the tool change arm 13 is rotated between a ready position shown in solid 
lines in FIG. 1 and a tool grip position shown in phantom lines to grasp 
or release the tools. When the piston 49 is moved relative to the inner 
cylinder 50 which is restrained from movement relative to the outer 
cylinder 51 at its right or left end position, the tool change arm 13 is 
rotated 180 degrees to change the tools. 
Referring now to FIG. 4, a detent pin 55, engageable with the key-way 36 of 
the tool T, is slidably received in each of the tool grippers 13a, 13b and 
urged by a spring 56 in the radial direction of the tool T for restricting 
the rotational movement of the tool T. However, the detent pin 55 is 
chamfered at the edges so as to allow the rotation of the tool T when the 
tool T is forced to rotate by the spindle 11 through the key engagement 
between the key 35 and the key-way 36. 
Description is now made to a stopping device, shown in FIGS. 3, 5 and 6, 
for stopping the axial movement of the tool change arm 13 at a 
predetermined intermediate position immediately before the flange portion 
37 of the tool T comes into contact with the key 35. To the upper portion 
of the support body 40 is secured a support bracket 65, as shown in FIGS. 
5 and 6 in detail, in which a link holder 66 is secured above the support 
shaft 41. The link holder 66 is provided with a fixed pin 67 horizontally 
secured thereto at the upper portion thereof and a vertically elongated 
groove 66a formed at the lower portion thereof. The fixed pin 67 rotatably 
supports one end portion of a first link 68. A movable pin 70 horizontally 
secured to one end portion of a second link 69 is received slidably in the 
axial direction of the support shaft 41 in the elongated groove 66a. A 
connecting pin 71 rotatably supports the other end portions of the links 
68, 69 so that the distance between the fixed pin 67 and the movable pin 
70 may be varied. A roller 72, engageable with the top end of the support 
shaft 41, is rotatably supported at the intermediate portion of the 
movable pin 70. 
Accordingly, when the first and second links 68, 69 are in a bent position, 
as shown in solid lines in FIG. 5, the support shaft 41 may be moved 
upward toward the uppermost position where the piston 45 comes into 
contact with the upper end wall of the cylinder 44, however, when they are 
in the straight position, as shown in phantom lines in FIG. 5, the support 
shaft 41 is prevented from moving upward further from the intermediate 
position which is lower than the uppermost position by a predetermined 
distance S due to the engagement of the roller 72 with the top end of the 
support shaft 41. The intermediate position is adjusted in such a way that 
the flange portion 37 of the tool T gripped in the tool change arm 13 is 
apart a predetermined distance .DELTA.d from the key 35 of the tool 
spindle 11, as shown in FIG. 8. A limit switch 74 is mounted on the 
support bracket 65 and actuated in cooperation with a dog member 73 
secured to the support shaft 41 in order to confirm that the support shaft 
41 is stopped at the intermediate position. Further secured to the support 
bracket 65 is a solenoid 75 having an actuating rod 76, one end of which 
is connected through a connecting link 78 with one end of a link 77 which 
is secured to the second link 69. The other end of the link 77 is pulled 
upward by a tension spring 79 attached to the support bracket 65 so as to 
tend to straighten the first and second links 68, 69. However, when the 
solenoid 75 is actuated to hold the actuating rod 76 at the upper position 
shown in solid lines in FIG. 5, the first and second links 68, 69 are 
maintained in the bent position against the force of the tension spring 
79. Therefore, the solenoid 75 constitutes a releasing device for 
releasing the abovementioned stopping operation of the stopping device. 
Referring now to FIG. 7, the spindle drive motor 31 is controlled to be 
rotated at a speed depending upon any of the various tools inserted in the 
spindle 11. When a rotational speed command (S-code) is applied from the 
numerical control device NC to a register 80, the speed command is 
converted by a digital to analog converter 81 into a corresponding voltage 
which is, in turn, applied as a speed command voltage to a motor drive 
circuit 83 through an amplifier 82. The actual rotational speed of the 
drive motor 31 is detected by a speed detector 84, and the detected actual 
speed is fed back to the motor drive circuit 83. Accordingly, the 
rotational speed of the drive motor 31 is controlled in such a manner that 
the detected actual rotational speed becomes equal to the commanded 
rotational speed. When a d.c. motor is used as the drive motor 31, a 
thyristor Leonard device is used as the motor drive circuit 83. When an 
a.c. motor is used as the drive motor 31, a variable frequency inverter 
device is used as the motor drive circuit 83. 
In order to perform a tool change operation, it is necessary to reduce the 
rotational speed of the spindle 11 from a speed depending upon any of 
various tools to a predetermined low speed, such as several tens rpm. A 
setting device 85 of setting such predetermined low speed command is 
connected to the digital to analog converter 81 through a switching 
circuit 86. When the numerical control device NC generates a tool change 
command MO6, the switching circuit 86 applies, instead of a rotational 
speed command set in the register 80, the predetermined low speed command 
set in the setting device 85 to the digital to analog converter 81. As a 
result, the motor drive circuit 83 controls the rotation of the motor 31 
so as to rotate the spindle 11 at the set low speed. When engagement 
between the key-way 36 of the tool T and the key 35 is confirmed by a 
limit switch 104 in cooperation with a dog member 103 secured to the 
support shaft 41, as shown in FIG. 3, the switching circuit 86 is changed 
over to cause the rotational speed command set in the register 80 to be 
applied to the digital to analog converter 81, whereby the spindle 11 is 
rotated at a speed depending upon a tool T inserted therein. 
Referring now to FIG. 9, wherein the spindle 11 is rotated in a clockwise 
direction indicated by an arrow, angular positions P1, P2 indicate the 
timing when the first and second proximity switches 34a, 34b generate the 
first and second signals in cooperation with the first and second dog 
members 33a, 33b, respectively, and an angular position P0 indicates the 
timing when the key 35 of the spindle 11 reaches the corresponding 
position of the key-way 36 of a tool T. An angular distance .theta.1 
between the angular positions P1 and P0 corresponds to the rotational 
angular range of the spindle 11 while the tool change arm 13 is axially 
moving the distance .DELTA.d from the intermediate stop position in 
response to the first signal. Similarly, an angular distance .theta.2 
between the angular positions P2 and P0 corresponds to the rotational 
angular range of the spindle 11 while the tool change arm is moving 
downwardly in response to the second signal until the key 35 and the 
key-way 36 are disengaged. 
In this embodiment, since the distance .DELTA.d is set rather small, the 
angular distance .theta.2 is larger than the angular distance .theta.1. It 
is noted, however, the distances .theta.1, .theta.2 can be varied by 
changing the angular positions of the first and second dog members 33a, 
33b. 
The operation of the machine tool with an automatic tool change function 
according to the present invention will now be described. The spindle 11 
is usually rotated within a wide range from 20 to 3,000 rpm, and the 
shiftable gear 30 is operated at the intermediate of such range to change 
the reduction gear ratio. For example, the shiftable gear 30 is shifted to 
a low speed range when the rotational speed is lower than 1,100 rpm, and 
to a high speed range when the rotational speed is higher than 1,100 rpm. 
Accordingly, frequency in use at the low speed range is higher in usual 
machining operations, so that the shiftable gear 30 is hereunder assumed 
to be shifted to the low speed rage for convenience of description. 
Upon completion of a machining operation by a predetermined tool, the 
spindle 11 continues to rotate at a high speed depending upon the 
rotational speed command set in the register 80. The spindle head 10 is 
moved upward to its upper end position for a tool change operation. When 
the tool change command MO6 is generated from the numerical control device 
NC, the switching circuit 86 is changed over to apply a rotational speed 
command set in the setting device 85,. Accordingly, the drive motor 31 is 
applied with an electrical braking torque so as to rotate the spindle 11 
at a predetermined low speed suitable for key engagement. Thereafter, the 
tool change arm 13 is rotated to grip, by the tool grippers 13a and 13b 
thereof, the tools T held in the vertically oriented tool socket 16 and 
the spindle 11. The unclamping cylinder 24 is subsequently operated to 
move the drawing rod 22 downwardly against the springs 23, thereby 
unclamping the tool T held in the spindle 11. When the spindle 11 is 
rotated to the predetermined position P2, where the second proximity 
switch 34b is changed from OFF to ON state, pressurized fluid is supplied 
to the upper chamber of the cylinder 44 to move the tool change arm 13 
downwardly, thereby withdrawing the tools T from the spindle 11 and the 
tool socket 16. The key-way 36 of the tool T is disengaged from the key 35 
of the spindle 11 by such withdrawal of the tool T from the spindle 11, 
whereby rotation of the tool T withdrawn from the spindle 11 is 
immediately stopped by the grip force of the tool change arm 13. 
Accordingly, the key-way 36 of the tool T grasped by the tool change arm 
13 is maintained at a substantially predetermined angular position, which 
corresponds to the position of the key-way 36 of each tool T held in the 
tool socket 16 of the tool magazine 15. 
After the tool change arm 13 is moved to its lower end position, the piston 
49 is moved, with movement of the inner cylinder 50 being restrained, to 
rotate the tool change arm 13 by 180 degrees. During the withdrawing 
movement of the tool change arm 13 and the rotation of the tool change arm 
13, the solenoid 75 is caused to be demagnetized to lower the actuating 
rod 76. As a result, the first and second links 68, 69 are straightened by 
the force of the spring 79, as shown in phantom lines in FIG. 5, and the 
roller 72 is caused to extend downwardly by the predetermined length S. 
After the tool change arm 13 is rotated by 180 degrees, pressurized fluid 
is supplied to the lower chamber of the cylinder 44 to move the tool 
change arm 13 upwardly to insert the tool T withdrawn from the tool socket 
16 into the tapered bore 11a of the spindle 11 and the tool withdrawn from 
the spindle 11 into the tool socket 16. However, since the roller 72 is in 
the extended position, the upward movement of the tool change arm 13 is 
stopped at the intermediate position immediately before the flange portion 
37 of the tool T comes into contact with the key 35 of the tool spindle 11 
rotating at the predetermined low speed due to the engagement of the top 
portion of the support shaft 41 with the roller 72. This intermediate stop 
of the tool change arm 13 is detected by the actuation of the limit switch 
74 with the dog member 73 secured to the support shaft 41. Subsequently, 
when the first proximity switch 34a detects that the key 35 of the 
rotating tool spindle 11 comes into the predetermined position P1 relative 
to the key-way 36 of the tool T grasped by the tool change arm 13 with its 
angular position maintained by the detent pin 55, the solenoid 75 is 
actuated to move the actuating rod 76 upward, whereby the first and second 
links 68, 69 are bent against the force of the spring 79 so as to move the 
roller 72 upward and permit the support shaft 41 to move from the 
intermediate position. Accordingly, the tool change arm 13 is again moved 
upward by pressurized fluid applied to the cylinder 44, thereby to make 
engagement of the key-way 36 of the tool T with the key 35 of the tool 
spindle 11. The rotation of the spindle 11 is transmitted through the key 
35 to the tool T to forcibly rotate the same gripped by the tool gripper 
13a of the tool change arm 13. 
Simultaneously with this, the tool T which is previously inserted into the 
spindle 11 and now gripped by the other tool gripper 13b is returned to 
the tool socket 16 in such a manner that the key-way 36 of the tool T is 
engaged with the detent pin 16a of the tool socket 16 to avoid its 
rotation. 
Accordingly, a large diameter tool with a radially projected cutter is 
prevented from interference with an adjacent tool on the tool magazine 15. 
Further, a predetermined one of the two key-ways 36 is always engaged with 
the key 35 of the spindle, whereby the position of the tool T relative to 
the spindle 11 is maintained even after several tool change operations to 
thereby achieve a precision machining operation. 
After the tool change arm 13 is moved to its upward end position, and the 
tools T gripped by the tool grippers 13a , 13b are inserted into the 
spindle 11 and the tool socket 16, the key engagement between the key 35 
and the key-way 36 is confirmed by the actuation of the limit switch 104 
with the dog member 103 secured to the support shaft 41. The confirmation 
of key engagement causes the unclamping cylinder 24 to be deactivated to 
thereby release the urging force of the drawing rod 22. Accordingly, the 
tool T is clamped on the spindle 11 by means of the springs 23. 
Subsequently, the tool change arm 13 is rotated back to its ready 
position, thereby completing a tool change operation. With the tool change 
operation being completed, the tool change command is cancelled so that 
the switching circuit 86 renders a command signal from the setting device 
85 inoperative and a command signal from the register 80 operative. The 
spindle 11 is thus rotated at a high speed depending upon a newly inserted 
tool for the next machining operation. 
In the above-described embodiment, the tool change arm 13 is used as a tool 
support device. However, the present invention can be applied to a machine 
tool wherein tools are directly changed between the tool magazine and the 
spindle. In such a case, the tool magazine is used as the tool support 
device. 
Further, a stopping device is provided with a link mechanism for stopping 
the support shaft 41 and the tool change arm 13 at the intermediate 
position, and with a solenoid 75 for releasing its stopping operation. 
However, the present invention is not limited to this embodiment and other 
devices may be used. 
Furthermore, in the above-described embodiment, two sets of a dog member 
and a proximity switch are provided for generating two signals for a tool 
change operation, however, only one set of a dog member and a proximity 
switch is necessary if the distance .DELTA.d is adjusted to correspond to 
the length of the key engagement between the key 35 and the key-way 36 so 
as to equalize the angular distance .theta.1 to the angular distance 
.theta.2. In this case, a signal generated from the set of the dog member 
and the proximity switch is used to indicate proper timing for both 
insertion and withdrawal of a tool. 
As described above, according to the present invention, a tool change 
operation is carried out while the spindle is rotated. Therefore, there is 
no need to provide a device to stop the spindle at a predetermined angular 
position, as in the conventional apparatus, whereby the tool change time 
is considerably shortened, resulting in an increase in the machining 
efficiency. 
Further, according to the present invention, a key of a spindle is engaged 
with a key-away of a tool without sliding contact therebetween, whereby 
the tool and the key are prevented from being worn or scratched. 
Furthermore, according to the present invention, a tool is removed from the 
rotating spindle in response to a signal confirming the predetermined 
angular position of the spindle, whereby the key-way of a tool returned 
from the spindle to the tool magazine is maintained at a substantially 
predetermined angular position. This arrangement and control is 
particularly effective for large sized tools. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.