Machine tool with automatic tool changer, having mechanism for utilizing relative movements of tool and tool changing gripper to clamp and unclamp the tool

A machine tool equipped with an automatic tool changing device, including a tool support having a clamping mechanism for holding a cutting tool, a tool transfer device having a tool gripper for transferring the tool to and from the tool support at a tool change position, and a device for moving the tool support and the tool transfer device in a direction perpendicular to the axis of the tool held on the tool support, the tool changing device including a mechanism for converting a first relative movement of the gripper and the tool support toward each other, into a movement of the clamping mechanism for unclamping the tool from the tool support, and converting a second relative movement of the gripper and the tool support away from each other, into a movement of the clamping mechanism for clamping the tool to the tool support, wherein the gripper has a pair of jaws shaped for engagement with the tool held on the tool support before the tool is unclamped, and for permitting completion of the first relative movement at the tool change position after the tool is unclamped.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a machine tool equipped with an automatic 
tool changing device, and more particularly to such automatic tool 
changing device which is simple in construction. 
2. Discussion of the Related Art 
There is known a universal or multi-function machine tool or machining 
center capable of performing a variety of machining operations on 
workpieces and equipped with an automatic tool changing device which 
includes a tool magazine or tool storage drum accommodating a relatively 
large number of cutting tools, of either rotary type such as taps, drills, 
milling cutters (e.g., end milling cutters) and boring tools or non-rotary 
type such as lathe tools. The automatic tool changing device is adapted to 
return a used tool to the tool magazine, and select a new tool from the 
tool magazine and mount the selected new tool on a spindle of the machine, 
for example. Examples of machine tools equipped with such automatic tool 
changing device are disclosed in JP-A-63-267136 and JP-A-2-274448 
(laid-open publications of unexamined Japanese Patent Applications). 
The automatic tool changing device disclosed in JP-A-63-267136 utilizes 
vertical reciprocating movements of a spindle head to activate two cam 
mechanisms for exchanging tools at the tool mounting end of the machine 
spindle. Described more specifically, one of the cam mechanisms is used to 
control operations of a tool clamping mechanism for unclamping a used tool 
from the spindle and clamping a new tool to the spindle, and the other cam 
mechanism is used to control operations of a rotary tool changer arm for 
exchanging the tools. A crank lever provided on the spindle head is 
pivoted by a cam during upward and downward movements of the spindle head, 
and pivotal movements of the crank lever are converted into movements of 
the tool clamping mechanism to unclamp and clamp the tools. The rotary 
tool changer arm is rotatably disposed on the tool magazine, which is 
indexable to select a desired tool. The tool changer arm is spring-biased 
toward the spindle head, and the vertical movements of the spindle head 
cause a cam to rotate the tool changer arm for removing the used tool from 
the spindle and installing the new tool on the spindle. 
In the automatic tool changing device disclosed in JP-A-2-274448, the 
spindle is moved to a predetermined tool change position at which the used 
and new tools are exchanged, and then returned to a machining position. 
The tool clamped on the spindle located at the tool change position is 
first gripped by one of a plurality tool grippers provided on an indexable 
tool magazine. Then, the tool is unclamped from the spindle by a hydraulic 
cylinder, and the tool magazine is advanced to remove the used tool from 
the spindle, rotated for indexing to bring the new tool into alignment 
with the spindle, and finally retracted to install the new tool on the 
spindle. The installed new tool is clamped by activation of the hydraulic 
cylinder, and the spindle is moved from the tool change position to the 
machining position. 
Although the automatic tool changing devices described above are adapted to 
handle rotary cutting tools, similar mechanisms for exchanging the tools 
as described above are applicable to non-rotary cutting tools. 
However, the automatic tool changing device disclosed in JP-A-63-267136 
which uses a cam mechanism to control the tool clamping mechanism also 
uses another cam mechanism to control the rotary tool changer arm for 
exchanging the tools and is accordingly complicated in construction. On 
the other hand, the automatic tool changing device disclosed in 
JP-A-2-274448 requires an exclusive power source to activate the hydraulic 
cylinder for operating the tool clamping mechanism, and a detecting device 
for controlling the operation of the hydraulic cylinder. The use of such 
exclusive power source and detecting device leads to increased complexity 
of the tool changing device. Thus, the known automatic tool changing 
devices described above suffer from a relatively high cost of manufacture, 
and a relatively low degree of operating reliability, due to the 
constructional complexity. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a machine 
tool equipped with an automatic tool changing device which is simple in 
construction and reliable in operation. 
The above object may be achieved according to the principle of the present 
invention, which provides a machine tool equipped with an automatic tool 
changing device, including (a) a tool support device which is adapted to 
hold a cutting tool for performing a machining operation on a workpiece 
and which comprises a tool clamping mechanism for holding the cutting tool 
on the tool support device, (b) a tool transfer device for transferring 
the cutting tool to and from the tool support device, at a predetermined 
tool change position, the tool transfer device comprising a tool gripper 
having a pair of gripper jaws for gripping a chucking portion of the 
cutting tool, such that the axis of the tool gripped by the tool gripper 
is parallel with the tool held on the tool support device at least when 
the tool support and transfer devices are located at the tool change 
position, the tool gripper at the tool change position and the chucking 
portion of the tool held on the tool support device being aligned with 
each other in a direction parallel to the axis of the tool held on the 
tool support device, (c) a moving device for moving the tool support 
device and the tool transfer device toward and away from each other in a 
direction perpendicular to an axis of the tool held on the tool support 
device, and (d) a motion converting mechanism for converting a first 
relative movement of the tool gripper of the tool transfer device and the 
tool support device toward each other near the tool change position, into 
a movement of the tool clamping mechanism for unclamping the tool from the 
tool support device, and converting a second relative movement of the tool 
gripper and the tool support device away from each other near the tool 
change position, into a movement of the tool clamping mechanism for 
clamping the tool to the tool support device, and wherein the pair of 
gripper jaws of the tool gripper are shaped so as to engage the gripping 
portion of the tool held on the tool support device before the tool is 
unclamped by the tool clamping mechanism, and to permit the first relative 
movement to be completed at the predetermined tool change position after 
the tool is unclamped. 
In the machine tool equipped with the automatic tool changing device 
constructed according to the present invention as described above, the 
tool is automatically unclamped and clamped with respect to the tool 
support device such as a machine spindle, when the tool support device and 
the tool transfer device are moved toward each other and away from each 
other. 
Described in detail, when the tool support device carrying the cutting tool 
clamped thereto and the tool transfer device having the tool gripper are 
moved toward each other in the direction perpendicular to the longitudinal 
direction of the tool held on the tool support device, this relative 
movement is converted by the motion converting mechanism into the movement 
of the tool clamping mechanism for unclamping the tool from the tool 
support device. To avoid removal or displacement of the unclamped tool, 
the gripper jaws of the tool gripper of the tool transfer device engage 
the tool during the relative movement of the tool and the tool gripper 
toward each other, before the unclamping of the tool is initiated. 
The gripper jaws of the tool gripper are shaped so as to permit the 
mutually engaging tool and tool gripper to be further moved toward each 
other until they are located at the predetermined tool change position 
(where the distance between the tool support device and the tool transfer 
device is the shortest). Thus, the tool is unclamped only after the 
gripper jaws have engaged the tool and before the tool change position is 
reached. Since the tool gripped by the tool gripper of the tool transfer 
device has been unclamped from the tool support device before the tool 
change position is reached, the tool can be removed from the tool support 
device by a subsequent action of the tool transfer device in the tool 
change position, and replaced by another tool which is mounted on the tool 
support device by a further action of the tool transfer device. After the 
exchange of the tools is completed, the tool transfer device and the tool 
support device are moved away from each other. This movement causes the 
newly mounted tool to be clamped to the tool support device before the new 
tool is released from the tool gripper during the movement. 
The automatic tool changing device of the present machine tool utilizes the 
movements of the tool support device and the tool transfer device toward 
and away from each other, which are converted by the motion converting 
mechanism into the movements of the tool clamping mechanism to unclamp and 
clamp the tool with respect to the tool support device. The gripper jaws 
of the tool gripper continuously engage the used tool supported on the 
tool support device, during a terminal portion of the movement of the tool 
and the tool gripper toward each other before the tool is unclamped, and 
also engage the new tool until that tool is clamped to the tool support 
device during an initial portion of the movement of the tool and the tool 
gripper away from each other. This arrangement prevents removal or 
displacement of the tools from or with respect to the tool support device 
after the unclamping of the used tool or before the clamping of the new 
tool. 
The automatic tool changing device is simpler in construction and more 
economical to manufacture, than the known automatic tool changing device 
using two cam mechanisms one for the rotary tool changer arm as disclosed 
in the above-identified laid-open publication JP-A-63-267136, and the 
known automatic tool changing device using an exclusive power source for 
the hydraulic cylinder for actuating the tool clamping mechanism as 
disclosed in the above-identified JP-A-2-274448. 
It is noted that the term "cutting tool" used above should be broadly 
interpreted to comprehend not only a cutting tool alone or per se, but 
also a combination of a cutting tool and a suitable tool holder or adaptor 
used to mount the tool on the tool support device such as the spindle of a 
drilling or milling machine or a machining center. 
The tool clamping mechanism may use a draw bar for unclamping the tool from 
the tool support device when the draw bar is advanced in a direction 
toward the cutting tool, and clamping the cutting tool to the tool support 
device when the draw bar is retracted in a direction away from the cutting 
tool. In this case, the motion converting mechanism converts the first and 
second relative movements of the tool gripper and the tool support device 
into advancing and retracting movements of the draw bar, respectively. 
In one form of the above arrangement, the tool support device is a spindle 
head of the machine tool, which comprises a housing body, and a main 
spindle which is rotatably supported by the housing body and which holds 
the cutting tool at one end thereof. The main spindle has a center bore in 
which the draw bar is axially slidably movable, and the tool clamping 
mechanism further includes a biasing member for biasing the draw bar 
toward a fully retracted position thereof. 
In the above form of the invention, the motion converting mechanism may 
include: an unclamping lever supported by the housing body pivotally about 
an axis which is spaced apart from an axis of the main spindle and which 
is perpendicular to the axis of the main spindle; a linear-rotary 
conversion mechanism for converting the first and second relative 
movements of the tool gripper and the spindle head into pivotal movements 
of the unclamping lever; and a rotary-linear conversion mechanism for 
converting the pivotal movements of the unclamping lever into the 
advancing and retracting movements of the draw bar. 
The linear-rotary conversion mechanism indicated above may include a cam 
and a cam follower, the cam being provided on one of the unclamping lever 
and a separate member whose distance to the housing body of the spindle 
head changes during the first and second movements of the tool gripper and 
the spindle head. In place of the cam and cam follower, the linear-rotary 
conversion mechanism may use a pivotable lever which is pivotally 
connected at one of opposite ends thereof to the separate member indicated 
above, and at the other end to the unclamping lever, such that the 
pivotable lever is inclined with respect to the axis of the main spindle, 
and so that the unclamping lever is pivoted about the free end so as to 
move the draw bar during the relative movements of the tool gripper and 
the spindle head. 
The separate member indicated above may be a portion of a body of the 
machine tool, and the spindle head may be moved by the moving device 
relative to the body of the machine tool. In this case, the 
above-indicated portion of the machine tool body may be a column which 
extends upright and which slidably supports the spindle head. In this 
arrangement, the moving device is operated to move the spindle head on the 
column. 
The rotary-linear conversion mechanism may comprise an abutting member 
which extends in a radially inward direction of the main spindle from one 
of the unclamping lever and the draw bar, through a hole formed through 
the cylindrical wall of the main spindle, so that the abutting member 
abuts on the other of the unclamping lever and the draw bar when the 
unclamping lever is pivoted. This arrangement permits the unclamping lever 
act on the draw bar, at an axially middle portion of the main spindle, and 
therefore makes it possible to dispose the bearings for the main spindle 
such that the outermost bearings are spaced apart from each other by a 
considerable distance in the axial direction of the main spindle. The same 
arrangement also makes it possible to position the unclamping lever within 
the length of the main spindle. 
The abutting member may be a member which extends from the draw bar in the 
radially outward direction of the draw bar, so that the member is 
abuttable on the unclamping lever. Alternatively, the abutting member may 
extend from the unclamping lever in the radially inward direction of the 
draw bar, so that the member is abuttable on a suitable portion of the 
draw bar or a member fixed to the draw bar. 
In the above arrangement using the abutting member extending through the 
hole formed through the cylindrical wall of the main spindle, the 
unclamping lever may be pivotally supported by the housing body of the 
spindle head, at one of longitudinally opposite ends thereof, and has at 
the other end one of a cam and a cam follower which are engageable with 
each other, the other of the cam and the cam follower being provided on a 
separate member whose distance to the housing body of the spindle head 
changes during the first and second movements of the tool gripper and the 
spindle head. In this case, the unclamping lever further has a 
through-hole formed through an intermediate portion thereof between the 
longitudinally opposite ends, and the main spindle extends through this 
through-hole, with a radial clearance therebetween. The abutting member 
may be a pair of extensions such as pins fixed to the draw bar, which are 
abuttable on respective parts of the intermediate portion of the 
unclamping lever which are opposed to each other via the through-hole in 
the diametric direction of the draw bar. This arrangement permits the 
unclamping lever to engage the draw bar via the two extensions at an 
axially middle portion of the main spindle, and is effective to protect 
the unclamping lever against a moment about an axis parallel to the 
longitudinal direction of the unclamping lever, thereby making it possible 
to reduce the size of the components such as the unclamping lever and the 
member or members pivotally supporting the unclamping lever. 
In place of the above arrangement in which the abutting member extends from 
the draw bar or the unclamping lever through the hole formed through the 
cylindrical wall of the main spindle, the rotary-linear conversion 
mechanism may use an arrangement in which the rear end portion of the draw 
bar extends through the rear open end of the main spindle in the axial 
direction, so that the unclamping lever per se or a roller attached to the 
unclamping lever is abuttable on the rear end portion or rear end face of 
the draw bar or a member attached to the rear end portion of the draw bar. 
In the above form of the present invention wherein the tool clamping 
mechanism uses a draw bar slidably received in the center bore of the main 
spindle of the spindle head, the motion converting mechanism may be 
adapted to include: a slave cylinder comprising a first piston coaxially 
with the draw bar and axially slidably and fluid-tightly received in the 
center bore, and a closure block fixedly received in the center bore, the 
closure block cooperating the main spindle and the first piston to define 
a fluid chamber; a master cylinder comprising a cylinder housing provided 
on one of the housing body of the main spindle and a separate member whose 
distance to the housing changes during the first and second movements of 
the tool gripper and the spindle head, the master cylinder further 
comprising a second piston which is axially slidably and fluid-tightly 
received in the housing and which is moved by the other of the housing 
body and the separate member, to apply a fluid pressure to the fluid 
chamber; and a connector for connecting the fluid chamber of the slave 
cylinder and the master cylinder while permitting rotation of the main 
spindle. 
In a further form of this invention, the pair of gripper jaws are pivotable 
to effect opening and closing actions on the cutting tool, and include a 
pair of gripping portions for positioning and gripping the tool at the 
chucking portion such that the tool is immovable in a radial and an axial 
direction thereof, and a pair of latch portions extending substantially 
parallel to each other from the gripping portions, respectively, toward 
free ends of the gripper jaws. The latch portions are engageable with the 
chucking portion of the tool such that the tool is movable in the radial 
direction but immovable in the axial direction. Each of the gripping 
portions may have an arcuate inner edge having a curvature corresponding 
to an outer circumference of the chucking portion of the tool. 
The pair of latch portions indicated above may consist of a pair of 
straight portions having respective straight inner edges opposed to each 
other, and a pair of guide portions extending from the straight portions 
toward free ends of the gripper jaws. The guide portions have respective 
inner edges which are inclined with respect to the straight inner edges of 
the straight portions such that a distance between the inner edges of the 
guide portions increases in a direction toward the free ends. 
Alternatively, the latch portions may consist of a pair of cam portions 
having respective curved inner edges formed such that a distance between 
the curved inner edges increases in a direction toward free ends of the 
gripper jaws, at a rate which increases in the direction toward the free 
ends. 
The pair of gripper jaws may include a pair of pivotable members pivotable 
on a plane so as to effect opening and closing actions on the chucking 
portion of the tool, and a pair of rotatable members rotatably attached to 
the pair of pivotable members, respectively. The rotatable members are 
rotatable about respective axes which are perpendicular to the plane in 
which the pivotable members are pivoted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to the front and side elevational views of FIGS. 1 and 2, a 
machine tool in the form of a drilling machine has a base 10, a column 12 
fixed to the base 10, a spindle head 14 slidably mounted on the column 12, 
a tool magazine actuator 16 secured to the column 12, and a tool magazine 
18 which is rotatably supported by the actuator 16 and which has a 
plurality of tool grippers 26. The spindle head 14 is almost entirely 
received within an opening 20 formed in the column 12 so as to extend in 
the vertical direction. The spindle head 14 is fed in the vertical 
direction by a servo motor 22 mounted atop the column 12, via a ballscrew 
24 connected to the motor 22. 
The tool magazine 18 is capable of accommodating a plurality of rotary 
cutting tools 40 (drilling tools, tapping tools, etc.) held in respective 
tool holders 42, such that the tool holders 42 are gripped by the 
respective tool grippers 26. As most clearly shown in FIG. 1, the tool 
grippers 26 are equally spaced apart from each other in the rotating 
direction of the tool magazine 18. As described below, the tool magazine 
18 is rotated by the actuator 16 to select a desired one of the cutting 
tools 40, and is moved by the actuator 16 in a direction parallel to the 
axis of rotation. 
Referring further to FIGS. 3 and 4, the construction of the spindle head 
14, the tool magazine actuator 16 and the tool magazine 18 will be 
described in detail. 
The spindle head 14 is provided with a tool support device in the form of a 
main spindle 28, a spindle drive motor 30, and an unclamping lever 32. The 
main spindle 28 is connected to the motor 30 through a coupling 34. 
As shown in FIG. 4(A), the main spindle 28 is rotatably supported by a 
housing body 37 of the spindle head 14, via a plurality of bearings 36. 
The spindle 28 has a center bore 38 formed therethrough in the axial 
direction. The front end portion of the bore 38 is tapered and provides a 
mounting hole 44 for receiving a tapered shank of the tool holder 42 which 
carries a cutting tool 40 to be used for a machining operation on the 
workpiece. The remaining portion of the bore 38 consists of holes having 
different diameters, in which is received a draw bar 46 in coaxial 
relation with the main spindle 28. The draw bar 46, which is axially 
slidable with respect to the bore 38, consists of a front clamping portion 
48 adjacent to the tapered mounting hole 44, an intermediate rod portion 
50, and a rear piston portion 52. 
The clamping portion 48 has a recess open axially at its front end face. 
The cylindrical wall defining the diameter of this recess has a plurality 
of radial holes 53 formed in the radial direction of the draw bar 46. The 
radial holes 53 are arranged in an equally spaced apart relation with each 
other in the circumferential direction of the clamping portion 48. Each 
radial hole 53 accommodates a steel ball 54 such that the ball 54 is 
movable in the radial direction of the clamping portion 48. The radial 
hole 53 is shaped and dimensioned to prevent the steel ball 54 from moving 
out of the hole 53. As the draw bar 48 is retracted in the direction away 
from the tapered mounting hole 44, the balls 54 are pushed inwardly of the 
radial holes 44, by a cam surface 56 which partially defines a portion of 
the stepped bore 38 near the mounting hole 44, whereby the balls 54 engage 
a pull stud 58 provided at the rear end of the tool holder 42, as most 
clearly shown in FIG. 7. When the draw bar 46 is placed in the fully 
retracted position, the tapered shank of the tool holder 42 is forced 
against the mounting hole 44, and is thus clamped to the main spindle 28. 
When the draw bar 46 is placed in the fully advanced position, on the 
other hand, the steel balls 54 are movable radially outwardly of the 
radial holes 44, whereby when the tool holder 42 is pulled out of the 
mounting hole 44, the balls 54 are forced by the pull stud 58, radially 
outwardly of the radial holes 44, and permit the pull stud 58 to be 
released from the balls 54. Thus, the tool holder 42 is unclamped from the 
spindle 28 when the draw bar 46 is located at its fully advanced position. 
The piston portion 52 provided at the rear end of the draw bar 46 has an 
abutting member in the form of a pin 60 fixedly extending therethrough in 
the radial direction, and also through elongate holes 62 formed through 
the cylindrical wall of the spindle 28, as shown in FIG. 5. The elongate 
holes 62 are elongated in the axial direction of the spindle 28. A series 
array 66 of belleville springs (coned disk springs) 64 is disposed around 
the intermediate rod portion 50 between the front clamping portion 48 and 
the rear piston portion 52. The spring array 66 consisting of the 
belleville springs 64 is held in pressing contact at one end with a 
shoulder 68 of the stepped bore 38, and at the other end with the front 
end of the piston portion 52, so that the draw bar 46 is biased toward its 
fully retracted position in which the tool holder 42 is normally clamped 
to the spindle 28. 
The unclamping lever 32 is supported by the housing body 37, pivotally 
about a pivot pin 70 fixed to the body 37. The pin 70 is spaced from the 
axis of the main spindle 28, and extends in the horizontal direction 
parallel to the direction of extension of the pin 60, that is, 
perpendicular to the axis of the main spindle 28. As shown in FIG. 5, the 
unclamping lever 32 has a through-hole 72 formed in a middle portion 
thereof, which permits the spindle 28 to extend therethrough, with a 
radial clearance therebetween. The lever 32 also has contact portions 74 
formed for abutting contact with the opposite ends portions of the pin 60 
secured to the piston portion 52 of the draw bar 46. The lever 32 further 
has a cam surface 76 on its side remote from the contact portions 74. As 
shown in FIGS. 4(A) and 4(B), a rotatable cam follower 78 is provided on 
the column 12, so that the cam surface 76 of the unclamping lever 32 comes 
into engagement with the cam follower 78 when the spindle head 14 is moved 
up and located at a position a short distance below a predetermined tool 
change position 108 indicated in FIG. 2. With the unclamping lever 76 
pushed at the cam surface 76 by the cam follower 78, the lever 76 is 
pivoted counterclockwise to the position of FIG. 4(B), whereby the draw 
bar 46 is eventually moved to its fully advanced position to unclamp the 
tool holder 42 from the spindle 28. 
The tool magazine actuator 16 is constructed as shown in FIG. 3. More 
specifically, the tool magazine actuator 16 includes a feeding nut 82 and 
a spline member 86, which are rotatably received within respective 
housings 80 and 84 mounted on a top surface 79 of the column 12. The nut 
82 and the spline member 86 are coaxial with each other and operatively 
connected to a magazine shaft 88 which supports the tool magazine 18, such 
that the magazine 18 and the shaft 88 are rotated as a unit. The magazine 
shaft 88 has an externally thread portion in the form of a ballscrew 
engaging the feeding nut 82, and a splined portion engaging the spline 
member 86. 
A shaft feed motor 90 is secured to the housing 80 and is connected to the 
feeding nut 82 by a timing belt 92. To the housing 84, there is secured a 
shaft rotating motor 94 connected to the spline member 86 by a timing belt 
96. To move the magazine shaft 88 (tool magazine 18) in the axial 
direction without rotation thereof, only the shaft feed motor 90 is 
activated to rotate the feeding nut 82. To rotate the shaft 88 (tool 
magazine 18) without an axial movement thereof, the shaft feed motor 90 
and the shaft rotating motor 90 are synchronously operated to rotate both 
the nut 82 and the spline member 86. The rotation of the nut 82 in 
synchronization with the spline member 86 permits the shaft 88 to remain 
in the same axial position, even though the shaft 88 is rotated by the 
spline member 86. 
The tool magazine 18 has a body in the form of a disk 97, at which the 
magazine 18 is attached to the front end of the magazine shaft 88. The 
disk 97 carries ten tool grippers 26 fixed at its outer periphery such 
that the tool grippers 26 are arranged at a predetermined angular spacing 
along the circumference of the disk 97. As shown in FIG. 6, each tool 
gripper 26 includes a pair of pivotable members in the form of a pair of 
gripper jaws 100 each pivotable about respective support pins 98. The 
pivotable jaws 100 are opened and closed in a vertical plane. Each gripper 
jaw 100 has a gripping portion 102 located relatively near the pin 98. The 
gripping portion 102 has an arcuate inner edge having a curvature 
following the outer circumferential surface of the tool holder 42. The two 
gripper jaws 100 are biased by a coil spring 104 so that the two gripping 
portions 102 cooperate to position and grip the tool holder 42. Each 
gripper jaw 100 further has a straight portion 105 contiguous to the 
arcuate inner edge of the gripping portion 102, and a guide portion 106 
contiguous to the straight portion 105. The straight portion 105 has a 
straight inner edge and a constant width as measured perpendicularly to 
the longitudinal direction of the jaw 100. The guide portion 106 is 
provided at one end of the jaw 100 opposite to the end at which the coil 
spring 104 is provided. The guide portion 106 has an inner edge inclined 
with respect to the straight inner edge of the straight portion 105, so 
that the width of the guide portion 106 increases in the direction from 
the straight portion 105 toward the extreme end of the guide portion 106. 
As shown in FIG. 7, the gripping, straight and guide portions 102, 105 and 
106 of the gripper jaw 100 have a trapezoidal cross sectional shape 
similar to a profile of a V-groove 110 formed in the outer surface of a 
chucking portion of the tool holder 42. 
In the present embodiment, the tool magazine 18 functions as a device for 
accommodating or storing the cutting tools 40 (with the tool holders 42), 
and cooperates with the actuator 16 to function as a tool transfer device 
for transferring the tools 40 to and from the main spindle 28. 
It will be understood that the automatic tool changing device includes: the 
tool magazine actuator 16; the tool magazine 18 having the tool grippers 
26; a tool clamping mechanism having the draw bar 46, balls 54, cam 
surface 56, and spring array 66; a motion converting mechanism having the 
unclamping lever 32, pin 60 and cam follower 78; and a moving device 
including the servo motor 22 and ballscrew 24 for moving the spindle head 
14. 
There will next be described an operation of the automatic tool changing 
device provided on the drilling machine. 
After a machining operation on a workpiece using a cutting tool 40 held by 
the tool holder 42 mounted on the spindle 28 is finished, the rotation of 
the spindle 28 is stopped, and the spindle head 14 is moved up toward the 
predetermined tool change position 108, by means of the servo motor 22 and 
ballscrew 24. Before the spindle head 14 reaches the tool change position 
108, the tool holder 42 mounted on the spindle 28 comes into engagement 
with the guide portions 106 of the gripper jaws 100 of the lowermost tool 
gripper 26 placed in the tool change position 108, namely, the tool 
gripper 26 right above the axis of the spindle 28. In this condition, the 
tool gripper 26 is aligned with the V-groove 110 of the tool holder 42 
mounted on the spindle 28. As the tool holder 42 is moved up with the 
spindle head 14 a further distance, the gripper jaws 100 are opened by the 
tool holder 42, against a biasing force of the coil spring 104, and the 
V-groove 110 of the tool holder 42 then engages the straight portions 105 
of the gripper jaws 100, as shown in FIGS. 6 and 7. In this condition, the 
tool holder 42 is prevented from axially moving relative to the spindle 
28, and is still kept clamped to the spindle 28 under the biasing action 
of the belleville springs 64, because the cam surface 76 of the unclamping 
lever 32 provided on the spindle head 14 is still spaced apart from the 
cam follower 78 provided on the column 12, with the contact portions 74 of 
the lever 32 being spaced apart from the pin 60, as shown in FIG. 4(A). 
As the spindle head 14 is further moved up, the cam surface 76 of the 
unclamping lever 32 is brought into abutting contact with the cam follower 
78, and the lever 32 is pivoted counterclockwise about the support shaft 
70 toward its unclamping position, as shown in FIG. 4(B). This pivotal 
movement of the unclamping lever 32 causes the contact portions 74 to abut 
on the pin 60, resulting in an advancing movement of the draw bar 46 
against the biasing force of the belleville springs 64. As a result, the 
tool holder 42 is unclamped from the spindle 28. In this condition, 
however, the tool holder 42 is prevented from moving in the axial 
direction away from the mounting hole 44 of the spindle 28, because the 
V-groove 110 of the tool holder 42 engages the straight portions 105 of 
the gripper jaws 100 of the tool gripper 26. The unclamped tool holder 42 
is moved a further distance with the spindle 28, until the spindle 28 
reaches the predetermined tool change position 108, at which the upward 
movement of the spindle head 14 is stopped. In this tool change position 
108, the tool holder 42 is securely gripped by the gripping portions 102 
of the gripper jaws 100, and the straight portions 105 function as latch 
portions for preventing the tool holder 42 from moving down from the 
gripping portions 102 and from moving in the axial direction relative to 
the jaws 100. The tool magazine actuator 16 is then activated to effect an 
automatic tool changing operation as described below. 
Initially, the feeding nut 82 is rotated to advance the tool magazine 18, 
for thereby removing the tool holder 42 from the mounting hole 44 of the 
spindle 28. Then, the feeding nut 82 and the spline member 86 are 
synchronously rotated by an amount corresponding to an angle of rotation 
of the tool magazine 18 necessary to bring the next tool 40 to the tool 
change position 108. That is, the tool magazine 18 is rotated until the 
tool holder 42 having the tool 40 to be used next is aligned with the axis 
of the spindle 28 located in the tool change position 108. Subsequently, 
the feeding nut 82 is rotated in the reverse direction to retract the tool 
magazine 18 toward the actuator 16, so that the tool holder 42 having the 
next tool 40 is mounted on the spindle 28. Then, the spindle head 14 is 
moved down away from the tool magazine 18, for performing a machining 
operation using the new tool 40 now mounted on the spindle 28. 
During an initial period of the downward movement of the tool holder 42 
with the spindle head 14, the V-groove 110 of the tool holder 42 on the 
spindle 28 continues to engage the straight portions 105 of the gripper 
jaws 100 of the tool gripper 26, thereby maintaining the tool holder 42 in 
the predetermined axial position relative to the spindle 28 (mounting hole 
44). As the spindle head 14 is further lowered, the cam surface 76 of the 
unclamping lever 32 is disengaged from the cam follower 78 on the column 
12, whereby the lever 32 is pivoted clockwise, allowing the draw bar 46 to 
return to the clamping position under the biasing action of the belleville 
springs 64. Thus, the tool holder 42 is clamped to the spindle 28 by the 
biasing force of the belleville springs 64. With a further downward 
movement of the tool holder 42 with the spindle 28, the tool holder 42 is 
released from the gripper jaws 100 of the tool gripper 26 in the tool 
change position 108. Now, a next machining operation with the new cutting 
tool 40 can be started. 
It will be understood from the above description that the vertical 
movements of the spindle 28 (spindle head 14) to and from the tool change 
position 108 cause or give rise to automatic unclamping and clamping of 
the tool holder 42 to and from the spindle 28, automatic transfer of the 
unclamped tool holder 42 to the tool gripper 26 of the tool magazine 18, 
and automatic release of the new tool holder 42 from the tool gripper 26. 
These automatic tool changing actions are performed sequentially with high 
reliability, in a relatively short length of time, during which the 
spindle head 14 is moved to and from the tool change position 108. 
Further, since the cam mechanism (76, 78) to clamp and unclamp the tool 
holder 42 with respect to the spindle 28 is activated by the movements of 
the spindle head 14, the present automatic tool changing device does not 
require an exclusive power source (e.g., hydraulic power source) for 
clamping and unclamping the tool holder 42, and proximity sensors or 
similar detecting means for controlling such exclusive power source. Thus, 
the present automatic tool changing device is simple in construction, 
economical to manufacture and reliable in operation. 
In the above first embodiment of FIGS. 1-7, each gripper jaw 100 of the 
tool gripper 26 has the straight and guide portions 105, 106 in addition 
to the gripping portion 102. However, the gripper jaws 100 may be modified 
as desired, provided the modified gripper jaws function to prevent an 
axial movement of the tool holder 42 relative to the spindle 28 during 
upward movement of the spindle head 14 to the tool change position 108. 
Examples of modifications of the tool gripper are illustrated in FIGS. 8 
and 9. 
In a second embodiment of this invention, the tool magazine 18 uses tool 
grippers 26a as shown in FIG. 8. Each tool gripper 26a has a pair of 
gripper jaws 100a, each having the arcuate gripping portion 102 as 
provided on the tool gripper 26, and a cam portion 105a having a curved 
inner edge 111 contiguous to the V-shaped inner edge. The curved inner 
edges 111 of the two gripper jaws 100a are shaped such that a distance 
between the two inner edges 111 increases in the direction from the 
gripping portion 102a toward the free ends of the jaws 100a, at a rate 
which increases in the same direction. The cam portion 105a performs the 
same function as the straight portion 105 (latch portion) and the guide 
portion 106 of the tool gripper 26 used in the first embodiment. 
In a third embodiment of the invention, the tool magazine 18 uses tool 
grippers 26b as shown in FIG. 9, Each tool gripper 26b has a pair of 
gripper jaws 100b, each carrying a rotatable member in the form of a 
roller 112 at its end removed from the end at which the jaw 100b is biased 
by the spring 104. The pins 98 pivotally supporting the gripper jaws 100b 
extend from a plate 113, which has two stopper pins 114 for determining 
the angular positions of the two gripper jaws 100b in which the tool 
holder 42 is finally gripped by the jaws 100b. When the tool holder 42 is 
gripped by the tool gripper 26b, the tool holder 42 forces the rollers 112 
rotatably supported by the gripper jaws 100b, whereby the gripper jaws 
100b are pivoted about the respective pins 98 such that the rollers 112 in 
rolling contact with the V-groove 110 of the tool holder 42 are moved away 
from each other, permitting the tool holder 42 to be moved into the tool 
gripper 26b until the tool holder 42 engages an arcuate recess 113a formed 
in the plate 113, whereat the pivotal movements of the gripper jaws 100b 
are stopped by the respective stopper pins 114. The plate 113 has a key 
113b fixed thereto for engagement with a groove formed in the tool holder 
42, for circumferential positioning of the tool holder 42. However, the 
key 113b may be fixed to the tool holder 42. In this embodiment, the 
rollers 112 and the arcuate recess 113a function as tool gripping 
portions. The rollers 112 also function as latch portions like the 
straight and guide portions 105, 106. Each roller 112 has an annular ridge 
formed on the outer circumferential surface, which ridge is shaped 
following the profile of the V-groove 110 of the tool holder 42. The 
surface defining the arcuate recess 113a also has a ridge corresponding to 
the V-groove 110. 
In the above three embodiments, the unclamping lever 32 having the contact 
portions 74 and cam surface 76, the pin 60 fixed to the draw bar 46, and 
the cam follower 78 provided on the column 12 cooperate to provide the 
motion converting mechanism for converting the vertical movements of the 
spindle 28 toward and away from the tool magazine 18 (tool transfer device 
having the tool grippers 26, 26a, 26b), into advancing and retracting 
movements of the draw bar 46 to unclamp and clamp the tool holder 42 (tool 
40) with respect to the spindle 28. 
Although the cam surface 76 and the cam follower 78 are provided on the 
unclamping lever 32 and the column 12, respectively, a reverse arrangement 
is shown in FIG. 10, which shows a fourth embodiment of the present 
invention, wherein a cam follower 77 is fixed to the free end of the 
unclamping lever 32 while a cam member 79 having a cam surface 79a is 
fixed to the column 12. 
In a fifth embodiment of the present invention, however, the combination of 
the cam surface 76 and the cam follower 78 which constitutes a principal 
part of the motion converting mechanism in the above embodiments is 
replaced by an arrangement as shown in FIG. 11, in which the unclamping 
lever 32 having the contact portions 74 is pivotally connected to at its 
upper or free end (remote from the pin 70) to one end of a pivotable lever 
115, which in turn is pivotally connected at the other end to a pin 116 
fixed on the machine column 12. When the spindle head 14 is located at a 
position lower than the tool change position 108 (FIG. 2), the two levers 
32, 115 are inclined relative to the axis of the main spindle 28, and 
relative to each other, as indicated by two-dot chain line in FIG. 10. 
According to this arrangement, an upward movement of the spindle head 14 
by a distance L up to the tool change position 108 causes a pivotal 
movement of the unclamping lever 32 by an angle .theta.. A predetermined 
terminal fraction of the pivoting angle .theta. of the unclamping lever 32 
is used to move the draw bar 46 in the advancing direction, with the 
contact portions 74 of the lever 32 abutting on the pin 60 fixed to the 
draw bar 46 as described above. This embodiment is preferred where the 
spindle head 14 is fixed in its vertical position during a machining 
operation, or where the vertical stroke of the spindle head 14 used for a 
machining operation is relatively short. 
Referring next to FIG. 12, there will be described a sixth embodiment of 
this invention using a further modified form of the motion converting 
mechanism, which does not use a cam mechanism to clamp and unclamp the 
tool holder 42. 
In the fifth embodiment of FIG. 12, a spindle head 118 has a housing body 
120 which rotatably supports a main spindle 124 incorporating a draw bar 
122. The housing body 124 has an axial through-hole 126 through which the 
spindle 124 extends, and an annular protrusion 128 which projects radially 
inwardly into the through-hole 126. The annular protrusion 128 has a 
circumferential groove 130 formed in an inner circumferential surface 
thereof which slidably contacts the rotating spindle 124. The spindle 124 
has a spindle bore 132 in which the draw bar 122 is axially slidably and 
fluid-tightly received, and a radial hole 134 formed through its 
cylindrical wall. The radial hole 134 is aligned with the circumferential 
groove 130 of the annular protrusion 128. The spindle bore 132 also 
accommodates a closure block 138 fixed therein so that the block 138 
cooperates with the spindle 124 and a rear piston portion 142 of the draw 
bar 122, to define a fluid chamber 144. The block 138 has a passage 136 
which communicates with the fluid chamber 144, and with the 
circumferential groove 130 through the radial hole 134. The passage 136, 
radial hole 134 and groove 130 provide a fluid passageway 140 for feeding 
a pressurized fluid to the fluid chamber 144 to advance the draw bar 122 
and thereby unclamp the tool holder 42 from the spindle 124. Sealing 
members 150 are provided between the outer circumferential surface of the 
spindle 124 and the annular protrusion 128, while sealing O-rings 152 are 
provided between the inner circumferential surface of the spindle 124 and 
the block 138 and the piston portion 142 of the draw bar 122, for securing 
fluid-tightness between the spindle 124 and the piston portion 142, and 
between the spindle 124 and the block 138. 
The spindle head 118 is provided with an unclamping master cylinder 154 
connected to the fluid passageway 140 through a conduit 156 and a joint 
158. The master cylinder 154 has a piston 164 axially slidably and 
fluid-tightly received in a housing 165. The master cylinder is moved with 
the spindle head 118 and adapted to deliver a pressurized fluid for 
thereby increasing the fluid pressure in the fluid chamber 144 of the 
slave cylinder when the piston 164 is lowered. Described in detail, when 
the spindle head 118 is moved up toward the tool change position as 
indicated at 108 in FIG. 2, a piston rod 166 fixed to the piston 164 of 
the master cylinder 154 comes into abutting contact with an abutment 
provided at an appropriate position on the column 12, whereby the piston 
164 is lowered to its unclamping position, to feed the pressurized fluid 
into the fluid chamber 144 through the conduit 156 and the passageway 140. 
As a result, the draw bar 122 is advanced against the biasing force of 
belleville springs (coned disk springs) 168 disposed around the bar 122. 
The main spindle 124, the piston portion 142 of the draw bar 122, and the 
block 138 cooperate to constitute a slave cylinder having the fluid 
chamber 144 communicating with the fluid passageway 140. The fluid 
passageway 140, conduit 156 and joint 158 provide a connector for 
connecting the master cylinder 154 and the fluid chamber 144, while 
permitting the rotation of the spindle 124. 
When the spindle head 118 is moved down away from the tool change position, 
the piston 164 is permitted to return to the clamping position in which 
the fluid pressure in the fluid chamber 144 is low enough to allow the 
draw bar 122 to return to its clamping position under the biasing force of 
the belleville springs 168. 
While the present invention has been described above in its presently 
preferred embodiments with a certain degree of particularities, it is to 
be understood that the present invention is not limited to the details of 
the illustrated embodiments, but may be embodied with various changes, 
modifications and improvements such as those described below, which may 
occur to those skilled in the art. 
Although the automatic tool changing device as applied to a drilling 
machine using the rotary cutting tools 40 has been described for 
illustrative purpose only, the principle of the present invention is 
equally applicable to other types of machine tools such as turning 
machines or lathes which use non-rotary cutting tools. Where the automatic 
tool changing device of the present invention is applied to a turning 
machine, for example, a tool magazine accommodating non-rotary cutting 
tools is disposed at one end of the machine bed, for instance, and an 
automatic tool changing operation between the tool magazine and a tool 
support device in the form of a non-indexable tool post or an indexable 
tool turret is effected by utilizing the movements of the tool post or 
tool turret to and from a predetermined tool change position near the tool 
magazine. In this case, at least one tool clamping mechanism is provided 
on the tool post or tool turret and is adapted so that the movements of 
the tool post or turret cause automatic clamping and unclamping of the 
tool holders on the tool post or turret. 
In the illustrated embodiments, exchanges of the tool holders 42 (tools 40) 
are effected between the spindle 28, 124 and the tool magazine 18. Namely, 
the tool holder 42 accommodating the used tool 40 is returned from the 
spindle 28, 124 directly to the tool magazine 18, and the tool holder 42 
accommodating the new tool 40 is transferred from the tool magazine 18 
directly to the spindle 28, 124. However, the automatic tool changing 
device may use a tool transfer device in the form of a tool changing arm 
or arms having a tool gripper or grippers, which is disposed between the 
spindle and the tool magazine, so that the tool holder is first 
transferred to the tool changing arm before the tool holder is mounted on 
the spindle or returned to the tool magazine. For instance, a tool 
changing arm has two tool grippers at its opposite ends, so that when the 
used and new tools are exchanged, the tool holder mounted on the spindle 
is gripped by one of the two tool grippers, while one of the tool holders 
which has been selected from the tool magazine by suitable indexing of the 
tool magazine is gripped by the other tool gripper. 
In the illustrated embodiments, the spindle head 14 is vertically moved 
relative to the tool magazine 18 fixed on the column 12 when the tool 
changing operation is effected. However, the tool magazine 18 and the tool 
magazine actuator 16 may be designed to be vertically movable relative to 
the spindle head 14 located at a predetermined tool change position 
selected along the operating stroke of the spindle head, so that the 
movements of the tool magazine 18 cause automatic unclamping and clamping 
of the tool holder 42 and automatic transfer of the tool holder 42 between 
the tool gripper 26 and the main spindle 28. 
It will be further understood that the present invention may be embodied 
with various other changes, modifications and improvements, which may 
occur to those skilled in the art, in the light of the foregoing 
teachings.