Turret tool post for machine tool and apparatus for controlling indexing of the same

A turret tool post for a machine tool has a turret having a plurality of turret faces each equipped with a tool for machining, a turret shaft for rotating the turret, a cam follower provided on the turret shaft, a cam having a cam surface engaged with the cam follower to cause the cam follower to rotate, and an indexing motor for driving the cam to index the turret faces. A straight raceway portion is formed on the cam surface of the cam so that the cam follower is not driven to rotate through a predetermined angle. Also disclosed is an apparatus for controlling indexing of the turret tool post which has a turret controller for controlling the rotation of the indexing motor. The speed of the indexing motor is controlled in accordance with whether a door attached to a cover covering the turret and other elements is open or closed.

BACKGROUND OF THE INVENTION 
The present invention relates to a turret tool post for a machine tool and 
an apparatus for controlling indexing of the same. More particularly, the 
present invention pertains to a turret tool post designed to enable 
ultra-high speed indexing and an apparatus for controlling the indexing 
process conducted by the turret tool post. 
In the case of using a plurality of tools on a machine tool, it is common 
practice to use a turret tool post for indexing various tools 
successively, thereby efficiently conducting various kinds of machining 
operation without the need to change tools for each particular machining 
operation. More specifically, machining operations, for examples, turning, 
face milling, drilling, boring and threading, are efficiently carried out 
by successively indexing the required tools. There are known a variety of 
turret tool posts which may be classified into the following types: square 
turrets, hexagon turrets, flat turrets and drum-shaped turrets. If the 
indexing speed of a turret tool post is slow, the actual cutting time is 
shortened, which results in lowering of the cutting efficiency. 
On the other hand, curvic coupling mechanism and knock pin mechanism 
wherein positioning is effected by insertion of a knock pin are known as 
indexing and positioning mechanisms for use in turret tool posts. Japanese 
Utility Model Unexamined Publication (Kokai) No. 62-95804 (1987) discloses 
a turret tool post for use in a machine tool or the like as being an 
intermittent indexing apparatus, which has a globoidal cam and a plurality 
of cam followers which are radially mounted on the peripheral surface of a 
shaft in such a manner as to be in engagement with the globoidal cam so 
that the cam followers are intermittently rotated to index and set a 
desired tool at a desired position. 
The above-described conventional indexing and positioning mechanisms for a 
turret tool post need two operations, that is, an indexing operation and a 
clamping operation. The clamping operation is conducted in such a manner 
that, after the turret tool post has been rotated so as to reach a desired 
position, it is fixed in this position by oil-hydraulic or other similar 
driving means. Thus, there has heretofore been restriction on achievement 
of a reduction in the time needed for the indexing of the turret tool post 
that involves the above-described two operations. 
The turret tool post that is disclosed in Japanese Utility Model Unexamined 
Publication (Kokai) No. 62-95804 (1987) set forth above does not need the 
above-described two operations. However, this turret tool post cannot 
provide discrete angles with a high degree of accuracy in indexing process 
unless both the cam shaft and the cam follower shaft are precisely 
positioned relative to each other. It is necessary in order to precisely 
provide a desired angle in indexing process to employ an apparatus for 
controlling the indexing process. Such a control apparatus is complicated 
as well as expensive. In addition, since there has recently been a demand 
for a high degree of positioning accuracy, it has heretofore been 
impossible to increase the indexing speed unconditionally. 
Meanwhile, the body of a machine tool such as a lathe is covered with a 
machine cover for the reasons of design, safety and prevention of splash 
of cutting oil. The operator opens a door attached to the machine cover to 
replace a workpiece with another or change tools on the turret tool post. 
Accordingly, if the indexing speed of the turret tool post is increased, 
the operator is in danger when conducting an operation with the door of 
the machine cover kept open for effecting a setup or the like. 
SUMMARY OF THE INVENTION 
In view of the above-described circumstances, it is an object of the 
present invention to provide a turret tool post for a machine tool which 
is designed so that a necessary turret face is made available simply by 
effecting indexing without the need to conduct a clamping operation. 
It is another object of the present invention to provide an indexing 
mechanism for use in a turret tool post of a machine tool which is capable 
of effecting a high-speed indexing operation. 
It is still another object of the present invention to provide an apparatus 
for controlling indexing of a turret tool post of a machine tool which is 
suitable for an indexing mechanism which enables a necessary turret face 
to be made available simply by effecting indexing without the need to 
conduct a clamping operation. 
It is a further object of the present invention to provide an indexing 
mechanism for use in a turret tool post of a machine tool which is capable 
of optimal control so that a high-speed indexing operation can be 
performed. 
It is a still further object of the present invention to provide an 
indexing control apparatus for a turret tool post which is designed so 
that the operation of opening and closing a door attached to a cover that 
covers a machine tool is electrically interlocked with the indexing 
operation of the turret tool post. 
To these ends, the present invention provides a turret tool post for a 
machine tool having a turret having a plurality of turret faces each 
equipped with a tool for machining, a turret shaft for rotating the 
turret, a cam follower provided on the turret shaft, a cam having a cam 
surface engaged with the cam follower to cause the cam follower to rotate, 
and an indexing motor for driving the cam to index the turret faces, 
wherein the improvement comprises a straight raceway portion formed on the 
cam surface of the cam so that the cam follower is not driven to rotate 
through a predetermined angle. 
According to another of its aspects, the present invention provides an 
apparatus for controlling indexing of the turret tool post for a machine 
tool set forth above, the control apparatus comprising a sensor for 
detecting an angle which is provided on the cam, and a controller in which 
a time constant is set so that the cam comes to rest when the cam follower 
is in engagement with the straight portion in response to a signal output 
from the sensor. 
It is even more effective if the sensor comprises a stop confirmation 
sensor for detecting an angle of the cam and a stop command sensor for 
delivering a stop command signal to the indexing motor. 
According to another of its aspects, the present invention provides, in a 
machine tool having a turret having a plurality of turret faces, an 
indexing motor for rotating the turret to index the turret faces, a turret 
controller for controlling the rotation of the indexing motor, and a door 
attached to a cover covering the turret and other elements, an apparatus 
for controlling indexing of the turret comprising the turret controller 
which has means for detecting whether the door is open or closed, and 
means for instructing, in response to a signal from the detecting means 
which represents the fact that the door is open, the indexing motor to 
rotate at a lower speed than in the case of an indexing operation 
conducted during normal machining process. 
Thus, since the turret tool post according to the present invention need 
not have a clamp mechanism nor a speed change mechanism, it is possible to 
effect considerably high-speed indexing with a relatively simple 
structure. 
In addition, since the indexing speed of the turret tool post is lowered in 
interlocking relation to the door of the machine cover, the operator can 
conduct a setup operation with safety. As a result, the operating 
efficiency is enhanced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described hereinunder in 
detail with reference to the accompanying drawings. 
Referring first to FIG. 1, which is a partially sectional view of a turret 
tool post 1 according to the present invention, a turret body 2 is in the 
shape of a box which has a space therein. The turret body 2 is formed from 
a cast material. The turret body 2 is mounted on a carriage (not shown). 
In machining process, the carriage, together with the turret body 2, is 
moved to effect machining with a tool provided on a turret 7. A turret 
shaft 3 is accommodated inside the turret body 2. The turret shaft 3 is 
rotatably supported at both ends thereof by bearings 4 which receive force 
acting in the thrust direction. 
A flange face 6 is provided at one end of the turret shaft 3. An output 
shaft 5 projects from the flange face 6. The turret 7 is secured on the 
output shaft 5 and in close contact with the flange face 6. That portion 
of the turret shaft 3 which extends between the bearings 4 is provided 
with a plurality of cam followers 8 in such a manner that the central axis 
of each cam follower 8 extends perpendicular to the axis of the turret 
shaft 3. Each cam follower 8 is rotatably provided on a cam follower shaft 
9 through a bearing or other similar means. The cam follower shaft 9 is 
rigidly secured to the turret shaft 3. 
Thus, a plurality of combinations of a cam follower 8 and a cam follower 
shaft 9 are disposed around the outer periphery of the turret shaft 3 at 
equal spacings. On the other hand, a roller gear cam 20 has a spiral 
projection 21 formed on the outer periphery thereof, the projection 21 
having a trapezoidal cross-section (see FIG. 2). The projection 21 is in 
engagement with cam followers 8. The roller gear cam 20 rotates about the 
axis 29 of shaft 22. FIG. 3 is a development view showing the roller gear 
cam 20. The turret shaft 3 is rotated through engagement between the 
projection 21 and a pair of cam followers 8 which sandwich the projection 
21 therebetween. 
The projection 21 formed on the roller gear cam 20 comprises a slope 
portion 31, a straight portion 30 and a steep slope portion 32. Each of 
the slope and steep slope portions 31 and 32 spirals at a predetermined 
pitch along the axis of the roller gear cam 20. The straight portion 30 of 
the projection 21, which extends through the distance a, has no pitch 
angle. The straight portion 30 has the advantage that, even if the 
accuracy of angular positioning of the roller gear cam 20 is somewhat low, 
there is no adverse effect on the angular position at which the turret 
shaft 3 is suspended. Positioning of the turret shaft 3 in indexing 
process is effected using the straight portion 30. 
Provision of the straight portion 30 enables the speed of rotation of the 
roller gear cam 20 to be increased to the maximum level of the driving 
capacity of a motor 26 for indexing. The shaft 22 has a timing belt pulley 
23 rigidly secured thereto, the pulley 23 having teeth formed on the outer 
periphery thereof at a predetermined pitch. A timing belt 25 is engaged 
with the timing belt pulley 23. The other end of the loop of the timing 
belt 25 is engaged with another timing belt pulley 24 which is directly 
coupled to the indexing motor 26 so as to be driven by it. 
FIG. 4(a) is a functional block diagram of the turret tool post 1. An NC 
unit 40 is a known numerical control unit. When a T code command, which is 
a command given to effect indexing of the turret tool post 1, is issued 
from the NC unit 40, this command is transmitted to a controller 41 
(signal 1'). In response to the T code command, the controller 41 issues a 
tool post control unit 42 with commands such as a forward/reverse command 
and a start command (signal 3'). The tool post control unit 42 outputs 
electric power to the indexing motor 26 to drive it (signal 4'). 
The rotation of the indexing motor 26 is transmitted to the turret shaft 3 
to index the turret 7. Dogs 45 and 46 are provided around the outer 
periphery of the roller gear cam 20 (see FIG. 5). The dogs 45 are provided 
for detection so that a switch (described below) issues a stop command to 
the indexing motor 26. The dogs 46 are provided to confirm that the turret 
7 of the turret tool post 1 is in a given indexed position. For this 
purpose, a stop command LS 43 and a stop confirmation LS 44 are provided 
on the turret body 2 in correspondence with the dogs 45 and 46, 
respectively, so that the LS 43 and 44 are activated in accordance with 
whether or not a turret face of the turret 7 has been indexed as detected 
by dogs 45, 46. 
The stop command LS 43 is disposed at a position corresponding to a 
position where a turret face is indexed. When activated, the stop command 
LS 43 delivers a signal 5' to the controller 41. In response to this 
signal, the controller 41 delivers a command signal 3' to the tool post 
control unit 42. The stop confirmation LS 44 is disposed at a position 
where it is possible to confirm that the turret 7 has been indexed to a 
predetermined position at a predetermined angle. When activated, the stop 
confirmation LS 44 delivers a signal 6' to the controller 41. In response 
to the signal 6', the controller 41 starts counting with an up/down 
counter to know which turret face (hereinafter referred to as simply 
"face") of the turret 7 is presently indexed. 
In addition, it is checked with the stop confirmation LS 44 whether or not 
there is an indexing mistake when the turret 7 is suspended to index a 
particular face. It should be noted that, if it is impossible to confirm 
that the door of the machine cover is closed, as described later, the 
signal 5' is ignored and the command signal 3' is also controlled on the 
basis of the signal 6' from the stop confirmation LS 44. Since the stop 
command LS 43 and the stop confirmation LS 44 are arranged to detect an 
angular position in cooperation with the dogs 45 and 46 which are provided 
on the roller gear cam 20, the range of rotation is relatively wide, so 
that it is possible to effect accurate positioning even if the arrangement 
is somewhat rough. 
A turret index switch (start button) 47 is used when the controller 41 is 
set in the manual operation mode. When the turret index switch 47 is 
pressed in the manual operation mode, a signal 7' is delivered therefrom 
to the controller 41. In response to the signal 7', the controller 41 
delivers a signal 3' to the tool post control unit 42 to cause the 
indexing motor 26 to rotate. A door position confirmation LS 48 is 
provided to detect whether or not a door 62 (described later) is closed. 
The controller 41, when in the manual operation mode, receives a signal 8' 
from the door position confirmation LS 48 and delivers a signal 3' to 
control the indexing motor 26 such that the motor 26 is decelerated or 
rotated at a speed in the steady state, as described later. 
FIG. 4(b) is a functional block diagram schematically showing the 
arrangement of the controller 41. When the T code command 1' is issued 
from the NC unit 40, the command 1' is subjected to arithmetic processing 
in an arithmetic processing circuit 50. Then, it is determines in a 
forward/reverse judging circuit 51 whether the indexing motor 26 is to be 
rotated forward or backward to reach a desired turret face through the 
shorter distance. An indexing condition judging circuit 52 determines with 
a sensor (not shown) or the like whether or not there is an obstruction to 
the rotation of the turret. More specifically, the circuit 52 determines 
whether or not mechanical conditions are appropriate, e.g., as to whether 
or not there is an obstruction to the rotation of the turret shaft 3. If 
the mechanical conditions are determined to be satisfactory, an indexing 
start circuit 53 is activated to give a command to a motor rotation 
command circuit 54. 
In response to this command, the motor rotation command circuit 54 
instructs the tool post control unit 42 to rotate the indexing motor 26 
forward or backward. On the other hand, the door position confirmation LS 
48 confirms that the door is closed and transmits a signal to a low/high 
speed judging circuit 55. The circuit 55 determines whether the indexing 
motor 26 for the turret tool post 1 is to be rotated at high or low speed. 
The judging circuit 55 is being supplied with a signal indicating that the 
apparatus is set in the manual or automatic operation mode from the NC 
unit 40. When the door is determined to be open in the manual operation 
mode, the indexing motor 26 is decelerated, as described later. The signal 
from the stop confirmation LS 44 is transmitted to a present position 
counter 57 to effect counting for making a determination as to which 
turret face is presently indexed. A stop control circuit 56 is supplied 
with signals delivered respectively from the low/high speed judging 
circuit 55, the present position counter 57 and the stop command LS 43 to 
control suspension of the indexing motor 26. When the operation instructed 
by the T code command is completed, the stop control circuit 56 delivers 
an operation completion signal to the NC unit 40. 
FIG. 6 is a front view of an NC lathe 60. A machine cover 61 which covers 
the whole NC lathe 60 is made of a metallic plate material. In this 
example, the left-hand portion of the machine cover 61 (as viewed in the 
figure) mainly covers the spindle portion of the NC lathe 60, while the 
right-hand portion of the machine cover 61 mainly covers the turret tool 
post. A door 62 is provided in the substantially central portion of the 
machine cover 61 such that the door 62 can be opened and closed as 
desired. The door 62 is movable sideward as viewed in FIG. 6. When it is 
necessary to open the door 62, for example, when a workpiece is to be 
attached to or detached from a holding device of the lathe 60, the 
operator moves the door 62 leftward to thereby open it. The door 62 is 
normally kept closed when the machine tool is in operation. 
Wheels 63 are rotatably attached to the lower end of the door 62. The 
wheels 63 roll on a rail 64 which is provided on the inner surface of the 
bottom of the machine cover 61. A rectangular window member 65 is attached 
to the upper part of the door 62 through a known fixing means such as a 
rubber packing. The window member 65 is made of a transparent synthetic 
resin material that is resistant to heated cuttings which may collide with 
it. A handle 66 is secured to one end of the door 62 so that the operator 
grips the handle 66 to open or close the door 62. The door position 
confirmation LS 48 is provided at an appropriate position on the door 62 
to detect whether or not the door 62 is closed. 
A control panel 70 of the NC unit 40 is secured to the right upper portion 
of the front side of the machine cover 61. 
Operation Flow of Turret Tool Post 
FIG. 7 is a time chart showing the operation of the indexing motor 26, the 
roller gear cam 20 and the stop command LS 43. The indexing motor 26 and 
the roller gear cam 20, which are directly coupled together through the 
timing belt 25, are activated simultaneously. The reference symbol t.sub.M 
denotes the point of time at which the power supply to the indexing motor 
26 is cut off. The reference symbol t.sub.B denotes the point of time at 
which the roller gear cam 20 comes to rest after the power supply to the 
motor 26 has been cut off. Normally, the roller gear cam 20 does not 
suspend immediately because of a delay determined by time constants 
involving the inertia acting on the rotor of the indexing motor 26 and the 
inertia acting on the roller gear cam 20. The point of time t.sub.A (i.e., 
point A of dog 45) at which the output of a stop command signal is started 
is coincident with the point of time at which the command from the stop 
command LS 43 terminates. 
The time .vertline.t.sub.M -t.sub.A .vertline. corresponds to a lag in 
processing from the instant a stop command is received until the power 
supply to the indexing motor 26 is cut off. The time .vertline.t.sub.B 
-t.sub.M .vertline. is a period of time (determined by time constants) 
from the instant the power supply to the indexing motor 26 is cut off 
until the motor 26 has come to rest. When the time .vertline.t.sub.B 
-t.sub.A .vertline. has elasped after the point A shown in FIG. 5 has 
passed the stop command LS 43, the roller gear cam 20 comes to rest at the 
point of time t.sub.B. The arrangement is such that the roller gear cam 20 
comes to rest when a pair of cam followers 8 are in contact with the 
straight portion 30 of the roller gear cam 20, as shown in FIG. 3. The 
mechanism should be designed so that the speed of rotation of the roller 
gear cam 20 is increased to the maximum level of the driving capacity of 
the indexing motor 26 by taking into consideration each of the 
above-described time constants through experiments or calculation. 
Indexing Operation of Turret Tool Post 1 
FIGS. 8 and 9 are flowcharts showing the operation of the turret tool post 
1. The process is started in Step P.sub.1. It is determined in Step 
P.sub.2 whether or not the machine is set in the automatic operation mode. 
The process will be explained below in regard to the automatic cycle. It 
is determined in Step P.sub.3 whether or not a T code command signal 1', 
that is, a command given to effect indexing of the turret tool post 1, has 
been issued from the NC unit 40. If NO, the process ends. 
This end, however, does not mean suspension of the control operation, but 
the process returns to Step P.sub.1 to repeat the sequence. If YES is the 
answer in Step P.sub.3, the process proceeds to Step P.sub.4 where it is 
determined whether or not the command is coincident with the present 
value, that is, whether or not a face which is instructed to be indexed is 
coincident with the presently indexed face. If YES, a T function 
completion signal (Step P.sub.23) is delivered and then the process ends. 
If NO is the answer in Step P.sub.4, the process proceeds to Step P.sub.5 
where it is determined whether or not the conditions for rotation of the 
indexing motor 26 are satisfactory. If NO, the process proceeds to Step 
P.sub.17 where an alarm which indicates that there is a tool post indexing 
failure is given and then the machine is suspended (Step P.sub.18). 
If YES is the answer in Step P.sub.5, the process proceeds to Step P.sub.6 
where it is determined whether or not the indexing motor 26 should be 
rotated forward to reach a commanded face through the shorter distance. If 
NO is the answer in Step P.sub.6, the process proceeds to Step P.sub.11 
where the motor 26 is rotated backward. Next, the process proceeds to Step 
P.sub.12 where it is determined whether or not the stop confirmation LS 44 
is ON, that is, whether or not the turret has been indexed to a 
predetermined position at a predetermined angle. If YES, the face number 
is counted in Step P.sub.13. It is determined in Step P.sub.14 whether or 
not the presently indexed face is coincident with the desired face, that 
is, the face instructed to be indexed by the T code command. If NO is the 
answer in Step P.sub.14, the process returns to Step P.sub.11 and the 
sequence is repeated in the same way as the above until the face that is 
presently indexed is determined to be coincident with the desired one. 
If YES is the answer in Step P.sub.6, the process proceeds to Step P.sub.7 
where the indexing motor 26 is rotated forward, and the process then 
proceeds to Step P.sub.8 where it is determined whether or not the stop 
confirmation LS 44 is ON. If NO, the indexing motor 26 is continued to 
rotate forward. If YES is the answer in Step P.sub.8, the process proceeds 
to Step P.sub.9 where the face number is counted, and the process then 
proceeds to Step P.sub.10 where it is determined whether or not the face 
that is presently indexed is coincident with the desired one. If NO is the 
answer in Step P.sub.10, the process returns to Step P.sub.7 to repeat the 
above-described sequence until the face that is presently indexed is 
determined to be coincident with the desired one. When it is determined in 
Step P.sub.10 or P.sub.14 that the desired face has been indexed, the 
process proceeds to Step P.sub.15 where it is determined whether the stop 
command LS 43 is ON or OFF. 
If the stop command LS 43 is determined to be OFF, a turret stop command is 
issued to suspend the indexing motor 26 in Step P.sub.20. It is then 
determined in Step P.sub.21 whether the stop confirmation LS 44 is ON or 
OFF. If it is determined that the LS 44 is OFF, that is, the turret has 
been indexed to a predetermined position, the process proceeds to Step 
P.sub.22. If NO is the answer in Step P.sub.21, the process proceeds to 
Step P.sub.17 where the machine gives an alarm and then comes to rest. If 
YES is the answer in Step P.sub.21, the process proceeds to Step P.sub.22 
where it is determined whether or not the machine is set in the automatic 
operation mode. If YES, the process proceeds to Step P.sub.23 where a T 
function completion signal is delivered and then the process ends. If NO 
is the answer in Step P.sub.22, the process ends because the machine is 
set in the manual operation mode. 
Control Operation Conducted When Door is Opened 
If the door 62 is determined to be closed in Step P.sub.16, it is then 
determined in Step P.sub.30 whether or not the turret index switch 47 is 
ON. If YES, the controller 41 issues a command to the indexing motor 26 so 
that it is rotated forward (Step P.sub.31). Next, when the stop 
confirmation LS 44 is activated (Step P.sub.32), a stop confirmation 
signal is delivered to the controller 41. 
If the door 62 is determined to be open in Step P.sub.16, the flow F (see 
FIG. 9) is executed. More specifically, the indexing motor 26 is 
decelerated in Step P.sub.34. When the turret index switch 47 is turned on 
(Step P.sub.35), the indexing motor 26 starts to rotate forward (Step 
P.sub.26). Next, it is determined whether the stop confirmation LS 44 is 
OFF or ON (Step P.sub.37). If the LS 44 is determined to be ON, the count 
of the face number is incremented by one in Step P.sub.38 because the 
rotation of the motor 26 is forward. As long as the turret index switch 47 
is ON, the sequence from Step P.sub.36 to Step P.sub.38 is repeated. 
During this period of time, the operator indexes each particular turret 
face equipped with a desired tool from necessity of, for example, setting 
up the turret tool post 1. Since the indexing operation is conducted at a 
lower speed than in the case of normal machining process by the command 
issued in Step P.sub.34, the operator can conduct a setup operation with 
safety. 
If the turret index switch 47 is not pressed any more, the process proceeds 
to Step P.sub.39 where it is determined whether or not the stop 
confirmation LS 44 is OFF. If YES, it is determined that the desired 
turret face has been indexed and therefore the indexing motor 26 is 
suspended immediately (Step P.sub.40). Then, the process ends. 
Other Embodiments 
Although in the foregoing the indexing mechanism employs a roller gear cam 
and cam followers, the present invention is not necessarily limitative 
thereto. It is also possible to employ any other similar cam mechanism 
which is arranged such that no looseness is produced between the cam and 
the cam followers, as described above. The door position confirmation LS 
48 which is employed to confirm that the door 62 is closed may be replaced 
with other known detecting means such as photoelectric, magnetic or 
ultrasonic sensor means. 
Although the present invention has been described through specific terms, 
it should be noted here that the described embodiments are not necessarily 
exclusive and that various changes and modifications may be imparted 
thereto without departing from the scope of the invention which is limited 
solely by the appended claims.