High-frequency motor incorporating tool drawing-up device therein

This invention is characterized by that the high-frequency motor is adapted to provide the tapered surface engagements in both engaging parts between a draw bar set in a rotary shaft of the motor and a slit hook engaged with the draw bar, and between this hook and a holder for the hook, and to reverse mutually the inclined directions of these tapered surfaces so as to obtain a large clamp force.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to a high-frequency motor incorporating a tool 
drawing-up device therein. 
(2) Description of the Prior Art 
In the machine tool, a high-frequency motor is used as a main shaft, then a 
tool is inserted in a rotary shaft of the high-frequency motor. The tool 
is drawn to be secured to the tip end of the rotary shaft by means of a 
tool drawing-up device. However, this depends upon the drawing-up force of 
the spring in the past, so that when the stronger load than the spring 
force is applied to the tool, it is slipped to cause the so-called 
fretting phenomenon. 
This phenomenon may be prevented if the powerful spring is mounted in the 
high-frequency motor, however the result has defects that the 
high-frequency motor becomes large-sized and expensive construction. 
SUMMARY OF THE INVENTION 
This invention is intended to resolve the defects of the above conventional 
example and summarizes a high-frequency motor incorporating a tool 
drawing-up device therein which can increase the clamping force for the 
tool without increasing the spring force and provide a simple and 
inexpensive construction. Namely, this invention is characterized by that 
the high-frequency motor is adapted to define tapered surface engagements 
in both engaging parts between a draw bar set in the rotary shaft and a 
slit hook engaged with the draw bar, and between this slit hook and a 
holder for the hook, and to reverse mutually the inclined directions of 
these tapered surfaces thereby to provide a large clamp force.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
This invention is illustrated in detail with the embodiment shown in 
drawings; FIG. 1 shows a high-frequency motor according to this invention 
which comprises a rotary shaft B retained in a case body A, a rotor C 
attached to the periphery of the rotary shaft and a stator D attached in 
the case body A in accordance with this rotor. The above rotary shaft B is 
provided with a tool inserting part 1 in the tip end thereof and with a 
tool drawing-up device therein as shown in FIG. 2. 2 is a tool, of which a 
pull stud part 2a is engaged with a first hook 3. The first hook 3 may be 
slidden by a first draw bar 4 to insert and remove the tool 2 against the 
tool inserting part 1. 5 is a holder fixed in the rotary shaft B, in which 
a second hook 6 is movably set and which is provided with a backwardly 
spread taper surface 5a in the back end thereof. The second hook 6 is slit 
and divided to three parts as well as the above first hook 3, and the tip 
end 6a of the second hook is engaged with a pull stud part 4a on a back 
end of the above first draw bar 4. The back end portion of the second hook 
6 is provided on the periphery with a first tapered surface 6b which is 
engaged with a tapered surface 5a of the above holder 5. The inner surface 
of the second hook 6 is provided with a second tapered surface 6c reduced 
backwardly. 7 is a second draw bar, a tip end of which is inserted in the 
second hook 6 and provided with a tapered surface 7a which is engaged with 
the above second tapered surface 6c. A spring receiving member 9 is 
secured through a nut 8 to the back end portion of the second draw bar and 
a drawing-up spring 11 is disposed between the spring receiving member and 
an auxiliary holder 10. The auxiliary holder 10 is provided with pawl 
pieces 10a projected toward the front side thereof, as shown in FIG. 5. 
The tip ends of the pawl pieces are engaged with notches 5b formed in the 
back end edge of the above holder 5 to provide a stop reinforcing action 
against the rotation of the holder. 
This invention is constituted as stated above, so that when the tool 2 is 
drawn up by the spring 11, the tapered surface 7a of the second draw bar 7 
is contacted with the second tapered surface 6c of the second hook 6 and 
the tapered surface 5a of the holder 5 is also contacted with the first 
tapered surface 6b of the second hook 6 as shown detailedly in FIG. 4. 
Accordingly, the back end of the second hook 6 is spreadly opened and 
pushed on along the tapered surface 5a of the holder 5, whereby a clamp 
force N for strongly clamping the pull stud part 4a of the first draw bar 
4 is applied to the second hook 6, so that the tool 2 may be firmly 
secured through this first draw bar 4 and the first hook 3 to the 
inserting part 1. Then, the clamp force N is represented by the following 
equation (1); 
EQU N=F/tan .lambda. (1) 
wherein F is a drawing-up force of the spring and .lambda. is an inclined 
angle of the second tapered surface of the second hook. 
Therefore, a large clamp force N may be obtained under a constant spring 
drawing-up force F by setting the inclined angle .lambda. of the tapered 
surface at the proper values. 
When the inclined angle .lambda. of the tapered surface is also set to 
satisfy the following equation (2), the tool is self-locked to provide the 
same effects as the tool is drawn up by a screw means. 
EQU tan .lambda..ltoreq.tan .rho. (2) 
wherein .rho. is a friction angle between the tapered surface of the second 
draw bar and the tapered surface of the second hook. 
To remove the tool 2 from the high-frequency motor, the back end of the 
second draw bar 7 is pushed against the spring 11 by a press means 12 such 
as a cylinder shown in FIG. 2. Namely, when the second draw bar 7 is 
pushed on by the cylinder 12, it is disengaged from the tapered surface of 
the second hook 6 and advanced forwardly to press the first draw bar 4, 
whereby the first hook 3 is pushed to open the front engaging part so as 
to be disengaged from the pull stud part 2a of the tool 2. The second hook 
6 is also slidden in the holder 5 to open the front engaging part. This 
operation is carried out mainly when the tool 2 is exchanged for, and to 
attach again the tool to the rotary shaft, the tool is inserted into the 
tool inserting part 1 to return the above press means 12 to the original 
position. Accordingly, the tool is drawn up with a repelling force of the 
spring 11, so that the tool may be certainly secured to the rotary shaft 
in the above operation. 
As stated above, this invention is intended to incorporate a powerful tool 
drawing-up device in the rotary shaft of the high frequency motor so as to 
provide excellent effects that the tool may be firmly held in the rotary 
shaft to prevent the fretting phenomenon completely, to assure the high 
processing precision, and to prevent the breakage of the tool previously. 
According to this invention, the clamp force of the tool may be increased 
without increasing the spring force, so that it is able to provide 
inexpensively the high-frequency motor having a miniatured and compact 
construction and a powerful tool holding function.