Machine tool

Details Machine tool Machine tool

2001-10-02

2003-09-09

Wellington, A. L. (Department: 3722)

Turning

Lathe

With program control

C082S133000, C409S147000

Reexamination Certificate

active

06615697

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a machine tool like a lathe and a grinding machine and so on.
BACKGROUND OF THE INVENTION
In general, with regard to a machine tool like a lathe as shown in
FIG. 7
, in case that the feed control of a tool base
51
is carried out by a control unit
50
like NC units, the semi-closed loop control using the feedback signal F/B which is obtained from an encoder
53
of a servomotor
52
is adopted. The drive of the servomotor
52
is transmitted to the tool base
51
through a ball screw
56
.
It is usually the case that a mechanical origin (O
m
) in the control unit
50
is set to position the location where the tool base
51
is the most far from a headstock
54
.
FIG. 8
shows the mechanical origin (O
m
) that is the origin in the coordinate of the feedback signal F/B by the encoder
53
.
However, the thermal expansion is generated in the ball screw
56
as the cutting heat by the process and the other part heat by the machine operation is generated. Therefore, the semi-closed loop control has a substantial margin of error. In other words, a process origin (O
w
) as shown in
FIG. 8
is the center of a work (W) which is gripped by a spindle
55
(
FIG. 7
) and is positioned far from the mechanical origin (O
m
) that is the origin of the feedback signal F/B, so that the substantial margin of error comes out even if the feedback control is carried out, if there are the thermal expansion of the ball screw
56
and the mechanical deformation. The high accuracy amendment is difficult though the thermal expansion is amended, so that there is a limit to improve the process accuracy.
In order to improve the process accuracy, the closed loop control is also adopted by providing a linear sensor
57
as shown in the dash-dot line in FIG.
7
. The linear sensor
57
is attached along the slide surface of the machine, for example a guide of the tool base (not shown in the drawings) in a bed
58
. According to this, the position of the tool base
51
can be detected directly without acting on the thermal expansion of the ball screw
56
.
However, as shown in the same drawings with emphasizing the displacement, in case of the disturbance like the minute lean in the headstock
54
, the error becomes big even by the closed loop control in the same drawings. The above-mentioned disturbance is difficult to be amended by the control as it happens by the cutting heat, the load condition and the surroundings and the like, and the displacement is not fixed.
It is an object of the present invention to provide a machine tool that the process accuracy does not deteriorate even if the accuracy of the machine itself changes to some extent.
It is another object of the present invention that the high accuracy process mentioned above is carried out in a simple structure.


REFERENCES:
patent: 3571834 (1971-03-01), Mathias
patent: 3600987 (1971-08-01), Kvasnicka
patent: 4014227 (1977-03-01), Adams
patent: 4354404 (1982-10-01), Ramusino
patent: 4451892 (1984-05-01), McMurtry
patent: 4608747 (1986-09-01), Link et al.
patent: 4664566 (1987-05-01), Peddinghaus
patent: 4784541 (1988-11-01), Umehara et al.
patent: 6038489 (2000-03-01), Pickles et al.
patent: 2002/0066201 (2002-06-01), Boge et al.

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