Gear cutting – milling – or planing – Milling – Process
Reexamination Certificate
1999-09-30
2001-05-22
Briggs, William (Department: 3722)
Gear cutting, milling, or planing
Milling
Process
C409S135000, C700S159000, C700S173000
Reexamination Certificate
active
06234730
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a thermal change computation apparatus for use with a machine tool, for computing amount of thermal change that is generated on the machine tool.
2. Description of Related Art
Machine tools include generally a machining mechanism for cutting or drilling a workpiece and assembling product component parts on a base plate, and a driving mechanism for changing a relative position between the machining mechanism and a workpiece. In general, machine tools for cutting a workpiece or the like include a holding mechanism for holding tools such as drills and taps, a main driving mechanism for rotating tools held on the holding mechanism, an X-axis feed mechanism for feeding tools in the X-axis direction, a Y-axis feed mechanism for feeding tools in the Y-axis direction, a Z-axis feed mechanism for feeding tools in the Z-axis direction, and an electronic control apparatus for controlling these feed mechanisms.
For example, as shown in
FIG. 13
, a machine tool is covered with a splash guard
100
for preventing cut wastes from splashing. In the inside of the splash guard
100
, there are disposed a table
101
for holding a workpiece (not shown), an automatic tool change (ATC) magazine
102
for changing tools, such as drills and taps, and a machine tool body
103
. The splash guard
100
provides a control panel
104
, a work change opening
105
for loading or ejecting a workpiece and an inspection hatch
106
used mainly for maintenance.
As shown in
FIG. 14
, the body
103
includes a main shaft
107
for holding tools such as drills and taps, a main shaft motor
108
for rotating the main shaft
107
, a ball thread mechanism
109
which comprises a nut
109
a
housing a number of steel balls and which is fixed to the main shaft side and a ball thread
109
b
inserted into and engaged with the nut
109
a
, a Z-axis motor
110
for rotating the ball thread
109
b
, a guide rail
111
disposed in parallel with the ball thread
109
b
, a slide
112
for coupling the guide rail
40
and the main shaft
28
(not shown).
In this body
103
, the ball thread mechanism
109
and the Z-axis motor
110
constitute the Z-axis feed mechanism for feeding the main shaft
107
in the Z-axis direction. When the Z-axis motor
110
rotates the ball thread
109
b
, the main shaft
107
is moved in the Z-axis direction. Moreover, the table
101
may be moved in the X-axis direction and Y-axis direction. As the main shaft
107
may be moved in the Z-axis direction, relative positions among a workpiece and tools in the X-axis, Y-axis and Z-axis directions may be changed.
In this type of machine tool, as the ball thread mechanism
109
is operated, a frictional heat is generated and the ball thread
109
b
expands. Also in other mechanisms, a thermal change occurs due to the heat thus generated. When such thermal change occurs in the Z-axis direction, for example, an error occurs in a depth of flute and a height of stepped portion formed on a workpiece. If a dimensional tolerance of the workpiece is sufficiently larger than a thermal change amount, then a machining error caused by such thermal change is negligible. If not, such a thermal change should be corrected.
Therefore, there is provided a thermal change computation apparatus for computing a thermal change amount of a machine tool in Japanese laid-open Patent Publication No. 62-88548. In this computation apparatus, when a drive mechanism is controlled in accordance with a predetermined work program, a machining error is corrected in response to the computed thermal change amount.
However, in this machine tool thermal change computation apparatus, since the thermal change amount is continuously computed while the machine tool is operated, a system for executing such computation processing should be operated constantly as well, resulting in an increase in the computation processing load.
In view of the fact that a heat generated amount and a heat radiated amount are placed in the equilibrium state as the temperature rises while a machine tool is continuously operated, a method of computing a thermal change amount was proposed in Japanese laid-open Patent Publication No. 10-143217.
That is, during a period in which the machine tool is operated, a thermal change amount at each timing point is computed based on a saturated thermal change amount (thermal change amount in the equilibrium state) and a machine tool driving time. When the computed thermal change amount becomes nearly equal to the saturated thermal change amount, the value of the saturated thermal change amount will be used as the thermal change amount. In this case, if an accurate saturated thermal change amount is given, a thermal change amount at each timing point may be computed, thus reducing a computation processing load.
However, in the above thermal change computation apparatus, a saturated thermal change amount is fixed. When the machine tool operating program, which includes a step for driving a machine tool at a high speed and a step for driving a machine tool at a low speed, is executed in the apparatus, the thermal change amount computation accuracy is slightly lowered. Since the saturated thermal change amount is fixed relative to an average driving speed, it is unavoidable that the above computation method computes the thermal change amount as a smaller thermal change amount in the step of driving a machine tool at a high speed, and computes the thermal change amount as a larger thermal change amount in the step of driving a machine tool at a low speed.
SUMMARY OF THE INVENTION
The invention proposes a thermal change computation apparatus that can compute an accurate thermal change amount in accordance with a driving state at every moment of the operation of a machine tool. In the machine tool, an increase-decrease characteristic of the thermal change amount generated in the driving mechanism of the machine tool, a characteristic of a saturated thermal change amount in accordance with the driving condition of the driving method (a characteristic of the maximum thermal change amount), and a holding time where a thermal change substantially remains, are preset. Based on the preset characteristics, holding time and the state of the driving mechanism, the thermal change amount at every moment the driving mechanism operates, is computed in consideration of past thermal change amount, thus the thermal change amount is corrected.
In the case where a thermal change amount computation program common in a plurality of machine tools is installed on the machine tool, if an average holding time common in the machine tools is set, it is expected that problems will occurs, as set forth below.
For a small-sized machine tool, the influence of a thermal change amount disappears in a relatively short time, but a great deal of memory is needed for the thermal change amount computation because a longer holding time is set. On the other hand, for a large-sized machine tool, the influence of a thermal change amount remains relatively long, so that the thermal change amount computation accuracy is lowered because a shorter holding time is set.
Therefore, one aspect of the invention is to provide a thermal change computation apparatus that can set a holding time suitable for a machine tool to be used and compute an accurate thermal change amount at every driving state of the machine tool, a thermal change amount computation method, and a computer-readable memory medium that stores a thermal change amount computation programs.
The thermal change computation apparatus of the invention is to be used with a machine tool that includes a machining mechanism for machining a workpiece and a driving mechanism for changing a relative position between the machining mechanism and the workpiece. The thermal change computation apparatus comprises a driving state detecting unit for detecting a driving state of the machine tool; a holding time computing unit for computing a holding time where a thermal change substantially remains; a change amoun
Briggs William
Brother Industries Ltd.
Oliff & Berridg,e PLC
LandOfFree
Thermal change computation apparatus for machine tool does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thermal change computation apparatus for machine tool, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermal change computation apparatus for machine tool will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2490512