Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Reexamination Certificate
2001-02-27
2003-01-07
Donels, Jeffrey (Department: 2837)
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
Reexamination Certificate
active
06504333
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the improvement of a numerical control apparatus employed to control a machine tool, for example.
2. Description of the Related Art
In the prior art, upon working a die or mould having a free-form surface, tool path data are formed by representing approximately the tool path by infinitesimal segments such as a straight line, a circular arc, a curve, etc. when the tool is moved virtually by using the CAD/CAM system so as to come into contact with the free-form surface, and then the cutting is executed by providing such tool path data to the numerically controlled machine tool.
In general, in case the curved surface working is executed by the numerically controlled machine tool, the number of tool path data items formed by the CAD/CAM system is enormous. In particular, in recent working by the high speed cutting, a method is employed so that a surface close to a specular surface can be produced by reducing the working pick feed to be as small as possible and thus the burden of the subsequent polishing step can be reduced or the polishing step can be omitted.
In such working, the working precision must be improved by increasing the number of commands of the infinitesimal segments constituting the tool path data. However, when the number of shape commands of the infinitesimal segments is increased, the tool is stopped at every joint of the shape commands and thus the working efficiency is lowered.
In order to overcome such problem, there is the method disclosed in Patent Application Publication (KOKAI) Hei 7-239708, for example. This method implements working with good efficiency by moving the tool at a maximum speed that does not exceed the allowable speed of the machine, without stopping the tool at every joint of the shape commands.
Also, sometimes correction of the tool diameter is needed on the spot because of tool wear and tool exchange. However, in three-dimensional curved-surface working, it is difficult to correct an offset distance since a surface is often cut by a ball end mill, and therefore an enormous number of tool path data must be calculated again and again by using the CAD/CAM system.
In the numerical control apparatus in the prior art, the tool path data are formed by approximating the tool path by the infinitesimal segments based on mould shape data, and then interpolation points are calculated to instruct the tool positions, by interpolating the segments of the numerical control apparatus. Therefore, it cannot be assured whether the tool can be brought into contact with the curved-surface when the tool is arranged at the interpolation points.
Then, an increase in the number of infinitesimal segments of the tool path data that are formed by the CAD/CAM system and transferred to the numerical control apparatus is limited from the viewpoint of data transfer. Also, if the working speed is increased up to the limit of the allowable speed of the machine, as in Patent Application Publication (KOKAI) Hei 7-239708, the allowable speed must be checked at every joint of the infinitesimal segments and thus the time to check the data processing is increased. Further, since the acceleration/deceleration of the tool is carried out by setting the time constant of the machine constant, the acceleration/deceleration cannot be carried out up to the limit of the allowable acceleration. Thus, since it takes a lot of time to execute the acceleration/deceleration, it is impossible to reduce the working time.
Also, in order to interpolate smoothly the tool path derived by the tool path data and reproduce an accurate comer of an edge, a deceleration area must be estimated based on the information of the infinitesimal segments. Thus, it is impossible to disregard the error caused at the end of the segment as the segments are minimized more and more to get a sufficiently smooth tool path. For this reason, it is impossible to decide which one of a comer portion and a part of a curve is represented by a segment, and thus there is the problem that working quality cannot be improved.
Further, correction of tool diameter is needed on the spot because of tool wear or tool exchange, and thus the enormous number of tool path data items must be calculated each time by the CAD/CAM system. As a result, the operation efficiency is significantly decreased.
In addition, since the worked surface of the working object is not evaluated in itself, it is impossible to improve the working efficiency by increasing the working speed as highly as possible according to the situation of the worked surface itself.
Further, correction of tool diameter is needed on the spot because of tool wear or tool exchange, and thus the enormous number of tool path data items must be calculated each time by the CAD/CAM system. As a result, the operation efficiency is significantly decreased.
SUMMARY OF THE INVENTION
The present invention has been made to overcome above problems, and it is an object of the present invention to provide a numerical control apparatus and a numerically controlling method described as follows.
a. The preparation of tool path data transmitted to the numerical control apparatus from a CAD/CAM system in the prior art can be omitted, and a tool position as a process applying portion position can be decided based on a shape of a worked surface of a working object as a processed surface of a processing object.
b. The appropriate moving speed and the process applying portion position can be quickly decided in response to the shape of the processed surface based on evaluation data obtained by evaluating a shape of the processed surface of the processing object, and thus a processing time can be reduced.
c. An amount of stored data can be reduced by executing evaluation of the processed surface of the processing object and decision of the process applying portion position in real time, and thus an overall data processing time can be shortened.
d. The productivity can be improved according to above features.
In order to achieve the above object, a numerical control apparatus of the present invention comprises evaluating means for forming evaluation data of an evaluation point containing a pointer representing a position of a succeeding clamp point, a path length to the succeeding clamp point, and a passing speed of a process applying portion to be passed through the evaluation point if the evaluation point corresponds to a clamp point, by arranging virtually the process applying portion of a system to be numerically controlled on a given scheduled path locus to come into contact with a processed surface of a processing object and by setting a plurality of evaluation points to evaluate a shape of the processed surface, where the clamp point signifies the evaluation point that is decided based on the shape of the processed surface such that the passing speed of the process applying portion passing through the evaluation point is subjected to restriction; command speed deciding means for deciding a command speed, at which the process applying portion is moved, by calculating a distance from a current process applying portion position to a closest succeeding evaluation point and then deciding necessity of a deceleration based on a path length from the current process applying portion position to the succeeding clamp point, that is calculated by reading the path length to the succeeding clamp point in evaluation data of the closest succeeding evaluation point and then adding such path length to this distance, the passing speed in the evaluation data of the clamp point, that is calculated by employing the pointer in the evaluation data of the closest succeeding evaluation point, and a speed of the current process applying portion; and process applying portion position data forming means for calculating a process applying portion position by arranging virtually the process applying portion to separate from a current process applying portion position by a predetermined distance and to come into contact with the processed surface,
Iriguchi Kenji
Kato Kiyotaka
Takahashi Nobuyuki
Donels Jeffrey
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
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