Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2002-10-01
2004-06-29
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S183000, C318S568110
Reexamination Certificate
active
06757581
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an offset apparatus for an NC machine tool, and more particularly to an offset apparatus for offsetting the amount of operation of a motion mechanism in accordance with the result of performance analysis of the NC machine tool.
2. Description of the Prior Art
Operation of an NC machine tool is controlled by a numerical controller provided for the NC machine tool. More specifically, the numerical controller sequentially analyzes an NC program and generates operation command signals for spindle motor, servo motor of feed system, etc. and, based on the thus generated operation command signals, the spindle motor, feed system servo motor, etc. are controlled for operation.
Here, the condition of the NC machine tool is not constant at all times but varies from moment to moment according to its operation condition. For example, the cutting edge of the tool wears due to machining, and the machining accuracy gradually degrades. Therefore, to ensure proper machining accuracy, it is commonly practiced to offset the amount of operation of the feed system servo motor by the amount of wear.
Further, the bearing for supporting the spindle generates heat during its rotation due to the friction between the rolling element and bearing ring, and the generated frictional heat is transmitted to the spindle, causing the temperature of the spindle to rise and deforming the spindle due to the thermal expansion caused by the temperature rise. As a result, the relative positional relationship between the tool and work changes, resulting in a machining error. In view of this, it is commonly practiced to measure the spindle temperature by a temperature sensor, estimate the amount of thermal deformation of the spindle from the measured spindle temperature and, based on the estimated amount of thermal deformation, offset the amount of operation of the feed system servo motor so as to compensate for the thermal deformation.
Likewise, the bearing for supporting the feed screw in the feed system also generates heat during its rotation due to the friction between the rolling element and bearing ring, and the generated frictional heat is transmitted to the feed screw, causing the temperature of the feed screw to rise and deforming the feed screw due to the thermal expansion caused by the temperature rise. As a result, the positioning accuracy of the feed system degrades, resulting in a machining error. In view of this, it is commonly practiced to detect the thermal deformation of the feed screw by a displacement sensor and, based on the detected amount of thermal deformation, offset the amount of operation of the feed system servo motor so as to compensate for the thermal deformation.
However, the heat generated at the above bearings is transmitted not only to the spindle and the feed screw but, via these parts, to the entire structure such as the bed, headstock, spindle head, saddle, and column that constitute the machine tool, and thus the entire structure suffers thermal deformation, causing the relative positional relationship between the tool and work to change and resulting in a machining error. Therefore, to achieve high accuracy machining, not only must offsets be applied for the deformations of the spindle and the feed screw caused by the temperature rise of the bearings, but the thermal deformation of the entire structure must also be analyzed so that offset appropriate to the thermal deformation can be applied. In the prior art, however, such advanced offset has not been performed.
Further, the machine tool generates vibrations during machining, and if the frequency is close to the natural frequency of the machine tool, the machine tool resonates, and the effects of the vibrations are transferred to the machined surfaces, degrading the machining accuracy and the quality of the machined surfaces. Accordingly, to achieve high accuracy, high quality machining, it is preferable that both the frequency during machining and the natural frequency of the machine tool be analyzed and the rotational speed and/or feed speed of the tool and work be offset so as to prevent the above frequencies from coming close to each other.
The present invention has been devised in view of the above situation, and it is an object of the invention to provide an offset apparatus for an NC machine tool, that can achieve high accuracy, high quality machining by analyzing the behavior of the NC machine tool (the performance of the machine tool motion mechanism) and by offsetting the amount of operation of the motion mechanism in accordance with the result of the analysis.
SUMMARY OF THE INVENTION
The present invention which achieves the above object concerns an NC machine tool offset apparatus that is provided for an NC machine tool equipped with a numerical controller for controlling operation of a motion mechanism in accordance with an operation command signal, and that offsets the amount of operation of the motion mechanism which is driven and controlled in accordance with the operation command signal, comprising:
analysis data storing means for storing three dimensional model data of the motion mechanism and condition data for performance analysis;
analyzing means for analyzing the performance of the motion mechanism, based on the operation command signal in the numerical controller and on the three dimensional model data of the motion mechanism and the condition data for performance analysis stored in the analysis data storing means;
data accumulating means for storing performance analysis data analyzed by the analyzing means;
offset amount computing means for computing, from the performance analysis data stored in the data accumulating means, the amount of offset to be applied to a commanded operation amount directed by the operation command signal; and
offset executing means for offsetting the amount of operation of the motion mechanism, based on the amount of offset computed by the offset amount computing means.
The motion mechanism in the present invention collectively refers to the mechanisms constituting the machine tool excluding the controller, and includes: structures such as a bed, table, spindle, headstock or spindle head, saddle, and column; a feed mechanism comprising a feed screw, nut, feed motor, etc.; a spindle motor; and peripheral devices such as a tool changer and a pallet changer.
According to this offset apparatus, first the analyzing means analyzes the performance of the motion mechanism, based on the operation command signal in the numerical controller and on the three dimensional model data of the motion mechanism and the condition data for performance analysis stored in the analysis data storing means, and the analyzed performance analysis data is stored in the data accumulating means. Next, the offset amount computing means computes, from the performance analysis data stored in the data accumulating means, the amount of offset to be applied to the commanded operation amount directed by the operation command signal; then, based on the amount of offset computed by the offset amount computing means, the offset executing means offsets the amount of operation of the motion mechanism. Here, a technique such as a finite element method or boundary element method is used as the technique for analysis.
Examples of the performance of the motion mechanism include, besides the deformation of the motion mechanism due to load, the natural frequency of the motion mechanism itself and vibrations caused by machining, but the performance is not limited to these factors. Examples of the load include, besides the thermal load from a heat generating source such as a bearing and the machining load due to machining, a varying load the acting point of whose own weight varies due to the movement of a movable body such as a saddle, table, or column.
In this way, when offsetting for the deformation of the motion mechanism due to thermal load, for example, first the amount of heat generated by heat generating sources, such as the spindle suppo
Akamatsu Yoshiaki
Fujishima Makoto
Bahta Kidest
Mori Seiki Co. Ltd.
Westerman Hattori Daniels & Adrian LLP
LandOfFree
Offset apparatus for NC 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 Offset apparatus for NC machine tool, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Offset apparatus for NC machine tool will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3341598