Measuring and testing – Frictional resistance – coefficient or characteristics
Reexamination Certificate
1998-08-03
2001-04-10
Kwok, Helen (Department: 2856)
Measuring and testing
Frictional resistance, coefficient or characteristics
C073S862680
Reexamination Certificate
active
06212935
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a main-shaft malfunction-state detector in an air bearing type machine tool, using for detecting an abnormal contact of a main shaft in a machine tool for a cutting process of a relatively heavy load in which the main shaft is supported in an air static-pressure bearing, and so on.
2. Description of the Related Art
Conventionally, a machine tool is used for, for example, cutting various metallic materials.
The machine tool has a cutting tool attached at an end of a main shaft rotatably supported, in which the tool is rotated by rotatably driving the main shaft with a shaft driving motor, thereby performing a cutting process for a work piece.
Support for the Main Shaft
The conventional machine tool uses various bearings for rotatably supporting the main shaft.
For example, an air static-pressure bearing is used for the machine tool for carrying out a ultra-precise cutting process for the cutting light load (e.g., in the case of a mirror finish of light-metal material by using diamond bit).
In the aforementioned process, it has been difficult to produce deformation of the main shaft because of the light load, and there is little possibility that the main shaft will be in contact with the housing.
As to the Air Bearing
The air bearing is, conventionally, used for only process for the light load, however, the present applicant proposes the air bearing type machine tool which is capable of being used for the heavy load by enlarging a bearing clearance (see Japanese Patent Application Laid-open No. Hei 8-70219).
Here, where the air bearing type machine tool is used in the process for the high load, the deformation of the main shaft caused by the load occurs easily, so that attention to the abnormal contact of the main shaft is required.
Further, in the normal cutting process, there is the potential that the process is carried out under conditions exceeding the forecast made in the design.
For example, in the process where the tool attached at the main shaft is projected more than usual, a large moment is acted to the bearing portion. Generally, in the air bearing, the main shaft should not be in contact with the bearing portion of the housing, but an abnormal contact is produced when the degree of the deformation of the main shaft, caused by the moment, exceeds the space between the bearing and the main shaft.
If the operation continues while the abnormal contact of the air bearing described above remains, the disadvantage is that a seizure is produced resulting in a break.
In order to avoid the break, it is required the main shaft is immediately stopped to stop the process when the aforementioned abnormal contact is produced.
In order to avoid breaking, it is required that the process is immediately stopped by stopping the main shaft when the aforementioned abnormal contact is produced. The detection of the abnormal contact, conventionally, depends on the alertness of an operator, resulting in disadvantages concerning operating efficiencies, a delay in the detection, and so on.
It is an object of the present invention to provide the main-shaft malfunction-state detector for the air bearing type machine tool, in which an abnormal contact of the main shaft with the housing is reliably and automatically detected.
SUMMARY OF THE INVENTION
The present invention is a main-shaft malfunction-state detector in an air bearing type machine tool, detecting an abnormal contact of a main shaft with a housing by providing in the machine tool in which the main shaft is supported in the housing with an air bearing, which is characterized by including: contact detection means for detecting and outputting an electrical and mechanical contacting state of the main shaft and the housing; and contact decision means for determining the contact of the main shaft with the housing by using an output signal sent from the contact detection means.
In the present invention described above, the contact detection means detects and outputs the electrical and mechanical contacting state of the main shaft and the housing. The contact decision means determines the contact of the main shaft with the housing based on the output signal sent from the contact detection means. Thus automatic and certain preventative measure, such as the main shaft of the machine tool stops and so on, are based on the above decision.
More specifically, the following structures can be employed.
In the machine tool in which the housing is electrically insulated from a main body of the machine tool, the contact detection means detects electric conductivity between the housing and the main body of the machine tool; and the contact decision means determines the contact when the electric conductivity exceeds a predetermined threshold value.
The aforementioned structure shows the main shaft is in an electric conductive state with the main body of the machine tool through a tool and a processed work piece, thereby allowing the contact detection means to detect the electric conductivity resulted from the contact of the main shaft with the housing. The contact detection means detects the conductivity between the main shaft and the housing, and then, the contact decision means checks current or the like caused by the conductivity, with the result that the presence of the contact is determined.
The detection or the decision is the decision for the electric conductivity caused by the contact, so that the reliable contact decision can be carried out.
The contact detection means is an AE sensor detecting acoustic emission created in the housing; and the contact decision means determines the contact when the output signal sent from the AE sensor exceeds a predetermined threshold value.
The aforementioned structure shows the contact detection means detects the acoustic emission (AE; the phenomenon of high-frequency sound created when distortion energy accumulated in a solid is released with plastic deformation or demolition of the solid) created in the housing by the contact of the main shaft with the housing, and the contact decision means carries out the contact decision.
The machine tool structure is such that the operations can be carried out simply by the AE sensor, or the likes.
The contact detection means is an acceleration vibration meter detecting vibration of the housing; and the contact decision means determines the contact when the output signal sent from the acceleration vibration meter exceeds a predetermined threshold value.
According to the aforementioned structure, vibration created in the housing by the contact of the main shaft with the housing is detected by the contact detection means and the contact decision is carried out by the contact decision means.
The machine tool structure is such that the operations can be carried out simply by the acceleration vibration meter, or the likes.
In the machine tool in which the housing is electrically insulated from the main body of the machine tool, the contact detection means detects electrostatic capacity generated between the housing and the main body of the machine tool; and the contact decision means determines the contact when the electrostatic capacity exceeds a predetermined threshold value.
According to the above structure, the main shaft is in the electrical conductive state with the main body of the machine tool through the tool and the processed work piece. The main shaft and the housing are adjacently opposed to each other to be spaced slightly by the air bearings in a state that the main shaft and the housing are electrically insulated. Thereby electrostatic capacity is generated by using the main shaft and the housing as a pair of electrodes. The generated electrostatic capacity is detected by the contact detection means and changed by the contact of the main shaft with the housing or the other reasons.
Therefore, the contact detection means detects the electrostatic capacity generated between the main shaft and the housing and the contact decision means can carry out the contact decision.
REFERENCES:
Fujie Hideo
Momochi Takeshi
Nagashima Kazuo
Shiozaki Masahito
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kwok Helen
Toshiba Kikai Kabushiki Kaisha
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