Gear cutting – milling – or planing – Milling – Process
Reexamination Certificate
1999-04-19
2001-02-20
Briggs, William (Department: 3722)
Gear cutting, milling, or planing
Milling
Process
C318S561000, C340S680000, C409S141000, C451S011000, C700S173000, C700S177000
Reexamination Certificate
active
06190098
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a numerical control system for a machine tool having a feed speed overriding unit and a main spindle rotational speed overriding unit, in particular, to a numerical control system for a machine tool achieving a satisfactory processing in a state controlled by a feed speed overriding unit and a main spindle rotational speed overriding unit.
2. Description of the Related art
When the work is being processed, for example, during a cutting operation, by a machine tool, the cutting blade of the machine tool intermittently abuts the work piece and makes it vibrate.
If the frequency of the vibration of the work piece caused by the blade of the tool is near the resonance frequency of the work piece, the vibration called chattering may be generated which may produce an unsatisfactory machining process.
During a machining process, if the frequency of the vibration of the blade of the tool is near the resonance frequency of the tool, the vibration called chattering may also be generated which may also produce an unsatisfactory machining process. This tends to happen if the tool is long.
In order to prevent the chattering and maintain a satisfactory machining processing, it is required to prevent the vibration of the work piece whose frequency is near the resonance frequency of the machining process or the tool. According to the prior art, this is achieved by decreasing the feed speed and the main spindle rotational speed.
However, the processing time increases if the feed speed and the main spindle rotational speed are decreased during the entire processing. Thus, the feed speed and the main spindle rotational speed are preferably decreased only in some cases out of necessity. A numerical control system is known which comprises a feed speed overriding unit and a main spindle rotational speed overriding unit, as a numerical control system for a machine tool for decreasing the feed speed and the main spindle rotational speed only in some cases depending upon the necessity. In such a control system, the feed speed overriding unit outputs a signal for an overriding control of the feed speed according to an input of a feed speed overriding, and the main spindle rotational speed overriding unit outputs a signal for an overriding control of the main spindle rotational speed according to an input of the main spindle rotational speed overriding.
In the conventional numerical control system as described above, the operator has to manually conduct the input of the feed speed overriding to the feed speed overriding unit and manually conduct the input of the main spindle rotational speed overriding to the main spindle rotational speed overriding unit, while supervising the machining.
For example, the operator conducts overriding inputs in such a manner that the feed speed and the main spindle rotational speed are increased when the machine process starts, and that the feed speed and the main spindle rotational speed are decreased when the resonance occurs and grows during the machine process.
In the overriding inputs, the feed speed and the main spindle rotational speed have to be changed synchronously with each other in order to maintain an even feed of each cutting blade.
However, it is difficult for the operator's manual inputs to change the feed speed and the main spindle rotational speed synchronously with each other, thus, it is difficult to achieve a good processing state. Therefore, the processed surfaces of the work may tend to be uneven. In addition, the operator is over burdened by conducting several manual inputs, so that the operator can only be assigned to work a limited number of machines.
On the other hand, special tools with higher stiffness are available in order to prevent the generation of the chattering. However, the special tools are very expensive.
Therefore, the object of this invention is to provide a numerical control system for a machine tool which can effectively prevent the resonance phenomenon when performing a machining process on a workpiece.
SUMMARY OF THE INVENTION
To achieve the above object, this invention is characterized by the following features. That is, this invention provides a numerical control system for a machine tool comprising: a feed speed setting unit for outputting a signal of a setting feed speed of the machine tool, a feed speed overriding unit for outputting a signal of a feed speed overriding according to an input of the feed speed overriding, a feed speed determining unit connected with the feed speed setting unit and the feed speed overriding unit, for determining a command signal of a feed speed of the machine tool according to the signal of the set feed speed and the signal of the feed speed overriding, a main spindle rotational speed setting unit for outputting a signal of a set main spindle rotational speed of the machine tool, a main spindle rotational speed overriding unit for outputting a signal of a main spindle rotational speed overriding according to an input of the main spindle rotational speed overriding, and a main spindle rotational speed determining unit connected with the main spindle rotational speed setting unit and the main spindle rotational speed overriding unit, for determining a command signal of a main spindle rotational speed of the machine tool according to the signal of the set main spindle rotational speed and the signal of the main spindle rotational speed overriding, wherein the main spindle rotational speed determining unit is connected with the feed speed determining unit, and changes the command signal of the main spindle rotational speed synchronously with the change of the command signal of the feed speed when the command signal of the feed speed is changed at the feed speed determining unit by the signal of the feed speed overriding.
According to the invention, by the main spindle rotational speed determining unit, the command signal of the main spindle rotational speed is changed synchronously with the command signal of the feed speed changed by the signal of the feed speed overriding. Thus, the operator's burden of conducting manual inputs is less than the conventional method. In addition, this invention can achieve an improved processing state in an overriding control state.
This invention also provides a numerical control system for a machine tool comprising; a main spindle rotational speed setting unit for outputting a signal of a setting main spindle rotational speed of the machine tool, a main spindle rotational speed overriding unit for outputting a signal of a main spindle rotational speed overriding according to an input of the main spindle rotational speed overriding, a main spindle rotational speed determining unit connected with the main spindle rotational speed setting unit and the main spindle rotational speed overriding unit, for determining a command signal of a main spindle rotational speed of the machine tool according to the signal of the set main spindle rotational speed and the signal of the main spindle rotational speed overriding, a feed speed setting unit for outputting a signal of a set feed speed of the machine tool, a feed speed overriding unit for outputting a signal of a feed speed overriding according to an input of the feed speed overriding, and a feed speed determining unit connected with the feed speed setting unit and the feed speed overriding unit, for determining a command signal of a feed speed of the machine tool according to the signal of the set feed speed and the signal of the feed speed overriding, wherein the feed speed determining unit is connected with the main spindle rotational speed determining unit, and changes the command signal of the feed speed synchronously with the change of the command signal of the main spindle rotational speed when the command signal of the main spindle rotational speed is changed at the main spindle rotational speed determining unit by the signal of the main spindle rotational speed overriding.
According to the invention, by the feed speed determ
Fujita Jun
Katoh Kouichi
Briggs William
Pillsbury Madison & Sutro LLP
Toshiba Kikai Kabushiki Kaisha
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