1. Field of the Invention
The present invention relates to a tool-changing apparatus and method for exchanging a tool set on a main spindle of a machine tool and a tool set on a tool magazine of the same with each other.
2. Description of Related Art
A machine tool that exchanges a tool set on its main spindle and a tool set on its tool magazine has a tool-changing apparatus. In this machine tool, a gripping portion formed at an end of a tool-changing arm constituting a tool-gripping mechanism grips a tool set on the main spindle and a tool set on the tool magazine, and then the tool-changing arm swings or turns to exchange the two tools with each other by changing the positions of the two tools.
The tool-gripping mechanism is divided into two types depending on the manner of gripping tools. In one type of tool-gripping mechanism, the tool is sandwiched by the tool-gripping portion thereof. In the other type of tool-gripping mechanism, one side of the tool is caught by the tool-gripping portion and then pressingly locked to a tool-mounting portion.
The tool-gripping mechanism of the latter type is disclosed in Japanese Utility Model Publication No. 5-13469. The process of moving the tool-changing arm of the tool-gripping mechanism disclosed in this Japanese publication first swings the tool-changing arm by a predetermined angle from the arm-waiting position to the tool-changing position so that the tool-gripping portion formed at ends of the tool-changing arm grips a tool used and set on the main spindle and a new tool set on the tool magazine. The process then moves the tool-changing arm axially and swings it by 180.degree. at a predetermined position spaced from the tool-changing position to change the positions of the two tools each other. The process moves the tool-changing arm axially to move the tool-changing arm to the tool-changing position so that the tool-changing arm installs the new tool on the main spindle and then releases the tool used from the tool-gripping portion to accommodate it in the tool magazine. The process finally swings the tool-changing arm reversely to return it to the arm-waiting position again.
In this process, the tool-changing arm must be driven reversely in the space between the arm-waiting position and the tool-changing position and the tool-changing arm must be positioned accurately to inset a tool into the main spindle accurately. It is therefore necessary to use a complicated mechanism, namely, to use an expensive roller gear cam having a cam groove formed thereon, or to switch the swinging direction of the tool-changing arm by driving a plurality of gears.