Tool selection method for machine tool, control device, and numerically controlled lathe

A tool selection controlling device, for use in a machine tool including a tool rest movable along first and second control axes orthogonal to each other, for automatically selecting a desired tool from a plurality of tools mounted on said tool rest in a parallel arrangement laid in a first control-axis direction with respective tips thereof being oriented in an identical direction, said device comprising:

• a storage section for storing, as inherent data of said tool rest, a clearance distance for spacing said tips of said tools from a workpiece during tool selection and tip distances of all of said tools mounted on said tool rest, each tip distance being defined from a reference tip position set for said tool rest to an actual tip position on said tool rest;
• a processing section for calculating, from said inherent data stored in said storage section, a maximum tip distance identified from among said tip distances, in relation to a currently selected tool as to be firstly used, a next designated tool as to be secondary used and an intermediate tool, if any, disposed between said currently selected tool and said next designated tool, in all of said tools, and also calculating a tool-change starting position where a tip of said currently selected tool is spaced from the workpiece along said second control axis by a distance provided by adding said clearance distance to a difference between said maximum tip distance and a tip distance of said currently selected tool, a tool-change terminating position where a tip of said next designated tool is aligned with the workpiece in said second control-axis direction and a tool-selection completing position where said tip of said next designated tool is spaced from the workpiece by said clearance distance along said second control axis, to issue a position command corresponding to these positions;
• and
• a drive control section for controlling, in accordance with said position command issued from said processing section, a feed motion of said tool rest along said first and second control axes, wherein said drive control section is configured to:
• move said tool rest in the second control-axis direction after a machining operation using said currently selected tool is completed and place said tool rest at said tool-change starting position;
• move said tool rest from said tool-change starting position in said first control-axis direction and place said tool rest at said tool-change terminating position;
• and
• move said tool rest from said tool-change terminating position in said second control-axis direction and place said tool rest at said tool-selection completing position.