Indexing device and method of driving the same

A method of driving an indexing device comprising:

• a base table, a rotary table which is indexed about a given rotary center relative to the base table, a pair of positioning engaging members which are engageable with or disengageable from each other between the base table and rotary table and which prevent the rotary table from rotating when they engage with each other;
• a screw feed mechanism comprising a screw provided on a rotary center of the rotary table and a nut screwed onto the screw, said screw feed mechanism permitting the positioning engaging members to engage with or disengage from each other;
• a first motor for driving said screw feed mechanism;
• and,
• a second motor for indexing the rotary table;
• said method comprising:
• driving the screw feed mechanism in a direction for permitting the positioning engaging members to disengage from each other when the first motor rotates;
• indexing the rotary table when the second motor rotates after releasing the engagement between the positioning engaging members;
• and
• simultaneously rotating the first motor in a given rotating direction with a given ratio of rotating speed relative to a rotation of the second motor so as not to change a relative position between the screw and nut of the screw feed mechanism.