Indexing apparatus using ultrasonic feedback

An apparatus for positioning a stapling device relative to a set of sheets, including:

• means for moving the stapling device to a selected stapling position;
• and
• ultrasonic means for sensing the linear position of the stapling device while being moved by said moving means, said ultrasonic means comprising,
• first transducer means, permanently affixed at a stationary location, for emitting an ultrasonic signal in response to a first oscillating signal having a selected period,
• a first frequency divider for producing a first reduced frequency signal in response to said first oscillating signal,
• second transducer means, operatively associated with the stapling device, for continuously generating a second oscillating signal, also having the selected period, in response to receiving the ultrasonic signal produced by said first transducer means,
• a second frequency divider for producing a second reduced frequency signal in response to said second oscillating signal, and
• means for determining the linear position of the stapling device as a function of the ultrasonic signal propagation time represented by the phase difference between the first and second reduced frequency signals.

A method of monitoring the position of a sheet stapling device with respect to a stationary reference position, in an apparatus having means for transporting the stapling device in a linear direction, substantially parallel to an edge of a set of sheets, comprising the steps of:

• generating a first oscillating signal having a frequency in the ultrasonic range;
• using a first transducer positioned at the stationary reference position to transmit an ultrasonic energy wave in response to the first oscillating signal;
• producing a first reduced frequency signal in response to the first oscillating signal;
• receiving the ultrasonic energy wave with a second transducer, operatively associated with the stapling device;
• producing a second oscillating signal in response said receiving step;
• producing a second reduced frequency signal in response to the second oscillating signal;
• determining the time required for the ultrasonic energy wave to propagate from the first transducer to the second transducer as a function of a time delay between the first and second reduced frequency signals;
• and
• calculating the position of the stapling device as a function of the ultrasonic energy wave propagation time.