Electronic tachometer and combined brushless motor commutation and tachometer system

A combined electronic tachometer and position determining system for producing a first signal indicative of the rotational velocity of a motor and a second signal indicative of total angular rotation of said motor, comprising:

• transducer means, attached to said motor, for producing first and second triangular wave signals of the same period but offset in phase with respect to each other by a fixed angular amount, said same period being directly proportional to the rotational velocity of said motor, said transducer means including:
• an optically encoded disc driven by the shaft of said motor and containing a plurality of equally angularly spaced sector marks, and
• first and second optical sensors arranged with a fixed angular offset therebetween, each sensor detecting the passage of said sector marks so that the outputs of said optical sensors comprise said first and second triangular wave signals,
• first and second differentiators connected to differentiate respectively said first and second triangular wave signals and to produce corresponding first and second differentiator output signals indicative respectively of the first time derivative of said first and second triangular wave signals,
• gating control means for deriving from said first and second triangular wave signals a set of time sequential sample signals for sampling said differentiator output signals respectively during the intervals between occurrence of the corresponding triangular wave peaks,
• sampling means, actuated by said sample signals, for alternatively sequentially sampling both said first and second differentiator output signals and for providing the resultant sampled outputs to a common line as said velocity indicative signal,
• an accumulator, and
• position increment means, responsive to occurrence of each of said sample signals, for providing to said accumulator a value indicative of the extent of positional change of said encoded disc required to produce each sample signal, the resultant accumulated contents of said accumulator representing total angular rotation of said motor shaft.