ANDed motor control system for motorized ophthalmic instrument

Claim 1

In an ophthalmic instrument comprising: a base; a rotatable optical element; a stepping motor having a plurality of detent positions and a shaft for rotating said element; means, including a rotatable support for said element, for coupling said shaft to said element, whereby said motor can rotate said element relative to said base, one of the positions of said element wherein said motor is in one of said detent positions, constituting a reset or zero position; means for sending signals to said motor to rotate said element; and means for interrupting said signals to said motor before the magnetic detent position where said element is in said reset position but subsequent to the immediately preceding detent position, said means including at least two reflective blocks secured to said coupling means, a pair of encoders, decoder logic means for transforming analog signals to digital signals coupled to said encoders, and latch means coupled to both said decoder logic means and said means for sending signals to said motor, each of said encoders including an LED and a phototransistor, each of said phototransistors sending analog signals to said decoder logic means, which signals change when the light emitted by said corresponding LED is reflected back to said phototransistor by said corresponding block, said decoder logic means changing said digital signal when said analog signals from said encoders are concurrently above their threshold values and the resultant signals ANDed, said latch latching as a function of said change in digital signal and sending a signal to said means for sending signals to said monitor to stop sending signals to said motor.