Multiple-beam triangulation-based range finder and method

A method for determining a time-varying distance between a housing, the housing defining an axis extending from the housing toward a target disposed along the axis, comprising:

• emitting a first light beam from a first location on the housing with an orientation to intersect the axis at a first distance from the housing;
• emitting a second light beam from a second location on the housing, different from the first location, with an orientation to intersect the axis at the first distance from the housing;
• collecting light from the first and second light beams that is reflected from the target with a multi-element detector;
• subtracting a first of at least two signals produced by elements of the multi-element detector from a second of the at least two signals produced by the elements of the multi-element detector to form a trigger signal that has a first value when the target is spaced from the housing by less than half the first distance and has a second value, different from the first value, when the target is spaced from the housing by more than half the first distance, and
• wherein the trigger signal switches from the second value to the first value, triggering an action.

A multiple-beam triangulation-based range finder, comprising:

• a housing defining an axis extending from the housing toward a target to be measured, a light source coupled to the housing, the light source configured to simultaneously emit first and second light beams from respective first and second locations on the housing, the first and second light beams having orientations to both intersect the axis at a first distance from the housing, the light source modulating the first and second light beams at respective first and second frequencies;
• a quadrant detector coupled to the housing, centered with respect to the axis, and configured to receive light from the first and second light beams that is reflected from the target when the target is positioned along the axis;
• and
• circuitry coupled to the quadrant detector and configured to produce a trigger signal that has a first value when the target is spaced from the housing by less than half the first distance and has a second value, different from the first value, when the target is spaced from the housing by more than half the first distance, the circuitry associating signals from the quadrant detector at the first frequency with the first light beam, the circuitry associating signals from the quadrant detector at the second frequency with the second light beam, the circuitry forming the trigger signal using signals from both the first and second light beams, wherein the trigger signal switches from the second value to the first value, triggering an action.