Variable-capacitance position transducing

A variable-capacitance transducer for detecting the angular position of a rotatable member, said transducer comprising,

• a first capacitance plate comprising a plurality of electrically conductive, capacitance electrodes,
• a second capacitance plate spaced from said first capacitance plate,
• a dielectric element located between said first and second capacitance plates,
• said dielectric element or one of said capacitance plates being fixedly mounted on said rotatable member,
• said first and second capacitance plates and said dielectric element being constructed in a manner such that said electrodes on said first capacitance plate, in conjunction with said second capacitance plate, form a plurality of capacitances that vary as said angular position of said rotatable member changes,
• said second capacitance plate and said electrodes being adapted for connection to a detector for measuring said capacitances between said second capacitance plate and said electrodes,
• said transducer further comprising a conductive guard at least partially enveloping said electrodes on said first capacitance plate, said conductive guard comprising a central portion, located within an interior space defined by said electrodes, and a band, located in an exterior space surrounding said electrodes.

A variable-capacitance transducer for detecting the angular position of a rotatable member, said transducer comprising

• a first capacitance plate comprising a planar circuit board, said circuit board comprising a plurality of planar electrodes and a conductive trace interconnecting at least two of said planar electrodes,
• a second capacitance plate spaced from said first capacitance plate,
• a dielectric element located between said first and second capacitance plates,
• said dielectric element or one of said capacitance plates being fixedly mounted on said rotatable member,
• said first and second capacitance plates and said dielectric element being constructed in a manner such that said electrodes on said first capacitance plate, in conjunction with said second capacitance plate, form a plurality of capacitances that vary as said angular position of said rotatable member changes,
• said second capacitance plate and said electrodes being adapted for connection to a detector for measuring said capacitances between said second capacitance plate and said electrodes,
• said planar circuit board of said first capacitance plate further comprising a conductive guard at least partially enveloping said planar electrodes, and a conductive guard at least partially enveloping said conductive trace to electrically shield said trace.

A variable-capacitance transducer for detecting the angular position of a rotatable member, said transducer comprising

• a first capacitance plate,
• a second capacitance plate spaced from said first capacitance plate,
• a dielectric element located between said first and second capacitance plates,
• said dielectric element or one of said capacitance plates being fixedly mounted on said rotatable member,
• said first and second capacitance plates and said dielectric element being constructed in a manner such that a capacitance between said first and second capacitance plates varies as said angular position of said rotatable member changes,
• said first and second capacitance plates being adapted for connection to a detector for measuring said capacitance between said first and second capacitance plates,
• said transducer further comprising a spacer defining the distance between said first and second capacitance plates, said spacer having a coefficient of thermal expansion and dimensions that cause the distance between said first and second capacitance plates to vary by an amount calculated to compensate for changes in plate area with temperature.

A Variable-capacitance transducer for detecting the angular position of a rotatable member, said transducer comprising

• a first capacitance plate,
• a second capacitance plate spaced from said first capacitance plate,
• a dielectric element located between said first and second capacitance plates,
• said dielectric element or one of said capacitance plates being fixedly mounted on said rotatable member,
• said first and second capacitance plates and said dielectric element being constructed in a manner such that a capacitance between said first and second capacitance plates varies as said angular position of said rotatable member changes,
• said first and second capacitance plates being adapted for connection to a detector for measuring said capacitance between said first and second capacitance plates,
• said transducer further comprising an adjustable parasitic capacitor plate, the position of said adjustable parasitic capacitor plate in said transducer being adjustable in order to compensate for parasitic capacitance between a plurality of parts of said variable-capacitance transducer.

A variable-capacitance transducer for detecting the angular position of a rotatable member controlled by a driver, said transducer comprising

• a first capacitance plate,
• a second capacitance plate,
• a dielectric element located between said first and second capacitance plates,
• said dielectric element or one of said capacitance plates being fixedly mounted on said rotatable member,
• said first and second capacitance plates and said dielectric element being constructed in a manner such that the capacitance between said first and second capacitance plates varies as said angular position of said rotatable member changes,
• said first and second capacitance plates being adapted for connection to a detector for measuring said capacitance between said second capacitance plate and said interconnected electrodes,
• said transducer further comprising an electromagnetic shield constructed and positioned with respect to said driver in a manner such that said electromagnetic shield tends to prevent electromagnetic radiation from said driver from affecting said capacitance between said first and second capacitance plates as measured by said detector.

A high performance moving iron scanning galvanometer for driving an optical element at frequencies substantially greater than 2 Khz, comprising

• a galvanometer housing,
• front and rear axially aligned bearings mounted on said housing,
• a moving iron rotor located within said housing between the bearings, with front and rear ends adjacent to said front and rear bearings, respectively,
• an output shaft connected to said front end of said rotor, supported by said front bearing, and extending beyond said front bearing sufficiently to provide mounting for the optical element,
• a rear shaft connected to said rotor at said rear end and supported by said rear bearing, and
• a low inertia capacitive position indicating element for providing indication of the instantaneous rotational position of said rotor and mounted on a portion of said rear shaft disposed outwardly of said rear bearing, i.e. on the side of said bearing opposite from said rotor, and
• fixed transducer means positioned in cooperative relationship with said position indicating element for velocity of said shaft,
• the overall inertia of the rotating portions of said galvanometer excluding the optical element being below 7.5 g.cm.sup.2,
• the low inertia of said capacitive position indicating element and its location on the shaft portion outward of the space between said bearings enabling maximization of the first cross-axis resonant frequency of said galvanometer to a frequency substantially higher than 2 KHz.