US 4,319,134 A · Optical encoder

Abstract

An optical encoder for producing an electrical signal representative of the angular position and velocity of a rotatable shaft. A flexible code disk, which is coupled to the shaft via a hub portion, has a plurality of slots located adjacent its outer rim, for alternately blocking and permitting transmission of a light beam to each of a plurality of separate photocells, as the disk is rotated. The rim of the disc is disposed in a special low-friction seat, whereby the slots are maintained in proper alignment with the photocells, even though the shaft may have a slight angular misalignment relative to the encoder. The photocells are formed on a common silicon substrate that has a single diffusion layer, and the electrical outputs of separate photocells are connected in a push-pull circuit arrangement. This produces an electrical signal whose successive zero crossings are an accurate representation of the angular position of the rotatable shaft, regardless of variations in the intensity of the light beam or irregularities in the transducing sensitivities of the photocells. Additionally, the encoder has a control loop that includes a separate photocell segment formed on the same common silicon substrate, for regulating the intensity of the light beam so as to produce a constant peak voltage level for the electrical signal output.

Claims5

Dependent claims

A method of making an optical shaft encoder of a type that produces an electrical signal having a phase angle representative of the relative position of a movable shaft, said encoder including a source of light, a photocell positioned to receive the light, means coupled to the movable shaft for blocking transmission of the light to the photocell in accordance with the relative position of the shaft, and amplifier means coupled to the photocell for producing the electrical signal, said amplifier means including variable resistance means for use in controllably adjusting the peak amplitude of the electrical signal, said method comprising the steps of:

mounting said photocell and said amplifier means on a circuit board,
energizing said source of light and said amplifier means and moving said movable shaft in a prescribed fashion,
monitoring the peak amplitude of the electrical signal produced by said amplifier means, and comparing it to a prescribed level,
directing a laser beam onto the variable resistance means in said amplifier means, while continuing to monitor the peak amplitude of the electrical signal and to compare it to the prescribed level, said laser beam having an intensity sufficient to alter the resistance of the variable resistance means, thereby controllably adjusting the peak amplitude of the electrical signal, and
terminating the step of directing a laser beam when it has been determined in said step of comparing that the peak amplitude of the electrical signal is substantially equal to the prescribed level.

2 more elements

A method of making an optical shaft encoder of a type the produces an electrical output signal having a phase angle representative of the relative position of a movable shaft, said encoder including a source of light, first and second photocells positioned to receive the light, means coupled to the movable shaft for blocking transmission of the light to the two photocells in an alternating fashion in accordance with the relative position of the shaft, and differential amplifier means coupled to the photocells for subtracting the electrical signal produced by one photocell from the electrical signal produced by the other photocell, to produce the electrical output signal, said amplifier means including variable resistance means for use in controllably adjusting the peak amplitude of the electrical signal produced by each photocell, said method comprising the steps of:

mounting said first and second photocells and said amplifier means on a circuit board,
energizing said source of light and said amplifier means and moving said movable shaft in prescribed fashion,
monitoring the peak amplitude of the electrical signal produced by said first photocell, and comparing it to a prescribed level,
directing a laser beam onto the variable resistance means in said amplifier means, while continuing to monitor the peak amplitude of the electrical signal produced by said first photocell, said laser beam having an intensity sufficient to alter the resistance of the variable resistance means, therebly controllably adjusting the peak amplitude of the electrical signal,
terminating the step of directing a laser beam when it has been determined in said step of comparing that the peak amplitude of the electrical signal produced by said first photocell is substantially equal to the prescribed level, and
repeating the steps of monitoring, directing, and terminating for the electrical signal produced by said second photocell, whereby the peak amplitudes of the electrical signals produced by said first and second photocells are both controllably adjusted to the prescribed level, and the resultant output signal has a phase angle that varies in a prescribed fashion in accordance with the relative position of the movable shaft.

3 more elements

In an optical encoder of the type having an encoder disc attachable to a shaft for rotation therewith, and having a light source and photosensor means disposed in a housing on opposite sides of said disc for sensing indicia on said disc to provide signals indicative of angular position of said disc and shaft, the improvement wherein:

said housing has two side members each with supporting ribs, each side member being attachable to the other to establish a unitary housing structure, said improvement further comprising:
means within said unitary housing structure for defining an internal circular chamber of diameter slightly larger than that of said disc, said internal chamber containing said disc,
a hub on said disc, said hub extending axially thereof and including a bushing for receiving said shaft,
a central circular coaxial opening in each of said housing side members, each opening being larger than said hub, said hub extending through one of said openings, said one opening and said chamber together permitting limited radial offset of said disc and hub to accommodate concomitant limited radial offset of said shaft with respect to said encoder housing, there being no journal attachment between said housing and any of said hub, shaft and disc,
alignment boss members, extending between said side members, for providing alignment of said side members including said chamber delivery means so as to align said internal chamber when said side members are attached, and
a metallic mask configured for aligned attachment to one of said side members covering said photosensor means,
said light source being a single light emitting diode, the other of said side members including a boss extending outwardly of said housing structure, said light emitting diode being situated in an opening which extends through said outwardly extending boss to said internal chamber.

4 more elements

Dependencies are inferred from the claim text.

Optical encoder

Life of this patent

Optical encoder

Life of this patent

Abstract

Claims5