Shaft Position Encoder

1. Field of the Invention

The present invention relates to shaft position indicating systems, and more particularly to an opto-electronic shaft encoder conformed for inline mounting with a selected rotary shaft.

2. Description of the Prior Art

Shaft encoders utilizing photoelectric coupling have been known in the past. Most frequently as resolution and accuracy increases are desired, the radial size of these prior art encoders increases. This trade-off of accuracy against radial dimension has a compounding effect by increasing moment of inertia, which in the case of high speed devices may turn out to be prohibitive. Alternately, the radial clearance around a measured shaft is often insufficient to accommodate such prior art encoders, again precluding full utilization thereof. In addition, most of the prior art encoders are tightly packed with coating apertures, thus precluding convenient manual inscription of a specifically desired code. This tight packing further complicates sensor spacing both in dynamic systems use and in the convenience of assembly.

Accordingly, it is the general purpose and object of the present invention to provide a cylindrical shaft encoder and which by expansion of its length can be expanded in resolution and accuracy.

Further objects of the invention are to provide a cylindrical shaft encoder which introduces minimal additional inertia to a measured rotary shaft.

Yet additional objects of the invention are to produce a shaft encoder which can be specifically coded for any desired use.

Yet additional objects of the invention are to produce a shaft encoder which is simple to produce, convenient in use, and entails minimal alignment problems.

Briefly, these and other objects are accomplished within the present invention by conforming an encoder in a manner of a cylindrical segment, the cylindrical segment including either a plurality of fiber optic strands embedded therein or comprising a translucent structure. In the first instance, the fiber optic strands are aligned as a group longitudinal within the segment, selected ones thereof being turned at various longitudinal stations of the cylinder to expose the second end surfaces thereof on the cylinder surface. The first ends of the fibers are exposed in common at the end surface of the segment to be illuminated by a light source such as a light emitting diode or laser. In this form, rotation of the cylindrical segment advances the various radially aligned fiber ends into the field of reception of phototransistors arranged as a longitudinal bank, sequentially rendering each corresponding transistor conductive to indicate a particular angular position of the shaft or may be used with an electronic system for binary counting.

The foregoing arrangement of parts can be adapted for special coding by the structure of an alternative cylinder segment. More specifically, the alternative embodiment entails the use of a translucent cylindrical segment which around the periphery thereof is grooved to provide a plurality of peripheral strips, the strips and grooves being coated with a reflective opaque coating. The grooves are formed to provide maximum reflection of light within the cylinder. The segment is ground at one end and exposed to a light source and the peripheral strips are variously polished off to provide selectively located apertures into the translucent interior of the light carrier. The selective coding of each strip allows for any desired coding sequence which once more are detected by way of a bank of phototransistors.

In each instance the inventive structure herein utilizes the length of the shaft rather than radius to increase coding resolution. It is to be noted that various logic devices triggered at the leading and trailing edge of each light aperture can be utilized, thus permitting relatively high accuracy with simple manual technique.

FIG. 1 is a perspective illustration of a first embodiment of an encoding cylinder useful with the invention herein containing optical fibers;

FIG. 2 is yet another perspective illustration of a second embodiment of a coding cylinder constructed according to the present invention;

FIG. 3 is a perspective illustration of the coding cylinder shown in FIG. 2 prior to the light apertures formed therein;

FIG. 4 is a sectional view of a shaft encoder assembly illustrating the use of the first coding cylinder therein; and

FIG. 5 is yet another sectional view of a shaft encoder assembly utilizing the second coding cylinder therein.

While the following description sets forth several implementations of a shaft encoder assembly, these examples are illustrative only. It is to be understood that various other alternatives may be utilized according to the principles set forth herein and no intent to limit the scope of the invention by way of these examples is expressed.

The first form A of the invention as shown in FIG. 4, includes a coding cylinder 10 that has an external surface 11 and bearing journals 12 and 13, respectively of reduced diameter. Journal 12 at the free end thereof is ground and polished to a smooth end surface 14, exposing the first ends of a plurality of optical fibers 15.sub.1 through 15.sub.7 embedded as a longitudinal group on the interior of the coding cylinder 10. The fibers 15.sub.1 through 15.sub.7 at predetermined stations of cylinder 10 extend outwardly radially relative to the cylinder to terminate at surface 11, the second ends of the fibers 15.sub.1 through 15.sub.7 thus being exposed at the peripheral surface 11. To illustrate this longitudinal spacing the disposition of the optical fibers 15.sub.1 through 15.sub.7, shown in FIG. 4, is illustrated in a common plane. It is to be understood that the second end of each fiber is aligned along a radial arc corresponding to the increment of rotation to be measured thereby, as shown in FIG. 1.

Optical fibers 15.sub.1 through 15.sub.7 are cast integrally with the casting of cylinder 10, the material structure of the cylinder being opaque or having a sufficient refractive index to limit each optical fiber to the function of a wave guide for communicating light therethrough.

Cylinder 10 is mounted for rotation by way of the end journals 12 and 13 in a support frame B comprising two end bearing assemblies 21 and 22 attached to an elongate rigid member 43 provided with a plurality of transverse bores 44, each bore receiving corresponding phototransistors 25.sub.1 through 25.sub.7. Bearing assemblies 21 and 22 are secured to member 43 by screws 43a, with the bearing assemblies resting on a base 47 to which they are secured by conventional means. In the embodiments herein phototransistors 25.sub.1 through 25.sub.7 may be any conventional electronic devices and phototransistors of appropriate gain are adequate for the use herein. Transistors 25.sub.1 through 25.sub.7 furthermore are deployed in a common plane parallel to the axis of rotation of cylinder 10 at stations aligned to register the light passed through the radially directed ends of fibers 15.sub.1 through 15.sub.7.

To provide for the necessary rotary engagement bearing assemblies 21 and 22, each include a corresponding bore 23 and 24, bore 23 being conformed to receive journal 12, with bore 24 being conformed to receive journal 13. Bore 24 furthermore is reduced across a shoulder 25 to provide a shaft opening 27. Similarly the other support, i.e., the bore 23 reduces to a smaller diameter opening 26 conformed to receive a light emitting diode 28 which is thus exposed to transmit light to the ground end surface 14 and therefore to first ends of fibers 15.sub.1 through 15.sub.7 that are flush therewith.

A rotatable connector 31 and the opposing surface of journal 13 are provided with key slots 32 and 33 respectively, for receiving a rectangular key 34 therein. Alternatively, connector 31 may be bonded to the free end of journal 13 (not shown). Connector 31 terminates in a chuck assembly 35 provided with a central recess 36 conformed to receive rotary output shafts C of various diameters that are to be monitored by the invention A. The end portion of a shaft C is centered in recess 36 and is frictionally engaged by a number of circumferentially spaced screws 37 that extend through radially disposed tapped bores 35a formed in the chuck assembly. Similarly the other support, i.e., the bore 23 reduces to a smaller diameter opening 26 conformed to receive a light-emitting diode 28 which is thus exposed to transmit light to the ground end surface 14 and therefore to the common exposed first ends of fibers 15.sub.1 through 15.sub.7.

By virtue of this arrangement, the light emitting diode 28 produces the light which is then communicated by the fibers to points exposed on the lateral exterior of cylinder 11. These fiber ends as they are advanced in rotation illuminate the corresponding ones of the phototransistors 25.sub.1 through 25.sub.7, thus indicating the angular position of the shaft C.

By way of a similar arrangement an alternative embodiment shown in FIGS. 2, 3 and 5 is implemented. More specifically the same carrier structure is utilized for this implementation and for that reason the same numerals are followed to describe the quotation thereof, the variation being in the cylinder itself. More specifically as shown in FIG. 2 an alternative cylinder generally designated by the numeral 50 includes a cylindrical segment 51 provided with a plurality of peripheral grooves 52 separating the exterior lateral surface thereof into a plurality of ring-shaped strips. The angles of the grooves or any like deformation of the cylinder is arranged to provide maximum reflection of light to the strips. It is intended to form cylinder 50 out of a translucent light carrying material, cylinder 50 once more including the end journals 12 and 13, journal 12 terminating in a free end surface 14 again polished and ground for light transmission. Deposited on the exterior of cylinder 50 is an internally reflective opaque coating or layer 53 which may be of a flective material like silver or aluminum coating which can be selectively stripped away and polished at desired positions to provide the necessary light transmission apertures 53.sub.1 through 53.sub.7. In FIG. 2 this aperture arrangement is shown as a spiral alignment of apertures 53.sub.1 through 53.sub.7 corresponding to the function of fibers 15.sub.1 through 15.sub.7. This provision of apertures 53.sub.1 through 53.sub.7 may be made in any convenient manner, by way of a sharp cutting tool or other conventional device for removing the outer coating for any desired selective manual coding. Should it be desired the apertures 53.sub.1 through 53.sub.7 may be arranged to provide a binary code or similar other parallel coding scheme.

It is to be understood that the foregoing second embodiment allows for extensive convenience in use, the exposed apertures being easily recoated by brush depositing technique. This latter feature is of particular significance in allowing the use of the device in laboratory or experimental applications, where, for example, the highest density strip may be left precoded while the other strips are coded to achieve the highest code efficiency.

In each instance the connection of the encoder to the measured shaft entails minimal connecting structure variously achieved, the minimal weight and inertia of the cylinder imposing minimal connection loads. Alternatively the cylinder may be joined to a hand knob assembly for manual shaft imputs which concurrently are converted to hold readout.

Obviously many modifications and variations to the above disclosure can be made without departing from the spirit of the invention. It is therefore intended that the scope of the invention be determined solely on the claims appended hereto.