Optical System for Determining the Position of a Cursor

This invention relates to optical digitzers, and more in particular to a cursor and optical digitizing system wherein the position of a cursor in a coordinate system may be automatically digitized.

It is frequently desirable to determine the location digitally, in a two or three coordinate system. Various techniques have been employed in the past for this purpose, employing various position sensing devices, such as piezoelectric devices and magnetostrictive devices. While such arrangements have been in general satisfactory from the standpoint of the results that are achieved, they do have certain problems. For example, the boards or surfaces upon which the cursor is moved must be especially designed and relatively expensive, thereby increasing the cost and reducing the portability of the system.

The present invention is therefore directed to the provision of an improved digitizing system and cursor, wherein optical position sensing techniques are employed.

Briefly stated, in accordance with one embodiment of the invention, the movable cursor includes means for scanning a beam of light across the coordinate system, i.e., parallel to the surface upon which the cursor is to be moved. While the light may be visible light, it is of course apparent that light in other spectral ranges, such as infrared radiation as produced by a laser, falls within the meaning of the term "light" as employed herein. The cursor also includes a detector of light reflected back thereto from the angle at which the beam of light is instantaneously being directed. Simple reflectors are placed at determined points in the coordinate system, such that the detection of reflected light received by the cursor enables the determination, by triangulation, of the position of the cursor in the coordinate system.

In a particularly advantageous embodiment of the invention, the light is derived from a laser, and directed to the cursor by way of a flexible fiberoptic cable. This light is directed by way of a beam splitter to a rotating mirror that affects the scanning of the beam. Reflected light received at the rotating mirror is reflected, by way of the beam splitter, to a photo detector. In this arrangement, where a rectangular coordinate system is employed, curved mirrors are provided at the origin and spaced points on the coordinate axis, and plane mirrors extend along the coordinate axis.

In a further embodiment of the invention, the cursor may be a simple curved reflecting surface, with rotating scanning beam and detecting devices being employed at various points in the coordinate system.

In order that the invention will be more clearly understood, it will now be disclosed in greater detail with reference to the accompanying drawings, wherein:

FIG. 1 is a simplified plan view of an optical digitizing system in accordance with the invention, illustrating the principal of operation thereof;

FIG. 2 is a simplified block diagram of one embodiment of the optical digitizing system of the invention;

FIG. 3 is a partially cross-sectional side view of one embodiment of a cursor that may be employed in the invention;

FIG. 4 is a top view of the cursor of FIG. 3, shown connected to an external light source;

FIG. 5 is a simplified schematic illustration of a further embodiment of the invention.

Referring now to the drawings, and more in particular to FIG. 1, a cursor 10 is freely movable in a plane, for example, on a board 11. In the preferred embodiment of the invention a pair of orthogonal axes is defined on the board, such as the x axis 12 or abscissa, and the y axis 13 or ordinate, intersecting at the origin 14.

The cursor 10, as will be disclosed in greater detail in the following paragraphs, includes a source of light and a detector, these elements being continually rotated at a given rate, for example in the direction shown by the arrow 15 in FIG. 1. A curved reflector 20 is mounted at the origin 14, such that light falling thereon from the cursor at any point on the board, will be directly reflected back to the light detector in the cursor. A curved reflector 21 is mounted on the y axis at a point spaced from the origin, this reflector also being mounted to reflect light received from the cursor directly back to be detected by a light detector in the cursor.

A plane reflector 22 is provided extending along the y axis between the curved reflectors 20 and 21. This plane reflector 22 thus is arranged so that whenever the light from the cursor follows a path perpendicular to the plane of the reflector 22, this light will be reflected immediately back to the cursor for detection.

In a similar matter, a further curved reflector 24 is provided on the x axis, spaced from the origin, and a further plane reflector 25 is provided extending from the origin along the x axis to the reflector 24.

A geometrical analysis of the structure illustrated in FIG. 1 shows that: ##EQU1## wherein y is the spacing of the cursor from the x axis, D is the length on the y axis between the origin and the curved reflector 21, .alpha. is the angle between the lines from the cursor to the origin and the line from the cursor perpendicular to the y axis, and .beta. is the angle between the line extending from the cursor to the reflector 21 on the y axis and the perpendicular from the cursor to the y axis. In this relationship, since the distance D can be predetermined, it is evident that the distance y can be ascertained from a knowledge of the angles .alpha. and .beta.. If, now, the light source and detector in the cursor are rotating at a constant known rate, it is further evident that the time between detection of pulses by the detector from the curved reflector 20, plane reflector 22 and curved reflector 21, enable a determination of the angles .alpha. and .beta., and hence the calculation of the distance y from the cursor to the x axis.

FIG. 2 illustrates, in a simple manner one technique that may be employed for determining the angles .alpha. and .beta. and hence for calculating the distance y. In this figure, the cursor 10 is illustrated as having a light source 30, and a light detector 31, rotatable therewith. The detector 31 is coupled by conventional means, such as a lead 32, to a counter 33. It will be evident, from the above discussion, that, upon rotation of the cursor, a light pulse will be reflected back to and detected by the detector at each time the source is directed to the curved reflector 20, and the curved reflector 21, and also at each time the light beam is directed normal to the plane mirror 22.

In the above example, the counter 33 is a count by 3 counter, having outputs 35, 36, and 37 adapted to be energized sequentially upon receipt by the counter of a detected pulse. The term "energized" may refer, for example only, to a high logic state. As illustrated in FIG. 2, the output 35 is connected to the J input of a JK flip flop 39, and the output 36 is connected to the K input of the flip flop 39. The Q input of the flip flop is connected to gate clock pulses, in an AND gate 40, to a first counter 41. The Q output of the flip flop 39 is connected to gate clock pulses, by means of AND gate 42, to a second counter 43. The clock pulses are also applied, in conventional manner, to the flip flop 39. The output 37 of the counter 33 is connected, by way of inverter 44, to a third input of the gate 42.

Before proceeding with the discussion of the remainder of the circuit, its operation will be described. Assume, for example, that a pulse is detected by the detector 31, resulting from reflection from the origin 20, and that the counter has been set such that this pulse energizes the output 35. As a consequence, gate 40 will be enabled to pass clock pulses to the counter 41. The counter 41 will continue to count until the next pulse is received from the detector 31, i.e., when the light source is directed perpendicular to the plane mirror 22. At this time the output 35 will be de-energized, to stop counting in the counter 41, and the output 35 will control the flip flop 39 to enable the AND gate 42. As a consequence, clock pulses will now be counted in the counter 43. This will continue until the next pulse is received by the counter 33, at which time the output 37 will be enabled, and thereby, by way of inverter 44, to block the gate 42. Hence at this time, the counter 41 contains a count proportional to the angle .alpha. and the counter 43 contains a count proportional to the angle .beta.. These outputs may be applied to the calculator and indicator 50 of any desired design. The pulses may, for example, be clocked into the calculator as they occur. The output 37, which occurs when the two counters correspond to the respective angles, may thus be employed to enable the calculator to calculate the angles, and hence the distance y, in accordance with the above formula. In addition, the output 37 may be applied, by way of a delay circuit 51, to reset the counters 41 and 43.

For the above operation it must be of course insured that the energization of the output 35 occurs in response to detection of a light pulse reflected from the origin 20. For this purpose, the counts of counters 41 and 43 are compared, in comparator 60 and 61, with counts corresponding to large angles, for example, 90.degree. or more, since neither of the angles .alpha. or .beta. can be this large. Accordingly, when a count in one of these counters corresponds to such a large angle, this signifies that the count really corresponded to the outside angle, and hence the comparator in which such a comprison is found effects the resetting of the count by three counter 33. The next detected pulse will hence correctly be the pulse received from the origin, and will effect energization of the correct output 35.

One embodiment of a cursor that may be employed in the invention is illustrated in FIGS. 3 and 4. The cursor has a base 70 with a lower flat surface 71 adapted to engage the board. A circular aperture 72 is provided extending through the base, to permit alignment of the cursor with a desired position on the board. The optical elements of the cursor are provided within a cover housing 73 separately mounted upon the base.

In the illustrated embodiment of the invention, an external light source is provided, for example, the light source indicated by the block 75 in FIG. 4, and connected to the cover housing 73 by way of a flexible fiberoptic cable 76.

As illustrated in FIG. 3, light from the figeroptic cable is directed into entrance port 80 in a direction parallel to bottom surface 71. This light is directed to a beam splitter 81, for example by way of a focusing lens 82. Light passing the beam splitter 81 in this direction is directed to a stationary mirror 84 at an angle of 45.degree., this mirror reflecting the beam outwardly in the cursor to a rotating mirror 85. The rotating mirror 85 is at an angle of 45.degree. to the beam at this point, and hence deflects the beam again into a plane parallel to the base plane 71. The cover housing 73 has a horizontal slit 86 extending through an angle, for example, about 180.degree. with respect to the axes of the rotating mirror 85, so that the rotating mirror scans the beam through this opening. The mirror 85 is rotated by a constant speed motor 87 mounted, for example, in the top of the cover housing 73. This motor may be energized by a suitable power source in the base 70, for example, or it may be connected by flexible leads to an external source.

In order to enable precisely positioning the cursor at any desired point on the board, the mounting projection 90 for the mirror 84 may be provided with a downwardly extending aperture 91 centrally aligned with the hole 72 in the base, the mirror 84 being less than fully silvered so that light reflected thereto from the mirror 85 will be precisely directed at the central location of the aperture 72 on the board.

When the light reflected from mirror 85 falls upon one of the curved mirrors 20, 21, or 24, or when it is directed to one of the plane mirros 22 or 25 at an angle perpendicular to the respective mirror, light will be reflected back to the cursor, falling upon the rotating mirror 85. This light is then directed to the angled mirror 84, and back to the beam splitter 81. At the beam splitter the reflected light is directed to a detector, such as photo transistor 94 mounted directly above the beam splitter in the cover housing. The photo transistor may be coupled to the external calculating device, for example of the type illustrated in FIG. 2, by conventional means such as wire leads or the like.

In operation, the cursor is placed upon the board 11, and moved to a desired position. Assuming that only the y dimension is to be determined, such as illustrated in FIG. 1, the slit in the cursor is oriented in order to enable scanning of the beam continuously from the curved mirror 20 at the x axis to the curved mirror 21 at the extremity of the y axis. The resultant pulses of light detected at the cursor are received at times dependent upon the physical location of the cursor with respect to the x and y axes, so that the distance y to the x axis may be calculated in accordance with the above relationship. This calculation may of course be effected electronically, with a digital or other desired type of read-out. As discussed above, the distance between the mirrors 20 and 21 is known, as is the constant speed of rotation of the rotating mirror in the cursor.

It will of course be apparent that a similar technique may be employed for determining the distance x from the cursor to the y axis. The x distance may be determined separately from the y distance, in a manner similar to that shown in FIG. 1, or, alternately, the calculator may be modified to also count the relative timing of detection of pulses from the mirror 24 and 25. In this instance the slit in the cursor may have a greater angle, in order to enable full scanning of the curved and plane mirrors.

The optical digitizer of the invention, as disclosed above, thereby enables the rapid and accurate digitization of a position on a board or tablet. The board or tablet need not be stationary, and, in view of the use of optical measuring techniques, the device is not subject to electromagnetic interference. The measured distances may be relatively long, for example greater than several feet, since the light source may be a laser having significant beam intensity. The digitizing speeds, accuracy and resolution of the digitizer may be directly controlled by the operator. The circuit requires only a minimum of electronic circuitry, and is hence economical for both domestic and commercial applications. The arrangement is also readily adaptable to portable use, since, for example, the mirrors mounted on the board may be adapted to be folded so that they do not project from the surface of the board, for transportation. The curved mirrors mounted on the board may be comprised simply of silvered rods.

In a somewhat similar manner, the optical digitizer in accordance with the invention may employ a purely passive cursor, for example, a curved mirror or reflective rod 100, as illustrated in FIG. 5. In this arrangement, a rotating light source 101 is provided at the origin, rotating as indicated by the arrow 102. The source 101 also includes a detector, and may be fabricated much in the manner of the cursor structure illustrated in FIG. 3. A similar combined rotating light source and light detector 103, rotating in the direction of arrow 104, is provided at the extremity of the ordinate. Since the rotating assembly 101 is stationary on the board, it may have a reference position corresponding to the x axis built in, for example such that a pulse in emitted by the device at each crossing of the abscissa. Alternatively of course a curved mirror 105 may be provided at the extremity of the x axis, such that a count may be derived, for example employing a circuit similar to that of FIG. 2, that is proportional to the angle .delta. between the x axis and the line extending between the origin and the cursor, it being noted that the cursor reflects the light directly back to the origin. The angle .delta. is of course the same as the angle .alpha. in the arrangement of FIG. 1.

The rotating assembly 103 of FIG. 5, being stationary, may of course be referenced to the y axis, so that the angle .gamma. between the y axis and the line extending between the assembly 103 and the cursor may be readily determined. In this arrangement the angle .gamma. is of course the complement of the angle .beta., in the arrangement of FIG. 1. Instead of depending upon the absolute orientation of the light from device 103, this orientation may be determined for example by suitable reflecting means provided on the y axis. It is of course apparent that the reflectors for determining orientation with respect to the x and y axis may be placed at any other convenient position. It is similarly apparent that the arrangement illustrated in FIG. 5 for determination of the distance y may be similarly employed for determination of the distance of the cursor from the y axis.

While the invention has been disclosed and described with reference to a limited number of embodiments, it will be apparent that variations and modifications may be made therein, and it is therefore intended in the following claims to cover each such variation and modification as falls within the true spirit and scope of the invention.