Abstract:
A single-, two- or three-axis opto-electronic encoder, or error-inputting device, with an optical scale which is overall cylindrical, spherical or volumetric, as opposed to extant planar, circular optical scales; mostly parallel rays of light enter from the cylindrical or spherical surface of the scale, travel, with or without being modulated in intensity due to rotation/rotations of, or distortion/distortions in, the scale, along elliptical and/or circular sectional planes of the scale and exit to fall upon an obstructing opto-electronic sensor or a plurality of such sensors. A photo-transmissive spherical float on a photo-opaque liquid sealed inside a spherical optical scale, moving vertically under the influence of an external force, upwardly displacing the photo-opaque liquid to block the light that enters the spherical optical scale from reaching any of the opto-electronic sensors, produces a distinct electronic condition for auxiliary use in addition to or conjunction with encoder or error-inputting device output or outputs.

Description:
BACKGROUND OF THE INVENTION 
   The present invention is directed to the field of opto-electronic encoders with digital- or analogue-coded output or outputs. 
   In the related field, opto-electronic encoder devices essentially consist of an optical barrier, systematic removal of that barrier does encoding of a movement linked to the optical barrier. Documentation of pioneering work finds place in U.S. Pat. Nos. 2,537,427, 2,685,082 and 2,944,157. All of these patents have a rotatory disc with numerous radial apertures to allow light from a phototransmitter to pass. The thickness of the disc with coded scale was only governed by the strength of material with which it was fabricated. The thinnest possible discs became desirable, as the electrical light-producing methods were not very efficient. Their low efficiency and limited filament life marked incandescent lamps. Running them only at very low illumination levels could make them longer lasting. Initial light-emitting diodes (LEDs) too were not bright or efficient. That meant keeping the distance between the phototransmitter and the opto-electronic receiver as small as possible. Semiconductor manufacturers too started manufacturing such pairs housing a transmitter and a receiver spaced apart just by a fraction of a centimeter, in a package. This configuration made application of opto-electronics very easy for the encoder maker. U.S. Pat. Nos. 3,269,190, 3,304,434, 3,789,218 and 3,987,685 disclose the means to devise a multi-coordinate input device using two sets of disc encoders. Using another set of disc encoders to make it into a three-axis encoder could extend this scheme. 
   A simple three-axis encoder can be used to detect error signals and to make a toy robot remain upright. If the extended coordinate input device is used for this application, the ball has to have an eccentric center of gravity. Due to friction with the three rotating shafts rolling along the surface of the ball, the movement of the ball would not only be retarded, it could also fail to rotate sometimes. Friction-less data gathering solutions for comparative free rolling of the ball are disclosed in U.S. Pat. Nos. 5,831,553 and 6,686,584. U.S. Pat. No. 5,831,553 discloses a heavy ball as the central member with an eccentric center of gravity—suitable for the application presently discussed. The relative complexities involved in the implementation of both the schemes make them unsuitable for a cost-effective application. Furthermore, the use of a rolling magnetic element would cause ferromagnetic loose particles to attach to the rolling ball, and thus impede reliability. 
   For constructing a rotational single-axis encoder or input device, as noted earlier, use is made of an opto-electronic link placed axially on a circular optically coded disc. Though this construction has become an industry standard, there are two notable problems associated with this kind of axial mounting. The removal of the circular disc scale involves the removal of the optical transceiver pair; the minimum thickness of the whole encoder assembly together with the associated electronic components for processing the data seems to have reached a limit. There must be three layers in such an encoder—first, a printed circuit board (PCB) holding the phototransmitter and some electronics, next, the circular disc scale, and lastly, another PCB holding the opto-electronic receiver and the rest of the electronic components. By making use of thick-film technology, the overall thickness of this stack could be approximately 1.5 mm. Even a slight wobble in the disc scale due to anomalies would immediately damage the electronics on both the PCBs flanking the disc scale. Trying to increase the clearance on both the sides of the disc scale would definitely increase the thickness of the overall encoder assembly. There are also maintenance problems associated with this kind of construction. The accumulation of oil, moisture, or dirt on the scale goes unnoticed, until encoder failure takes place. Cleaning of the disc scale is possible with some care, but the cleaning of the optical transmitter and receiver active surfaces is very difficult. Replacement of a disc scale with a new one is also a complicated job, due to the basic axial positioning of the constituents of the optical transceiver pair on either flat side of the disc scale. Minute cracks in the body of a thermoplastic disc scale go unnoticed until mechanical failure occurs. U.S. Pat. No. 5,638,165 discloses a method of embedding optical fiber strands in a structure, and to gauge the thinning of the fibers at cracked positions. This method would be difficult to implement in a miniature mechanism like that of an opto-electronic encoder. The disc is constructed of transparent material, like glass or a transparent thermoplastic. A simple method which would give warning when small cracks appear in the circular disc would be of value, even with existing opto-electronic encoders. 
   BRIEF SUMMARY OF THE INVENTION 
   The existing optical encoder scales, though structurally three dimensional, are essentially two-dimensional in function; this invention presents optical encoder scales which necessarily have to be three-dimensional in order to provide encoder functions. Due to the considerably large functional third dimension of the optical encoder scale, which is parallel with the direction of the phototransmitter main beam, the phototransmitter and opto-electronic receiver are placed sufficiently apart to well accommodate the optical encoder scale of the present invention. 
   The single-axis version of the present invention consists of a cylindrical encoder disc made of transparent thermoplastic or glass, bearing an optical encoder scale on its cylindrical side close to the outer edge, a phototransmitter (a non-diffused LED), and an opto-electronic sensor unit facing the cylindrical optical encoder scale (henceforth, to be called cylindrical optical scale) in such a manner that the light emitted by the transmitter passes through the cylindrical optical scale, enters the transparent cylindrical optical scale cordially, undergoes refraction, and comes out from the area of focus on the opposite side where the opto-electronic sensor unit faces this rectangular beam after it has crossed the cylindrical optical scale again. This second crossing of the cylindrical optical scale creates the relevant optical pattern on the opto-electronic sensor unit, while the first crossing, just after the light leaves the phototransmitter, imparts slight modulation on the intensity of the beam. The openings and closings on the cylindrical optical scale are much smaller than the width of the light beam from the phototransmitter. Without using the cylindrical optical scale of the present invention, the new optical transmitter-receiver configuration is fit to be implemented on a conventional planar optical and in conjunction with axially located optical transmitter-receiver units to detect minute cracks in the body of the planar optical disc and accumulation of dirt on its sides and edges. 
   The single-axis version of the present invention appears as a flat assembly in contrast with the three-layer assemblies of conventional opto-electronic encoders. As mentioned in the beginning, though the thickness of the cylindrical optical scale might seem negligible in comparison to the diameter of the same, it does function as the medium in which the beam of light travels from the phototransmitter to the opto-electronic sensor unit. This thickness cannot be made smaller than the diameter of the lens of the phototransmitter LED without sacrificing the optical utilization of the phototransmitter output. In the case of conventional opto-electronic encoders, the thickness of a planar optical scale is only limited by structural constraints. Theoretically, in this case, a light-opaque metallic film a few microns thick can also function as an effective optical barrier. This superficially planar placement of a phototransmitter and opto-electronic sensor with reference to a cylindrical optical scale makes the present construction more accessible for inspection and cleaning and, moreover, physically easier to disassemble. 
   The two- or three-axis form of the present invention consists of a spherical shell with multiple optical apertures distributed all over or near its surface, functioning together as the spherical optical encoder scale. With either air or some transparent material inside the spherical shell, the active surfaces of the mainly diametrically placed phototransmitters and opto-electronic sensors face each other/face one another. The basic operation of this novel encoder with a spherical optical scale is similar to the single-axis encoder of the present invention described hereinabove. To encode the three axes, three sets of opto-electronic devices are fitted at their logical places with regards to the mechanical structure of the encoder, each set consisting of a phototransmitter (a non-diffused LED) and an opto-electronic sensor unit. The multi-aperture spherical optical scale described hereinabove is set in motion by external forces by employing various means. The addition of a transparent material inside the spherical optical scale would reduce the driving power of the phototransmitter LED to almost by converging light from the phototransmitter on to the opto-electronic sensor unit in each set. Another possibility is to fill the spherical optical scale with a liquid opaque to the light of the transmitter LED and to put another light-weight, hollow and transparent spherical body permanently afloat on the liquid, the level of the liquid just below the active area of the opto-electronic receiver units. In this form the spherical optical scale responds to an impacting or distorting force by blocking the optical signal to all the opto-electronic sensor units—this in itself could generate a distinct signal to be used for various purposes. By making one half of the spherical optical scale heavier than the other, the center of gravity of the spherical optical scale becomes eccentric and makes a free-to-roll spherical optical scale which always settles in only one approximate position under the influence of gravity. This sums up the construction of not only a simple encoding apparatus, but also of a balancing-error-inputting device for a toy robot to remain upright and to mimic various human actions. This construction does away with the conventional frictionally revolving encoder discs, previously necessary for encoding, but which impeded the freedom of the rolling device. At the same time, it keeps the process of reading an encoded movement uncomplicated. The removal of the frictional elements also makes the present invention capable to be used with a prosthetic or robotic ball-and-socket joint as an integral three-axis, contact-less encoder, without increasing size of the joint or its complexity. To achieve this, the spherical encoder is joined to one end of a limb to become the ball of the joint, while all the opto-electronics are put into the socket part of the joint. 
   Accordingly, a principle object of the present invention is to simplify overall construction of single-, two- and three-axis encoders. 
   It is another object of the invention that the disassembly, cleaning and re-assembly of a single-axis optical encoder disc scale, a phototransmitter and an opto-electronic receiver unit are uncomplicated. 
   It is a further object of the invention to detect cracks in the body of the rotatory disc scale, irrespective of the positioning of the actual optical scale on the disc. 
   Another object of the invention is to devise a two- or three-axis encoder or coordinate input device with minimum frictional members and maximum user accessibility to all the primary optical elements. 
   An additional object of the invention is to propose a completely free-to-roll error-inputting device used to control a toy robot to stand, to move upright and to mimic human action. 
   It is a further object of the invention to integrate a three-axis encoder with a robotic or prosthetic ball-and-socket joint. 
   It is again an object of the invention to generate an extra electrical signal in response to vertical bi-directional impact or force on the free-rolling element. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The drawings on five sheets are seventeen in number.  FIG. 6  through  FIG. 16  are drawn to landscape orientation, in order to bring out the cross-sectional details properly by using a larger scale. Numerals are employed to identify features and components of the drawings. Identical numerals denote functional and positional similarity throughout the several views. 
       FIG. 1  is a schematic representation, in perspective, of an arrangement for a phototransmitter (LED in this case), an encoder disc and an opto-electronic sensor to function as a single-axis encoder of the present invention. 
       FIG. 2  is a side view of the arrangement of  FIG. 1  with some of the graduations on the encoder disc omitted from the drawing in order to prevent the complete obscuring of the LED. 
       FIG. 3  is a plan view of the arrangement of  FIG. 1  also showing the possible directions of rotation. 
       FIG. 4  is a plan view of an arrangement for two phototransmitters (LEDs in this case), three opto-electronic sensors and a spherical optical scale to function as a triple-axis encoder of the present invention. 
       FIG. 5  is a side view of the arrangement of  FIG. 4  to function as a triple-axis encoder. 
       FIG. 6  is an enlarged cross-sectional view taken along line  6 — 6  in  FIG. 4  to show details of employing an internal transparent, hollow spherical float to generate an extra electrical signal. 
       FIG. 7  is an enlarged diagrammatic representation of a solid angle of approximately 8 degrees cut out of an undifferentiated spherical shape, employed to construct various encoder scales for two- or three-axis encoders of the present invention. This figure is a precursor to  FIG. 9  through  FIG. 16 . 
       FIG. 8  is an enlarged diagrammatic representation of a solid sector of approximately 8 degrees cut out of an undifferentiated cylindrical disc, employed to construct various encoder scales for single-axis encoders of the single-axis encoder of the present invention. This figure is a precursor to  FIG. 9  through  FIG. 11 . 
       FIG. 9  is a cross-sectional view taken along lines  9 — 9  in  FIG. 7  and  FIG. 8  to show details of a solid, transparent homogenous encoder-scale body. 
       FIG. 10  is a cross-sectional view taken along lines  10 — 10  in  FIG. 7  and  FIG. 8  to show details of a solid, partially transparent encoder-scale body with various dispersed elements. 
       FIG. 11  is a cross-sectional view taken along lines  11 — 11  in  FIG. 7  and  FIG. 8  to show details of a solid, transparent encoder-scale body with optical-scale elements positioned near the inside of the outer periphery of said body. 
       FIG. 12  is a partial cross-sectional view along line  12 — 12  of  FIG. 7  to show relevant details from a hollow encoder-scale body with actual optical-scale elements fully, constituting said body. 
       FIG. 13  is a partial cross-sectional view along line  13 — 13  of  FIG. 7  to show relevant details from a sealed, hollow encoder scale body made of transparent thermoplastic with optical-scale elements placed flush with the outer boundary of said body. 
       FIG. 14  is a partial cross-sectional view along line  14 — 14  of  FIG. 7  to show relevant details from a sealed, hollow encoder-scale body made of transparent thermoplastic with optical-scale elements placed inside the outer boundary of said body. 
       FIG. 15  is a partial cross-sectional view along line  15 — 15  of  FIG. 7  to show relevant details from a sealed hollow, spherical encoder-scale body made of transparent thermoplastic with fine optical-scale elements placed all around the outer boundary of said body. 
       FIG. 16  is a partial cross-sectional view along line  16 — 16  of  FIG. 8  to show relevant details from a sealed hollow, spherical encoder-scale body made of transparent thermoplastic with fine optical-scale elements placed inside the outer boundary of said body. 
       FIG. 17  is a schematic representation, in perspective, of a wired up arrangement for two phototransmitters (LEDs in this case), two dual-diode or dual-phototransistor opto-electronic sensors and a spherical optical scale with polygonal openings to function as a double-axis encoder of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , an approximately parallel beam of light of certain wavelengths or bandwidth is emitted by a phototransmitter, non-diffused LED  30 , towards the cylindrical surface  28  of encoder disc  29  made of a transparent material—a thermoplastic or glass. Said parallel beam of light would have crossed encoder disc  29  as secant lines. However, due to refraction in the medium which constitutes encoder disc  29 , said beam angles towards central axis  32 , comes out roughly from near opto-electronic sensor  31  and falls on the photosensitive part of it. Opto-electronic sensor  31  consists of twin photodiode, phototransistor or light-dependent resistor units with one pin from each unit connected together; the physical positioning of said units is one on the other with electrical connections pointing downwards, like opto-electronic sensor units  54  and  55  inside dual opto-electronic sensor  50  of  FIG. 6 . The travel of said beam of light through all circular and elliptical sectional planes of the cylindrical optical medium of encoder disc  29  is governed by four factors: one, transmittance of encoder disc  29 ; two, total internal refraction through the same; three, internal reflection by surfaces  34  and  35  ( FIG. 2 ); and, four, surface finish and texture of cylindrical surface  28  ( FIG. 1 ). If graduation  33 , consisting of various lines of varying or uniform width, opaque to the light emitted by LED  30 , is placed evenly or unevenly on cylindrical surface  28 , it produces a pattern of variation in the intensity of light falling on said sensitive area of opto-electronic sensor  31 , which induces proportional electrical changes in the electrical circuit to which opto-electronic sensor  31  is connected. In one way, graduation  33  is placed outside on the cylindrical surface of encoder disc  29  in said distribution. In other ways, it is either non-existent ( FIG. 9 ), embedded to a certain volumetric scheme or pattern (elements of varied opacity  41  in  FIG. 10 ), or embedded in a cylindrical fashion near the outer periphery of said disc (optical encoder elements  46  in  FIG. 11 ). Basic material for construction in  FIG. 9 ,  FIG. 10  and  FIG. 11  is any kind of transparent glass, but, alternatively, it can be a transparent and tough thermoplastic. 
   As mentioned hereinabove, the finish of surfaces  34  and  35  is of importance because greater reflection from surfaces  34  and  35  increases the intensity of light reaching said surface of opto-electronic sensor  31 . The present invention can easily be used to know the condition of the circular optical scale used with conventional opto-electronic encoders with axially placed opto-electronics. Without disturbing the existing placement of said opto-electronics, LED  30  and opto-electronic sensor  31  have to be positioned as shown in  FIG. 1 , while the existing opto-electronics remain facing surfaces  34  and  35 . The internal medium of encoder disc  29  is homogenous as shown in  FIG. 9 , and graduations  33  in any form are absent from cylindrical surface  28 . As encoder disc  29  accumulates dirt on its cylindrical surface  28  and flat surfaces  34  and/or  35 , starts chipping near the edges of cylindrical surface  28 , or develops internal cracks inside encoder disc  29 , the original optical homogeneity of disc  29  is lost and the pattern of intensity of light falling on said surface of opto-electronic sensor  31  alters. An analogue or digital processor circuit identifies said alteration translated into electrical variations in opto-electronic sensor  31 . This outputs an alarm to a desired electronic address or human monitoring position. 
   The construction of a single-axis encoder with the present invention consists of a printed circuit board annular in profile, or a plurality of printed circuit boards assembled on annular-profile base  59  forming orbicular confines to encoder disc  29 , containing LED  30  and opto-electronic sensor  31  in approximately the same orientation as shown in  FIG. 1 ,  FIG. 2  and  FIG. 3 , together with electronic components necessary for driving LED  30 , processing the output of opto-electronic sensor  31  and an electrical arrangement to connect to similar or other equipment. The arrangement and scheme of means or elements that allow the entry and exit of said light could be optimally selected by somebody familiar with related art. The resolution of the optical scale (means that allow the entry and exit of said light), graduations  33  in  FIG. 1 , is maximum when put on cylindrical surface  28 . Other variants of the optical scale, discussed hereinbefore, do not offer as high a resolution as do graduations  33  on cylindrical surface  28 . However, they too have distinct functional advantages—ranging from higher reliability to greater secrecy. The construction of said encoder is complete with the linkage of central axis  32  ( FIG. 1 ) to the prime rotational unit via a shaft or a screw passing through hole  36  ( FIG. 3 ), allowing bi-directional rotations in circular directions  27  ( FIG. 1  and  FIG. 3 ). 
     FIG. 4  and  FIG. 5  show the basic construction of a three-axis encoder or error-inputting device for a toy robot. Spherical body  37  is of spherical construction with distribution of means for entry into, exit from and travel along circular sectional planes of spherical body  37 , of said light from LED  30  arranged in any one of the manners shown in  FIG. 10  through  FIG. 16 . The manner shown in  FIG. 10  cannot easily produce a linear scale. The rest of the arrangements can be selected according to suitability for an application. The arrangement in  FIG. 11 , with optical encoder elements  46  embedded cylindrically or spherically near to the outer periphery, is suitable for making rugged and heavy two- or three-axis encoders or error-inputting devices, which function under the influence of gravity or in linkage or contact with a prime moving part or surface. Still, while functioning, if spherical body  37 , made according to  FIG. 11 , comes in frequent contact with abrasive particles, the external polish required for optimum optical performance of spherical body  37  would deteriorate, affecting the proper functioning of said encoders or devices. The arrangement shown in  FIG. 12  is most appropriate for functioning in extremely harsh environments. Spherical body  37  is built entirely from the elements of optical scale, encoder perforation  44  ( FIG. 12 ), which could be any material opaque to the light from LED  30  and able to withstand externally applied forces. The arrangements shown in  FIG. 13  through  FIG. 16  depict spherical body  37  constructed of any transparent thermoplastic, with elements of optical scale incorporated. This choice of material makes spherical body  37  susceptible to frictional and environmental degradation. In  FIG. 13 , the exterior of encoder perforation  44  is flush with the exterior of the transparent thermoplastic used to build spherical body  37 . In another variation, encoder perforation  44  in  FIG. 14  is laid spherically, roughly in the middle of the thickness of the transparent, thermoplastic, hollow embodiment of spherical body  37 . In its embodiments in  FIG. 13  and  FIG. 14 , encoder perforation  44  remains of the same thickness as depicted in  FIG. 12 , but could be made with a material, opaque to said light, but weaker in comparison to the one used to make encoder perforation  44  of  FIG. 12 .  FIG. 16  is identical in all other respects to  FIG. 14 , except for optical encoder elements  46  ( FIG. 16 ) being appreciably thinner than encoder perforation  44  ( FIG. 13  and  FIG. 14 ). The scheme for arranging optical encoder elements in  FIG. 13  has the danger of the chipping away of the transparent thermoplastic from the exterior of optical openings in encoder perforation  44 . That is avoided by utilizing the schemes in  FIG. 14  and  FIG. 16 . The scheme for arranging optical encoder elements in  FIG. 15  offers the highest resolution, but suffers from dirt accumulation in the cavities formed by optical openings  45  in optical encoder elements  46 . 
   In  FIG. 4 , dual opto-electronic sensor  50  senses encoded rotation of spherical body  37  in circular directions  51 . Likewise, two of dual opto-electronic sensors  50  are placed perpendicular to each other (locations  48  and  49 ,  FIG. 5 ) with their photosensitive openings facing spherical body  37  ( FIG. 5 ). Dual opto-electronic sensor  50  at location  48  ( FIG. 5 ) senses encoded rotation of spherical body  37  in circular directions  52  ( FIG. 5 ). Dual opto-electronic sensor  50  at location  49  ( FIG. 5 ) similarly functions during the rotation of spherical body  37  in circular directions  53  ( FIG. 4 ). The components comprising two numbers of LED  30 , three numbers of dual opto-electronic sensors  50  (one location unmarked, the other two marked  48  and  49  in  FIG. 5 ) as shown in  FIG. 4  and  FIG. 5  are assembled either on an annular-profile printed circuit board (PCB) or on a plurality of PCBs fixed on an annular-profile base, which encircles spherical body  37  roughly around the median plane—near about level  39  in  FIG. 6 . To make a two- or three-axis encoder or an error-inputting device, said components with said annular-profile PCB or base are assembled with appropriate elements to form orbicular confines  61  ( FIG. 17 ) within which spherical body  37  is able to rotate freely, or to roll on a supporting surface with orbicular confines  61  traversing along. Orbicular confines  61  to spherical body  37  are such as not to allow its release from the orbicular confines during normal functioning of the whole apparatus. Orbicular confines  61  appear overall from outside as a toroidal profiled object encircling spherical body  37 , containing said functional opto-electronic and electronic components. A ball-and-socket joint with integrated three-axis encoder is made by mechanically connecting the toroidal-profile orbicular confines  61  in a modified form to one end of a limb and connecting spherical body  37  to the logical end of another limb. This ball-and-socket joint with the integrated three-axis encoder of the present invention is easily adapted to prosthetic, as well as robotic, use. The replacement of standard, panel-mounting package of LED  30  with a miniature side-looker package or a subminiature flat surface mount reduces space taken up by the opto-electronics, facilitating implementation of the present invention in said joint. Discussed hereinbefore, various details of optical encoder elements determining the entry, travel and exit of light emitted by two numbers of LED  30  positioned as depicted in  FIG. 4  and  FIG. 5  are not shown on spherical body  37  in  FIG. 4  and  FIG. 5 , as said details are shown separately in  FIG. 9  through  FIG. 16 . 
   Also possible with this invention, as shown in  FIG. 6  is another extra function of generating an impact- or pressure-sensitive output. The light emitted by LED  30  travels above level  39  to reach dual opto-electronic sensor  50 , the relative positions of each opto-electronic sensor unit inside dual opto-electronic sensor  50  shown as  54  and  55 . There are two large and small, hollow spherical bodies  40  and  57 . The latter has a measured volume of liquid  38 , which has properties of being opaque to the wavelength or bandwidth of light emitted by LED  30 . Liquid  38  can be a solution and/or mixture of various chemicals, in which many gases may be/are dissolved. It could also be partially or fully a suspension of various solids in a liquid medium. The selection of liquid  38  is governed mainly by its ability to block the light emitted by LED  30 , its density and liquid  38  being non-toxic to humans in the volume present inside large, hollow spherical body  40 . Large and small, hollow spherical bodies, respectively  40  and  57 , have high transmittance for the light emitted from LED  30 . However, they can have properties to block the rest of the wavelengths. Small, hollow spherical body  57  remains afloat in liquid  38 ; and at the same time, the top outer crest of small, hollow spherical body  57  touches the top, inner surface of large, hollow spherical body  40 , amply shown in  FIG. 6 . In order to prevent the loss of liquid  38  or deterioration of physical properties of small, hollow spherical body  57 , large and small, hollow spherical bodies  40  and  57  are impervious to outside gases and liquids over a wide temperature range. With certain pressure applied on top of large, hollow spherical body  40  top, consequent distortion takes place in its shape, pushing down small, hollow spherical body  57  which in turn raises level  39  of liquid  38 . After a certain extent, this process completely blocks the path of light from LED  30  to dual opto-electronic sensor  50 . The same happens to the other one or two opto-electronic set or sets of transmitters and receivers, which are essentially two numbers of LED  30  and dual opto-electronic sensor  50  in arrangements discussed hereinabove and shown in  FIG. 4  and  FIG. 5 . This simultaneous absence of incidence of light emitted by two numbers of LED  30  from a plurality of dual opto-electronic sensors  50  produces a unique condition. This is easily translated either into an electrical signal, or into a data bit to an electronic address. Said signal or data bit is also generated due to an impacting force on, or physical disturbance of, said apparatus of the present invention, which acts on said spherical bodies  40 ,  57  and level  39  of liquid  38  in a manner similar to the one described just hereinbefore. 
   Hence, one well versed in similar art can easily construct from the preceding description of the present invention an error-inputting balancing device, which would additionally do inputting of rotational movements by a toy robot and would also facilitate its mimicry of human loss of consciousness following a blow. In order to be able to shift the center of gravity of spherical body  37  away from its geometric center, said body is made of two halves. One half is similar to the one in  FIG. 16 , while the other is similar to the one in  FIG. 14 . Optical encoder elements  46  and encoder perforation  44  are made of a strong, high-density metal, like brass, for obtaining a greater said shift in the center of gravity of spherical body  37 . Joining said two halves produces spherical body  37  with a shifted center of gravity. Another way is to first join the two semi-spherical halves of the outer construction as depicted in  FIG. 12 , but to use a comparatively much thinner, but stronger, metal sheet to produce encoder perforation  44  for one half, and then to join the two halves whose exteriors look identical; this also produces a porous form of spherical body  37  with said shifted center of gravity. Yet another way of achieving a marked shift in the center of gravity of spherical body  37  is to peripherally connect a cylindrical rod of much less diameter to spherical body  37  from position  56  in  FIG. 5 . Allowable space and functionality determine the length of the rod. This method makes use of a totally symmetrical form of spherical body  37 , hence easing its manufacture, but has the disadvantage of severely restricting its rotational mobility. 
   Similarly, a reference again to  FIG. 4  and  FIG. 5  is made to explain the construction of a two-axis encoder or inputting apparatus. The removal of dual opto-electronic sensor  50  with its companion LED  30  (one of the two numbers of LED  30  in  FIG. 4 ) converts the apparatus of  FIG. 4  into a polar coordinate-inputting device. Whereas, with reference to  FIG. 5 , the removal of dual opto-electronic sensor  50  from location  49  makes the apparatus of  FIG. 5  a Cartesian coordinate-inputting device. 
   The electronic processing and storage of various signals from the opto-electronic sensors is varied, widely known and used by those of skill in the related art. Likewise, electrical driving techniques for LEDs are also widely known. Organic light sources are electrically driven in manners peculiar to their design. An organic light-emitting device (OLED), not yet standardized, is electrically similar to an LED, and has a knee voltage of approximately 3 Volts. An OLED&#39;s current intake is very little compared to a normal industry-standard LED, as well as its luminous output. Rays from the Sun are parallel, and therefore are a perfect source of light to replace LED  30  in  FIG. 1  through  FIG. 6 . In  FIG. 5 , by placing two more of dual opto-electronic sensor  50  so that they are oriented to each other as between locations  48  and  49 , at position  56 , with photosensitive regions of said sensors facing spherical body  37 , a feature of solar tracking or avoidance is built into said error-inputting balancing device for a toy robot. Rays from the Sun enter the optical encoder elements of spherical body  37  from its top side ( FIG. 5 ) and travel through spherical body  37  to come out from said elements and strike said regions of two more numbers of dual opto-electronic sensor  50  placed in said orientation at position  56 . A toy robot fitted with said device with said addition at position  56  in  FIG. 5  would be able to distinguish between sunlight, diffused light and light from an incandescent source, with the addition of appropriate data processing circuits to the present invention. 
   A choice has to be made between an integrated dual photodiode sensor device schematically detailed in  FIG. 6  with the two opto-electronic sensor units  54  and  55  within the dual opto-electronic sensor  50  and other available opto-electronic devices functioning as opto-electronic sensor  31  ( FIG. 1  through  FIG. 6 ). An integrated common-anode double photodiode is widely available with good resolution to sense infrared light coming out of encoder element apertures as narrow as half a millimeter. The response time of a photodiode is also the shortest in comparison to the same of other opto-electronic sensors. The use can be made of phototransistors or photodarlington transistors even when the intensity of incident light is little or very little. Light-dependant resistors can also be used in slow-speed encoder applications. For critical applications, two photodiodes together with other signal shaping and detecting circuits fabricated on an integrated circuit (IC) can be used as dual opto-electronic sensor  50 . This is shown in  FIG. 17 , where IC  62  is connected to two dual opto-electronic sensors  50  via tracks on PCB  60 . Two LEDs  30  are connected in series via current limiting resistor  67  together with other electronic components necessary for driving LEDs  30  in IC  62 . The processing of the output of dual opto-electronic sensors  50  takes place in IC  62  and an electrical arrangement to connect to similar or other equipment is shown with connecting wires  63 ,  64 ,  65  and  66 . 
   The use of infrared LEDs and matching dual-photodiode sensors has tested the present invention. However, use can be made of other wavelengths and bandwidths according to the requirements of the application. Appropriate filters can be added to spherical body  37  or encoder disc  29  to only allow passage of relevant wavelengths or bandwidth to which the opto-electronic sensors used are most sensitive. These filter elements impart a definite tint to spherical body  37  or encoder disc  29 , making the details of an optical scale visually hard to locate, and in some cases, protecting the secrecy of a code on the optical scale. 
   Certain workings have shown that to make use of readily available electronic circuitry, like a standard computer inputting device (mouse) circuitry shown in  FIG. 17  with PCB  60  and IC  62  and associated components, which would function with dual opto-electronic sensor  50 , the area of the largest optical closing on chosen optical scale should be around one tenth of the effective area of illumination by the approximately parallel beam of light coming out of the chosen optical transmitter of the present invention.