Digital diagnostic apparatus and vision system with related methods

A high speed, low cost, apparatus and method of identification, examination of objects and quality control of manufactured parts and sheet materials, the apparatus including a comparator having memory storage of data representative of the surface of a first “standard” spatial linear distribution of light and memory storage of data representative of another portion of the surface, and including an algorithm for comparing data of the standard with data representative of the second spatial linear distribution of light reflected from a surface to determine if there is a correlation between the two spatial distributions.

FIELD OF THE INVENTION

This invention is primarily directed to an electronic apparatus and method for identifying and quantifying objects, their dimensions, condition or their conformity to specifications. It includes a sensor unit having a digital identifier or diagnostic unit. More particularly, the preferred embodiment is directed to an instrument for diverse functions such as: 1) determination of dimensions and conformity to specifications of parts formed of various materials, 2) inspection for abnormalities of a surface of flat materials including plastic, metal and woven and non-woven web and sheet, 3) identification of the type or quality of surfaces of a sheet material, 4) identification of the denomination of bills in a bill changer or counter and similar functions, and 5) determination of the presence or absence of components in a metal, plastic or wired assembly. The inventions disclosed are also applicable to other needs such as those of security and safety. For example, the inventions can sense intruders into an area and detect unsafe conditions such as a fire or failure of machine press operator to remove his hands from a press before it is closed.

In short, this invention is intended to be a low cost, fast and efficient alternative to the typical “machine vision” systems as well as to many of the “sensor” market systems although it will have application and uses in other fields as well. In part, the inventions disclosed and claimed herein are extensions and improvements of my earlier inventions disclosed in U.S. patent application Ser. No. 09/849,831 entitled DIGITAL SPECTRAL IDENTIFIER-CONTROLLER AND RELATED METHODS filed May 4, 2001 as a Continuation-In-Part application which has, as a primary focus, a method of identification of plants and objects using a color spectrum.

THE PRIOR ART

As understood, the prior art machine vision and sensor units used in production processes to identify dimensional flaws, missing parts, and improper assembly are relatively complex, intricate and expensive. They include cameras having linear or area array sensors that capture images of the part under consideration at high speeds. These images are then communicated in analog or digital form to a costly frame grabber that may be mounted in a computer such as a PC. The PC must be programmed with software so as to identify the flaws, missing parts, etc. Such software often includes various algorithms to rotate the image of the part and to make calculations regarding the part. In addition, the computer must be loaded with input data relating to design data such as the drawings and dimensions of the part under consideration. The software then reads the output of the array, (which is usually converted to digital form by the frame grabber), and compares it with the design data to check for flaws, missing parts and dimensions. Not only are these systems complex and expensive, they are believed to require considerable setup time. Representative of these systems are those sold by companies such as DVT Corporation of Norcross, Ga. and Cognex Corporation of Natick, Mass.

SUMMARY OF INVENTION

The present inventions are primarily directed to a less complex, low cost sensor and diagnostic apparatus that is easy to setup and maintain. The preferred embodiment includes a housing having a lens for receiving light and focusing it upon a sensor array. The pixels of sensor array receive light, generate a voltage and then communicate the magnitude of the light received by each pixel, as indicated by the developed voltage, to an analog to digital converter and then to an electronic comparator. This comparator takes the form of a logic chip with associated memory devices. Such may include the conventional microprocessor, a microcontroller, or a Digital Signal Processor (DSP), etc. These items, the array, the A-D converter and logic chip with memory, comprise the basic system hardware of my vision inventions. It is expected that the cost of the functional components, in volume, of this basic system may be less than ten dollars. In addition to this hardware, these inventions, however, also include software that preferably takes the form of one basic algorithm designed to run a relatively simple correlation calculation.

These inventions also include fast and efficient set up methods of using this system for the purposes of identification of flaws, verification of presence or absence of components, checking the dimensions of a part and of evaluating the surfaces of web materials formed plastics, woven materials, non-woven materials and metal for abnormalities such as spots and tears, etc. To avoid the input of data from drawings, the set up methods of my inventions focus on a “compare to standard” method rather than manual input of digital data from specifications and data. For example, to inspect a metal piece part for conformity, a good part is first made and checked for quality by a firm's quality control department. This checked item then becomes the standard against which other parts will be compared. Thus, a good part, not data from drawings or specifications, are used as the preferred standard of comparison although those skilled in the art will appreciate that the diagnostic unit may well function by making comparisons from input data.

This “compare to standard” method includes the steps of placing a product, object or surface, that is known to meet all quality standards, in front of the sensor or vision unit. Light reflected from the product, object or surface passes through the lens to impinge upon the sensor array, i.e., a series of pixels, to produce a spatial distribution of light thereon. Each pixel thus receives a portion of the spatial distribution and generates a voltage to indicate the intensity or magnitude of the light reflected from a small linear portion of the object, surface or product to define a spatial or linear fingerprint of the object along a line of the standard object. An output reflecting the linear fingerprint of the object is communicated to a “standard” memory location of the logic chip.

Thereafter, additional products, objects or surfaces from the population to the evaluated are passed under the vision system such that subsequent fingerprints of the remainder of the population are taken and placed into a different memory. The logic chip runs the software algorithm to compare the spatial distribution of the standard fingerprint with the spatial distribution of the object or additional products and produces an output signal from the logic chip to indicate the similarity or dissimilarity between the standard and the additional objects.

In addition to a focus upon one or more linear segments of a part, my invention can focus on an area by using an area array and running the regression analysis on the area by taking each line or each column of the area in sequence. Alternatively, my inventions can focus on a point of the “standard” part as well as upon a line extending across the part. The focal point focus is a method of checking the quality and sufficiency of a coating at a series of points on the metal part while the linear segments may continue to check dimensions, presence or absence, surface irregularities, etc. As will be shown this simultaneous coating and linear verification of a part may also be accomplished by the use of an area array. Importantly, the inventions of this application may be combined with the inventions of application Ser. No. 09/849,831 to simultaneously provide a full color spectral comparison and a black and white or grey scale comparison.

When using a linear array, these inventions are not limited to single line scan on each part. To the contrary, the inventions may confirm the quality of a substantial portion of the part, web or sheet of material. As the part comes down the conveyor at a speed of one part or one inch per second, these inventions may take a linear scan across part or web at a rate of several thousand scans or lines per second and each can be compared with the “standard” fingerprint immediately. As a result of multiple scans at high speeds, the quality and nature of the entirety of an object can be considered.

Accordingly, the goals and objectives of this invention are to provide, among other things, one or more of the following:1) a high speed, simplistic method for identifying objects, their dimensions, condition and their conformity to specifications;2) a low cost system and apparatus for identifying objects, their dimensions, condition and their conformity to a standard sample rather than specification data which must be manually input into a PC or other memory device;3) a method and a system for identifying objects and species of objects, their dimensions, condition and their conformity to specifications with a minimum of setup time and programming or data input;4) a very accurate method and apparatus for identifying objects and species of objects, their dimensions, condition and their conformity to specifications;5) low cost, high speed methods and apparatus for surface inspection of web, sheet and extrusions of metals, plastics woven and non-woven fabrics for tears, spots, stains, and other abnormalities;6) a simple, lost cost, high speed minimum maintenance apparatus and method for identifying, grading or selecting objects, plant and animal tissue by their spatial reflections of light;7) a low cost spatial scanning, sensing and identification unit that can use common or standard software for identification of objects, their dimensions, condition and their conformity to specifications;8) a low cost scanning and sensing device having a target or aiming system to identify an object whose spatial image is being generated;9) a light scanning and sensor unit having a digital identifier for selectively identifying and evaluating objects, plant and animal tissue of different colors for purposes of evaluation, processing, etc.10) A light sensor and diagnostic unit that can be used to scan a point, sequential lines or an area of a object, and run a correlation analysis to confirm that the point, lines or area of the object or its surface conforms to a standard;11) a low cost machine vision unit that eliminates the need for and cost of such items as frame grabbers, personal computers, costly data input and the creation of algorithms;12) a low cost and fast methods of installation that can avoid or minimize data input and the creation of new algorithms;13) a low cost security device that may be set to scan a target area or background and to identify changes in the background such as, for example, an intruder into the scanned area;14) a lost cost safety device that may be set to scan a target area of machinery and presses and to sound an alarm or stop a press when a person's hands would be injured by the closing of the machinery or the press; and15) a light sensor and diagnostic unit that minimizes the requirement for set up time, data or software input and relies primarily on a “compare to standard” method of part or surface diagnostics.

DETAIL DESCRIPTION

As depicted inFIG. 1, a preferred embodiment of the sensor or vision system10comprises a sensor unit20having a housing22. Within the housing is a lens28that receives reflected light from an object26whose identity is desired. In this alternative, the object26for identification is a five dollar bill. The light may be natural light, or if the unit is mounted in an enclosed bill changer or counter (not shown), the light may be generated by a lamp24. The lens28focuses the reflected light from along a line30on the bill to a sensor or linear array32such as part no. TSL 1301 from Texas Advanced Optoelectronic Solutions of Plano, Tex. This unit has102pixels, each of which comprises a PN junction. In operation, each of these pixels develops a voltage that correlates to the quantity or intensity of a spatial segment of light reflected from along the line30on the five dollar bill. The magnitude of the developed voltage of each pixel can be read by a logic chip, controller or comparator36such as a microprocessor, microcontroller, or preferably a Digital Signal Processor (DSP), such as DSP Model No TM320F243 which is made and sold by Texas Instruments of Dallas, Tex. In the first instance, a switch94is provided to enable the user to manually instruct the logic chip36to pulse the sensor array32to obtain a spatial distribution of the “standard” five dollar bill26. This pulse signal will sequentially generate an analog output from all of the pixels of the sensor array32and transmit them through an analog to digital converter to the Controller36to obtain in digital format the magnitude of the voltage developed by each pixel. As stated later, if the DSP Model TM320F243 is selected as the controller36, such has a built in A-D converter. The digital information or “fingerprint” of the standard is then placed into one of the memory elements of the Controller or Digital Signal Processor (DSP)36for storage and comparison purposes. When stored (memorized), the Controller or DSP36then has a spatial distribution or “fingerprint” of the wavelengths reflected by the true five dollar bills26to be identified as additional bills are inserted into the bill changer or counter. This first memorized print thus becomes the “standard” against which subsequent fingerprints are compared. Those skilled in the art will appreciate that, to insure greater, more reliable accuracy, two or more “standards” could be taken of the five dollar bill by moving the bill to a second or third position to the right and pulsing a second switch96to gain an additional fingerprint standard. Each “standard” would be placed into a separate memory element of the Controller36or into additional memory element associated with the Controller.

Thereafter, subsequent bills are placed into the bill changer or counter and they are moved into the same position as that shown for the sample bill26. Spatial distributions from these subsequent bills are sequentially obtained, placed in memory, and then compared with the spatial distributions of one or more samples. As will be explained, the controller or DSP36is programmed with an algorithm to perform this comparison function.

To quickly obtain accurate identification of the five dollar bills inserted into a bill changer, the Controller36is programmed to initialize reading the individual pixels of the linear sensor array32at a relatively high speed, such as once every 25 milliseconds. Thereafter, each clock pulse of the clock of the Controller or DSP36will serially read the voltage generated by each pixel or sensor to define a spatial linear image, frame or fingerprint of any subsequent bill placed into the changer or counter. As with the standard, this voltage is converted to digital information and then stored in other data memory locations of the Controller36. After the sensors are read and their output stored in the DSP36, the memorized or (“standard”) spatial distribution is compared with the spatial distribution of that reflected by the last bill. While only a few wavelengths could be compared to obtain a reasonably accurate determination of the similarity of the standard spatial distribution with that of the subsequent bill, this invention uses all of the 102 pixels and resulting data points made available by the TSL 1301.

Preferably, the comparison of the “standard” fingerprint with the subsequent spatial distributions is performed by a regression analysis algorithm that is programmed into the Comparator or DSP36or into an associated memory. Thus, as the bill is moved to the right as shown inFIG. 1, numerous spatial distributions of the bill will be developed by the linear array32. These distributions are repeatedly obtained from the array by the comparator36upon initiation of a clock pulse and a comparison of each new distribution is made with the standard. Since a DSP can obtain these distributions and make these comparisons at a rate of several thousand per second, the bill can be moved or conveyed across the lens relatively fast and yet permit sufficient comparisons to determine the existence of a match between any distribution and the standard, regardless of the position of the line from which the standard was taken. If the coefficient of correlation between the standard spatial distribution and any of the subsequent linear spatial distributions of the subsequent input bill is high or greater than the pre-set limit so as to reflect similarity or identity, the Controller36generates an output on lead37to count the bill as another five dollar bill or to provide change therefore or to provide a signal to initiate some other function.

If desired, a low cost target or aiming system can be added to the sensor unit20to identify for the user the position of the spatial line on the bill that is about to be scanned into memory as the standard. For example, a light emitting diode (LED)38can be placed on opposite ends of the linear array32and light from the LED's will focus a beam40and mark a spot42on each end of the spatial line from which the scan is taken. Such target spots will provide the user with visual and immediate feedback that the reflecting line30is on the bill.

As suggested earlier, two or more separate “standard” reflecting lines30may be scanned from the bill and used as a fingerprint to provide greater certainty that the bill is a five dollar bill. As the bill is moved by a conveyor or roller system (not shown) to the right, additional light data scans can be made and each will be compared with the “standard” scans to determine if there is a similarity or identity between a line on the present bill and that of the bill from which the standard was taken. If more than one standard is taken, an “and” gate (not shown) be used to couple the two output signals together to insure that all subsequent five dollar bills have two lines that matched the two fingerprinted standards. With the preferred DSP, several thousand comparisons could be made each second and the user would notice no delay.

As another alternative, many Controllers36can be selected that have sufficient memory to hold a plurality of “standard” reflection lines and such may be taken from several denominations such as one dollar bills, five dollar bills and ten dollar bills. Accordingly, with each additional bill that was placed in the bill changer or counter, the same correlation algorithm could be run for each standard. The output of the Controller could be modified to indicate if the bill is a one, five or ten dollar bill and provide appropriate change.

FIG. 2illustrates another application of these inventions. In this application, the invention is being used to inspect a web material44of plastic, paper, woven or non-woven fabric or sheet metal. As in the prior application, a “standard” spatial distribution is taken along the line30and placed into the memory of the Controller36. The material on this “standard” line is unblemished, contains no imperfections and fully meets the manufacturer's specifications. After the standard is placed into memory, the Controller36initiates the taking of additional spatial reflections as the web is moved in the direction of the arrow. The Controller36first places the additional spatial reflection in memory and then runs a similarity or regression algorithm to insure that subsequent light reflections are identical to or similar to the standard distribution of reflected light. If not, an output signal is emitted from the Controller36as on lead line37. In addition, in this embodiment, an analog scope is shown connected to the output lead33from the linear array30. As long as the web meets the “standard”, the scope will reflect a straight horizontal line modified by the uniformity of the illuminated light. However, when the web moves to the right such that the reflected line30is over a spot31, the reflected light will not be similar to or correlate with the “standard” placed in memory. This lack of correlation will be reflected by the analog scope by a decrease in voltage levels as shown at31′. In addition, the Controller36connected to the output line33of the array will emit an output signal showing a lack of correlation-and a defect in the web.

FIG. 3depicts another application of the inventions. This application is to test the presence or absence of components, (bolts46) of an assembly48. In this application, a standard was taken of an assembly in which two bolts46were properly placed in the assembly. Thereafter, subsequent assemblies48will be conveyed under the spatial reflection line30. When the second assembly48reaches the spatial reflection line, the Controller36will emit an output signal indicating a lack of similarity or correlation with the standard. Consequently and preferably, an output signal will be generated by the comparator36to indicate the dissimilarity and an actuator (not shown) will push the defective part off the conveyor. At the same time, the analog screen connected to lead33coming from the linear array32will show a substantial drop in voltage.

FIG. 4depicts an electronic circuit board64having mounted thereon a comparator such as a Digital Signal Processor (DSP)36that has been demonstrated to be effective for the purpose of these inventions. The circuit board64is provided with 5 volt power supply from an AC adapter62. In additional to its processor structure, the DSP36has, onboard, a clock, an analog to digital converter, an I/O unit, and memory. In addition, this DSP also has a 232 port, expansion memory, analog expansion and I/O expansion together with a JTAG port for receiving the algorithm program and placing it into the memory of the DSP36.

In operation, leads66and68prepare (SI) and initiating (CLK) data communication of the magnitude of the voltage contained in each of the pixels of the sensor array32. This accumulated data is communicated to the analog-to-digital (A-D) converter of the DSP via lead70. The A-D converter converts the analog signal to a binary digital signal and delivers the result to a memory address of the DSP36. A timer built into the DSP36repeatedly generates a clock pulse to take a new fingerprint of its visual area and deliver the fingerprint or spectral distribution in binary form back to the DSP or micro-controller36. With a proper light or lamp24, a new fingerprint or spatial distribution can be developed on the sensor unit32at a rate as high as several thousand per second.

When an identified part, web, bill, etc. has been checked for quality and conformance to a desired standard, it is placed below the array32and the user pushes “Standard” switch94. This action identifies the part as a “standard” and places its spatial distribution of reflected light in a first, standard or “fingerprint” memory on the DSP36. After the “standard” is set, the unit is ready to look at and evaluate subsequent parts, bills, webs, etc. that the user wishes to identify or evaluate.

After each spatial distribution is fed into the DSP36, it runs a preprogrammed regression analysis to determine the coefficient of correlation between the spatial distribution of the memorized standard and the spectral distribution of the object. The regression algorithm can easily be written by those skilled in the art and loaded into the DSP36through the JTAG port. This algorithm is a conventional regression calculation used to determine the degree of similarity of linear curve defined by one set of spatial data points with the linear curve defined by another set of data points. If one is looking to identify five dollar bills, the program must be designed to generate an output signal whenever the coefficient of correlation is equal to or greater than a predetermined value. Then the DSP36emits an output signal through the DSP bus to the I/O expansion board which closes a “normally” open switch to lead37that activates an LED72or other appropriate device such as a counter or a change machine. Preferably the result of the correlation computation is converted to an integer factor that is representative of the coefficient of correlation so as to simplify the decision and avoid a decimal number.

A second “standard” switch96can be used to set another “standard” for the five dollar bill, or and the DSP can be programmed to run a second regression analysis against this standard and the last spatial distribution of light received from the sensor32. If a high coefficient of correlation between each spatial distribution and each of two standards is made, such would provide greater certainty that the last input bill is, in fact, a five dollar bill.

The pre-set value or correlation limit established for actuation of the output signal or LED's72can be increased as desired through discriminating switches90and92. The non-grounded side of the more discriminating switch90is connected to pin15of the I/O expansion board. When this pin is activated, the program in the controller increases the limit of the correlation coefficient by 1/256. When pin16of the micro-controller is activated by pressing the less discriminating switch92the correlation coefficient limit is decreased by 1/256. The increment value, 1/256, may be decreased by a software change for greater accuracy.

To facilitate one's understanding of this invention, the flow chart ofFIGS. 5aand5bfurther discloses the functions of the software of the Controller36as described herein. Users of controllers and DSP will know or have available from the manufacturer knowledge of the set-up routines to initiate the each of the logic chips that might be used as the controller36. Thereafter, the steps of the program to be written for each alternative device are set forth in the flow chart.

Alternative Embodiments, Modes and Methods

Persons skilled in the art will appreciate that the disclosed scanning and identification invention can be utilized in several ways and is not limited to a specific mode. In addition, the present invention can take many forms and utilize numerous components that perform in substantially the same way to achieve substantially the same result. For example, numerous controllers or digital identifiers could be used in lieu of the preferred DSP disclosed in this specification. Those skilled in the art will appreciate that the essential functions of the digital diagnostic unit or controller36are those of providing memory for the storage of the spatial data and of the program steps reflecting the desired functions as well as logic circuitry having the ability to perform the desired functions and comparison. Such may include the identified chips which have a CPU and an arithmetic logic unit or its equivalent. In addition, the digital identifier36should have an Input/Output (I/O) capacity to receive data from the sensor array and to control at least one peripheral device such as the sensor array20. Consequently, any of the various microcontrollers, computers, microprocessors and digital signal processors (DSP) that have the necessary components will be acceptable alternatives and may be considered for the specific application of the user. Alternatively these individual devices such as the memory and I/O devices can be purchased separately and wired together on a circuit board to accomplish the necessary functions. Indeed, the comparators or controllers of these inventions can be obtained at a low cost so as to avoid the need for investment in frame grabbers, Personal Computers or other complex systems. Moreover, other devices can be selected for greater speed. For example, TM320f2820 from Texas Instruments Inc. is several times faster than the TMS 320f243 and, on information, could make several thousand line scans and comparisons of a surface per second.

In addition to the use of alternative processors, those skilled in the art will appreciate that different lamps may be utilized and that in many cases, the lamp will not be necessary with natural light being sufficient. Too, alternative array devices that are more sensitive or have different pixel counts may be utilized instead of the TSL 1301. For example, TSL 1401 from Texas Instruments, Inc. of Dallas, Tex. will permit the collection of 128 wavelength sectors rather than 102. And though the invention preferably uses a regression analysis to develop a coefficient of correlation, the invention may well provide the desired accuracy of object identification by merely comparing only three or four data points of the spatial light pattern. This could be accomplished by use of 3 or 4 discrete sensors properly located to sense the desired wavelengths of light and a simple comparison program that does not require a regression analysis or computation of the coefficient of correlation. A multiplicity of linear arrays or an area array, could be used to reduce the number of sensor units, with each column representing spectral information equivalent to one sensor unit. Those skilled in the art will also appreciate that, for purposes of this invention, CCD arrays will generally be equivalent to CMOS arrays with the CMOS devices being faster, but somewhat less accurate.

In another alternative, the light source24ofFIG. 1may be replaced by a set of multi-color lamps such as a red, green, blue and near infrared. The DSP could be programmed to turn on and off each lamp separately and digitize four images, one with reflected spatial distribution of light with each different lamp color. When the standard switch is activated, the DSP stores each spatial distribution as a standard in a separate memory location of the DSP or in additional associated memory. Future spatial distributions using all four colors from additional objects are compared to each standard using the regression analysis or a simple algorithm. The resulting analysis thus brings color into the diagnostic role of this invention. A decision could be made if any one of the four object spatial distributions provided a high correlation coefficient or comparison with any one or more of the four colored standard spatial distributions. Alternatively, the DSP could be programmed to require that there be a high correlation coefficient for all of the four color distributions before a positive output signal is activated.

Alternatively, the DSP could be programmed to add the four standard spatial distributions of each of the separate colors together to provide 4 times 102 or 408 data points and additional objects can be evaluated by a correlation analysis between the 408 data points of the standard and the 408 data points of the additional objects.

In yet another alternative, the imager32ofFIG. 1could be replaced with a color linear array such as KLI-2113 Tri-Linear Color Array Sensor manufactured and sold by the Eastman Kodak Company of Rochester, N.Y. Such would also provide the ability to include color in the discriminating process along a line. These arrays have three rows of photo elements and each is covered with red, green or blue filter strips for spectral separation. In addition, each row has a separate output and would use three of the digital converter inputs of the DSP. The logic and comparison are the same as described above. As persons skilled in the art will appreciate, other filters, such as a rainbow filter, can be used with the wide choices of linear arrays to also obtain spectral information. Alternatively, those skilled in the art will appreciate that the sensor unit20of my prior application, Ser. No. 09/849,831, further identified above, can also be operated in conjunction with a controller36of the present disclosure to add a spectral, color identification of an object to the spatial identification of the present disclosure. Under such a combination, both sensors would be tied to the controller36and it would be programmed to receive a standard spectral distribution as well as a standard spatial distribution and to run sequential correlation routines with the spectral and the spatial distributions.

Those skilled in the art will also appreciate that the controller36or the DSP can be programmed to run the correlation analysis in different ways. For example, the controller can programmed to run the correlation algorithm with on some or all of the data points of the “standard” spatial distribution and a similar selection of data points of the actual objects. Indeed, in some applications, the user will find that a limited number of data points control the decision making process at hand. In identifying denominations of bills of the United States, one might want to focus on the spatial distributions obtained from reflections of light from the green lamp or reflections through a green filter. Such provides additional spectral information that will aid in the identification process. Finally, the inventions disclosed herein could be coupled with the full spectral identifier of my copending application, Ser. No. 09/849,831 entitled DIGITAL SPECTRAL IDENTIFIER-CONTROLLER AND RELATED METHODS filed May 4, 2001 to provide a combination spectral-spatial identifier.

Those skilled in the various arts will also appreciate that the present inventions have broad uses in other diagnostic operations such as safety and security. For example, the unit could be mounted adjacent to an entrance to a home with the switch94being activated to establish the existing condition. Thereafter, if a person were to come into the view of the lens, a different spatial arrangement would be disclosed by the sensor array and the comparator can be programmed to set off alarms upon diagnosing a condition different from the “standard,” i.e., an unauthorized entry. Under such circumstances, those skilled in the art would appreciate that the standard or existing condition may be changed or refreshed periodically to accommodate a change caused by shadows resulting from movement of the sun or other reflected light. Similarly, the unit might be mounted on a machine tool or press with the switch94being activated to establish that condition. Thereafter, if the press were to be closed while the operator's hand was inside the press, the sensor could set off and alarm or disconnect power from the press upon diagnosing a conditions different from the “standard” or safe condition. Indeed, other uses and modifications of this invention such as these will be apparent to those of ordinary skill in the art from the contents of this application.