WO2009006306A1 - Networked optoelectronic sensor for detecting and counting objects - Google Patents

Abstract

A networked optoelectronic sensor for detecting and counting objects is provided. The sensor can count objects and/or people passing by the sensor, and can record both the direction of travel of the people and/or objects as well as the distance between the sensor and person and/or object. The sensor includes a pair of infrared transmitters and an associated pair of detectors for projecting two beams of light which are utilized to detect persons and/or objects in one or more desired areas. User-defined detection zones can be specified by the user, and movement of people or objects between the zones can be detected and counted. The sensor can be connected to a network so that detection events, as well as measured ranges and counts of detected objects, can be transmitted to a remote location, such as a central server.

Description

TITLE: NETWORKED OPTOELECTRONIC SENSOR

FOR DETECTING AND COUNTING OBJECTS

SPECIFICATION

BACKGROUND OF THE INVENTION

RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application Serial No.

60/946,753 filed June 28, 2007, the entire disclosure of which is expressly incorporated by reference.

FIELD OF THE INVENTION The present invention relates to optoelectronic devices, and more particularly, to a networked optoelectronic sensor for detecting and counting objects.

RELATED ART

It is often desirable to remotely detect and count objects within a space. For example, in premises monitoring and security applications, it is beneficial to remotely detect and count individuals within a specific area of a facility, as well as to remotely detect and monitor the movement of individuals from one area to another area.

Additionally, in industrial process control applications, it is often desirable to count objects as they move along a production line, as well as to detect the movement of such objects from one location to another location. Existing remote monitoring devices, which often utilize ultrasonic transducers or infrared detection components, suffer from a number of drawbacks. For example, existing monitoring systems often indicate only the presence of an object within a space, and are unable to count objects within the space or detect movement of the objects from one zone to another zone. Additionally, existing systems do not provide standalone detection systems that can be easily connected to a network to transmit information about a monitored area to a desired destination, such as to a central server. Moreover, existing detection systems often employ only a single transmitter and an associated receiver, which can result in diminished sensitivity of the detection system and an inability to discriminate between objects in a monitored space and to measure distances between the sensor and the detected objects.

Accordingly, what would be desirable, but has not yet been provided, is a networked optical sensor for detecting and counting objects which addresses the foregoing limitations of existing detection systems.

SUMMARY OF THE INVENTION

The present invention relates to a networked optoelectronic sensor for detecting and counting objects. The sensor can count objects and/or people passing by the sensor, and can record both the direction of travel of the people and/or objects as well as the distance between the sensor and person and/or object. The sensor includes a pair of infrared transmitters and an associated pair of detectors for projecting two beams of light which are utilized by the sensor to detect persons and/or objects in one or more desired areas. The sensor could be mounted horizontally at a sufficient height above the floor to avoid sensing specific objects (such as carts and small children) while detecting and counting desired objects. User-defined detection zones can be specified by the user, and movement of people or objects between the zones can be detected and counted. The sensor can be connected to a network so that detection events, as well as measured ranges and counts of detected objects, can be transmitted to a remote location, such as a central server. The sensor can also operate in a stand-alone mode, wherein detection events, counts, and ranges are stored by the sensor for later retrieval. Optionally, a display interface (e.g., an LCD display) could be provided for locally controlling the sensor.

BRIEF DESCRIPTION QF THE DRAWINGS

The foregoing features of the invention will be apparent from the following Detailed Description of the Invention, taken in connection with the accompanying drawings, in which:

FIG. 1 is a diagram showing the networked optical sensor of the present invention for detecting and counting objects;

FIG. 2 is diagram showing optical transmitter and receiver assemblies of the networked optical sensor of the present invention;

FIG. 3 is a diagram showing two optical beams generated by the networked optical sensor of the present invention illuminating two objects;

FIG. 4 is an electrical schematic diagram showing a circuit according to the present invention for driving the infrared transmitters of the networked optical sensor;

FIG. 5 is an electrical schematic diagram showing a detection circuit according to the present invention for each of the detectors of the network optical sensor;

FIG. 6 is a diagram showing a discrete Fourier transformation (DFT) processing algorithm implemented by the present invention;

FIG. 7 is a block diagram showing digital signal processing of detected signals implemented by the present invention; FIG. 8 is a diagram depicting the sampling method implemented by the present invention to compute a single-frequency DFT for use by the DFT processing algorithm illustrated in FIG. 6;

FIG. 9 is a block diagram of an algorithm according to the present invention for detecting the presence of objects and to discriminate between different objects;

FIG. 10 is a block diagram illustrating an algorithm according to the present invention for determining the range (distance) between an object and the sensor; and

FIG. 11 is a block diagram illustrating hardware and software components of the sensor of the present invention, as well as a direction counting algorithm.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a networked optoelectronic sensor for detecting and counting objects. The sensor can count objects and/or people passing by the sensor, and can record both the direction of travel of the people and/or objects as well as the distance between the sensor and person and/or object. The sensor includes a pair of infrared transmitters and an associated pair of detectors for projecting two beams of light which are utilized by the sensor to detect persons and/or objects in one or more desired areas. User-defined detection zones can be specified by the user, and movement of people or objects between the zones can be detected and counted. The sensor can be connected to a network so that detection events, as well as measured ranges and counts of detected objects, can be transmitted to a remote location, such as a central server. The sensor can also operate in a stand-alone mode, wherein detection events, counts, and ranges are stored by the sensor for later retrieval.

FIG. 1 is a diagram of the networked detection system 10 of the present invention for detecting and counting objects. The system 10 includes a networked sensor 12 which projects two light beams 14 and 16 into an inner region or space 18 and an outer region or space 20 beyond the inner region or space 18. The beams 14 and 16 allow for the detection and counting of objects within the inner and outer regions 18 and 20, as well as the directions in which the objects are traveling relative to the sensor 12. As shown, the sensor 12 can detect and count a person 22 within the inner space 18. When the person moves in the direction indicated by arrow A, the person 22 is first detected by the sensor 12 when the beam 14 reflects off of the person 22. Then, when the person crosses the beam 16, the beam 16 is reflected to the sensor 12 and the person 22 is detected. The sensor 12 measures the distance between the sensor 12 and the person 22 and calculates the time interval between the first detection using the first beam 14 and the second detection using the second beam 16. The measured distance and time interval can be used by the sensor 12 to indicate the direction that the person 22 has traveled relative to the sensor 12. Such motion can be used by the sensor 12 to determine traffic counts and flows. Also, as shown, a person 24 can be detected within the outer region 20, and the distance to the person 24 detected by the sensor 12. Thus, the sensor 12 can discriminate between objects or persons positioned or moving in the inner and outer regions 18 and 20. The detection ranges corresponding to the inner space 18 and the outer space 20 can be adjusted to provide desired sensitivity within a given environment. The beams 14 and 16 could include visible or invisible (e.g., infrared) beams of light, lasers, or non-optical electromagnetic or acoustic emissions. The sizes of the inner and outer spaces (zones) 18 and 20 can be adjusted as desired by a user. The sensor 12 could include a wired or wireless network transceiver, such as a wireless Ethernet or BLUETOOTH transceiver, to allow for the remote transmission and reception of data.

FIG. 2 is a diagram showing the networked sensor 12 of the present invention in greater detail. The sensor 12 includes a printed circuit board 30 on which is mounted a first light emitter assembly 32, a first light detector assembly 36, a second light detector assembly 40, and a second light emitter assembly 44. The light emitter assembly 32 emits the first beam 14, which is reflected by a target 50 (e.g., a person or an object) and detected by the light detector assembly 40. The light emitter assembly 44 emits the second beam 16, which is reflected by the target 50 and detected by the light detector assembly 36. The light emitter assemblies 32 and 44 include infrared light-emitting diode (LED) emitters 34 and 46 which could comprise the SFH4209 LED emitter manufactured by Osram, Inc., or any suitable equivalent. The light detector assemblies 36 and 40 include infrared position-sensitive detectors 38 and 42 which could comprise the IC-OD OBGA 04CD position-sensitive detector manufactured by Ichaus, Inc. Each of the assemblies 32, 36, 40, and 44 includes a stray light shield 52 and a baffle 56 for confining light, as well as a lens 54 for focusing the beams 14 or 16. The lenses 54 could include a dyed, acrylic plastic lens such as the RSlOOO lens manufactured by American Distributors, Inc., or any suitable equivalent. It is noted that lens 54 also functions as an infrared filter. The light emitter assemblies 32 and 44 and the light detector assemblies 36 and 40 are positioned to provide a maximum baseline separation between these devices. The components shown in FIG. 2 could be mounted in a molded, aluminized plastic housing which shields the components from radio frequency (RF) interference and which allows for easy assembly and alignment of optical components. Additionally, lens mounts could be provided for allowing easy removal and replacement of lenses. The components are arranged to allow for the detection and counting of objects using triangulation techniques.

FIG. 3 is a diagram illustrating interaction of first and second objects 58 and 64 (e.g., people) with the first and second beams 14 and 16 emitted by the detector 12. The beams 14 and 16 subtend angles resulting in large areas of the objects 58 and 60 being illuminated. As can be seen, the object 58 is only partially illuminated by the beam 14, such that a ray 60 is reflected by the object 58 while the ray 62 passes the object 58. The object 64 is illuminated by the entire beam 16, such that the rays 66 and 68 are reflected by the object 64. The reflections produced by the objects 58 and 60 are determined by the surface features of each object, and are utilized by the detector 12 to discriminate between objects, determine both the spatial location and movement of such objects, and to calculate the distances (ranges) between the objects and the sensor 12.

FIG. 4 is an electrical schematic showing a circuit, indicated generally at 70, according to the present invention for driving the infrared LEDs 34 and 46 of the infrared transmitter assemblies 32 and 44 shown in FIG. 2. It is noted that duplicate circuits 70 could be provided, one for each of the LEDs 34 and 46. A voltage source 71 charges a capacitor 76 through resistor 72. A field-effect transistor (FET) switch 80, when activated, allows current to flow through the LEDs 34 and 46, which can be limited by resistor 74. The capacitor 76 is a low equivalent series resistance (ESR) type device, has an ESR lower than resistor 72, and supplies the majority of a current pulse through the LEDs 34 and 46. The FET switch 80 is controlled by a pulse-width modulated (PWM) circuit 82, which provides a constant-frequency train of pulses 84 having a variable duty cycle. The PWM circuit 82 could include the DSPIC30F3010-30I/ML DSP microcontroller manufactured by Microchip, Inc., but other components could be substituted, such as a programmable logic device (PLD) or an application-specific integrated circuit (ASIC), each programmed to perform a PWM function. The duty cycle of the pulse train 84 is controlled by an automatic gain control signal 86 supplied to the PWM circuit 82. The PWM control signal 88 selectively switches the pulse train 84 on or off, so as to control a burst of light modulated at a particular PWM frequency set by the automatic gain control signal 86 and to alternate between the beams 14 and 16 (see FIGS. 1-3) generated by the LEDs 34 and 46. This also prevents interference between the beams 14 and 16. FIG. 5 is an electrical schematic diagram showing a circuit, indicated generally at 90, according to the present invention for receiving, amplifying, and filtering light signals detected by the detectors 38 and 42 of the detector assemblies 36 and 40 shown in FIG. 2. It is noted that duplicate circuits 90 could be provided, one for each of the detectors 38 and 42. Reflected light 91 impinges on the detectors 38 and 42, each of which could include a position-sensitive photodiode 92 and an internal amplifier and filter 94. Preferably, the internal amplifier and filter 94 has a center frequency of 100 kHz, but other values are possible. The output of the amplifier and filter 94 comprises a near signal 95 and a far signal 97. The near signal 95 is converted to a voltage signal that is referenced to circuit ground by a load resistor 96. A capacitor 98 functions as a low-pass filter together with the resistor 96 to limit high-frequency noise. A capacitor 100 together with a resistor 102 AC couples, filters, and level shifts the voltage signal produced by the internal amplifier and filter 94 and processed by the resistor 96 and capacitor 98. The processed output of the internal amplifier and filter 94 is then referenced to a voltage generated by a voltage reference circuit 108. In this arrangement, the signal can easily be referenced to a voltage that is preferably selected between the supply voltage and the circuit ground so as to allow AC signals to be conveniently digitized by a circuit supplied by a single-ended DC supply. The processed signal is further amplified and filtered by a bandpass amplifier circuit 104, which is also referenced to the reference signal generated by the voltage reference circuit 108. Preferably, the bandpass amplifier 104 has a cut-on frequency of 100 kHz and a cut-off frequency of 200 kHz with a -6 dB rolloff and a gain of 32 dB. Of course, other values are possible. The amplifier circuit 104 produces an analog near output signal 106. The far signal 97 generated by the integrated amplifier and filter 94 is processed in a nearly identical fashion. A resistor 114 converts the far signal to a voltage signal that is referenced to circuit ground. A capacitor 116 functions as a low-pass filter together with the resistor 114 to limit high-frequency noise. A capacitor 112 together with a resistor 110 AC couples, filters, and level shifts the voltage signal produced by the internal amplifier and filter 94 and processed by the resistor 114 and capacitor 116. The processed output is then referenced to the voltage generated by the reference circuit 108, and further amplified and filtered by a bandpass amplifier circuit 118, which is also referenced to the reference signal generated by the voltage reference circuit 108. The amplifier circuit 118 preferably has the same cut-on, cut-off, rolloff, and gain parameters as the amplifier circuit 104, and generates an analog far output signal 120. Advantageously, the circuit 90 mitigates interference common in indoor applications and generated by artificial light sources, such as fluorescent lights with electronic ballasts, as well as natural sources such as bright sunlight. At the same time, the circuit 90 amplifies the signals produced by the modulated light in the sensor beams.

FIG. 6 is a block diagram illustrating processing steps of a discrete Fourier transformation (DFT) algorithm, indicated generally at 122, according to the present invention for processing the output signals of the circuit 90 of FIG. 5. A series of serial output samples 123, which are selected from buffers 158 or 160 by switch 162 in FIG. 7 and are digitized samples of the near or far output signals 106 or 120 from the circuit 90 of FIG. 5, are input sequentially into the algorithm 122 of FIG. 6. A sine (SIN) / cosine (COS) data switch 124 alternately directs the data to the SIN or COS branch of the algorithm 90 depending on the position of the sample in the data stream. Inverter switches 126 and 128 direct the data either to an inverter 130 or 142, or directly to a SIN accumulator 132 or a COS accumulator 144. By selectively controlling the switches 124, 126, and 128, the algorithm 122 produces a sum of the multiplication of the sample stream by each of the SIN and COS waves in the SIN accumulator 132 and COS accumulator 144. The accumulation continues for a programmable number of samples determined by the desired "Q" factor of the filter. By increasing the number of samples, the Q factor can narrow a filter's response at the expense of a longer sampling time and a slower response. For maximum filtering, the number of samples can be programmed to 256, which results in a Q factor of 128 and a response time of 0.8 milliseconds. Once the accumulators 132 and 144 have summed the programmed number of samples, the magnitude of the complex representation of the transformation is computed by taking the root sum of squares of the result stored in the accumulators 132 and 144 using square fiinction modules 134 and 146. Then, after processing by the modules 134 and 146, the results are added by an adder 136 and processed by a square root function module 138. The output 140 generated by the square root module 138 represents the magnitude of the 100 kHz frequency component of the response.

FIG. 7 is a block diagram showing digital signal processing applied to the near and far output signals 106 and 120 of FIG. 5, generated by the circuit 90. Illustratively, two of the circuits 90 are shown in FIG. 7, one for light (e.g., "Beam A" corresponding to beam 14 of FIGS. 1-3) detected by one detector 38 and the other for light (e.g., "Beam B" corresponding to beam 16 of FIGS. 1-3) detected by the detector 42. The output signals 106 and 120 are fed to an analog-to-digital (ATD) converter module 156 which has the capability to simultaneously sample all four signals (i.e., Beam A near signal, Beam A far signal, Beam B near signal, and Beam B far signal) preferably at a frequency of 400 kHz. The four samples are converted to a digital representation by the converted module 156 sequentially between samples and stored in one half of a dual port buffer, illustrated at 158 and 160. After two sets of samples have been converted, the A/D converter module 156 switches buffers and signals a data switch 162 to begin processing the samples in the full buffer half. In this manner, samples can continue to be collected without interference, provided that the processing is completed before the next half of the buffer is filled. Once signaled, the data switch 162 proceeds to read data from each location in the buffer and loads data into respective Discrete Fourier Transform (DFT) filters 164-170 for each signal (i.e., DFT for Beam A near signal, DFT for Beam A far signal, DFT for Beam B near signal, and DFT for Beam B far signal). The DFT filters 164-170 each execute the DFT algorithm 122 described above with respect to FIG. 6.

The A/D converter 156 can be programmed to sample selective signals (e.g., only

Beam A or Beam B) signals, and to store the converted results in the buffers 158 or 160 such that one beam can be activated at a time and processed. Additionally, the data switch 162 can be programmed to load the appropriate DFT filter with the buffered data.

The outputs of the four DFT filters 164-170 are directed to AGC factor (FAC) blocks 172-178, each of which correct the resulting signal magnitudes for the AGC factor applied to the beam LEDs 34, 46 by the circuit 70 of FIG. 4. The two outputs "ANOUT" and "AFOUT" are combined by an adder module 180 to produce an "A" intensity signal ("AINTENSITY") that is representative of the total amount of light reflecting from the target being illuminated by the A beam. This allows for gain control of the A beam (i.e., beam 14 of FIGS. 1-3). If the response from the reflected light is greater than the saturation level of the circuit 90 of FIG. 5, an AGC control module 184 signals the PWM module 82 of FIG. 4 to reduce the duty cycle 84 and adjusts the AGC factor 86 so that the resulting output ANOUT represents the response that would have occurred if the beam were transmitted at full power, and so that signals at different gain levels can be compared directly. Another sample is then taken at the reduced duty cycle and the response is again compared to the sample level. A further reduction in the duty cycle is performed, and the process is repeated until the response is below the saturation level. The process is identical for the B beam signals "BNOUT" and "BFOUT," both of which are fed to an adder 182 to produce a "B" intensity signal ("BINTENSITY") which is transmitted to an AGC control module 186 for gain control of the B beam (i.e., beam 16 of FIGS. 1-3).

FIG. 8 is a diagram depicting the sampling method implemented by the present invention to compute a single-frequency DFT for use by the DFT processing algorithm 122 of FIG. 6. Since the majority of the energy transmitted in a beam is contained in the fundamental frequency of 100 kHz and all other frequencies can be ignored, this method isolates the fundamental frequency and rejects all others. The principle of the DFT filter is to multiply the sampled signal by a sine wave 190 and a cosine wave 192 at the fundamental frequency and to sum the results separately to produce the real and imaginary parts of the transformation. To reduce the computation and processing resources required to produce these sums, only the peak values of the sine and cosine waves 190 and 192 are used, corresponding to the maximum positive cosine value (COS+), the maximum positive sine value (SIN+), the maximum negative cosine value (COS-), and the maximum negative sine value (SIN-) illustrated in FIG. 8. At these points, the sin and cosine waves 190 and 192 are either at a value of 1 or -1, and the multiplication corresponds to either summing the sample directly or summing the negation of the sample. The diagram shows the how the timing of this sampling method results in the sampling period being ¹A of the fundamental period, resulting in the sampling frequency of 400 kHz being 4 times the fundamental frequency of 100 kHz.

FIG. 9 is a block diagram of an algorithm 200 according to the present invention for detecting the presence of objects and to discriminate between different objects. A change in the intensity of received light can used for this purpose. Reflected intensity data 202, which includes either the AINTENSITY or BINTENSITY signals generated by the AGC control modules 184 or 186 of FIG. 7 (depending upon which beam 14 or 16 of FIGS. 1-3 is being utilized), is provided as input to the algorithm 200. The intensity data 202 is controlled by a data switch 204, which is initially closed. When the switch 204 is closed, an infinite impulse response (IIR) filter 206 produces a sliding window time average of the intensity data 202. Divider module (1/n) 208 produces a programmable fraction of the filtered output. The fraction is then added to the output of the filter 206 by adder module 210 to produce a detection threshold signal. A comparator 212 compares the intensity data 202 to the detection threshold signal. If the intensity data 202 is greater that the detection threshold signal, the comparator 212 opens the data switch 204. In this manner, elevated signals produced by reflections from targets in the beams 14 and 16 of FIGS. 1-3 do not contribute to the background level average represented by the output from the IIR filter 206. Additionally, the comparator output is passed to a debounce module 214 which outputs an output flag signal 216. The debounce module 214 requires that the intensity data 202 be greater than the threshold level for a programmable number of samples. If so, it changes the state of the output flag 216. The debounce module 214 also requires the intensity level to be less than the detection threshold for a programmable number of samples in order to change the state of the output flag 216. The output flag 216 then represents the condition that a target has been detected in the beam and, and can be processed to count, determine the direction of travel, and the distance to the target.

FIG. 10 is a block diagram illustrating an algorithm 220 according to the present invention for determining the range (distance) of an object to the sensor. The ANOUT,

AFOUT, and A intensity values, as well as the BNOUT, BFOUT, and B intensity values discussed above in connection with FIG. 7, are processed by range function modules 228 and 250 to calculate the range (distance) to an object from the sensor of the present invention. Range values can be calculated using the A beam (i.e., beam 14 of FIGS. 1- 3) or the B beam (i.e., beam 16 of FIGS. 1-3). The range function modules 228 and 250 compute values proportional to an ideal range using the formulas:

A Range = (AFOUT - ANOUT ) /A Intensity B Range = (BFOUT - BNOUT) /B Intensity

The results are passed to calibration table modules 230 and 252, each of which contains a table of values corresponding to the actual range represented by the ideal range value as determined by a calibration process resulting in the stored, tabulated values. The calibration table and the calibration process are thus able to compensate for errors resulting from inexact optical alignment, loose assembly tolerances, variation in gain, and other effects known to produce errors in triangulation systems. The outputs of the calibration table modules 230 and 252 represent sets of discrete range values or bins. Preferably, each bin represents a distance of one foot, such that a target located between 0 feet and 1 foot from the sensor will result in an output from the calibration tables 230 and 252 of 1 foot. Any target located between 1 foot and 2 feet will result in an output of 2 feet, and likewise for each foot up to the maximum range of the sensor. Any desired distance could be selected for the size of the bin.

As each sample is processed by the calibration modules 230 and 252, the results are stored in a sliding window array such that a record of the last 5 samples is always available in the range array buffers 232 and 254. The A and B intensity signals are also stored in similar intensity array buffers 238 and 260. Additionally, the A and B intensity signals are directed to peak detector modules 236 an 258, as well as event signals for each of the A and B intensity signals that are generated by a detection state machine 286 of FIG. 11 (described below). The peak detector modules 236 and 258 compare each intensity signal to previous signals during a detected event to determine the peak in the reflected light from the target. When this peak occurs, the target is most likely located as illustrated by the object 64 in FIG. 3, i.e., the target is illuminated by an entire beam of light It is at this point that the effects of partial illumination illustrated in FIG. 3 are minimized, and the range as determined by the triangulation system is likely to be most accurate. To further improve the accuracy, the peak detectors 236 and 258 delay their outputs for an additional two samples, at which time the detectors 236 and 258 cause peak range arrays 234 and 256 to capture the contents of the range arrays 232 and 254. The result is that the peak range arrays 234 and 256 contain 5 range samples centered on the peak intensity and extending two samples before and two samples after the peak intensity occurred. The peak signals also trigger intensity array buffers 238 and 260 to freeze the buffer and store the 5 intensity values corresponding to the samples stored in the peak range arrays 234 and 256. The sum of these five values is computed by the intensity sum modules 240 and 262 and passed to a modal analyzer 242 to produce a range output signal 264 indicative of the range (distance) to the object from the sensor. FIG. 11 is a block diagram, indicated generally at 270, illustrating hardware and software components of the sensor of the present invention, as well as a direction counting algorithm, A digital signal processor (DSP) 272 programmed in accordance with the present invention as discussed herein produces the aforementioned A intensity, ANOUT, AFOUT, B intensity, BNOUT, and BFOUT signals, which are transmitted to a range processor module 288 programmed in accordance with the range processing algorithm 220 discussed above in connection with FIG. 10. The DSP 272 is connected to two of the circuits 70 described above with respect to FIG. 4 (illustratively, "Emitter A" and "Emitter B" circuits which, respectively, drive the LEDs 34 and 46 for producing the beams 14 and 16 of FIGS. 1-3), and provides the aforementioned PWM control and AGC control signals for these circuits.

The A intensity and B intensity signals are input into threshold detectors 278 and 280 to create flag signals for the A beam and B beam respectively, labeled A Flag and B Flag. The A Flag and B Flag signals are inputs to a detection state machine 286 which proceeds thru a sequence of states as flag signals A Flag and B Flag activate and deactivate from the passage of a target through the sensor beams. Depending on the timing and sequence of the flags, one of five outputs ABCOUNT, BACOUNT, INDETERMINATE, BLOCKED, and EVENT are outputted by the detection state machine 286 to a communication and control module 290. If the target passed from the A beam (i.e., beam 14 of FIGS. 1-3) to the B beam (i.e., beam 16 of FIGS. 1-3), and then exited both beams, the detection state machine 286 will produce the ABCOUNT signal. If the target passed through both beams in the opposite direction, the state machine 286 will activate output BACOUNT. If the flags do not follow a predetermined pattern or take longer to progress through the detection pattern and exceed a programmable time limit, a target is detected but the state machine is unable to determine the direction of travel and activates the INDETERMINATE output. If a target enters either one or both beams and remains in the beams for longer than a programmable time interval without leaving, the state machine responds by activating the BLOCKED output. Beginning with the activation of either A Flag or B Flag and during the period where either flag remains activated (indicating that a target is passing through the sensors beams) the state machine 286 maintains the EVENT output as active, which activates the range processor module 288.

Prior to an event occurring, the communications and control module 290 alternately activates beam A and beam B LEDs 34 and 46, and controls the DSP 272 to process the resulting signals and direct them to the threshold detectors 278 and 280. The module 290 controls the beams so that only a single beam is emitting at any one time and the corresponding detector signals are processed to prevent crosstalk between the beams. The module 290 continues to scan while an event occurs as indicated by the activation of the EVENT signal, and subsequently the EVENT signal deactivates, indicating that the event has passed and the results of the detection and range algorithms are ready for processing. The module 290 then reads the output of the detection state machine 286 and the range output signal 264 (see FIG. 10) caused by the event and generated by the range processor module 288. The module 290 compares the results to the inner and outer detection limits defined by the two regions 18 and 20 of FIG. 1, and determines if the event is valid. If the range result lies between the limits and is therefore valid, the module 290 transmits the result to a host system via a network communication module 292. The network communication module 292 can be any type of network communications such as Ethernet, RS-485, WIFI, or even proprietary networks. Preferably, the communications module 292 utilizes a multi-drop RS-485 serial transmission medium. The results of the detected events can also be displayed via an onboard display interface 294, such as a liquid crystal display (LCD). The onboard display interface 294 can also serve as a user interface and can provide the ability for the sensor to operate in a stand alone manner while not connected to a network.

Upon completion of an event, as signaled by the deactivation of the EVENT signal by the detection state machine 286, the modal analyzer 242 of FIG. 10 first determines which of the two beams captured the highest intensity sum. Such a beam is most likely to have had the least distortion in the result due to partial illumination. The analyzer 242 then determines the mode (the result occurring with the maximum frequency in the set) of the set of range values stored in the peak range arrays 234 or 256 corresponding to the beam with maximum intensity. This determination can be made either directly or using a weighting scheme where the peak value carries a weight of three, the sample immediately before and after the peak a weight of two, and the remaining two samples a weight of one. The decision whether to us weighting is determined by how often the maximum range occurs in the set of ranges stored in the peak range arrays 234 and 256. Weighting is used if the maximum range occurs less than a preprogrammed limit. The mode of the weighted or unweighted set is output as the range output signal 264. The result is that the modal analyzer 242 determines which range result occurred most frequently in the samples taken surrounding the peak intensity of the beam that detected the most reflected light from the target, with more weight being given to the samples near the peak if the target passed close to the sensor. The range output is passed to the module 290 of FIG. 11. As previously described, the partial illumination produced by extended beams employed by the sensor of the preset invention, combined with irregular moving surfaces of objects or people being detected, distorts the response of what would otherwise be an ideal triangulation ranging system. In addition, the small size of the optics and the loose tolerances resulting from an inexpensive assembly without adjustments for optical alignment could result in a wide variation from the ideal response, even when flat targets are presented to the sensor. The range processor illustrated in FIG. 10 functions to convert the signals produced by the digital signal processor 272 of FIG. 11 into a calibrated range signal, collects a series of range signals from each beam produced by the target as it passes through the beams, analyzes the collected ranges to remove the effects of partial illumination by the beams and irregular surfaces, and outputs a single value for the range to the target during the time the event signal was present.

Preferably, the A/D converter 156 of FIG. 7 and dual port buffer 158, 160 are implemented using a DSPIC30F3010-30I/ML DSP microcontroller manufactured by

Microchip, Inc. The PWM module 82 of FIG. 4 could also be implemented in such a microcontroller. All other blocks and modules in FIGS. 6, 7, 9, 10 and 11, with the exception of the circuit 90 discussed herein and the display interface 294 in FIG. 11, could be implemented in software running in such a microcontroller. These blocks and modules could also be implemented as programmable logic or as an application-specific integrated circuit (ASIC). The microcontroller and all other circuitry, including supporting circuitry such as voltage sources, could be implemented on the printed circuit board 30 of FIG. 2. Having thus described the invention in detail, it is to be understood that the foregoing description is not intended to limit the spirit or scope thereof. What is desired to be protected by Letters Patent is set forth in the appended claims.

Claims

What is claimed is: 1. An optoelectronic sensor comprising:

a first emitter for emitting a first beam of electromagnetic energy into a first detection zone;

a first detector for detecting a first reflected beam of electromagnetic energy reflected from the first detection zone when an object is positioned in the first detection zone, the first detector generating a first signal corresponding to the first reflected beam of electromagnetic energy;

a second emitter for emitting a second beam of electromagnetic energy into a second detection zone;

a second detector for detecting a second reflected beam of electromagnetic energy reflected from the second detection zone when the object is positioned in the second detection zone, the second detector generating a second signal corresponding to the second reflected beam of electromagnetic energy; and

means for processing the first and second signals to detect movement of the object from the first detection zone to the second detection zone.

2. The sensor of Claim 1, wherein the means for processing calculates a direction of travel of the object based upon the first and second signals.

3. The sensor of Claim 2, wherein the means for processing calculates a distance between the sensor and the object based upon the first and second signals.

4. The sensor of Claim 3, wherein the means for processing calculates a total Jiumber of objects in the first and second detection zones based upon the first and second signals.

5. The sensor of Claim 1, further comprising a network transceiver for transmitting detected movement of the object to a remote destination.

6. The sensor of Claim 5, wherein the network transceiver transmits a direction of travel or a distance to the object calculated by the sensor to a remote destination.

7. The sensor of Claim 6, wherein the network transceiver transmits a total number of detected objects calculated by the sensor to the remote destination.

8. The sensor of Claim 5, wherein the network transceiver comprises a wireless network transceiver.

9. The sensor of Claim 1, wherein the first and second emitters each comprise a laser, and the first and second beams of electromagnetic energy each comprise a beam of light.

10. The sensor of Claim 1, wherein the first and second emitters each comprise a light-emitting diode, and the first and second beams of electromagnetic energy each comprise a beam of light.

11. The sensor of Claim 1, wherein the first and second emitters and the first and second detectors each comprise a light shield and a baffle for confining light.

12. The sensor of Claim 11, wherein each of the first and second emitters and the first and second detectors each comprise a lens for focusing light.

13. The sensor of Claim 1, further comprising a printed circuit board to which the first and second emitters and the first and second detectors are mounted.

14. The sensor of Claim 1, wherein the first and second signals indicate intensities of the first and second reflected beams of electromagnetic energy.

15. The sensor of Claim 14, wherein the means for processing the first and second signals discriminates between a plurality of detected objects using the intensities.

16. The sensor of Claim 1, further comprising first and second pulse-width modulation circuits for pulse-width modulating the first and second beams of electromagnetic energy generated by the first and second emitters.

17. The sensor of Claim 16, further comprising first and second amplifier and filter circuits for amplifying and filtering the first and second signals generated by the first and second detectors.

18. The sensor of Claim 17, further comprising a discrete Fourier transformation algorithm applied to the first and second signals by the means for processing for controlling gains of the first and second beams of electromagnetic energy.

19. The sensor of Claim 1, wherein widths of the first and second beams of electromagnetic energy are adjustable to vary sizes of the first and second detection zones.

20. The sensor of Claim 1, further comprising a display in communication with the means for processing for displaying detection events, calculated distances to objects, and calculated directions of motion of detected objects.

21. A method for detecting objects, comprising:

projecting first and second beams of electromagnetic energy into first and second detection zones;

receiving reflected beams of electromagnetic energy from the first and second detection zones using first and second detectors; generating first and second signals with the first and second detectors when the first and second reflected beams of electromagnetic energy are received by the first and second detectors;

receiving the first and second signals at a processor; and

processing the first and second signals with the processor to detect movement of an object from the first detection zone to the second detection zone.

22. The method of Claim 21, further comprising calculating a direction of travel of the object based upon the first and second signals.

23. The method of Claim 21, further comprising calculating a distance between the sensor and the object based upon the first and second signals.

24. The method of Claim 21, further comprising calculating a total number of objects in the first and second regions of space based upon the first and second signals.

25. The method of Claim 21, further comprising transmitting detected movement of the object to a remote destination.

26. The method of Claim 25, further comprising transmitting a direction of travel or a distance to the object calculated by the sensor to the remote destination.

27. The method of Claim 26, further comprising transmitting a total number of detected objects calculated by the sensor to the remote destination.

28. The method of Claim 21, wherein the step of projecting the first and second beams of electromagnetic energy into the first and second detection zones further comprises transmitting first and second laser beams into the first and second detection zones.

29. The method of Claim 21, wherein the step of projecting the first and second beams of electromagnetic energy into the first and second detection zones further comprises transmitting first and second beams of light from first and second light- emitting diodes into the first and second detection zones.

30. The method of Claim 21, further comprising processing intensities of the first and second signals to discriminate between a plurality of detected objects.

31. The method of Claim 21, further comprising pulse-width modulating the first and second beams of electromagnetic energy prior to projecting the first and second beams of electromagnetic energy into the first and second detection zones.

32. The method of Claim 21, further comprising amplifying and filtering the first and second signals prior to remove noise prior to processing the first and second signals.

33. The method of Claim 31, further comprising processing the first and second signals using a discrete Fourier transformation algorithm to control gains of the first and second beams of electromagnetic energy.

34. The method of Claim 21, further comprising adjusting widths of the first and second beams of electromagnetic energy to vary the sizes of the first and second detection zones.

35. The method of Claim 21, further comprising storing detection events in a memory associated with the processor for later retrieval.

36. The method of Claim 35, further comprising storing calculated distances to objects in the memory for later retrieval.

37. The method of Claim 36, further comprising storing calculated directions of motion of detected objects in the memory for later retrieval.

38. The method of Claim 31, further comprising displaying detection events on a display associated with the processor.

39. The method of Claim 38, further comprising displaying calculated distances to objects on the display.

40. The method of Claim 39, further comprising displaying calculated directions of motion of detected objects on the display.