Abstract:
The adaptive system and method for ultrasound sensing comprises re-evaluating over time the detection threshold for predetermined sensing positions along the scanning direction to cope for the static target and environment changes at the sensing positions. The method includes comparing the measured echo value at each sensing position to a reference echo value corresponding to the same sensing position, and to iteratively determine a new reference value whenever the echo value is greater than the reference echo value and that the difference between the measured echo value and the reference echo value is lower than a detection assurance factor. The use of the adaptive ultrasound sensing system and method allows locating the sensor at different location without requiring a new calibration thereof, since the sensor learns the clutter dynamically and the detection thresholds are being built accordingly without being dependent on the environment in which the sensor is located.

Description:
This application claims the benifit of Provisional Application No. 60/436,455, filed Dec. 27, 2002. 

   FIELD OF THE INVENTION 
   The present invention relates to ultrasound sensing devices. More specifically, the present invention is concerned with a method and device for adaptive ultrasound sensing which finds applications, for example, in automatic door apparatus, bus and train doors safety sensors, machine tools, automatic self checkout systems, security sensors for valuables, and various proximity sensing systems. 
   BACKGROUND OF THE INVENTION 
   Automatic doors are in widespread use in various applications, such as elevators, buses, and trains. Considerations of personal safety require that doors are not to be closed when there is a danger that a person might be impacted thereby. While not compromising safety considerations, considerations of efficiency dictate that doors must be closed as promptly and quickly as possible. At the same time it is important that sensors, causing doors to close or alarming security systems to operate, should enable small changes in the environment and fixed patterns existence. 
   There exist various techniques and apparatus for sensing the existence of a person and his accouterments within a predefined zone and consequently operating an automatic door. 
   The following U.S. patents exemplify the state of the art: 
   
     
       
             
             
             
             
           
         
             
                 
             
             
               No. 
               Title 
               Date 
               Inventor(s) 
             
             
                 
             
           
           
             
               2,826,753 
               Object Detectors 
               Apr. 13, 1954 
               Chapin 
             
             
               4,029,176 
               Doorway Safety Device 
               Jun. 14, 1977 
               Gerald 
             
             
               4,590,410 
               Object Sensing 
               May 20, 1986 
               Jonsson 
             
             
                 
               Apparatus 
             
             
               4,779,240 
               Ultrasonic Sensor 
               Oct. 18, 1988 
               Dorr et al. 
             
             
                 
               System 
             
             
               4,976,337 
               Proximity Detection 
               Dec. 11, 
               Trett 
             
             
                 
               Systems 
               1990 
             
             
               5,001,557 
               Method of, and 
               Mar. 19, 1991 
               Begle 
             
             
                 
               Apparatus for, 
             
             
                 
               Controlling the Position 
             
             
                 
               of an Automatically 
             
             
                 
               Operated Door 
             
             
               5,149,921 
               Self Correcting Infrared 
               Sep. 22, 
               Picado 
             
             
                 
               Intrusion Detection 
               1992 
             
             
                 
               System 
             
             
               5,276,391 
               Door Mounted Safety 
               Jan. 4, 1994 
               Jonsson 
             
             
                 
               Apparatus 
             
             
               5,337,289 
               Phased-Array Ultrasonic 
               Aug. 9, 1994 
               Fasching et 
             
             
                 
               Surface Contour 
                 
               al. 
             
             
                 
               Mapping System and 
             
             
                 
               Method for Solids 
             
             
                 
               Hoppers and the Like 
             
             
               5,412,297 
               Monitored Radio 
               May 2 nd , 1995 
               Clark et al. 
             
             
                 
               Frequency Door Edge 
             
             
                 
               Sensor 
             
             
               5,420,430 
               Detection Systems for 
               May 30, 1995 
               Trett 
             
             
                 
               Detecting Obstructions 
             
             
                 
               in Doorways 
             
             
               RE 33,668 
               Detection Device Having 
               Aug. 20, 1991 
               Gray 
             
             
                 
               Energy Transmitters 
             
             
                 
               Located at Vertically 
             
             
                 
               Spaced Apart Points 
             
             
                 
               Along Movable Doors 
             
             
               RE 30,719 
               Doorway Safety Device 
               Aug. 25, 1981 
               Gerald 
             
             
                 
             
           
        
       
     
   
   U.S. Pat. No. 5,412,297 teaches a tactile obstruction detector, while U.S. Pat. Nos. 4,590,410 and 5,276,391 concern optical detectors. Tactile detectors are prone to suffer from a high degree of tear and ware and thus have a very low reliability. Furthermore they require physical contact and more specifically that a minimum force be applied thereon to be tripped, which makes them unsuitable for many applications. Optical sensors are sensitive to lighting conditions and do not function under daylight. Moreover, they do not allow differentiating between objects at a close proximity since such differentiation requires a measurement capability in the magnitude of the speed of light for small divergences. U.S. Pat. No. 2,826,753, relates to object detection in a confined environment and not to door opening or closing, for example. 
   U.S. Pat. Nos. RE 30,719, and 4,029,176 describe acoustic energy-based detectors. 
   Other distance and direction measuring apparatuses are described in the following U.S. patents: 
   
     
       
             
             
             
             
           
         
             
                 
             
             
               No. 
               Title 
               Date 
               Inventor(s) 
             
             
                 
             
           
           
             
               5,319,611 
               Method of 
               Jun. 7, 1994 
               Korba 
             
             
                 
               Determining Range 
             
             
                 
               Data in a Time-of- 
             
             
                 
               Flight Ranging System 
             
             
               5,339,075 
               Vehicular Collision 
               Aug. 16, 1994 
               Abst et al. 
             
             
                 
               Avoidance Apparatus 
             
             
               5,341,344 
               Obstacle-Detection 
               Aug. 23, 1994 
               O&#39; Brien et al. 
             
             
                 
               System 
             
             
               5,373,482 
               Distance Measuring 
               Dec. 13, 
               Gauthier 
             
             
                 
               System Arranged to 
               1994 
             
             
                 
               Limit False Indications 
             
             
                 
               of Distance 
             
             
                 
               Measurements 
             
             
               5,450,057 
               Stereophonic Warning 
               Sep. 12, 
               Watanabe 
             
             
                 
               Apparatus 
               1995 
             
             
               5,467,072 
               Phased Array Based 
               Nov. 14, 
               Michael 
             
             
                 
               Radar System For 
               1995 
             
             
                 
               Vehicular Collision 
             
             
                 
               Avoidance 
             
             
               6,344,642 
               Door Control 
               Feb. 5, 
               Agam et al. 
             
             
                 
               Apparatus 
               2002 
             
             
                 
             
           
        
       
     
   
   A common problem with ultrasonic sensors from the prior art is that they do not allow covering a volume where the signal fades and varies along the path and differentiating a legitimate clutter signal from a penetration signal. 
   Indeed, when dealing with ultrasonic sensors or other ultrasonic devices, one has to consider the “picture” the device see, i.e. the volume that the device can detect. This volume of course, is measured in terms of electrical voltage, and will be referred to herein as the “clutter”. 
   The clutter of a sensor includes echoes received from objects located within the sensor&#39;s beam. These objects may include static objects, which the sensor always detects, and therefore should ignore, and dynamic objects, which the sensor detects periodically when they enter its beam. Those dynamic objects are considered relevant targets and should be detected by the sensor. 
   A drawback of sensing methods and apparatuses from the prior art is that they do not allow discriminating between static objects and relevant targets to be detected. 
   OBJECTS OF THE INVENTION 
   An object of the present invention is therefore to provide improved device and method for ultrasound sensing. 
   Another object of the invention is to provide a system and method for adaptive ultrasound sensing free of the above noted drawbacks from the prior art. 
   SUMMARY OF THE INVENTION 
   More specifically, in accordance with a first aspect of the present invention, there is provided an adaptive ultrasound detecting method comprising: 
   emitting an ultrasound beam along a scanning direction and receiving an echo value e(i) from a number I of sensing positions i along the scanning direction; 
   comparing each the echo value e(i) to a detection threshold dt(i) corresponding to the sensing position (i); whereby, a detection occurs when the echo value e(i) is greater than the detection threshold dt(i); the improvement wherein at least one of the detection thresholds dt(i) is revaluated over time to cope for environment changes at sensing position (i) corresponding to the at least one of the detection thresholds dt(i). 
   According to a second aspect of the present invention, there is also provided a method for determining ultrasound detection thresholds along a scanning direction, the method comprising: 
   a) providing a reference echo (i) for each of a number I of sensing position (i) along a scanning direction; 
   b) providing at least one detection assurance factor; 
   for each sensing position (i) along the scanning direction: 
   c) emitting an ultrasound sensing beam along the scanning direction and receiving an echo value e(i) from the sensing positions (i); 
   d) comparing the echo value (i) obtained at sensing position (i) to the reference echo value (i) corresponding to the sensing position (i); 
   e) if the echo value (i) is lower or equal than the reference echo value (i) then the method stops, a target detection threshold for sensing position (i) being equal to the sum of the reference echo value (i) and the at least one assurance factor; 
   f) if the echo value (i) is greater than the reference echo value (i) then verifying whether a difference between the echo value (i) and the reference echo value (i) is lower than the detection assurance factor; 
   g) if the difference between the echo value (i) and the reference echo value (i) is lower than the detection assurance factor then gg1) storing the echo value (i) as the reference echo value (i) for sensing position (i) and, gg2) repeating steps c) to g); 
   h) if the difference between the echo value (i) and the reference echo value (i) is greater or equal than the detection assurance factor then a detection occurs and the method stops. 
   According to a third aspect of the present invention, there is further provided an adaptive ultrasound detecting system comprising: 
   an ultrasound pulse generator for generating an ultrasound pulse signal; 
   a transducer coupled to the ultrasound pulse signal generator for receiving the ultrasound pulse signal and for generating and ultrasound pulse and for receiving echo reflected from targets in response to the pulse; 
   a controller for receiving the echo from the transducer and for frequently computing a detection threshold by comparing the echo to a reference value and for re-evaluating the reference value; and 
   a power supply connected to the pulse generator, the transducer and the controller for energizing the pulse generator, the transducer, and the controller. 
   Finally, in accordance to a fourth aspect of the present invention, there is provided an adaptive ultrasound detecting system comprising: 
   first means for generating an ultrasound pulse signal; 
   second means coupled to the means for generating an ultrasound pulse signal for receiving the ultrasound pulse signal and for generating and ultrasound pulse and for receiving echo reflected from targets in response to the pulse; 
   third means for receiving the echo from the transducer and for frequently computing a detection threshold by comparing the echo to a reference value and for re-evaluating the reference value; and 
   fourth means connected to the first, second, and third means for energizing the first, second and third means. 
   The present invention is suitable for using, for example, with automatic doors, where it allows providing a secure and efficient sensing system, which maximizes sensing efficiency while minimizing the risk of injury to users. 
   The use of an adaptive ultrasound sensing system and method allows locating the sensor at different location without requiring a new calibration thereof, since the sensor learns the clutter dynamically and the detection thresholds are being built accordingly without being dependent on the environment in which the sensor is located. 
   In addition, the dynamic learning allows coping with the temperature, moisture, and wind changes. 
   Other objects, advantages and features of the present invention will become more apparent upon reading the following non restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the appended drawings: 
       FIG. 1  is a block diagram of an adaptive ultrasound detecting system according to an illustrative embodiment of a first aspect of the present invention; 
       FIG. 2  is a schematic view illustrating two ultrasound detecting systems from  FIG. 1 , positioned adjacent to one another; 
       FIG. 3  is a flowchart of an adaptive ultrasound detecting method according to an illustrative embodiment of a second aspect of the present invention; and 
       FIG. 4  is a flowchart of an ultrasound detecting method threshold builder according to an illustrative embodiment of a third aspect of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Turning now to  FIG. 1  of the appended drawings, an adaptive ultrasound detecting system  10  according to an illustrative embodiment of the present invention will be described. 
   The detecting system  10  comprises a controller  12 , a pulse generator  14  coupled to the controller  12 , a sensor driver  16  coupled to the pulse generator  14 , a transducer  18  coupled to the driver  16 , an analog circuit  20  coupled to both the transducer  18  and to the controller  12 , a memory means in the from of an EEPROM (Electrically Erasable Programmable Read Only Memory)  22  coupled to the controller  12 , input/output (I/O) means  24 , and an I/O interface coupled to the I/O means  24 . The controller  12 , pulse generator  14 , sensor driver  16 , transducer  18 , and analog circuit  20  are connected to a power supply  28 , in the form of a 12–24 DC (Direct Current) voltage source. Of course, the power supply  28  may take other forms allowing energizing the system  10 . 
   The pulse generator  14  includes an oscillating circuit and allows generating a pulsed signal having a frequency above the range of human hearing. This pulsed signal is amplified to the appropriate voltage and driven to the transducer  18  by the sensor driver  16 . The transducer  18  converts the voltage from the driver  16  to an ultrasonic pulse  30  that propagates through the air and reflects back in the form of an echo  32  to the transducer  18  from an object or another target (not shown). 
   The transducer  18  converts the reflected pressure wave (or echo)  32  into an echo voltage, which is amplified and filtered by the analog circuit  20 . The echo voltage is then digitized and compared by the controller  12  to a reference voltage stored in the EEPROM  22  to assess the presence of a relevant target within the field of view  34  (see  FIG. 2 ) of the detecting system  10  as will be explained hereinbelow in more detail. The controller  12  is configured to drive the transducer  18  via the pulse generator  14  and driver  16  to emit ultrasound wave pulses at a selected frequency and to collect echos at different period of time. 
   The controller  12  is further configured to generate an output signal indicative of the presence of a target and to output this signal to the I/O interface  26  via the I/O means  24 . 
   The controller  12  may take many forms, from an electronic circuit to a dedicated microchip or a programmed computer. 
   Of course, the memory  22  may also take other forms, such as a computer hard drive, a memory card used in connection with a memory card reader, a Read-Only Memory, etc. 
   The detection system  10  is enclosed in a casing (not shown), including an opening for the ultrasonic pulse, for protecting the detecting system  10  and for allowing its mounted on a structure (not shown). 
   Since, pulse generators, sensor drivers, transducers, EEPROM, I/O means and interfaces are believed to be well known in the art, they will not be described herein in more detail. 
   The detection system  10  may have other configuration allowing to implement an adaptive ultrasound detecting method according to the present invention as will be described hereinbelow in more detail. 
   As illustrated in  FIG. 2 , a series of detecting systems  10  may be mounted adjacent and/or parallel so as to cover more spaces and so as to provide overlapping fields of view  34 . Detection systems  10  may be positioned according to other configurations depending on the application. 
   Alternatively, a first transducer (not shown) can be used to emit an ultrasound wave pulse, and a second transducer (not shown) can be used to receive the reflected pulse. Of course, in that case, the first transducer is coupled to the driver  16  with a pulse generator  14 , and the second transducer is coupled to an analog circuit  20 . 
   According to further embodiments, a detection system according to the present invention may plurality of transducers  18  connected to the same controller and selectively driven therefrom. 
   An adaptive ultrasound detecting method  100  will now be described with reference to  FIGS. 3 and 4 . 
   As illustrated in  FIG. 3 , the method  100  includes emitting an ultrasound beam along a scanning direction (step  102 ), receiving an echo value e(i) from a number I of sensing positions (i) along the scanning direction (step  104 ), and comparing each echo value e(i) to a detection threshold dt(i) corresponding to the sensing position (i) (step  106 ). A detection occurs when one of the echo values e(i) is greater than the detection threshold dt(i) for that position (i). 
   The detection thresholds dt(i) for the different positions (i) along the scanning direction are stored in the EEPROM  22  and are retrieved by the controller  12  for comparison purposes. 
   The number and locations of the sensing positions (i) may of course vary depending on the required resolution globally and also locally. Indeed, even though the sensing positions (i) are equally distanced in most applications, they may also be unevenly distanced from the detecting system  10 . 
   As it is commonly known in the art, the distance position corresponding to an echo is being calculated by measuring the delay between the time a wave pulse is emitted by the detecting system  10  and the time a corresponding echo is received. 
   An interrupt module of the controller  12  allows to evaluate the delay and to compute the positions corresponding to the echos. 
   Since interrupt modules and ultrasound detecting time delays are believed to be well known in the art, they will not be described herein in more detail. 
   The thresholds dt(i) correspond to voltage values suitable for comparison with voltage values produced by the transducer  18  in response to its reception of an echo  32  following the emission of an ultrasound wave pulse  30 . 
   The method  100  further comprising at least one detection threshold dt(i) being revaluated overtime to cope for environment changes or configuration in static targets at sensing position (i). 
   Even though it is often more reliable to re-evaluate the thresholds dt(i) at all the sensing positions, in some applications it might be unnecessary to do so due to environment stability at some of the sensing positions. 
   Re-evaluating the thresholds dt(i) over time allows to cope for changes in the static targets configuration. Such static targets includes phenomenon that may cause changes in the voltage level of the received echos but do not correspond to an actual target to be detected. Static targets allow taking into consideration electrical noise caused by the detection system  10 . 
   Turning now to  FIG. 4 , a method for determining ultrasound detection thresholds along a scanning direction is illustrated. It is to be noted such method corresponds to step  108  in  FIG. 3 . 
   In step  110 , reference echos (i) for each of the number I of sensing positions (i) along the scanning direction are provided. A detection assurance factor is also provided. The detection threshold dt(i) at the sensing position (i) equals the sum of the reference echo (i) at that position and the assurance factor. 
   The assurance factor serves to minimize false detections caused by an echo signal from the background, i.e. not being caused by an actual target to be detected, being greater than the threshold. The assurance factor is selected so as to yield a margin over the measured voltage sufficient to minimize the tripping of the detection system  10  by noised signal. 
   In some applications, it is appropriate to provide more than one assurance factor, such as a predetermined assurance factor for each sensing position. 
   Step  112  allows iterating on all the sensing position. In step  114 , it is verified whether all the scanning positions have been processed. If all the thresholds have been re-evaluated for each sensing position, the method stops until a new re-evaluation of the thresholds. 
   The frequency and timing of the detection threshold evaluation (method  108 ) may vary. For example, a cycle may be established wherein the evaluation of the detection thresholds for all sensing positions alternates with the actual detection. Alternatively, the evaluation of the threshold for each position may be performed concurrently with the detection at each sensing position, as will be described hereinbelow. Of course, other detection threshold evaluation timing may be established. 
   In step  116 , an ultrasound sensing beam is emitted along the scanning direction and an echo e(i) corresponding to the sensing position (i)is received. The echo (i) is received in the form of a voltage value. 
   The echo (i) received for the distance corresponding to the current sensing position (i) is compared by the controller  12  to the reference echo (i) corresponding to the same distance from the detecting system  10  along the scanning direction (step  118 ), which is stored as voltage amplitude in the EEPROM  22 . 
   If the measured echo value (i) is lower or equal than the reference echo value (i) then the method proceeds with the next sensing position (i+1) and returns to step  112 . The target detection threshold for the sensing position (i) is equal to the sum of the reference echo value (i) and the assurance factor. 
   If the measured echo value (i) is greater than the reference echo value (i), then verification is performed as to whether the difference between the echo value (i) and the reference echo value (i) exceeds the detection assurance factor. If this is the case, then it means that an actual target has been detected (step  124 ) and the method stops. The method  100  then proceeds with the controller  12  sending an output signal via the I/O means  24  indicative of target detection. If not, than an iterative process begins where a) the echo value (i) is stored on the memory  22  as the new reference echo value (i) for the current sensing position (step  122 ), and b) steps  116 – 120  are repeated until the measured echo value (i) is lower or equal to the reference echo value (i). 
   The system  10  and method  100  can be implemented as stand-alone application. For example, the detecting system (sensor)  10 , may be used as a proximity sensor to protect a valuable object, such as a work of art, where the detection threshold is re-evaluated from time to time to minimize false alarms, while providing high sensibility. 
   The method  100  can also be embedded in another application, in its initialization stage for example. It can be used, for example, to improve the performance of a sensor in automatic checkout systems where a sensor is mounted on the tip of the checkout for scanning its front in order to detect customers approaching the checkout. In that case, the method  108  may be used to build the detection thresholds upon a reset or power-on of the checkout system. 
   Other applications of a system and method according to the present invention include, without being restricted to, proximity detections in automation process, and security sensors for robotic or machinery. 
   Of course, a system and method according to the present invention can be used in door control apparatus for automatic doors. 
   Although the present invention has been described hereinabove by way of preferred embodiments thereof, it can be modified without departing from the spirit and nature of the subject invention, as defined in the appended claims.