WO2012048420A1 - Système et procédé de positionnement optique - Google Patents

Système et procédé de positionnement optique Download PDF

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Publication number
WO2012048420A1
WO2012048420A1 PCT/CA2011/001162 CA2011001162W WO2012048420A1 WO 2012048420 A1 WO2012048420 A1 WO 2012048420A1 CA 2011001162 W CA2011001162 W CA 2011001162W WO 2012048420 A1 WO2012048420 A1 WO 2012048420A1
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WO
WIPO (PCT)
Prior art keywords
bars
target
reflective
light beam
pulses
Prior art date
Application number
PCT/CA2011/001162
Other languages
English (en)
Inventor
Pierre Boivin
Fred Rohrbacher
Euan Davidson
Original Assignee
Silonex Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Silonex Inc. filed Critical Silonex Inc.
Publication of WO2012048420A1 publication Critical patent/WO2012048420A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/74—Systems using reradiation of electromagnetic waves other than radio waves, e.g. IFF, i.e. identification of friend or foe
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
    • B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
    • B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
    • B66F9/075—Constructional features or details
    • B66F9/0755—Position control; Position detectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/46—Indirect determination of position data

Definitions

  • the present invention relates to the field of measurement systems and more specifically concerns an optical positioning system to determine the position of an object along X, Y and Z axes.
  • Positioning systems are used in various industries to measure the distance between an object and a reference point.
  • Typical optical systems include a light source emitting a laser beam onto a reflective i s surface and a detector reading the reflected laser beam.
  • the delay or time difference, also known as "time of flight" between the emission of the laser beam and the detection of the reflected beam is used to measure the distance of the object from the source, the time of flight being directly proportional to the distance of the object from the source. In other words, the farther away the object, the longer it will take for the 0 laser to hit the object and reflect back.
  • an optical positioning system for determining an XYZ position of an object relative to a reference position.
  • the system comprises:
  • the bars have predetermined parameters and are located on the object, at least one of the bars having an angled lateral side;
  • the system also comprises a trigger generator for generating a trigger signal including a trigger pulse;
  • a detector for detecting a reflected light beam reflected from the bars and for generating a target signal, the target signal including target pulses, each corresponding to a corresponding one of the reflective bars, each pulse having a width; and a) a processing assembly including at least one port for receiving said trigger and target signals, a memory for storing the scan angle, angular speed and predetermined parameters ; and a processor for computing, based on the angular speed, the scan angle and the predetermined parameters an X coordinate using a time delay between the trigger pulse and one of the target pulses; a Y coordinate using a duty cycle of at least two pulses of said signal; and a Z coordinate using the width of at least two target pulses of said signal, thereby determining the XYZ position of the object.
  • the reflective bars have a trapezoidal shape.
  • the reflective bars are made of retroreflectors, for allowing the reflected light beam to be reflected back towards said light source and said detector.
  • the scanning light source and the detector are located in proximate vicinity in a common enclosure.
  • the light beam is projected normal to the reflective bars.
  • the system also comprises a central reflective bar laterally aligned and centered between the reflective bars, for providing a central pulse reference in the target signal.
  • the number of reflective bars is pair, half of the reflective bars being located on a right side of the central bar, the other half being located on a left side of the central bar.
  • the processor computes the X, Y and Z coordinates of the object based on the target pulses associated with the two outermost reflective bars.
  • the processor corrects and verifies the computed XYZ position based on the target pulses of the other inner bars.
  • the trigger generator includes one photo-detector for generating the trigger pulse when hit by the laser beam. Still preferably, the trigger generator comprises an other photo-detector, for generating an other trigger pulse when hit by the laser beam, the processor computing the angular speed of the scanning light source based on the two trigger pulses.
  • the detector is a narrow-angle photo-detector adapted to detect the reflected light beam from a Z distance varying between 0.5 and 15 meters.
  • the processing assembly comprises an amplifying and conditioning module to amplify and condition the signal prior being processed by the processor.
  • the processor includes a Digital Signal Processor.
  • a method for determining an XYZ position of an object relative to a reference position comprises the steps of:
  • the bars have predetermined parameters and are located on the object, at least one of the bars having an angled lateral side; b) periodically projecting a light beam towards the reflective bars, the light beam being projected with a scan angle on said surface and transversally across the reflective bars at a given angular speed;
  • the target signal including target pulses, each corresponding to one of the reflective bars, each pulse having a width;
  • step b the light beam is projected normal to the reflective bars.
  • step c) comprises a step of generating an other trigger pulse.
  • the method comprises a step of computing the angular speed of the scanning light source based on the two trigger pulses.
  • step f for each target pulses, a centroid value is used to compute the X, Y and Z coordinates.
  • the method comprises a step of transmitting the XYZ position of the object computed in step f).
  • the method comprises a step of computing an angular deviation of the object relative to the reference position based two of the target pulses.
  • a reflective bar with angled lateral sides has a width which varies from the top to the bottom of the bar.
  • the light source is a rotating laser light source or an oscillating light source.
  • the target comprises three reflective bars, the two external bars having an asymmetrical shape and the center bar having a rectangular shape.
  • the target comprises seven bars, including six asymmetrical bars and a rectangular center bar.
  • the system comprises means for generating a fixed trigger point.
  • the reference point is located at the light source.
  • the position Z (equivalent to the displacement along the Z-axis) between the target and the source is determined by measuring the pulse width of the reflected beam, said pulse width being inversely proportional to the distance Z.
  • the position X of the target (equivalent to the displacement along the X-axis) is determined by calculating the delay between the time at which the light beam hits the center bar and the time at which the laser beam hits a trigger point located inside the light source enclosure.
  • the position Y of the target (equivalent to the displacement along the Y-axis) is determined using the duty cycle, (or ratio of high levels versus low levels of the signal), of the reflected light beam.
  • the optical positioning system of the invention is advantageous in that it allows one to determine the 3D position of an object, that is, the position along X, Y and Z coordinates with a minimum of two reflective bars. The system does not need to be calibrated prior to being used, it is simple to implement and inexpensive. Another advantage of the positioning system is that it is relatively insensitive to dust accumulation on the light source or on the reflective bars. Provided there is a minimum signal amplitude, degradation of the laser intensity or dust accumulation will have little effect on the system. Other features and advantages of the present invention will be better understood upon a reading of the preferred embodiments thereof, with reference to the appended drawings.
  • Figure 1 is a schematic top perspective view of the optical positioning system according to a preferred embodiment of the invention.
  • Figure 1A is a front view of a target with reflective bars, according to a preferred embodiment.
  • Figure 2 is a schematic perspective view of the optical positioning system according to another preferred embodiment of the invention.
  • Figure 3 is a schematic perspective view of a light source and of a detector, according to a preferred embodiment.
  • Figure 4 is a front view of two reflective bars, according to a preferred embodiment. W
  • Figures 5A, 5B and 5C are graphs representing a trigger signal, a target signal and the combined trigger and target signals, respectively, according to a preferred embodiment.
  • Figures 6A is a schematic view of a set of reflective bars positioned at a first X coordinate.
  • Figure 6B is a graph representing a target signal generated from a beam reflected from the bars of Figure 6A.
  • Figures 6C is a schematic view of a set of reflective bars positioned at a second X coordinate.
  • Figure 6D is a graph representing a target signal generated from a beam reflected from the bars of Figure 6C.
  • Figures 6E and 6F also represents target signal generated from the reflective bars of Figures 6A and 6C respectively.
  • Figures 7A is a schematic view of a set of reflective bars positioned at a first Y coordinate.
  • Figure 7C is a graph representing a target signal generated from a beam reflected from the bars of Figure 7A.
  • Figures 7B is a schematic view of a set of reflective bars positioned at a second Y coordinate.
  • Figure 7D is a graph representing a target signal generated from a beam reflected from the bars of Figure 7B.
  • Figures 8A is a schematic view of a set of reflective bars positioned at a first Z coordinate.
  • Figure 8C is a graph representing a target signal generated from a beam reflected from the bars of Figure 8A.
  • Figures 8B is a schematic view of a set of reflective bars positioned at a second Z coordinate.
  • Figure 8D is a graph representing a target signal generated from a beam reflected from the bars of Figure 8B.
  • Figure 8E is a schematic top view of the target of Figure 8A and 8B, relative to the light source.
  • Figure 9A is a schematic view of a set of reflective bars rotated along the Z axis.
  • Figure 9B is a graph representing a target signal generated from a beam reflected from the bars of Figure 9A.
  • Figure 10 is a block diagram of the optical positioning system, according to an embodiment of the invention.
  • Figure 1 1 is a side view of a lift truck, provided with an optical positioning system according to a preferred embodiment of the invention.
  • an optical positioning system 10 according to a preferred embodiment of the invention is shown.
  • the system includes multiple reflective bars 12, which are preferably part of a target, a scanning light source 14, a trigger generator 16, a detector 18, and a processing assembly 20.
  • multiple reflective bars it is meant that the object must be provided with at least two reflective bars.
  • the bars are positioned on the object for which the position is to be determined.
  • the light source 14 projects a moving light beam 22 towards the reflective bars 12 and the detector 18 detects a reflected light beam 24. This reflected light beam 24 is then converted into a target signal which can be processed by the processing assembly 20, in order to determine the position of the bars 12, and thus of the object 11 , relative to a reference point 15.
  • the system 10 includes multiple reflective bars 12, which are laterally aligned and spaced from each other on a planar, non-reflective surface 26. At least one of the bars is be provided with an angled lateral side 28. Preferably, both lateral sides of the bars are angled. While in the present case the bars have a trapezoidal shape, other shapes can be considered, as long as there is a variation in the slope of one of the lateral sides.
  • the angled lateral side does not necessarily need to be straight, it can also be curved. For example, it can be convex or concave.
  • the width of the bars 12 varies from top to bottom, and there is no symmetry axis about the X-axis. Each bar is defined by predetermined parameters, relative to the shape and dimension of the bars, and to the distance between the bars 12.
  • the target includes more than two bars 2. Still preferably, the bars 12 are located on each side of a central reflective bar 30, said central bar 30 being also laterally aligned and centered between the reflective bars 12.
  • the central bar 30 has perpendicular, non-angled lateral sides. In the present case, the central bar 30 has a rectangular shape.
  • the bars 12 are located on the object 1 1. If the object 1 1 already has a planar and non-reflective surface 26, the bars 12 can be simply affixed on the object 11. Otherwise, the reflective bars 12 can be affixed on a non-reflective material, for example, on a sheet or plate, forming with the reflective bars a target which can be affixed on the object 1 1 for which the position is to be measured.
  • the non- reflective surface 26 is black, and the reflective bars are white.
  • the reflective bars 12 are preferably made of retroreflectors, allowing the reflected light beam to be reflected back towards the light source 14 and the detector 18, reducing the need for a perfect optical alignment.
  • Figure 1 shows the light source 14, the detector 18 and the processing assembly 20 in a single enclosure, they can be distributed in distinct enclosures. In the case where the reflective bars are made of retroreflectors, the emitter 14 and detector 18 must be very close to each other.
  • the light source, or scanner, 14 and the detector 18 are preferably contained in a single casing.
  • the scanning light source 14 periodically projects a light beam 22 towards the reflective bars 12 with a given scan angle ⁇ .
  • the light beam is projected transversally across the reflective bars, at a given angular speed.
  • the angular speed can be already known to the system 10, for example by using the speed of the motor rotating the light source, or it can be measured more accurately, using photo-detectors, as it will be explained more in detail below.
  • the light source 14 is preferably a rotating laser light source, but another moving light source could be used, such as an oscillating light source.
  • the light source is preferably a scanner emitting a laser light beam.
  • the light beam is preferably projected normal, or perpendicularly, to the reflective bars.
  • the trigger generator 16 is for generating a trigger signal, including a trigger pulse.
  • the trigger generator 16 includes a photo- detector 32 which generates the trigger pulse when hit by the moving laser beam 22.
  • the photo- detector 32a will generate a trigger pulse at each rotation of the laser light source.
  • 1 1 reflective surface 26 is black, and the reflective bars are white.
  • the reflective bars 12 are preferably made of retroreflectors, allowing the reflected light beam to be reflected back towards the light source 14 and the detector 18, reducing the need for a perfect optical alignment.
  • Figure 1 shows the light source 14, the detector 18 and the processing assembly 20 in a single enclosure, they can be distributed in distinct enclosures. In the case where the reflective bars are made of retroreflectors, the emitter 14 and detector 18 must be very close to each other.
  • the light source, or scanner, 14 and the detector 18 are preferably contained in a single casing.
  • the scanning light source 14 periodically projects a light beam 22 towards the reflective bars 12 with a given scan angle ⁇ .
  • the light beam is projected transversally across the reflective bars, at a given angular speed.
  • the angular speed can be already known to the system 10, for example by using the speed of the motor rotating the light source, or it can be measured more accurately, using photo-detectors, as it will be explained more in detail below.
  • the light source 14 is preferably a rotating laser light source, but another moving light source could be used, such as an oscillating light source.
  • the light source is preferably a scanner emitting a laser light beam.
  • the light beam is preferably projected normal, or perpendicularly, to the reflective bars.
  • the trigger generator 16 is for generating a trigger signal, including a trigger pulse.
  • the trigger generator 16 includes a photo- detector 32 which generates the trigger pulse when hit by the moving laser beam 22.
  • the photo- detector 32a will generate a trigger pulse at each rotation of the laser light source. 12
  • This trigger pulse will serve as a reference to compute the X position, or the lateral displacement, of the object, as it will be explained more in detail below.
  • This photo- detector 32a is preferably located near the periphery of the window or aperture by which the laser beam exits the casing of the scanner 14.
  • the trigger generator 16 includes another photo-detector 32b, for generating another trigger pulse when hit by the laser beam 22.
  • This second photo-detector 32b advantageously allows the processing assembly 20 to compute the angular speed of the scanning light source 14 based on the two trigger pulses.
  • This second photo-detector 32b is preferably located at the periphery of the window or aperture of the casing of the scanner 14, opposite the first photo-detector 32a, along the light source trajectory.
  • the distance between the two photo-detectors 32a, 32b in the casing being known, the time elapsed between the two trigger pulses allows to determine precisely the angular speed of the scanning light source 14. This is particularly advantageous in applications requiring that the position of the object be determined with a high degree of precision.
  • the detector 18 is for detecting the reflected light beam 24 reflected from the bars 12, and for generating a target signal.
  • the target signal will thus include target pulses, each corresponding to one of the reflective bars 12.
  • Each target pulse will have a given width, which will vary according to the height at which the light beam 22 has crossed the bar 12.
  • the detector 18 includes a photosensitive element capable of reading back the reflected light beam 24 coming from the reflective bars 12, without being influenced by ambient or off-axis lights.
  • the moving light reflected on bars 12 of the target produces a series of target pulses with a signature, or characteristics, unique to the position of the bars 12 along the three axes X, Y and Z. These characteristics include the width, or duration, of the pulses, or the time elapsed between two given pulses.
  • the reflected beam 24 is detected and converted into a target signal which can be 13 analyzed by the processing assembly 20.
  • the scanning light source 14 and the detector 8 are located in proximate vicinity in a common enclosure 34.
  • the detector 18 is preferably a narrow-angle photo-detector adapted to detect the reflected light beam from a Z distance varying between 0.5 and 15 meters. This interval can vary, by increasing or decreasing the power of the light source or the sensitivity of the detector, for example. It is provided with a 1 pixel camera having a narrow field of view. Preferably, the detector does not operate using direct reflections, since it would not be desirable in such an industrial environment. Of course, other types of detectors 18 can be considered, according to the requirements of the application in which the system 10 is to be implemented.
  • the processing assembly 20 includes at least one input port 36, a memory 38 and a processor 40.
  • the input port(s) 36 is for receiving the trigger signal and the target signal.
  • the memory 38 is for storing the scan angle ⁇ and the angular speed ⁇ of the light source 14, and the predetermined parameters characterizing the reflective bars. These parameters can be for example, the slope of the lateral sides of the bars, the width at the base and summit of the bars and the distance between said bars at their base.
  • the angular speed ⁇ can be pre-programmed based on the motor speed provided by the manufacturer of the motor, or measured during each oscillating or rotating period, using the photo- detectors 32a, 32b.
  • the processor 40 computes the X, Y and Z coordinate of the object based on the angular speed w, the scan angle ⁇ and the predetermined parameters of the bars.
  • the memory 38 can be included within the processor 40.
  • the processor includes a Digital Signal Processor, commonly referred to as DSP.
  • the processing assembly 20 may also include an amplifying and conditioning module 42, in order to amplify and condition the target signal prior to being processed by the processor 40.
  • the assembly 20 can also include a communication module 44 for transmitting the XYZ position of the object. This communication module 44 can also be used to exchange other types of information, for example relative to the motor of the light beam.
  • the trigger and target signals can go through various algorithms to extract the three positions (Z, X, Y) at a high speed rate, such as 10 to 100 times per second for example.
  • the processing assembly 20 can include modules for filtering the signal and averaging the measurements.
  • the microprocessor 40 can also monitor the strength of the signals and send alarm signals if either the reflective bars 12, or the detector 18, requires maintenance.
  • the microprocessor 40 can control the scanning light source 14 and the communication with an outside host.
  • the measured position of the object can be communicated to a host computer via the communication module 44, which can include a serial link such as RS-232, RS-422, LIN-Bus, CAN-Bus, USB, or the like.
  • the position can be sent on-demand or continuously.
  • FIGs 5A represents a graph in time of the trigger signal generated by the trigger generator 16. Assuming the light source 14 is a rotating light source, it completes a rotation during a period T. In this graph, the first trigger pulse 46a of a given period T corresponds to the one generated by the photo-detector 32a, and the second trigger pulse 46b corresponds to the one generated by the photo-detector 32b.
  • Figure 5B represents a graph in time of the target signal generated by the detector 18, from reflections of the light beam 22 over the bars 12 of Figure 4.
  • the first target pulse 48 of a given period T corresponds to the one generated by the detector 18 on a first reflective bars 12
  • the second target pulse 48b corresponds to the one from the other reflective bar 12.
  • the object, and thus the target has moved from one period to another, and this is why the width of the pulses varies. From the first period to the second, the target has moved in Z toward the light source 14, since the width of the pulses is larger. From the second to the third period, the target was 15 tilted in the X-Y plane, or in other words, about the Z axis, since the width of the pulse 48a is larger than the pulse 48b.
  • Figure 5C represents a graph in time combining the trigger and the target pulses.
  • Figures 6A to 8D the computation of the X, Y and Z coordinate will be explained.
  • Figures 6A to 6F illustrate how the X coordinate is computed using a time delay between the trigger pulse and one of the target pulses.
  • Figures 7A to 7E illustrate how the Y coordinate is computed using a duty cycle of at least two pulses of the trigger signal.
  • Figures 8A to 8E illustrate how the Z coordinate is computed using the width of at least two target pulses.
  • FIG. 6A, 6C, 7A, 7B, 8A and 8B another example of a target 13 is shown.
  • Using multiple bars 12 will generate multiple pulses which can be used for redundancy, thus providing a more accurate measure by averaging readings of the pulse widths.
  • a pair number of reflective bars 12 are used, each with at least one angled side.
  • Half of the reflective bars 12 are located on a right side of the central bar 30, the other half being located on a left side of the central bar 30.
  • the processor can compute the X, Y and Z coordinates of the object based on the target pulses associated with the two reflective bars 12, and correct the position based on the target pulses of the other bars 12.
  • the target 13 includes six bars 12 having a trapezoidal shape, the center bar 30 being rectangular.
  • the reflective bars are preferably white and 3000 times brighter than a perfect white diffusive surface.
  • the target 13 is 300 mm wide and 150 mm high.
  • Figures 8A and 8B represents the target 13 at two different Z positions, the target 13b of Figure 8B being closer to light source 14 than the one of Figure 8A.
  • Figure 8C and 8D represent graphs of the target signal detected and generated from the reflected light beam over the target of Figure 8A, and Figure 8B, respectively.
  • the photo-detector detects a reflected light beam and generates a corresponding pulse 48.
  • the pulse width w is inversely proportional to the distance Z of the target 13 from the light source 14. In other words, when the target 13 is closer to the light source 14, the pulse width w, or pulse duration, will be greater than when the target 13 is far away from the source 14.
  • the system 10 uses the principle according to which a bar 12 will appear smaller to the detector when it's farther away, in order to estimate the position Z of the target 13 from the emitting-detecting device 14, 18. Since the scan angle ⁇ , the angular speed co, the actual dimensions and the shape of the bars are known, the Z distance of the object from the reference point can be obtained based on the width, or duration, of at least two of the target pulses, using known trigonometric equations. Using the respective widths of more than two bars 12 advantageously provides redundancy in the distance measurement.
  • Providing the object with a reflective central bar 30 between the reflective bars 12 advantageously allows the system 10 to determine the center of the target, even if some of the bars are out of the scanning zone, or "field of view", of the light source 14. Since the central bar 30 has a width smaller than the bars 12 with angled lateral sides, the system will detect a shorter pulse 50 from the reflection onto said central bar. It will therefore be able to determine which target pulse corresponds to which bar 12, based on this center pulse 50 associated with the center bar 30.
  • Figures 6A and 6C represent the target 13 at two different X positions, with reference to light source 14.
  • Figures 6B and 6D represent graphs of the target signal detected and generated from the reflected light beam over the target of Figure 6A, and Figure 6C, respectively.
  • reference number 32 is a schematic representation of the photo-detector 32a used to generate 17 a fixed trigger point, or trigger pulse 46a.
  • the photo-detector is preferably located near the light source 14, which, when hit by the rotating laser beam 22, generates a trigger pulse 46a.
  • a center bar with a distinct shape allows the system 10 to detect the X coordinate, or lateral movement along the X-axis, of the target 13, by measuring the time delay from the trigger pulse 46A to the center pulse 50 regardless of any displacement along the Z-axis.
  • a time delay can be measured, by calculating the difference between the time to at which the beam is reflected on the central bar and the time t-i at which the beam hits the photo- detector 32a.
  • the X coordinate of the target can be computed, based on the speed of the light source and the time delay.
  • the X coordinate of the target is obtained based on only two reflective bars 12a, 2b, without relying on the central bar 30.
  • the centroid, or center values, of the two pulses 48a, 48b are used to determine the X coordinate of the object.
  • the centroid of the other pulses can also be used to verify and validate the measured X position.
  • it can be considered to use only one target pulse 48a or 48b, to determine the X coordinate of the object.
  • Figures 7A and 7B represent the target 13 at two different Y positions, the target 13 of Figure 7B being "higher", than the one of Figure 7A.
  • Figure 7C and 7D represent graphs of the target signal detected and generated from the reflected light beam over the target of Figure 7A, and Figure 7B, respectively. 18
  • Y coordinate or transverse deviation (Y)
  • this information can be used to measure the Y coordinate.
  • movement of the target along the Y-axis can be obtained by measuring the duty cycle of at least two target pulses, regardless of the displacement along the Z-axis.
  • each of the target pulses will have a "high level” portion, W H L2, that is wider than the "low level” portion W L L2, the "high level” part of the pulse corresponds to the pulse hitting the reflective bar.
  • W H u narrower “high levels”
  • W L i_i narrower “low levels”
  • the Y coordinate of the target can be determined, by using the ratio of "high levels” versus "low levels", i.e. the duty cycle, of the target pulses.
  • the duty cycle is obtained by dividing the sum of the widths of the high levels of the pulses, by the sum of the widths of the low levels.
  • FIG. 9A a target which is tilted in the X-Y plane is shown.
  • Figure 9B represents the target signal generated from the reflected beam over the target of Figure 9A.
  • the duty cycle of the target pulses vary from the rightmost to the leftmost pulse.
  • the variation of the duty cycles can be used to compute the angular deviation ⁇ of the object based on the respective widths of two of the target pulses. It can also be used to cancel the effect of the rotation of the 19 target on the Z axis (twisting of the load) by comparing the duty cycles on the left side of the central bar 50 versus the duty cycles of the right side and by applying a compensation factor.
  • components of the system 10 according to a preferred embodiment are illustrated.
  • the system 10 comprises a target 13 formed by multiple reflective bars 12 aligned on a non-reflective surface 26.
  • a scanning light source 14 emits a light beam 22 towards the target 13 using a laser source 52 and rotating mirrors 56, thanks to a motor 54 controlled by the processor 40.
  • the reflected light beam 24 is detected through a lens 58.
  • a module 42 to amplify and condition the signal detected is provided, and the target signal indicative of the position of the target 13 relative to a reference point is generated.
  • the reference point corresponds to the rotating axis of the light source 14.
  • the system preferably includes a communication module 44 to communicate with external devices.
  • the system 10 will preferably go through an alignment process at the factory to ensure that the detector 18 is able to detect a laser reflection at the desired distance. Such an alignment can be made by aligning a view cone of the detector 18 over the target area. When installed, on a customer application or product, the enclosure containing the source 14 and detector 18 should be aligned such that the laser beam hits within a predetermined scan zone band. Both alignments are approximate and not critical, as long as they remain stable.
  • Container handler trucks must often stack loads of up to 30 metric tons at heights of around 12 meters. Precise positioning of the lift elevator is critical, so that the operator can evaluate if he has the necessary clearance to unload the containers.
  • a lift truck 60 is provided with the optical positioning system 10.
  • the reflective bars 12, 20 which are preferably part of a target 13, are positioned on one of the forks 62 of the lift truck 60.
  • the light source 14, trigger generator 16 and the detector 18 are positioned on the truck 60, near the ground, at a predetermined offset distance 64.
  • the processing assembly is in a separate enclosure, and can be linked to the control 5 system of the truck 60.
  • the system 0 can determine the position along any or all of the X, Y and Z axes of an object relative to a reference point (such as the detector for example) using the width, time delay and duty cycle of target pulses resulting from reflection of l o the moving light beam 22 on the reflective bars 12, as described above.
  • a method for determining the XYZ 15 position of an object is also provided. The method will be explained with reference to Figures 1 to .
  • the first step of the method is to provide the object with at least two reflective bars 12.
  • the reflective bars 12 must be placed on a planar and non-reflective surface. 20
  • Each bar 12 has at least one angled lateral side, and preferably both.
  • the shape and dimension parameters of the bars 12 are known and predetermined.
  • the next step is to project a light beam 22, and preferably a laser light beam, towards the reflective bars 12.
  • the light beam 22 is projected periodically, at a known scan 5 angle ⁇ and at a given angular speed ⁇ .
  • the light beam 22 is projected transversally across the reflective bars 12, preferably normally to the surface 26. 21
  • the method also includes a step for generating a trigger signal including a trigger pulse 46a.
  • This trigger pulse 46a is generated during each period, or in other words, each time the light beam is projected towards the reflective bars 12.
  • two trigger pulses 46a, 46b are generated during a period, for computing precisely the 5 angular speed ⁇ of the scanning light source 14.
  • the reflected light beam 24, reflected from the reflective bars 12, is then detected.
  • a target signal is then generated from this reflected light beam 24.
  • the target signal includes target pulses 48a, 48b, each corresponding to one of the reflective bars 12. 10
  • Each pulse is defined by a width w, which corresponds to a duration during which a reflection is detected.
  • the X, Y and Z coordinates of the object are computed.
  • the X coordinate is computed based on the time delay between the trigger pulse and one of the target pulses.
  • the Y coordinate is computed based on the duty cycle, or ratio of high versus low level, of the target signal, using two target pulses.
  • the Z coordinate is computed using the width of at least two of the target pulses.
  • the angular deviation of the object can be computed based on the widths of two of the target pulses. This deviation can be cancelled out by applying a compensation factor in the computations, this step being performed prior the 5 computation of the X, Y and Z coordinated. 22
  • the reflective bars 12 have no characters encoded within them, such as know bar codes, but that the information is embedded in the shape, width and spacing of the bars 12.
  • the reflective material and the shape, or pattern, of the reflective bars is designed so that the system 10 is insensitive to rotation of the target along the three axes. Indeed, when the light beam hits the reflective bars 12, the light beam 24 is reflected back towards the source 14, regardless of the angle of the target 13. In order to cancel the effect or rotation of the target on the Z axis the duty cycles of the left side of the central bar of the target can be compared to the duty cycle on the right side.
  • the target is passive, has no power source and emits no light.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Remote Sensing (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Transportation (AREA)
  • Structural Engineering (AREA)
  • Civil Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Mechanical Engineering (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

L'invention porte sur un système et sur un procédé de positionnement optique pour déterminer la position XYZ d'un objet, lequel procédé comprend les étapes consistant à : a) disposer de multiples barres réfléchissantes latéralement alignées et espacées les unes des autres sur une surface non réfléchissante plane, au moins l'une des barres ayant des côtés latéraux inclinés, des paramètres prédéterminés et étant située sur l'objet ; b) projeter périodiquement un faisceau de lumière vers les barres réfléchissantes, c) détecter un faisceau de lumière réfléchi, réfléchi à partir des barres ; d) générer un signal cible sur la base du faisceau de lumière réfléchi, le signal cible comprenant des impulsions cibles, correspondant chacune à l'une des barres réfléchissantes, chaque impulsion ayant une largeur ; et e) calculer, sur la base de la vitesse angulaire, de l'angle de balayage et des paramètres prédéterminés, et du signal cible, des coordonnées X, Y et Z ; de façon à déterminer ainsi la position XYZ de l'objet.
PCT/CA2011/001162 2010-10-15 2011-10-14 Système et procédé de positionnement optique WO2012048420A1 (fr)

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US39359510P 2010-10-15 2010-10-15
US61/393,595 2010-10-15

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2562127A1 (fr) * 2011-08-23 2013-02-27 STILL GmbH Lift height measurement method in an industrial truck
EP3176606A3 (fr) * 2015-11-16 2017-11-29 Sick Ag Procédé destiné à l'alignement d'un scanner laser
CN109081272A (zh) * 2018-10-23 2018-12-25 西安中科光电精密工程有限公司 一种基于激光与视觉混合引导的无人转运叉车及方法
CN109160452A (zh) * 2018-10-23 2019-01-08 西安中科光电精密工程有限公司 基于激光定位和立体视觉的无人转运叉车及导航方法
DE102019102783A1 (de) 2019-02-05 2020-08-06 Sick Ag Ausrichtziel und Verfahren zum Ausrichten einer Kamera
CN112557689A (zh) * 2020-11-27 2021-03-26 中国航发四川燃气涡轮研究院 一种基于非对称结构音轮的转速综合测量装置

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US6017125A (en) * 1997-09-12 2000-01-25 The Regents Of The University Of California Bar coded retroreflective target
US20020036779A1 (en) * 2000-03-31 2002-03-28 Kazuya Kiyoi Apparatus for measuring three-dimensional shape
US20020190190A1 (en) * 1996-10-25 2002-12-19 Miramonti John L. Method and apparatus for three-dimensional color scanning
WO2010015086A1 (fr) * 2008-08-06 2010-02-11 Creaform Inc. Système pour balayage tridimensionnel adaptatif de caractéristiques de surface

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Publication number Priority date Publication date Assignee Title
US20020190190A1 (en) * 1996-10-25 2002-12-19 Miramonti John L. Method and apparatus for three-dimensional color scanning
US6017125A (en) * 1997-09-12 2000-01-25 The Regents Of The University Of California Bar coded retroreflective target
US20020036779A1 (en) * 2000-03-31 2002-03-28 Kazuya Kiyoi Apparatus for measuring three-dimensional shape
WO2010015086A1 (fr) * 2008-08-06 2010-02-11 Creaform Inc. Système pour balayage tridimensionnel adaptatif de caractéristiques de surface

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2562127A1 (fr) * 2011-08-23 2013-02-27 STILL GmbH Lift height measurement method in an industrial truck
EP3176606A3 (fr) * 2015-11-16 2017-11-29 Sick Ag Procédé destiné à l'alignement d'un scanner laser
CN109081272A (zh) * 2018-10-23 2018-12-25 西安中科光电精密工程有限公司 一种基于激光与视觉混合引导的无人转运叉车及方法
CN109160452A (zh) * 2018-10-23 2019-01-08 西安中科光电精密工程有限公司 基于激光定位和立体视觉的无人转运叉车及导航方法
CN109160452B (zh) * 2018-10-23 2023-06-20 西安中科光电精密工程有限公司 基于激光定位和立体视觉的无人转运叉车及导航方法
CN109081272B (zh) * 2018-10-23 2023-09-29 西安中科光电精密工程有限公司 一种基于激光与视觉混合引导的无人转运叉车及方法
DE102019102783A1 (de) 2019-02-05 2020-08-06 Sick Ag Ausrichtziel und Verfahren zum Ausrichten einer Kamera
EP3693927A1 (fr) 2019-02-05 2020-08-12 Sick Ag Alignement d'une caméra à balayage linéaire avec des triangles comme cibles d'alignement
CN112557689A (zh) * 2020-11-27 2021-03-26 中国航发四川燃气涡轮研究院 一种基于非对称结构音轮的转速综合测量装置

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