Patent Application
20210395051
The present invention relates to a method for correlating position and profile measurements of an object performed for a hoisting appliance, and in particular an object that is to be handled by a hoisting appliance in a warehouse.
In the context of storage automatization in an industrial area, such as a warehouse hall, shipyard or the like, where objects are regularly stored and displaced, objects can be handled, moved and/or manipulated by a hoisting appliance.
Hoisting appliances 1 such as bridge cranes, gantry cranes or overhead travelling cranes usually comprise a trolley 2 which can move over a single girder or a set of rails 3 along a horizontal axis X, as shown in
A load suspension device 4 is associated with cables which pass through the trolley 2, the length of the cables 5 being controlled by the trolley 2 to vary, thereby enabling displacement of a load 6 along a vertical axis Z, referred to as hoisting movement.
In order to handle and move objects in the hoisting area, a two-dimensional, 2D, or three-dimensional, 3D, map of the warehouse hall and of the object located therein, including the position, orientation and shape, and free space around the object itself, need to be determined.
To this end, sensors installed on the hoisting appliance or near to it can be used to scan the ground while the hoisting appliance is moving. For example, sensors such as radars or scanners/cameras can be used to determine the position, orientation and profile of objects.
However, because of the delay in acquiring data by the sensor or sensors and communicating the data to a centralized processing control unit to calculate the object position, slow and numerous movements are generally performed to acquire sufficient data to determine location of objects, which delays operations of the hoisting appliance.
To enable applications such as automatization of the object manipulations, the determination of the object location needs to be accurate. Else, automatization is not possible and object manipulations would need to be manually performed by an operator.
A prior art solution consists in a system using a trolley above an object to be manipulated. Using two scanning units, the known solution scans the object while moving over it to determine its position and dimension. Then, another movement is necessary to grab the object. This solution therefore requires two phases (a scanning phase and a manipulation phase), thereby introducing loss of time, additional steps of stopping and starting of a motor of the trolley thereby deteriorating the system.
In another prior art solution, one scanning unit is used that slowly moves over the object to be handled, while the object is kept still in a resting position.
Automatization applications typically require determining with accuracy, less than 5 mm for example), the 2D or 3D location and dimensions of each object to be manipulated. To allow for improvements in speed compared to manual manipulations, determination of the object location needs to be efficiently performed by reducing the motions performed by the sensors and/or by enhancing the processing of the data acquired by the sensors.
It is therefore desired to have an accurate determination of an object to be handled by a hoisting appliance, while reducing the time required for such determination, so as to enhance operations of the hoisting appliance.
Referring to
The positioning system 7, in this example a radar system, including a radio emitter and a radio detector, will emit radio waves that will be reflected by structures of the surrounding environment, in this case a wall 9, that are to be detected by the detector of the radar. This will allow determining the distance between the trolley and the wall 9. In order to further increase precision, a second radio detector may be installed at a fixed reference position at a distal end of the rails 3. This will allow determining the distance between the trolley and the rail reference position. Movement of the trolley may interfere with the radio waves being emitted and radio waves being detected.
The scanning sensor 8, including a light source and two or more light sensors, will emit light via the light source that will be reflected by an object 10 present below the trolley. The reflected light may be detected by the light sensors of the scanning sensor 8. This will allow determining the distance between the trolley and the object 10 below it. Movement of the trolley will interfere with the light being emitted, the reflection against the object 10, and the detection of the reflected light by light sensors.
In order to determine the distance using the scanning sensor, the time of flight of the light emitted, reflected and detected needs to be determined. Thereto the light emitted will use pulses which can be detected, and the resulting time difference between the emittance of the pulse and the detection of the reflected pulse is measured. A pulsed or intermittent signal may be created by modulation of amplitude and/or frequency. As the light has travelled towards an object and back from that object, the light has twice travelled the distance between sensor and object. Using the speed of light constant c and the time of flight (t2−t1), the distance D can be determined.
More advanced scanning sensors may further include difference in phase angles of e.g. sinusoid signals in determining the time of flight. The principle of detecting reflected pulses and measuring remains the same.
Regardless of the type of scanning sensor used, the time measurements of pulses and distances need to be synchronized together with position measurements of the associated location of the sensor and the object. This becomes even more critical when object and sensor are moving in relation to one another. This is why thus far scanning of objects is performed at low speed with the objects kept still in a resting position.
It is therefore an object of the invention to provide a method that facilitates accurate measurements at high speed. According to the invention, this object is achieved by providing a method for correlating position and profile measurements of an object to be manipulated by a hoisting appliance, wherein the method includes receiving position sensor data from at least one position sensor, said sensor being configured to perform position measurements of the hoisting appliance within the hoisting area. The method further includes determining a speed of the hoisting appliance, refining a position of the object to be manipulated based on the position data received from the position sensor, and correlating the refined position and the profile data to calculate object dimensions.
The method may be implemented in a centralized control unit configured for controlling the hoisting appliance and comprising the following.
According to one aspect, there is provided a hoisting appliance, comprising a trolley provided with a position sensor ad a profile scanner, and a central control unit. And wherein the central control unit is configured for executing the method for correlating position and profile measurements.
According to a further aspect, there is provided a central control unit for a hoisting appliance, the central control unit being configured for executing the method as disclosed herein.
According to another aspect, there is provided a computer program executable by a processor and comprising instructions for, when executed by the processor, carrying out the steps of the method as disclosed herein.
According to yet another aspect, a non-transitory computer readable storage medium, with a computer program stored thereon, said computer program comprising instructions for, when executed by a processor, carrying out the steps of the method as disclosed herein.
By way of example only, the embodiments of the present disclosure will be described with reference to the accompanying drawings, wherein:
Referring to
The method includes receiving position sensor data 301 from at least one position sensor of a hoisting appliance, the position sensor being configured to perform position measurements of the hoisting appliance within the hoisting area. The method further includes receiving profile scanner data 302 from at least one profile scanner located on the hoisting appliance, the profile scanner being configured to perform profile measurements of an object located below the hoisting appliance. The method further includes obtaining a speed history 303 of the hoisting appliance, and determining a position correction to account for a resulting time delay. The time delay may be the result of a measurement delay representative of a measurement time of the sensor, a communication delay representative of a communication time between the at least one sensor and the centralized control unit, and a processing delay representative of a processing time of the centralized control unit. The resulting time delay is of relevance as the time instances at which the position measurement and the profile measurement are performed may not be simultaneous.
The method further includes refining 304 and/or correcting the position data of the object based on the determined speed of the hoisting appliance and associated position correction. The refined position measurement allows to correlate 305 the position measurement and profile measurement and provide accurate position and profile data of the object below the hoisting appliance. With this the dimensions of the object will be known and may be used when handling the object by the hoisting appliance
In order to receive the data from the hoist sensor, e.g. the profile scanner 8 in
It is further required to determine a position X, Y corresponding to the time instance when the “Z” measurement was performed. However, due to the use of PLC or programmable devices, that operate by assessing their inputs on a periodical basis, commonly referred to as a scan cycle, also the time delay introduced thereby is of relevance.
Referring to
At consecutive intervals, a position or profile measurement is performed. The measured value is then communicated to the central control unit. The time required for performing the measurement Tmeas, may also be communicated to the central control unit. As can be seen, the time till a communication is performed may vary depending on the moment of measurement and the next instance of communication. Similarly, the time for synchronizing with a next PLC scan cycle may also vary, and accordingly further delays are possibly introduced.
This means that at a calculation time instance when both the position X, Y and profile Z measurements are available at the control unit for further calculations, due to the movement of the trolley the position X, Y is not a true position corresponding with the time instance at which the profile Z was measured. Hence, it is required to correlate the profile measurement to a true i.e. exact position X′, Y′ of the hoisting appliance.
In order to achieve this, the history of the speed of the hoisting appliance from the first time instance when the position measurement was made is required. This may be obtained from the central control unit, which stores the history of speed of the hoisting appliance as it has also issued these as command values to the hoisting appliance. From the historical data of the speed from the first time instance of the position measurement the evolution of the position of the hoisting appliance may be further calculated.
ΔPosition=∫0tVdt eq. 2
When a second time instance at which the profile measurement is performed will be known, the position measurement may be refined to obtain the true position at which the profile measurement was performed by taking the integral of speed over the time difference of the first and second time instances. The result thereof provides a correction distance by which the position measurement needs to be refined.
Hence, the first and second time instances are required for the calculations, the time delay for position measurement i.e. Resulting_time_pos and the time delay for profile measurement i.e. Resulting_time_profile need to be known in advance. These may be provided by the supplier of the hoisting system, these may also be obtained on site during a calibration process.
Accordingly, the method may further include a calibration process. Thereto, a reference object of known size and dimension is scanned. And preferably at a fixed location in a known environment of defined dimensions.
The calibration process will scan the reference object with the hoisting appliance, i.e. the trolley, travelling at different speeds. This will allow to determine the measurement time, the communication delay time and the processing time for different speeds under various circumstances. These values may be stored in the central control unit.
Referring to
If a new calibration 501 is initiated, the hoisting appliance is moved 502 towards the reference object. The reference object is scanned 503 at a first reference speed V(n). And the resulting measurements are checked against the known dimensions and position of the reference object in order to determine 504 the resulting time delay due to measurement delay, communication delay and processing delay. The resulting time delay is stored.
Depending on the desired number of reference speeds, as may be set by an operator, the scanning is repeated 505 at another speed V(n+1). When a large enough set of reference speeds is obtained, the central control unit is updated 506 with the delay times for respective different reference speeds resulting from the calibration process. In this manner, a machine learning process is enabled, that allows the hoisting appliance to perform a self-check and update its' settings if so required.
When the exact dimensions and position of the reference object are not yet known, they may be acquired in an identification sequence 507 by moving the hoisting appliance to the reference object and performing measurements in a stop-motion manner, meaning at speed V(0), for which the hoisting appliance is moved and stopped over the reference object at a various number of positions. At each position P(x,y) a profile measurement Z is performed. As the hoisting appliance is kept in still in one position while performing the profile Z measurement, no errors in time delays due to movement are introduced.
The reference object preferably has a specific shape with an inclined surface having a continuous gradient, as e.g. shown in
As mentioned, the reference object is scanned 503 at a first constant speed V(n), which preferably is the maximum speed attainable by the hoisting appliance. The constant steady speed will provide enhanced accuracy for position calculation with speed historization. In addition, also measurements may be performed with constant acceleration. The scan results provide combinations of position and profile measurements. As the positions are known, the position error Pos_error for that speed V(n) may be calculated.
Starting with:
ΔPospos_global=Error for position measurement−Error for profile position measurement
ΔPospos_global=Resulting_time_pos*speed−Resulting_time_profile*speed
ΔPospos_global=(Resulting_time_pos−Resulting_time_profile)*speed
From which it follows that for 100% of maximum speed
Pos_error(100%)=(Resulting_time_pos−Resulting_time_profile)*speed(100%)
Which can be rewritten as:
Resulting_time_pos−Resulting_time_profile=ΔPospos_global/speed
Which further equals to:
ΔPospos_global/speed=Difference_resulting_time
When two or more scan sequences have been performed, the measurements may be listed in a table. As for the reference object, the profile is known for each exact position from the identification sequence, for the scan at speed V(n) the exact position may be correlated to each profile measurement at speed V(n). While also position measurements have been performed, the difference of positions, (exact position—position measurement), will allow to determine the Resulting_time_profile.
Knowing the Resulting_time_profile and Difference_resulting_time, the Resulting_time_pos may be calculated:
Resulting_time_pos=Resulting_time_profile+Difference_resulting_time
With these time delays known, the true position of the hoisting appliance at the moment of the profile measurement be calculated, and the correct dimensions of the object to be handled by the hoisting appliance may b determined.
Although the present invention has been described above with reference to specific embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the invention is limited only by the accompanying claims and, other embodiments than the specific above are equally possible within the scope of these appended claims.
Furthermore, although exemplary embodiments have been described above in some exemplary combination of components and/or functions, it should be appreciated that, alternative embodiments may be provided by different combinations of members and/or functions without departing from the scope of the present disclosure. In addition, it is specifically contemplated that a particular feature described, either individually or as part of an embodiment, can be combined with other individually described features, or parts of other embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20305680.9 | Jun 2020 | EP | regional |
