GB2459349A

GB2459349A - Contactless detection of the height of a load pickup means

Info

Publication number: GB2459349A
Application number: GB0904858A
Authority: GB
Inventors: Phillip Michael William Ireland
Original assignee: Linde Material Handling GmbH
Current assignee: Linde Material Handling GmbH
Priority date: 2008-04-22
Filing date: 2009-03-20
Publication date: 2009-10-28
Anticipated expiration: 2029-03-20
Also published as: DE102008020170A1; GB2459349B; GB0904858D0

Abstract

A method and an apparatus for the contactless detection of the position of a vertically moveable load pickup means 2 evaluates movement-dependent changes in an image of a target object 4 detected by a reception device 3, the target object 4 moving along with the load pickup means 2. The target object 4 may have patterns (1-6 fig. 4), over which a suitable light beam of a light source associated with the reception device 3 passes in the horizontal direction when the target object 4 is removed from the reception device 3. The reception device 3 may be a CCD sensor and the light source may be a laser. Evaluation of the contrast and/or resolution of the patterns imaged may be used to identify contamination of the reception device 3. If a disruptive element is detected a fault message may be produced.

Description

Method and apparatus for the contactiess detection of the position of a vertically moveable load pickup means of an industrial truck The invention relates to a method for the contactless detection of the position of a vertically moveable load pickup means of an industrial truck and to an industrial truck equipped with an apparatus for the contactiess detection of the position of the load pickup means.

Industrial trucks have a load pickup means with which, for example, loads located on pallets can be raised.

The load pickup means is conventionally provided with a bearing fork, which can be raised and lowered along a lifting mast by means of a lifting device. In this way, a load can be raised to a storage area, for example on a shelf, which is arranged above the travel path of the industrial truck. In particular in the case of relatively large lifting heights, it is helpful for the driver to be able to read the respectively current height during the positioning operation using a measurement system with a display. Likewise, the storage area intended for the load can be approached automatically by means of a control device on the basis of the measured height in conjunction with an input value.

Lifting devices of industrial trucks generally have a carriage with the load pickup means, which carriage is moved by means of rollers in a possibly multi-element mast system in the vertical direction, generally driven via hydraulic cylinders.

In order to measure the lifting height, the height of the carriage or of another part moving proportionally with respect to the carriage movement (for example piston of a hydraulic cylinder) relative to the industrial truck or to the travel path needs to be detected.

Nowadays, use is predominantly made of measurement systems with mechanical sensing of a moving part, such as cable-pull or friction-wheel measurement systems.

However, these systems are susceptible to contamination, touching contact and damage. They are therefore restricted to specific application areas.

Problems can occur, for example, given certain environmental conditions. During use in cold storage houses, the systems are subjected to temperature fluctuations of from, for example, -24°C to +7°C when the truck is driven in and out. In cable-pull systems, freezing of the cable may occur, for example.

Mechanical measurement systems are generally also restricted to certain lifting heights and are generally not suitable for detecting the lifting height in the free-lift range of the load pickup means. In addition, they require a large amount of maintenance.

Contactless measurement systems manage without any additional moveable and therefore susceptible mechanical components. Present systems function on the basis of the principle of the running time measurement in conjunction with reflection of a measurement medium on a surface determining the distance from the measurement system. The light of a laser, microwaves (radar) or ultrasound waves belong to the known measurement media.

The present invention is based on the object of configuring a method and an industrial truck of the type mentioned at the outset in such a way that precise and quick position detection of the load pickup means is made possible largely independently of environmental influences.

In terms of the method, the object is achieved according to the invention by virtue of the fact that an image of a target object, which is capable of moving relative to a reception device, is detected by the reception device, the relative movement of the reception device and the target object being correlated with the movement of the load pickup means, and movement-dependent changes in the image of the target object being evaluated for the purpose of determining the position of the load pickup means.

In contrast to the previously conventional methods for the contactiess position determination of the load pickup means of industrial trucks, in which the running time of a signal emitted by a transmitting device as far as a reception device is measured and the lifting height is calculated from this, the invention is based on the principle of image identification, in particular of pattern identification. As the distance between the target object and the reception device increases, the image of the target object changes. In the case of a viewing angle, from the point of the reception device, which remains the same and is predetermined by a lens, for example, the image area detected by the reception device of the target object increases, for example, and additional image constituents, for example additional patterns, becOme identifiable. The movement-dependent change in the image can be used to calculate the position of the load pickup means.

In order to determine the position on the basis of the relative movement between the target object and the reception device, it is necessary for the relative movement to be correlated with the movement of the load pickup means. The most expedient way of achieving this is for the target object to be moved along with the load pickup means, while the reception device is fixed firmly on the industrial truck. For this purpose, the target object can be fixed, for example, to a component part which moves along with the load pickup means. When the industrial truck is designed to have a lifting mast and a bearing fork, the target object is preferably fitted at that end of the bearing fork which is on the lifting-mast side (the lower end), while the reception device is preferably arranged at the lower end of the lifting mast between the mast spars.

Alternatively, the positions of the target object and the reception device can also be swapped over, i.e. the reception device is arranged in such a way that it is capable of moving along with the load pickup means, while the target object is fixed firmly on the industrial truck.

It is also conceivable for both the target object and the reception device to be moveable. For example, they can be fitted to different height sections of a multi-element, telescopic lifting mast, with the result that the two can move relative to one another when the load pickup means is raised or lowered. As a result of computational compensation of the movement of the reception device, it is possible to draw conclusions on the position of the target object.

The target object expediently used is a flat element, for example in the form of a plate, whose surface normal is preferably oriented substantially parallel to the imaginary connecting line (line of vision) between the target object and the reception device, with the result that best-possible imaging of the target object on the reception device can be provided.

The reception device is expediently a CCD (charge coupled device) sensor, i.e. an integrated electronic component part for image detection. In this case, a two-dimensional CCD sensor (2 D-CCD) is advantageously used, as is used, for example, also in digital cameras.

The target object is preferably provided with patterns, which are detected optically by the reception device.

Movement-dependent changes in the image of the patterns are evaluated by a signal processing device for determining the position of the load pickup means. If a constant, narrow imaging angle is presupposed, the image area detected by the reception device increases as the distance from the reception device increases, with the result that additional patterns can be identified. In the simplest embodiment, it is possible to draw conclusions on the lifting height of the load pickup means from the number of detected patterns.

In accordance with a particularly preferred embodiment of the invention, the target object is illuminated by at least one light source. For this purpose, preferably a light source with a narrow radiation angle, in particular a laser light source, is used. In this case, the light source and the reception device are expediently arranged in the direct vicinity of one another, in particular in a common unit.

A particularly advantageous configuration of the invention provides that the light beam is oriented in such a way that it encloses an angle with respect to the vertical and, in the event of a movement of the load pickup means, passes over at least part of the target object in the horizontal direction. Preferably, different patterns are applied to the target object, with the result that, when the target object is passed over in the horizontal direction, various patterns on the target object are irradiated, and these patterns are detected by the reception device and evaluated by means of pattern identification for the purpose of determining the position of the load pickup means.

Given a conventional design of the industrial truck with a lifting mast and a bearing fork, which is capable of moving along the lifting mast, as the load pickup means, expediently the light source and the reception device are therefore fitted at the lower end of the lifting mast on the industrial truck, while the target object, for example in the form of a marking, is arranged in the region of the bearing fork, in particular at that end of the bearing fork which is on the lifting-mast side (the lower end) . In this embodiment, the light beam is preferably oriented at an angle with respect to the lifting mast, with the result that it passes over the target object, which is fitted in the region of the bearing fork, in the horizontal direction when the bearing fork moves away from the light source. The reception device therefore sees different patterns, which are provided on the target object and are irradiated successively by the light beam, for example, when the bearing fork moves away.

Pattern identification can therefore be used to draw conclusions on the lifting height of the bearing fork.

In accordance with a development of the concept of the invention, the patterns applied to the target object are also used for identifying contamination of the reception device. By evaluating the contrast and/or resolution of the patterns imaged on the reception

device, it is possible to draw conclusions on the

degree of contamination. When a predetermined degree of contamination is exceeded, a cleaning operation can automatically be introduced. For this purpose, a wiping device can be activated, for example, which wiping device cleans the reception device again.

In order to avoid malfunctions during unintentional introduction of disruptive elements into the line of vision between the reception device and the target object, the patterns provided on the target object are also used for identifying the target object. By evaluation of the patterns by means of the signal processing device, a distinction is drawn between the detection of the image of the target object and the detection of the image of a disruptive element and, in the event of the detection of the image of a disruptive element, a fault message is output. This indicates to the driver of the industrial truck that the system for lifting height measurement is not functioning properly.

In one development the industrial truck can also be stopped automatically when a fault message is output.

In accordance with a particularly interesting development of the concept of the invention, the position determination of the load pickup means is used for identifying mechanical deformations and/or oscillations. In the case of mechanical deformations and/or oscillations of the component parts bearing the load pickup means as well, the image detected by the reception device of the target object changes in such a way that by evaluating the image changes the deformation states or oscillation states can be detected and countermeasures can be introduced.

Compensation oscillations can be automatically induced in the event of a predetermined oscillation intensity of the mechanical oscillations being exceeded.

In addition to the method for the contactiess detection of the position of a vertically moveable load pickup means of an industrial truck, the invention also relates to an industrial truck equipped with a corresponding apparatus.

In terms of the apparatus, the object on which the invention is based is achieved by virtue of the fact that the apparatus for the contactiess detection of the position of the load pickup means has at least one target object and at least one reception device, which is designed to detect an image of the target object, the target object and the reception device being arranged on two component parts, which are capable of moving in relation to one another, and the moveability of the component parts being correlated with the moveability of the load pickup means, and the reception device being designed to detect movement-dependent changes in the image of the target object, and the reception device having an associated signal processing device for determining the position of the load pickup means.

Expediently, the target object is fitted on a component part which moves along with the load pickup means, and the reception device is fixed on a component part of the industrial truck which does not move along with the load pickup means, there being a visual connection between the target object and the reception device in all states of the vertical movement of the load pickup means.

In accordance with a particularly preferred configuration of the apparatus according to the invention, the reception device has at least one associated light source, whose light beam is oriented towards the target object.

The light source is advantageously in the form of a laser light source, whose light exit beam is oriented in such a way that it encloses an angle with respect to the vertical and, in the event of a movement of the load pickup means, passes over at least part of the target object in the horizontal direction.

The reception device preferably has an associated signal processing device, which can be programmed with an image processing program for evaluating movement-dependent changes in the image of the target object for the purpose of determining the position of the load pickup means.

In order to facilitate the evaluation of movement-dependent changes in the image of the target object, advantageously at least one pattern is applied to the target object, which pattern can be detected as an image by the reception device and can be evaluated by the signal processing device, the signal processing device being capable of being programmed with an image processing program comprising pattern identification.

The invention makes available a contactiess system for detecting the position of a load pickup means of an industrial truck which functions in a manner which is largely independent of external influences, such as temperature fluctuations or contamination. In particular the high precision made possible by the invention in terms of the lifting height measurement and the speed of detection of changes in position are also advantageous. As a result, the system according to the invention is also highly suitable for active compensation of oscillations and/or deformations of the lifting mast of industrial trucks. Overall a technically elegant solution for lifting height measurement is therefore made available which, with a low cost expenditure, at the same time provides a series of advantages, such as high degree of reliability, little maintenance, particularly high precision and speed of measurement and the additional use of the possibility of active oscillation abatement and dynamic and static mast deformations.

Further advantages and details of the invention will be explained in more detail with reference to the exemplary embodiment illustrated in the schematic figures, in which: Figure 1 shows an industrial truck in a side view, Figure 2 shows a reception device in a plan view, -10 -Figure 3 shows a reception device in a side view, Figure 4 shows a target object with patterns, and Figure 5 shows a block circuit diagram.

The industrial truck illustrated in Figure 1, for example a reach truck, has a multi-element lifting mast 1, which can be extended and retracted telescopically in a vertical direction. The dashed illustration 5 shows the lifting mast 1 in the retracted state. A bearing fork 2 is fitted in the upper region of the lifting mast 1. In order to measure the lifting height of the bearing fork 2, an optical reception device 3, which is arranged between the spars of the lifting mast 1 and therefore is not illustrated in the side view in Figure 1, is located at the lower end of the lifting mast 1. In addition, in the region of the bearing fork 2 on the lifting mast 1, a target object 4 is fixed between the spars of the lifting mast 1. The target object 5 is preferably arranged on the underside of the bearing fork 2 or the underside of a lifting carriage, on which the bearing fork 2 is fixed and which is guided in the lifting mast 1. In all states of the vertical movement of the lifting mast 1, there is a visual connection between the target object 4 and the reception device 3. When the lifting mast 1 is extended, the distance between the optical reception device 3 and the target object 4 is increased. As a result, the image detected by the reception -+device 3 of the target object 4 also changes. The change in the image can be used to draw conclusions on the position of the bearing fork 2.

Figure 2 illustrates a unit which contains an optical reception device 1, which comprises a CCD sensor and a lens fitted above this with an antireflective coating.

The CCD sensor 1 is accommodated in a housing filled -11 -with inert gas, in particular nitrogen, in order to protect it against environmental influences. Two laser light sources 2 and 3 are arranged to the side of the CCD sensor. LEDs with a narrow light exit angle are used as the laser light sources. The unit is closed off at the top by a scratch-resistant glass cover 4. A wiping device 5 for cleaning the glass cover 4 is arranged over the glass cover 4.

Figure 3 shows a side view of the unit illustrated in Figure 2. In this case, the wiping device 5 with the drive motor 6 can clearly be seen. The entire unit can be oriented towards the target object via adjusting screws 7.

The optical reception device 1 illustrated in Figures 2 and 3 has a highly sensitive CCD sensor with at least 25000 pixels in the transverse direction (at right angles with respect to the orientation of the bearing fork) and at least 300 pixels in the longitudinal direction (parallel to the orientation of the bearing fork). The CCD sensor is intended to produce at least one image of the target object with a grey scale of 16 bits. A higher resolution or colour resolution represents a significant advantage, however. The imaging power should be at least 1500 images per second for the lifting height measurement and 3000 images per second for the forward deflection, i.e. the detection of oscillation states and/or mast deformations of the lifting mast.

The light beams of the laser light sources 2 and 3 are inclined relative to the lifting mast, as is shown in Figure 3, with the result that, when the target object moves away, the light beams pass over the target object in the horizontal direction. Given corresponding calibration and compensation, the distance of the target object from the reception device 1 can be derived from the lateral movement of the light beam on the target object. The lifting height measurement can be carried out with a precision of better than � 2mm with a lifting speed of 1.0 m/s. At least one of the light sources should be oriented at right angles with respect to the optical reception device 1 in order to provide a reference signal which is independent of the movement of the lifting mast.

In order to achieve as high a level of accuracy as possible, the target object should be as large as possible. The size is only limited by the available area between the spars of the lifting mast. The accuracy can also be improved by virtue of the fact that light sources with different angles of inclination are used. As a result, the light beams pass over the target object differently. This may be necessary, for example in the case of a low lifting height of the lifting mast, if the optical reception device cannot detect the entire image of the target object.

The target object illustrated in Figure 4 has identification patterns 1, with the aid of which the reception device can distinguish the target object from possible disruptive elements. This prevents, for example, a hand held in the light beam or any other object from incorrectly being identified as the target object. In addition dirt identification patterns 2 are applied on the target object which make it possible to determine the degree of contamination of the lens of the reception device by means of evaluation of the image quality of the patterns which are imaged. In this case, a plurality of patterns are provided, with the complexity increasing from pattern to pattern, with the result that the required resolution of the optical reception device increases for complete evaluation. As a result of a comparison with stored pattern input values, the degree of contamination can be determined by digital evaluation.

The patterns applied on the target object differ sufficiently from quadrant to quadrant, with the result that the orientation of the target object relative to the reception device can be determined.

The markings 3 provided at the edges of the target object are used for establishing the maximum deflection of the lifting mast. The markings 4 reproduce the state of the zero deflection of the lifting mast. The points 5 are the target points of the laser light beams for the lifting height measurement. Point 6 is the target point of the reference light beam, which is oriented at right angles and which remains fixed independently of the lifting height.

The block diagram shown in Figure 5 reproduces the wiring of the individual components of the lifting height measurement system. The CCD sensor 1 is connected to a digital signal processing device 3 via an image buffer 2. The signal processing device 3 is connected to a microprocessor 4 with a storage unit 5.

The microprocessor 4 controls a heating device 7, a wiper motor 8 and the laser light sources 9 via a control unit 6. In addition, temperature sensors 10 are connected. The lifting height measurement system is connected to the controller of the industrial truck via a CAN bus 11.