Elevator – industrial lift truck – or stationary lift for vehicle – With monitoring – signalling – and indicating means – Monitors operational parameter
Reexamination Certificate
2000-01-21
2001-08-07
Salata, Jonathan (Department: 2837)
Elevator, industrial lift truck, or stationary lift for vehicle
With monitoring, signalling, and indicating means
Monitors operational parameter
C187S222000, C414S273000, C414S635000
Reexamination Certificate
active
06269913
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an industrial lift truck with a load lifting device and a device for moving the load lifting device on the lift truck having at least one element that can move, together with the load lifting device, along an essentially straight guide, and with a position measuring device for monitoring the position relative to the guide of the load lifting device or of the element movable with the load lifting device.
BACKGROUND
Industrial lift trucks with a position measuring device for determining the position of the load lifting device relative to a reference point on the lift truck in question are known.
For instance, DE 195 08 346 C1 discloses an industrial lift truck with a position measuring device for determining the lift height of an adjustable-height load lifting device. The load lifting device is driven by a hydraulic cylinder supplied by a hydraulic pump, which is driven by an electric motor. Starting from an initial position of the load lifting device, the rotations of the hydraulic pump are counted up in one direction of rotation and down in the opposite direction of rotation, and are evaluated in light of the overall efficiency of the lift system to determine the current lift height.
Moreover, with regard to industrial lift trucks, there has already been proposed the concept of providing the lifting frame for a load lifting device with proximity switches at predetermined intervals, which switches respond to a marking that is movable with the load lifting device in order to determine the current lift height of the load lifting device.
Known from DE 32 11 486 A1 is a forklift vehicle with the features mentioned at the outset, wherein the position measuring device includes a rotating disk with radial slits on its edge that is arranged on the shaft of a pinion provided in the upper region of the moving part of the lift mast to deflect a lift chain for the load carrying fork. An optical sensor arrangement with a light-emitting diode and a phototransistor is provided in the vicinity of the edge of the disk to measure the rotational motion of the disk. As the disk rotates, the light path formed by the light-emitting diode and the phototransistor is alternately unblocked by the edge slits and blocked by the teeth between the edge slits, so that the phototransistor delivers a pulsed electrical signal whose pulse count at any point corresponds to the angle of rotation of the disk and that of the chain sprocket that is rotationally fixed to the disk. The current change in lift height of the load carrying fork is determined from the angle of rotation of the chain sprocket that is engaged with the lift chain. Since the rotation of the chain sprocket when the load carrying fork is raised or lowered is determined by the length of the section of chain that passes over the chain sprocket, changes in the chain length such as those which frequently occur during operation under load will lead to errors in determining lift height. A further disadvantage of this known solution is that the sensor components (light-emitting diode, phototransistor, rotating disk) must be arranged on the moving part of the lift mast, since the chain sprocket attached to the rotating disk must be arranged on the moving lift mast section for functional reasons. This not only produces a design constraint, but is also invariably subject to the problems that arise when electrical signals are transmitted by moving sensors.
SUMMARY
It is an object of the invention to provide an industrial lift truck of the type described at the outset wherein the position measuring device can be realized with simple means, and thus economically, while reliably providing position measurement results with high precision and resolution.
This object is attained in accordance with the invention by the provision, in an industrial lift truck, of a position measuring device which includes at least one roller body that either a) is arranged on the element that is movable with the load lifting device such that it is capable of rotation and its circumference contacts a path running along the guide in such a way that it is forced to roll along the path by movement of the element that is movable with the load lifting device, or b) is arranged on an element that is stationary relative to the guide such that it is capable of rotation and its circumference contacts the element that is movable with the load lifting device in such a way that it is forced to rotate by movement of the element that is movable with the load lifting device, and wherein the roller body acts in combination with a sensor which transmits an electric signal as a function of the rotational movement of the roller body to an analysis circuit which evaluates the signal for determining the position of the element that is movable with the load lifting device or the position of the load carrier relative to the guide.
In an industrial lift truck in the form of a lift truck, the load lifting device is usually a load carrying fork that is arranged on a fork carrier and is vertically movable, together with the fork carrier, on a lifting frame or mast. For measuring the lift height of the load carrying fork, in accordance with alternative a) the roller body is arranged on the fork carrier or an element attached thereto for movement along the guide in such a manner that, for instance, it rolls along a path on the lifting frame that is parallel to the direction of lift. The rotational movement of the roller body is measured by the sensor so that the analysis circuit connected to the sensor can evaluate the electrical signal for determining the lift height supplied by the sensor.
On the other hand, the roller body can be arranged in accordance with alternative b), on an element that is stationary relative to the guide, where its circumference contacts the element that is movable with the load lifting device in such a way that it is forced to rotate by movement of the element that is movable with the load lifting device. Alternative b) has the advantage that the signal lines need not move, and can thus be laid in a fixed position.
The sensor is preferably a digital angular position sensor that is designed as an incremental sensor, and the analysis circuit contains a counter circuit that counts the pulses emitted by the angular position sensor as a function of the roller body's change in angle of rotation. Preferably, the incremental angular position sensor is designed to have at least two channels so that it emits two count pulse signals, preferably in quadrature, when the roller body revolves. The analysis circuit evaluates the count pulse signals in order to determine the roller body's direction of rotation and to count the count pulses from at least one of the count pulse signals, either up or down, depending on the direction of rotation. For example, when the load lifting device is raised, it can count up, and when the load lifting device is lowered, it can count down, so that the current count value at any given time can be used to determine lift height. To this end, the analysis circuit can be designed to redundantly evaluate both of the phase-shifted count pulse signals for safety reasons, in order to be able to detect any measurement errors.
In accordance with a preferred embodiment of the invention, the roller body is part of a roller bearing, for example, the outer ring of a roller bearing, or is arranged on the element that is movable with the load lifting device so as to rotate with the aid of a roller bearing. The use of a roller bearing with an integrated angular position sensor offers the advantage that only extremely small frictional torques need be overcome and the roller body can thus roll along its rolling path with no opposing torque to speak of. In test measurements, the roller body demonstrated no slip errors detectably impairing the reproducibility of the measurement results even after a number of translational movement cycles of the load lifting device. Even under conditions of a rolling path contaminated with a lubrican
Kollmannsberger Otto
Vockinger Johann
Wichmann Martin
Baker & Botts L.L.P.
Salata Jonathan
Steinbock Boss GmbH Fördertechnik
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