GB2058508A

GB2058508A - Photo-electric measurement of the height of a load carrier on a vehicle

Info

Publication number: GB2058508A
Application number: GB8022445A
Authority: GB
Original assignee: Jungheinrich Unternehmensverwaltung KG
Current assignee: Jungheinrich AG
Priority date: 1979-08-14
Filing date: 1980-07-09
Publication date: 1981-04-08
Also published as: FR2463390A1; GB2058508B; DE2932899B1; FR2463390B1; DE2932899C2

Abstract

The height of the forks 9 of a fork-lift truck is measured by an opto- electronic system comprising a transmitter 11, e.g. an infra-red radiator, on the base of the truck and a reflector 10 on the forks which reflects the radiation to a receiver 12 on the truck adjacent to the transmitter 11. A floor sensor may be provided to compensate for changes in the height of the transmitter above the floor, for example as a result of the imposition of a load on the load truck. The forks are moved to their desired position hydraulically by a system in which a desired height representing voltage is compared with a voltage produced by the measuring system. <IMAGE>

Description

SPECIFICATION Contactless measurement of the height of a load carrier on a load-carrying vehicle above a reference point This invention relates to the contactless measurement of the height of a load carrier on a load-carrying vehicle above a reference point.

By reference to a load-carrying vehicle is meant particularly a high-shelf stacker. Such loadcarrying vehicles or high-shelf stackers have a mast on which the load carrier can be lifted high.

Problems of obtaining an accurate measurement of the height of the load carrier above the floor or above the vehicle result from this, particularly when operating the vehicle with automatic height preselection. In the case of measurement relative to the vehicle it is assumed that a reference position is provided on the vehicle, by virtue of its construction, which remains at a fixed distance from the floor.

The establishment of the height of the load carrier is of particular significance for stacking and unstacking procedures. For such procedures it is known for example from US patent specification 3319816, to have an automatic control for a floor-travelling shelf stacker both in respect of the lift height and also in respect of horizontal swing of the slide. For the height measurement, real value transmitters in the form of potentiometers are provided. The real value transmitter is driven by a friction wheel, with the result that uncertainties arise, since friction wheel drives involve slip which can vary for all sorts of different reasons. Wear and tear also leads to further uncertainties. For the rest, in the known arrangement, a comparison of real and desired values takes place and the driver can turn particular actuating knobs in order to select particular lift heights.

From the journal "Deutsche Hebe-und Fördertechnik",1967, Volume 8, it is known to provide an automatic control for crane installations or shelf-stacking systems. This involves a comparison of desired and actual values, in order to actuate an evaluator. Pulse generators are used to supply counting pulses, generated by markings on the crane track or on the lifting mast, the markings either being reflective marks which are sensed photoelectrically or being metallic plates which are sensed by initiators.

By this method, as also with other contactless sensing of reflection devices on shelving racks, one does not ascertain the absolute height of the load carrier above the floor or in relation to a reference point on the load carrier guide, but on the contrary the stacking apparatus or shelves must be equipped with reflectors, which means that sensing surfaces have to be provided on each shelf bay.

Such arrangements, for a mechanical system, are also known, for example from published West German patent application 1 946545.

Such systems, whether contactless or mechanical, are very expensive, since a shelf storage system has a great number of shelving bays which, moreover, may not always be the same size.

Consequently, there is the need for a large expenditure not only on the installation but also for the maintenance of elements which are not easily accessible.

Attempts have already been made to measure the height of the load carrier above a reference point on the vehicle or above the floor directly by means of an extensible measurement element, and for this, assuming that one has an accurately working proportional mast, one needs to measure the length of a steel strip which is drawn out from the load carrier or to sense coded information on such a steel strip. However, this has a disadvantage that such a measuring system operates inaccurately as a result of contamination or bending of the strip due to wind pressure either while stationary or while moving, and moreover the sensing contact no longer remains accurate through the results of wear and tear. Other adverse effects can also arise, through defects in a spring-wound motor for the strip, which additionally can represent a considerable potential danger to persons in its vicinity.

It is an object of the present invention to provide apparatus of the type first mentioned above on a load-carrying vehicle, particularly on a high-shelf stacker, which establishes the absolute height of the load carrier in relation to a reference point with reliability without mechanical action, with tolerances in the mechanical structure of a lifting mast having such influences eliminated, with the result that with automatic height selection an outward extension of the load carrier in front of a bay of shelves can take place when the vehicle itself is still positioned in the aisle.

In accordance with the present invention there is provided apparatus for contactless measurement of the height of a load carrier on a load-carrying vehicle, particularly a high-shelf stacker, above a reference point, comprising optoelectronic distance measuring means arranged on the vehicle and associated reflector means on the load carrier for the reflection of radiation therebetween.

Also in accordance with the invention there is provided a method of measuring the height of a load carrier on a load-carrying vehicle above a reference point without mechanical measuring contact between the load carrier and the floor or a reference point on the vehicle which comprises emitting radiation from a transmitter on the vehicle, reflecting it from a reflector on the load carrier to a receiver on the vehicle, and on the vehicle evaluating the height from a measurement representative of the transit time of the radiation between transmitter and receiver.

An opto-electronic, contactless remote measuring system using infra-red radiation is known for film cameras, as described in the Development Report No. 23 of Texas Instruments European Applications Laboratory. However, shelf-stacking vehicles work with mechanical means, if no marks or reflectors are sensed, and such mechanical means do not permit absolute accuracy of their own tolerance values by reason of the mechanical means. The present invention, by virtue of the contactless distance measurement, which moreover demands no space on the lifting mast, provides a-very accurate height measurement system which considerably improves the advantages of the automation of industrial storage facilities, since a signal in analogue form is made with certainty.

Thus, initially one can start from a reference point on the load-carrying vehicle which represents a definite reference value in relation to the floor, Insofar as differences may result in dependence on the load because of the construction of the load-carrying vehicle, these can easily be equalised by separate additional means.

Preferably, an infra-red radiation transmitter is provided on the vehicle which emits signals at a particular frequency, which produces a reference signal for comparison with the first reflected signal, and which comprises comparator means for comparing the phases of the two frequency signals. This results in an application of the known per se distance measuring system, which in its use on a load-carrying vehicle, especially on a highshelf stacker, brings with it surprising advantages.

Preferably, a real-value voltage is produced in the comparator means of the transmitter, this voltage being proportional to the load carrier height, and adjacent to the transmitter there is provided receiver means connected to a differential amplifier which receives both this realvalue voltage and a desired-value voltage, the output of this differential amplifier being connected to setting means in the drive circuit for the load carrier. In relation to this it is pointed out that the differential amplifier does not need automatically to be integrated into the transmitter; it can alternatively be located externally of it. The height movement of the load carrier can be controlled by these means. Naturally, it is possible to provide a manual control instead of a real-value voltage.However, if the system is to be automated, then this necessitates the comparison with a desired-value voltage.

The setting means is determined by the type of drive provided for the load carrier. For example, it can be an electrical or electronic device. In one preferred embodiment, the setting means is a proportional valve arranged in a hydraulic drive system for the load carrier.

It is particularly advantageous if the one input of the differential amplifier for the desired-value voltage can be connected to different desiredvalue voltages. By this means one can preselect a particular height level. By this means very good accuracy is achieved because of the fact that intermediate effects arising from tolerances in mechanical components and operation of the lifting equipment are by-passed.

In one embodiment, a poteritiometer is provided at the one input and can be set to different desired-value voltages. In this way all intermediate values with regard to the lift height can be selected. This is an important advantage, since one avoids distance steps which are always linked to a particular installation. However, in the preferred embodiment, a stepping swtich is provided at the one input and can be connected to different desired-value voltages from different sources. This gives a favourable solution in a practical application.

Insofar as the reference point on the vehicle is variable in relation to the floor in dependence upon the load, for example for the reason that the wheels are resiliently supported or comprise pneumatic tyres which can deform in dependence upon the load, one preferred embodiment provides for a floor sensor to be provided on the vehicle, for example in the form of a sensing roller which can be extended to the floor, and the position of the sensing roller in relation to the transmitter actuates an adjustment device for the desired value voltage. This does not exclude the possibility that a contactless floor sensing could be effected by the transmitter itself. The mechanical sensing by means of a sensing roller has the advantage however that contamination or dirt has no effect.

The invention is described hereinafter with particular reference to an embodiment which is given by way of example and which is shown in the accompanying drawings.

In the drawings: Fig. 1 is a schematic side view of a load carrying vehicle; Fig. 2 is a schematic diagram illustrating the inter-relationship of the control values; Fig. 3 is a detail of the transmitter system; Fig. 4 shows a modification of Fig. 3; Fig. 5 shows a further modification of Fig. 3; and, Fig. 6 shows a vehicle corresponding to Fig. 1 but illustrating an additional feature.

In all the Figures the same or corresponding elements or components are indicated by the same reference numbers.

The load-carrying vehicle, for example a highshelf stacker, has a chassis 1 with wheels 2, 3, a driver's seat 4, a driving and control unit 5, as well as a mast 6 which preferably can be constructed' as a telescopic mast in a manner known per se, and on which a load carrier 7 is mounted by means of a lifting slide 8 so that it is adjustable in respect of its height, for example by a hydraulically actuated piston/cylinder device (not shown). The load carrier 7 has fork arms 9 on which a load rests. It is possible that the mast 6 can bend as a result of the turning moment which arises from the placing of a load on the fork arms 9, and that such a load can affect telescopically extensible mast sections as well as causing problems in the guidance of the lifting slide 8 on the mast track. In order to prevent such adverse effects a reflector 10 for a beam of radiation is arranged directly on the load carrier 7, preferably beneath the fork arms 9, the radiation being emitted by a transmitter 11 which is mounted on the vehicle chassis. Preferably, the reflector 10 is positioned beneath the fork tips; this is preferable in order to be able to measure the height of the fork tips so that one thereby additionally makes proper allowance for the bending of the forks under the weight of the load.

So far as the transmitter 11 is concerned, this is preferably an infra-red transmitter which emits signals at a fixed frequency vertically upwards with a small generating angle in order to strike the reflector 1 0. In the case of an infra-red transmitter, the reflector can be a mirror. Adjacent to the transmitter 11 there is positioned a receiver in the form of an indicator device 12, which can be positioned concentrically around the transmitter, or adjacent to it, and which picks up the reflected signals at the fixed frequency. Because of the transit time of the signals emitted by the transmitter 11 in travelling to the receiver 12 there results a phase displacement of such frequency signals in relation to a reference frequency which is generated in the transmitter for direct transmission to the receiver 12.This phase displacement is therefore proportional to the signal path length from the transmitter 11 to the reflector 10 and back to the receiver 12 and thus represents an absolute reference value for the distance between the transmitter 11, or the vehicle chassis 1, on the one hand and the load carrier 7 on the other hand.

By this means one can establish the absolute height of the load carrier and evaluate this on the vehicle.

Preferably, from the comparision of the frequencies or from the phase displacement between these frequencies, a voltage is produced which is proportional to the height of the load carrier.

In Fig. 2 is shown a diagram in which the ordinate 13 represents this voltage and in which the abscissa 1 4 represents the lift height. From this it is evident that the lift height H, corresponds to a voltage U1 and that a lift height H2 corresponds to a voltage U2, since the circuit elements are so designed that the plotted characteristic 1 5 is a straight line passing through the zero point.

In the transmitter/receiver arrangement 11, 12 there is provided, according to Fig. 3, a differential amplifier 16 having two inputs 17, 18. The one input 1 8 is connected to a source 1 9 for a desired voltage; the other input 1 7 is connected to a source 20 which is connected to a comparison device 21 in which the two frequency signals are compared and which for its part has two inputs 22, 23 for a reference signal and the first reflected signal respectively.

The output 24 of the differential amplifier 1 6 is fed to a setting device 25 in a drive circuit 26 for the load carrier 7, so that the load carrier is adjustable in a manner which is accurately proportional to the height. Preferably, the drive circuit 26 is part of a hydraulic drive system, and 25 is a proportional valve.

According to Fig. 4, the differential amplifier 16 has its one input 18, to which the desired-value voltage is applied, connected to a potentiometer 27 having a slider 28 which is adjustable by a setting motor 29 in dependence upon an input desired-value magnitude. The setting motor 29 can drive a splindle 30 fitted with a nut 31 to which the slider 28 is connected, the latter being connected to the amplifier input 18 by way of a connection 33.

According to Fig. 5, the one input 18 of the differential amplifier 1 6 is connected to a stepping switch 34 with different switch contacts 35-38 which are connected to respective sources 39-42 for different desired-voltage values. Thus, by this means, a particular lift height can automatically be pre-controlled.

The reference point in the embodiment hereinbefore described is the transmitter 11, or the receiver 12. According to Fig. 6 a floor-level adjustment device 43 is provided in the receiver 12 and is connected with a voltage-generating circuit 44 for the representative voltage which is applied to amplifier input 1 7. An intermediate coupling transmission member 46 is arranged between this adjustment device 43 and a driving member 45, the intermediate coupling transmission being arranged to be switched between open and closed states so that during a lowering or lifting movement there is no shifting of the adjustment device 43, and that this is only actuated within a limited control range when the intermediate coupling transmission member 46 is closed. The driving member 45 is connected to a carrier 47 for a sensing roller 48 which can be lowered to the floor. For this purpose, and also for raising it, a lifting device 49 in the form of an electromagnet is provided. After the roller 48 is lowered and makes contact with the floor the electromagnet is switched on so that the desired voltage is then generated.

Electronic evaluation circuitry 50 for example is provided on the vehicle, and is attached by cable 51 to the transmitter/receiver unit 11, 1 2 and is connected to the driving and control unit 5.

Claims

1. Apparatus for contactless measurement of the height of a load carrier on a load-carrying vehicle, particularly a high-shelf stacker, above a reference point, comprising opto-electronic distance measuring means arranged on the vehicle-and associated reflector means on the load carrier for the reflection of radiation therebetween.

2. Apparatus as claimed in claim 1, in which an infra-red radiation transmitter is provided on the vehicle which emits signals at a predetermined frequency, which generates a reference signal for comparison with the first reflected signal, and which comprises comparator means for comparing the phases of the two frequency signals.

3. Apparatus as claimed in claim 2, in which a real-value voltage is produced in the comparator means of the transmitter which is proportional to the load carrier height, in which adjacent to the transmitter there is provided receiver means connected to a differential amplifier which is fed with the real-value voltage and a desired-value voltage, and in which the output of the differential amplifier is connected to setting means in the drive circuit for the load carrier.

4. Apparatus as claimed in claim 3, in which the setting means comprises a proportional valve in a hydraulic drive system for the load carrier.

5. Apparatus as claimed in claim 3 or 4, in which one input of the differential amplifier can be switched to one of a plurality of different desiredvalue voltages to serve as the desired-value voltage.

6. Apparatus as claimed in claim 5, in which a potentiometer is connected to said one input and is adjustable to different desired-value voltages.

7. Apparatus as claimed in claim 5, in which a stepping switch is connected to said one input and can be switched to different desired-value voltages from respective different sources.

8. Apparatus as claimed in any preceding claim, in which a floor sensor is provided on the vehicle and the position of the sensor in relation to the transmitter actuates an adjustment device for the desired-value voltage.

9. Apparatus as claimed in claim 8, in which said floor sensor comprises a sensing roller which can be lowered to the floor.

10. Apparatus as claimed in any preceding claim, in which the load carrier includes a fork and the reflector is positioned beneath the outer end of the fork.

11. Apparatus for contactless measurment of the height of a load carrier on a load-carrying vehicle above a reference point, substantially as hereinbefore described with reference to Figs. 1 to 3, or Figs. 1 to 3 as modified by Fig. 4, Fig. 5 or Fig. 6, of the accompanying drawings.

12. A load-carrying vehicle equipped with apparatus for the contactless measurement of the height of its load carrier as claimed in any preceding claim.

1 3. A method of measuring the height of a load carrier on a load-carrying vehicle above a reference point without mechanical measuring contact between the load carrier and the floor or a reference point on the vehicle which comprises emitting radiation from a transmitter on the vehicle, reflecting it from a reflector on the load carrier to a receiver on the vehicle, and on the vehicle evaluating the height from a measurement representative of the transit time of the radiation between transmitter and receiver.