GB1594856A - Control of vehicles movabel in two dimensions over a surface - Google Patents

Description

(54) CONTROL OF VEHICLES MOVABLE IN TWO DIMENSIONS OVER A SURFACE (71) We, JUNGHEINRICH UNTERNEH MENSVERWALTUNG KG., a German company, of Friedrich-Ebert-Damm 129, 2000 Hamburg 70, West Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to control apparatus for vehicles movable in two dimensions over a surface, such as stacking vehicles, and providing for an automatic approach to stopping points within a given layout.

In particular the invention is concerned with providing an improved approach to a stopping point by special utilization of the acceleration and braking properties of a vehicle under different loads. These properties may also depend upon the position of the braking axle on the vehicle.

A positioning system of industrial trucks is known. According to this system signal markers are provided within the system which are picked up by the vehicle as its travels forward and which in consequence give an indication of the position of the vehicle within an aisle or gangway. Between individual signals, special distance measuring devices can be triggered which enable the approach to a predetermined stopping point, The signals associated with a stopping point can, according to this system, be designed in connection with signal levels so that a determination of direction results, with the result that a control action is initiated in dependence upon values measured in relation to the direction of travel by which the vehicle, once it enters into the region of a stopping point, is automatically moved forward into its true, i.e. exact, working position.

In such positioning systems, as is known from other sources, such as for example from the journal "Deutsche Hebeund Fördertech- nik" of August 1967, pages 25 to 31, the driver drives the vehicle arbitrarily forward towards the stopping point which he has chosen. It is also known that the driver can switch to a creep motion in good time before the approach to the stopping point, in which mode the vehicle then responds to the receipt of a signal from the positioning control system, i.e. it is stopped here by the stop marker. The switch over to creep approach is effected arbitrarily by the driver. Both the switch over to creep approach, and also, if this is not used, the beginning of the braking of the vehicle leads to considerable uncertainty. For one thing, disregarding the ground or floor surface conditions, the braking distance of a vehicle depends upon the load of the vehicle and upon the velocity from which it is braked. Thus, the braking distance can be affected by a strong or weak application of the brakes. The effect of the vehicle load upon the braking distance cannot generally be calculated accurately by the driver, mainly because this load is always changing. The velocity is only converted into an action by the driver on the basis of his sensation of speed, and it is known from experience that considerable errors can arise from such estimates. The strength of a braking action is not accurately controllable by the driver since this is dependent for the one part on the movement of the brake pedal which is actuated by the driver's foot and is dependent for the rest on the efficiency of the brakes which are affected now and then by weather conditions.

The uncertainties in the approach to a stopping point are increased by the fact that the driver usually endeavours to approach the stopping point rapidly, with the result that he then overshoots the stopping point.

Furthermore, it has been observed that a heavily loaded vehicle cannot generally be subjected to a maximum braking effort, since under these circumstances it would have an adverse effect on the load. If too rapid an approach is made to the stopping point, then this can easily occur. If on the other hand the vehicle approach is too cautious, for example perhaps because the driver is being excessively careful with a given load, then this can result in time losses arising from the slow approach manoevres of the vehicle to the stopping point. However, even greater loss of time would occur in carrying out a safe approach maneovre if the vehicle initially overruns the stopping point, since then the vehicle has to be reversed.

For these reasons or procedures delays occur, and, more importantly, the concentration of the driver of the vehicle is required to a very considerable degree.

It is desirable to provide an arrangement by means of which, within a given layout positioning system, the approach of a vehicle to a stopping point not under the control of the driver is substantially rationalised, while ensuring that, independently of the vehicle load, a favourable vehicle control is provided in respect of braking or even acceleration in dependence upon the distance of the vehicle from the stopping point.

In accordance with the present invention there is provided a vehicle freely movable in two dimensions over a surface under the control of an operator, and including control apparatus which provides for an automatic non-operator control in the approach to stopping points within a given layout on the surface, said apparatus comprising a) a braking zone unblocking unit including first comparator circuitry which simultaneously receives and compares characteristic values of the vehicle and the given layout and delivers a first control signal to remove control of the vehicle from the operator at a given point which, in dependence on the distance of the given point from the stopping point and the actual vehicle velocity, represents the minimum distance for a safe approach to the stopping point in the case of a vehicle load which is unfavourable for braking, b) second comparator circuitry which is triggered by the first control signal from the braking zone unblocking unit and which compares a desired velocity value related to the vehicle and the given layout and a real value related to the actual vehicle velocity, the second comparator circuitry delivering a second control signal and c) additonal control circuitry which in accordance with the respective value of the second control signal initiates brakin > or effects acceleration, the vehicle being a celerated if the real value is smaller than the desired value and braking being initiated if the real value is the same as or larger than the desired value.

Thus, in practice, a control signal is derived which gives a value, dependent upon the distance of a chosen stopping point and the vehicle speed, and possibly the load, which signals the fact that a certain braking action carried out in a predetermined manner will lead to a rational drive control and decrease of speed sufficient for the vehicle to approach the stopping point correctly. It is.

preferable if the braking action under unfavourable conditions produces as a control signal a desired value signal which is determined in dependence upon a working level which is dependent upon a fixed value corresponding to the distance between or a multiple of the distance between two working station zones and a pallet station separation value, while the real value signal is determined in accordance with a vehicle speed measurement and the particular changing vehicle conditions.

In order to derive the control signal, a directional monitor is provided by means of which a counter can be triggered in opposition to fixed values fed thereto from a store.

The braking zone is generated, upon coincidence of the actual direction of travel and the direction of travel determined on the bases of the control signal, from a pallet station separation signal in dependence upon the freedom to brake from the maximum vehicle velocity, and this braking zone signal triggers the difference comparison between the real and desired values, the braking zone signal varying with a change in the distance from the stopping point. Thus, the difference comparison produces a regulating signal which, according to its polarity and amplitude, leads to an automatic acceleration or braking of the vehicle, with the result that the control signal at the same time disconnects the functional connection of a drive pedal controlled by the driver to the motorised drive unit.

Thus, no creep motion drive needs to be provided. The invention provides an automatic stopping point approach control system which takes account of all influencing parameters in dependence on the particular vehicle speed. This automated system is first brought into action when the vehicle has approached sufficiently close to the stopping point for it to be possible for it to be brought tò a halt at the stopping point by a safe braking action preselected in the light of all possible adverse influences, this braking action being quite close to the most unfavourable braking conditions. Included within this is the fact that under certain conditions, up to the onset of braking, even an acceleration of the vehicle may be possible under automatic control. Above all, with respect to the acceleration or braking, the vehicle is withdrawn from the control of the driver at a predetermined position. Thus, with this arrangement, the driver need only approach a stopping point at a maximum speed which he considers to be suitable and then, automatically, upon the triggering of the automatic control even in advance of its point of introduction the necessary braking function will be applied automatically in the most favourable manner.

According to a preferred embodiment of the invention, in which a creep motion drive system is provided in the vehicle drive, the braking is discontinued upon reaching a predetermined low speed and at this point the creep motion drive is energised, this being interruptable in dependence upon a signal received from a positioning system in order to initiate the braking of the vehicle to a halt. In this way a particularly effective approach to the stopping point is achieved.

The aforementioned signal, which can fluctuate, preferably initiates a braking control action, i.e. the automatic braking of the vehicle can be varied as to its intensity.

An embodiment of the invention is described hereinafter with reference to the accompanying schematic drawings. These include a graphical diagram to illustrate the underlying principles of the braking of a vehicle. In the drawings: Fig. 1 is a graphical diagram which shows the movement and braking characteristics of a vehicle schematically; and Fig. 2 is a block diagram of a control system for a vehicle.

In the diagram shown in Figure 1 the velocity at which the vehicle can travel is represented along the ordinate 1, the representation being independent of absolute values and showing a range of possible velocities of 0 to 100 per cent. The abscissa 2 is divided into units which represent the distance of the vehicle from a datum point in terms of numbers of pallet stations at which pallets can be picked up and/or set down, each pallet station comprising a rack of shelving for example. Range positions 1 to 7 are marked along this axis, and, thus for example at the range marker 5 a stopping point 3 may be chosen at which the vehicle should come to a halt. Another abscissa line 4 is shown with reversed numbering, starting from the stopping point 3 and counting towards the zero point of the co-ordinate system, this abscissa line 4 giving range difference figures in relation to the stopping point in terms of pallet station separation units.

There follows a consideration of how one can brake a heavily loaded vehicle which is travelling at 100 per cent velocity so that it will reliably approach and stop at the stopping point 3.

Under very favourable braking conditions, possibly with very light loads, one can achieve a velocity-distance braking characteristic 5 according to which the vehicle would come to a halt at 6, i.e. after the beginning of the deceleration it would come to a standstill in a distance equal to the distance between 2.5 pallet stations. However, one cannot ensure safe control from a consideration of the most favourable conditions, which is why the diagram includes a less favourable braking characteristic line 7, for example for when the vehicle is fully laden, the brakes do not work well and the surface on which the vehicle is moving is not favourable for braking. Even an unfavourable load distribution on the vehicle itself is catered for by this characteristic line 7. Thus, under the unfavourable conditions corresponding to the line 7 the vehicle would come to a standstill at a distance approximately equal to 4.25 pallet stations, i.e. at the position denoted by the reference numeral 8.

In the knowledge of these facts the position of the stopping point 3 is chosen for reliable control so that the braking characteristic line 9 from the 100 per cent velocity to the stopping point 3 lies beyond even the most unfavourable braking characteristic line 7, but fairly close to the latter.

From this it follows that the vehicle, if it decelerates according to the characteristic line 9, and indeed if it starts from any point on this line and decelerates according to the given rate, then it will be certain that it can be brought to a standstill at the stopping point 3. Even if on occasion the region beyond this braking characteristic line is entered, the position of this braking characteristic line 9 in relation to the line 7 means that it is still possible to intitiate a stronger braking action in order to return to the braking characteristic line 9.

If for example the vehicle is travelling at a 50 per cent velocity, measured against its possible maximum velocity, then, following the line 10 of constant velocity, it will reach the braking characteristic line 9 at the point 11, i.e. in this case, by chance, above the point 6 on the abscissa 2. This means that a range from the datum point corresponding to 2.5 pallet stations the automatic control will first be initiated for optimum braking with a view to bringing the vehicle to a stop at the point 3.

It follows from this analysis that, corresponding to the braking characteristic line 9 in an automatic vehicle control system, a control value is generated from which a braking zone signal is developed which changes in dependence upon the distance to the stopping point, but which can reach a magnitude such that, even at 100 per cent vehicle speed and with an unfavourable loading of the vehicle, a braking action is triggered in sufficient time for the stopping point to be approached automatically and with certainty. This braking zone signal, which is responsive to a signal coming from a measurement of the speed of the vehicle.

triggers the brake control action in dependence upon a comparison of desired and actual velocity values, the actual value being determined from a velocity measurement and corresponding to the value on the ordinate 1 and the desired value being determined from specific installation and vehicle data and conditions according to a preselected value on the abscissa 2. The specific installation data includes the distance between two pallet station zones and the amount in reserve for the automatic system in dependence upon the forward movement towards the forthcoming station zone.

Even if the vehicle velocity. with reference to Fig. 1, is below the braking characteristic line 9 at any given position, for example as shown by the characteristic line 12, in comparative proximity to the stopping point 3, it can be seen that if a braking zone is chosen corresponding to the distance for unfavourable conditions, an acceleration of the vehicle is in fact still possible until a velocity is achieved at which, for example at the point 13, the braking characteristic line 9 is intersected so that automatic control is brought into play.

In the following description a number of terms will be used, whose meanings are defined below, in addition to those terms referred to already.

A pallet station zone includes a number of adjacent pallet stations, which however are separated among themselves. Pallet station zones may be shelf gangways or aisles for example. The pallet station separation is the distance between two adjacent pallet stations. Included in this is the one particular arrangement where the pallet station separation and the pallet station zone have the same value in terms of dimensional magnitude. The desired travelling direction of travel for which the control values are provided in order to achieve a target which is being approached. Actual travelling direction is that direction of travel of the vehicle which the vehicle actually follows, and for which for example a signal is generated in dependence upon the position of a vehicle turn indicator or compass or from an incremental transmitter which emits a timed signal sequence representative of direction of rotation.

The automatic control system shown in Fig. 2, which is installed on a vehicle, includes components for generating a desired-value signal which is supplied by way of a line 14 to a difference comparator unit 15, and also a device for producing a realvalue signal which is supplied by way of a line 16 to the difference comparator unit 15.

Both signal values are produced in dependence upon the triggering of a 'clear-tomove' circuit 17 which is arranged to be triggered by means of a control input 18, referred to as the 'zone clear' control. A signal corresponding to a desired direction of travel is fed into this 'clear-to-move' circuit 17 on line 19. This signal comes from a source 20, for example in dependence upon the setting of a counter or the like or upon selected programming. On the receipt of a zone clear indication a constant value store 21 is also triggered in which are stored the distances between pallet station zones. Thus, one can select which sections of the different pallet station zones have to be traversed by the vehicle. This unit may include a so-called micro-processor by means of which one can select how large the distance is between respective zones, and from the vehicle position, and in which zone the vehicle's position lies. The position of the vehicle is also fed in with the zone clear signal. An incremental transmitter 22 is associarted with the 'clearto-move' circuit 17. The transmitter 22 supplies both angularly dependent signals for determining the actual direction of travel and also frequency signals which are proportional to the velocity of the vehicle. Such an incremental transmitter is preferably located on a freely-rotating vehicle axle or it can be sited on a measuring wheel which can be lowered from the vehicle to the ground. The signal which corresponds to the direction of travel is fed into an up-down, i.e. reversible, counter 24 from circuit 17 by way of a line 23, the counter 24 also receiving the signals from the fixed value store 21. In dependence upon a comparison of the desired direction of travel and the actual direction of travel an addition or subtraction is made in the counter 24 and the resulting signal is fed over a line 25 to a digital-to-analogue converter 26.

One is concerned here with one component only of the desired value signal, which component depends upon the spacing of the pallet zones which exists when clearance is given. Another component of the desired value signal comes from a digital-to-analogue converter 27 into which is fed a signal 28 from a source 29, this signal corresponding to the so-called pallet station separation, i.e. the distance between individual pallet stations in a pallet zone. In connection with this it is to be understood that the source 29 is additionally programmable by setting means so that one can travel towards one particular pallet station within a pallet station zone which is being traversed. The signals coming from the converters 26 and 27 are fed into a humming circuit 32 by way of lines 30 and 31, and the so-called desired value appears at the output 33 of the summing circuit.

From the output of the 'clear-to-move' circuit 17 the frequency signal from the incremental transmitter 22 is fed by way of a line 34 to a frequency-to-voltage converter 35 for the velocity measurement, the output 36 of this converter being fed by way of a line 16 as a real-value signal to the difference comparator circuit 15.

Referring back now to Fig. 1, it will be appreciated that this gives the magnitudes which represent the actual values which are dependent upon the vehicle and its load in relation to other values according to the distance-braking characteristic line 9. In order to be able to introduce one particular such value which corresponds to the characteristic line 9, a so-called braking zone unblocking unit 37 is provided into which, from sources (not shown) for example source 20 and incremental transmitter 22, is fed a desired value 57 for the direction of travel and a real value 58 for the direction of travel, the signals being fed into the unit 37 over the correspondingly numbered lines. Furthermore, a signal corresponding to the pallet station separation is derived from the source 29 by way of the lines 28 and 59. In connection with this reference is made to the lower abscissa 4 of Fig. 1. In order to be able to find the actual position in dependance upon the triggering operation, a signal corresponding to the actual vehicle velocity is fed into the unit 37 by way of a line 60. A reference value from a source 38 is also fed bbto the braking zone unblocking unit 37, this source 38 providing a predetermined output signal in dependence upon the vehicle velocity and a pallet station separation figure preselected in accordance with the vehicle characteristics.

The unit 37 has an output line 39 which is connected by line 40 to a device 41. The unit 37 is effective to actuate the device 41 which disconnects the accelerator or drive pedal. By way of an associated line 42 a signal is also fed into the difference comparator circuit 15 in order to adjust the control signal at its output 43 to the circuit 44 to such a value that an electrically operated auxiliary brake is appropriately controlled in order to achieve the optimum braking action. In this connection it is also to be noted that a line 45 is also connected to the output 43 from the unit 15 which actuates a device 46 which is in the form of a so-called braking start-stop unit having an output 47 which can possibly completely suppress the mechanical vehicle brakes. This action occurs as a rule in normal use later than the contfol function exerted via the line 43 by the brake unit 44.

The line 42 is also connected by way of a branch line 48 to a device 49 which serves to control the switching in of a creep motion and a speed comparator. By way of the branch line 48 there only comes the signal that the vehicle has reached a zone in which the normal drive pedal is to be disconnected and the braking action initiated. A signal corresponding to the velocity is fed in to the device 49 from the line 16 by way of a branch line 50, and a further signal by way of a line 51 from a receiver 52 is fed in from a positioning unit that has to halt the vehicle soon after in dependence upon its approach to a stopping point. There is an intermediate connection 53 between the device 49 and the device 46 such that on the one hand a creep motion drive is switched on by way of an output 54 and on the other hand nevertheless the device 46 is switched in for absolute brake application if the stop signal occurs on the line 51 and the device 15 for the difference comparison of the signals on lines 14 and 16 causes a corresponding clear signal.

Having regard to the description above it is pointed out that a vehicle which is approaching a given stopping point under the control of the driver has its distance from the stopping point monitored by a positioning control system, and at a predetermined distance from the stopping point or at some other value dependent therefrom control of the vehicle is taken over by an automatic control system.

This automatic control takes care in particular of the approach to a point in dependence upon the speed and upon the distance from the stopping point, a point from which automatic braking takes place. This does not however exclude the fact that an automatic acceleration towards this point could occur.

Thus, one can ensure that a vehicle velocity is maintained upon approaching a stopping point, dependent upon the particular distance from the stopping point, at which under the most unfavourable conditions a braking action must take place, wherein an automatic control is provided which disconnects the drive pedal and prevents the driver having any influence on the vehicle and additionally generates a signal for a regulated application of the brakes, possibly by way of a second brake, until the distance measurement shows that a full braking can be achieved by mechanical vehicle brakes.

It is also preferred if the vehicle has a normal brake which is actuated mechanically, the actuating means or a second brake associated with an electro-mechanical actuator or an electrical brake, each of which are actuated in a controlled manner, being operative by way of the device 44 before the total braking occurs initiated by the signal on line 47. The control signal from the device 44 is made use of for an automatic acceleration which can be derived from the signal amplitude and/or signal polarity.

WHAT WE CLAIM IS: 1. A vehicle freely movable in two dimensions over a surface under the control of an operator, and including control apparatus which provides for an automatic non-opera

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. for the velocity measurement, the output 36 of this converter being fed by way of a line 16 as a real-value signal to the difference comparator circuit 15. Referring back now to Fig. 1, it will be appreciated that this gives the magnitudes which represent the actual values which are dependent upon the vehicle and its load in relation to other values according to the distance-braking characteristic line 9. In order to be able to introduce one particular such value which corresponds to the characteristic line 9, a so-called braking zone unblocking unit 37 is provided into which, from sources (not shown) for example source 20 and incremental transmitter 22, is fed a desired value 57 for the direction of travel and a real value 58 for the direction of travel, the signals being fed into the unit 37 over the correspondingly numbered lines. Furthermore, a signal corresponding to the pallet station separation is derived from the source 29 by way of the lines 28 and 59. In connection with this reference is made to the lower abscissa 4 of Fig. 1. In order to be able to find the actual position in dependance upon the triggering operation, a signal corresponding to the actual vehicle velocity is fed into the unit 37 by way of a line 60. A reference value from a source 38 is also fed bbto the braking zone unblocking unit 37, this source 38 providing a predetermined output signal in dependence upon the vehicle velocity and a pallet station separation figure preselected in accordance with the vehicle characteristics. The unit 37 has an output line 39 which is connected by line 40 to a device 41. The unit 37 is effective to actuate the device 41 which disconnects the accelerator or drive pedal. By way of an associated line 42 a signal is also fed into the difference comparator circuit 15 in order to adjust the control signal at its output 43 to the circuit 44 to such a value that an electrically operated auxiliary brake is appropriately controlled in order to achieve the optimum braking action. In this connection it is also to be noted that a line 45 is also connected to the output 43 from the unit 15 which actuates a device 46 which is in the form of a so-called braking start-stop unit having an output 47 which can possibly completely suppress the mechanical vehicle brakes. This action occurs as a rule in normal use later than the contfol function exerted via the line 43 by the brake unit 44. The line 42 is also connected by way of a branch line 48 to a device 49 which serves to control the switching in of a creep motion and a speed comparator. By way of the branch line 48 there only comes the signal that the vehicle has reached a zone in which the normal drive pedal is to be disconnected and the braking action initiated. A signal corresponding to the velocity is fed in to the device 49 from the line 16 by way of a branch line 50, and a further signal by way of a line 51 from a receiver 52 is fed in from a positioning unit that has to halt the vehicle soon after in dependence upon its approach to a stopping point. There is an intermediate connection 53 between the device 49 and the device 46 such that on the one hand a creep motion drive is switched on by way of an output 54 and on the other hand nevertheless the device 46 is switched in for absolute brake application if the stop signal occurs on the line 51 and the device 15 for the difference comparison of the signals on lines 14 and 16 causes a corresponding clear signal. Having regard to the description above it is pointed out that a vehicle which is approaching a given stopping point under the control of the driver has its distance from the stopping point monitored by a positioning control system, and at a predetermined distance from the stopping point or at some other value dependent therefrom control of the vehicle is taken over by an automatic control system. This automatic control takes care in particular of the approach to a point in dependence upon the speed and upon the distance from the stopping point, a point from which automatic braking takes place. This does not however exclude the fact that an automatic acceleration towards this point could occur. Thus, one can ensure that a vehicle velocity is maintained upon approaching a stopping point, dependent upon the particular distance from the stopping point, at which under the most unfavourable conditions a braking action must take place, wherein an automatic control is provided which disconnects the drive pedal and prevents the driver having any influence on the vehicle and additionally generates a signal for a regulated application of the brakes, possibly by way of a second brake, until the distance measurement shows that a full braking can be achieved by mechanical vehicle brakes. It is also preferred if the vehicle has a normal brake which is actuated mechanically, the actuating means or a second brake associated with an electro-mechanical actuator or an electrical brake, each of which are actuated in a controlled manner, being operative by way of the device 44 before the total braking occurs initiated by the signal on line 47. The control signal from the device 44 is made use of for an automatic acceleration which can be derived from the signal amplitude and/or signal polarity. WHAT WE CLAIM IS:

1. A vehicle freely movable in two dimensions over a surface under the control of an operator, and including control apparatus which provides for an automatic non-opera

tor control in the approach to stopping points within a given layout on the surface, said apparatus comprising (a) a braking zone unblocking unit including first comparator circuitry which simultaneously receives and compares characteristic values of the vehicle and the given layout and delivers a first control signal to remove control of the vehicle from the operator at a given point which, in dependence on the distance of the given point from the stopping point and the actual vehicle velocity, represents the minimum distance for a safe approach to the stopping point in the case of a vehicle load which is unfavourable for braking, (b) second comparator circuitry which is triggered by the first control signal from the braking zone unblocking unit and which compares a desired velocity value related to the vehicle and the given layout and a real value related to the actual vehicle velocity, the second comparator circuitry delivering a second control signal, and (c) additional control circuitry which in accordance with the respective value of the second control signal initiates braking or effects acceleration, the vehicle being accelerated if the real value is smaller than the desired value and braking being initiated if the real value is the same as or larger than the desired value.

2. A vehicle according to claim I wherein the first control signal is passed to a device which automatically disconnects the vehicle operator acceleration control.

3. A vehicle according to one of the preceding claims, wherein the additional control circuitry is associated with a braking start and stop unit which is actuable in dependence on the second control signal.

4. A vehicle according to claim 3, wherein the additional control circuitry is associated with a second brake which is electrically actuable.

5. A vehicle substantially as hereinbefore described with reference to the accompanying drawings.