IMPROVED TELESCOPIC LOADER

Abstract

A method (30) of actuating a variable boom loading arrangement (1) that includes a variable length boom (2) that can be extended and retracted using a length actuator (3). A first end of the variable length boom (2) is pivotally attached to a frame, and the variable length boom (2) can be pivoted relative to the frame by means of a pivot actuator (5). A second end of the variable length boom (2) is used for handling loads. An input command that is given by an operator is modified if the variable boom loading arrangement (1) reaches a predefined tipping moment, resulting in a modified output command to the actuators (3, 5), so as to avoid a tipping of the variable boom loading arrangement (1). The input command is used to calculate an unmodified commanded direction of the second end of the variable length boom (2) in an external reference frame, in particular in an external Cartesian coordinate reference frame, wherein the modification scheme that is applied to the input command and that results in a modified output command to the actuators depends on the calculated unmodified commanded direction in the external reference frame.

Claims

1. A method of actuating a variable boom loading arrangement, comprising a variable length boom that can be extended and retracted using a length actuator, wherein a first end of the variable length boom is pivotally attached to a frame, and wherein the variable length boom can be pivoted relative to the frame by means of a pivot actuator, and wherein a second end of the variable length boom is used for handling loads, wherein an input command that is given by an operator is modified if the variable boom loading arrangement reaches a predefined tipping moment, resulting in a modified output command to the actuators, so as to avoid a tipping of the variable boom loading arrangement, wherein the input command is used to calculate an unmodified commanded direction of the second end of the variable length boom in an external reference frame, in particular in an external Cartesian coordinate reference frame, wherein the modification scheme that is applied to the input command and that results in a modified output command to the actuators depends on the calculated unmodified commanded direction in the external reference frame.

2. The method according to claim 1, wherein the data of at least one load sensor, one position sensor and/or one angle sensor is used as an input for determining the predefined tipping moment.

3. The method according to claim 1 wherein the second end of the variable length boom relates to a tool mounting point.

4. The method according to claim 1, wherein the predefined tipping moment comprises a critical tipping moment, wherein irrespective of the commanded actuation of at least one of the actuators the modified output command to the respective actuator is zero, at least for certain modification schemes and/or at least for certain calculated unmodified commanded directions in the external reference frame.

5. The method according to claim 4, wherein the predefined tipping moment comprises a range between an upper bound tipping moment and the critical tipping moment, wherein only a reduced amount of the commanded actuation of at least one of the actuators is applied to the respective actuator as the modified output command, at least for certain modification schemes and/or at least for certain calculated unmodified commanded directions in the external reference frame, wherein preferably the fraction of the commanded actuation is monotonically decreased, in particular linearly decreased.

6. The method according to claim 1, wherein below a certain size of the input command, the commanded actuation of the actuators will be modified in a way that the calculated unmodified commanded direction in the external reference frame is not changed, at least for certain modification schemes and/or at least for certain calculated unmodified commanded directions in the external reference frame.

7. The method according to claim 1, wherein the commanded actuation of the actuators is not modified if the calculated unmodified commanded direction in the external reference frame brings the second end of the variable length boom away from the predefined tipping moment, in particular the critical tipping moment and/or the upper bound tipping moment.

8. The method according to claim 1, wherein in case the unmodified commanded direction points in an upward and forward direction, the modification scheme reduces the input command of the length actuator, while it maintains the input command of the pivot actuator.

9. The method according to claim 1, wherein in case the unmodified commanded direction points in a forward and predominantly downward direction, the modification scheme maintains the input command of the pivot actuator, while the input command of the length actuator is modified in a way that the actual direction of the second end of the variable length boom is the vertical direction, where in case the available actuation power is not sufficient to maintain this modification scheme, the modification scheme reduces the input command of the length actuator and the input command of the pivot actuator, wherein the reduction is chosen in a way that the actual direction of the second end of the variable length boom is the vertical direction and the available actuation power can maintain the modified command.

10. The method according to claim 1, wherein in case the unmodified commanded direction points in a downward and predominantly forward direction, the modification scheme reduces the input command of the length actuator and the input command of the pivot actuator, wherein the reduction is the same for both actuators, or wherein the reduction for the length actuator is larger than the reduction for the pivot actuator.

11. The method according to claim 10, wherein in case the unmodified commanded direction points in a downward/forward transition region between the forward and predominantly downward direction, and the downward and predominantly forward direction, the modification scheme is applied in a way that the actual direction of the second end of the variable length boom is monotonically changed towards a vertical direction, when approaching the commanded forward and predominantly downward direction, in particular in a linear way.

12. The method according to claim 10, wherein the limiting direction between the commanded forward and predominantly downward direction and the commanded downward and predominantly forward direction, preferably between the commanded forward and predominantly downward direction and the downward/forward transition region, is a function of the commanded speed, wherein with a higher commanded actuation speed, the limiting direction has an increasing component in the forward direction.

13. The method according to claim 1, wherein when a changeover between two different modification schemes occurs, a transitional modification scheme is performed.

14. A variable boom loading arrangement comprising an input device, a variable length boom that can be extended and retracted using a length actuator, wherein a first end of the variable length boom is pivotally attached to a frame, and wherein the variable length boom can be pivoted relative to the frame by means of a pivot actuator, wherein the variable length boom comprises a tool mount at a second end of the variable length boom, the variable boom loading arrangement further comprising an electronic control unit that inputs an input command that is applied to the input device by an operator and that applies an output signal to the length actuator and the pivot actuator, wherein the electronic control unit is designed and arranged in a way that it performs the method according to claim 1.

15. The variable boom loading arrangement according to claim 14, wherein at least one load sensor, one position sensor and/or one angle sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Further advantages, features, and objects of the invention will be apparent from the following detailed description of the invention in conjunction with the associated drawings, wherein the drawings show:

[0043] FIG. 1: a schematic setup of a variable boom loading arrangement according to a possible embodiment in a schematic sketch;

[0044] FIG. 2: the possible range of movements for the tool point of an embodiment of a work vehicle with a variable boom loading arrangement in a schematic side view;

[0045] FIG. 3: a detail concerning the possible range of movements for the tool point of the work vehicle according to FIG. 2;

[0046] FIG. 4: a possible dependence of a maximum allowed flow limit in dependence of the position of the variable length boom relative to a predefined tipping moment;

[0047] FIG. 5: a graph, illustrating a possible dependence of the angle ?_IV in dependence of the maximum allowed fluid flow;

[0048] FIG. 6: a schematic setup of a control scheme for employing a method for actuating a variable boom loading arrangement.

DETAILED DESCRIPTION

[0049] In FIG. 1, a schematic setup of a variable boom loading arrangement 1 according to a possible embodiment is shown as a schematic setup. As it is known as such in the prior art, the variable boom loading arrangement 1 comprises a variable length boom 2 that can be extended and retracted using a length actuator, presently a length varying hydraulic piston 3. Furthermore, the variable length boom 2 is pivotally attached to a frame, like a vehicle chassis 27 (not shown in FIG. 1; partially shown in FIG. 2) by means of a pivoting hinge 4. By appropriately actuating a pivot actuator that is presently designed as a pivoting hydraulic piston 5, the variable length boom 2 can be pivotally raised and lowered.

[0050] At its other end, opposite of the pivoting hinge 4, the variable length boom 2 shows a tool mount 6, to which a tool, presently a fork 7, can be attached. As it is also quite common in the prior art, the attitude of the fork 7 can be varied by means of a tilting actuator, which is presently designed as a tilting hydraulic piston 8.

[0051] The variable boom loading arrangement 1 is controlled by an operator. Presently, the input device for the operator is a control joystick 9. The control commands from the control joystick 9 are transmitted by means of a vehicle bus system 10 to an electronic controller 11. The electronic controller 11 performs the method, as presently proposed, and actuates a valve arrangement 12 that distributes the pressurised hydraulic oil of hydraulic pump 13. The outlets of the various actuated valves of the valve arrangement 12 is fed via hydraulic pipes and hydraulic hoses to the various actuators 3, 5, 8. Also, return lines are provided. The hydraulic pump 13 is driven by a combustion engine 14, that can also supply additional hydraulic consumers 15 (which is optional).

[0052] Furthermore, a plurality of sensors 18a, 18b, 18c is used. In the presently shown embodiment a variable length boom angle sensor 18b, a length sensor 18a, measuring the length of the variable length boom 2, and a load sensor 18c, measuring the load on the variable length boom 2/variable boom loading arrangement 1 are used.

[0053] By moving the control joystick 9, the operator commands to perform a movement of the tool point 16, which is representative of the second end of the variable length boom 2, to which a tool 7 is attached. The tool point 16 can be equivalent to a tool mount 6, in particular to a rotation axis of the tool 7, in case that the tool mount 6 is designed to tiltable.

[0054] FIG. 3 is an enlargement of the possible range of movements of the tool point 16. It is to be noted that depending on the actual position of the variable length boom 2 (with respect to length and angle), not necessarily all directions can be realised. As an example, if the variable length boom 2 is already fully extended, a movement in the extension direction of the variable length boom 2 is not possible, of course.

[0055] Letter x indicates a forward movement direction of the variable boom loading arrangement 1 (for example a telescopic loader), as seen in the external reference frame (the surroundings). The time derivative of x:

[00001]$\stackrel{?}{x}=\frac{\mathrm{dx}}{\mathrm{dt}}$

is equivalent to the speed in the x-direction v.sub.x. Consequently, y denotes the vertical direction (upward) with

[00002]$v_y=\stackrel{?}{y}=\frac{\mathrm{dy}}{\mathrm{dt}}.$

[0056] The angle ? is ?=0? in the horizontal, forward direction. The value of a increases in the counter-clockwise direction 17 of FIGS. 2 and 3. Hence, 0???<90?, can be addressed as quadrant I. Consequently, quadrant II is defined by 90???<180?, quadrant III by 180???<270?, and quadrant IV by 270???<360?. Further, quadrant IV is divided into two sub-areas by transition line a.sub.IV 19 at transition angle ?.sub.IV=?.sub.IV,i+?.sub.IV,ii. Please note that due to the conventions chosen, ?.sub.IV, ?.sub.IV,i and ?.sub.IV,ii usually show negative values.

[0057] In the presently shown example, ?.sub.IV,ii is chosen to be ?.sub.IV,ii=?15?. However, ?.sub.IV,ii and therefore ?.sub.IV=?.sub.IV,i+?.sub.IV,ii do vary with the commanded flow. An example of such a possible dependence is shown in FIG. 5. The abscissa 20 of FIG. 5 shows the flow rate, while the ordinate 21 shows the angle ?.sub.IV (negative value). If (almost) no flow is commanded by the operator, an is presently chosen to be ?.sub.IV=?90? (situation 22). With increasing flow demand, angle ?.sub.IV increases linearly (magnitude of angle decreases linearly). At situation 23, with a flow rate being approximately 50% of the maximum flow rate, the angle ?.sub.IV is now a ?_IV=?45?. Here, a kink exists and again the magnitude of angle ?.sub.IV decreases towards situation 24, where the flow command is approximately 75% of the maximum fluid flow, and ?.sub.IV=?15?. Further increase in the commanded fluid flow does not alter angle ?.sub.IV any more.

[0058] Contrary to this variation, the size of the transition region ?.sub.IV,ii is presently chosen to be invariable; currently ?.sub.IV,ii is chosen to be ?.sub.IV,ii=?15?.

[0059] Depending on the direction that is commanded by the operator (raw, unmodified actuation), the input command signal is modified before it is applied to the various actuators 3, 5, 8 of the variable boom load arrangement 1. This will be described in detail in the following.

[0060] A particular method of modification is a reduction of the applied command by a multiplicative factor C with respect to the original input command. It is to be noted that this reduction will typically be dependent on the load level, as shown in FIG. 4 (which may also apply to the following formulae). In FIG. 4, the abscissa 20 shows the drop compensated load level in percent of the maximum, while the ordinate 21 shows the maximum flow as a percentage of the maximum flow rate possible. Drop compensation is a compensation that compensates for inertial effects. As an example, sometimes a drop in the load signal is seen when a fast lowering command is initiated, due to acceleration of the load. Drop compensation as such is known in the present technical field. It is to be noted, that the reduction factor C is presently chosen to be different for the variable length boom's length 25 (C.sub.tele) and for the variable length boom's angle/attitude 26 (C.sub.boom).

[0061] FIG. 6 shows a control schematic 30 that may be used for realising the method of actuating a variable boom loading arrangement 1 according to the present suggestion.

[0062] The input commands CMD.sub.boom,sp, CMD.sub.tele,sp that are entered by the joystick 9 are read in at block 31 (boom stands for actuation/position/speed of the pivoting actuator 5, tele stands for actuation/position/speed of the length variation actuator 3, CMD stands for command, sp for the unmodified command (no apostrophe)). These input commands CMD.sub.boom,sp, CMD.sub.tele,sp are consequently recalculated to fluid flow commands Q.sub.boom,sp, Q.sub.tele,sp (block 32; Q stands for fluid flow rate) and speeds for the actuators {dot over (x)}.sub.boom,sp, {dot over (x)}.sub.tele,sp (block 33). Also, sensor data from sensors 18a, 18b, 18c is read in, namely the position x.sub.boom,act of the variable length boom 2, the length x.sub.tele,act of the variable length boom 2, the mass M load and the load moment level (usually essentially the tipping over moment) from the load sensor F.sub.LLMS, F.sub.LLMS,cutoff. F.sub.LLMS is the load moment level, while F.sub.LLMS,cutoff is the reported most critical load, i.e. when movements increasing the load moment have to be stopped (LLMS=Load Level Moment Sensor). Furthermore, based on the input command that is read in from the joystick 31, block 34 calculates the position of transition line an, based on the commanded speed/fluid flows.

[0063] Various input data is fed into the forward kinematics 35, where various data is calculated from the input, in particular the position of the boom (angle ?, length x.sub.tele,act), including the position x=(x, y) of the tool point in the x-y-reference frame, the direction of the unmodified commanded direction (raw input) in the x-y-reference frame

[00003]$?={\tan }^{-1}\left(\frac{{\stackrel{.}{x}}_y}{{\stackrel{.}{x}}_x}\right)$

and the Jacobian matrix ?. Based on the calculated data, it is determined, which quadrant is commanded by the operator (block 36). This also includes which part of quadrant IV is commanded by the operator.

[0064] In parallel, based on additional input data, block 37 calculates the pivoting actuator's fluid flow limit C.sub.boom,lim, and block 38 calculates the length varying actuator's fluid flow limit C.sub.tele,lim.

[0065] All such input data, including data that is calculated therefrom, is fed into the LLMC core block 40 (LLMC=Longitudinal Load Moment Controller). Here, the input command by the operator is modified, depending in which quadrant (including sub-quadrant of quadrant IV) the unmodified commanded direction ? is located. Consequently, a modified actuation command is calculated, and the requested fluid flows are applied to the various actuators (command application block 41).

[0066] The simplest modification is employed if the unmodified commanded direction ? lies in quadrant II or III. In these quadrants, both aspects of movement bring the tool point 16 into a safer region, i.e. away from the predefined tipping moment (the critical tipping moment and/or the upper bound tipping moment). Therefore, the original operator input is simply left unmodified and consequently applied to the actuators 3, 5.

[0067] In case a small percentage of the maximum actuation speed is commanded (for example up to 5%, 10%, 15% of 20% of the maximum speed), this is considered to be a delicate operating situation, where the input command is-if necessary-reduced, where the reduction factor is the same for both aspects of movement, i.e. for the length variation command and for the pivoting command of the variable length boom 2. In other words, formulae

Q.sub.boom,sp=min(Q.sub.boom,sp,Q.sub.boom,raise,max.Math.C.sub.boom,lim,Q.sub.boom,raise,max.Math.C.sub.tele,lim)

and

Q.sub.tele,sp=min(Q.sub.tele,sp,Q.sub.tele,ext,max.Math.C.sub.tele,lim,Q.sub.tele,ext,max.Math.C.sub.boom,lim)

are used, where the ext stands for extension and raise speaks for itself.

[0068] If a faster actuation is applied (it is normally sufficient that only one aspect of the commanded movement is fasti.e. the commanded actuation is not fully in the aforementioned slow command region) a distinction of cases is necessary.

[0069] In case the command is in a predominantly lowering state combined with a telescopic retraction or no telescoping, the situation is located in a sub-part of quadrant IV, lying between-90???<?.sub.IV. If, in this case, a somewhat fast movement is commanded by the operator, the flow command for the valves is maintained for the pivoting aspect (pivoting hydraulic piston 5), while a telescoping aspect (length variation hydraulic piston 3) is modified in a way that in the external reference frame a vertical lowering of the tool point 16 occurs.

[0070] For this, the following formulae are used:

[00004]$\left[\begin{array}{c}{\stackrel{?}{x}}_{\mathrm{boom},\mathrm{sp}}\\ {\stackrel{?}{x}}_{\mathrm{tele},\mathrm{sp}}\end{array}\right]=\left[\begin{array}{cc}{?}_{{\stackrel{\_}{q}}_{1,1}}^{-1}& {?}_{{\stackrel{\_}{q}}_{1,2}}^{-1}\\ {?}_{{\stackrel{\_}{q}}_{2,1}}^{-1}& {?}_{{\stackrel{\_}{q}}_{2,2}}^{-1}\end{array}\right]\left[\begin{array}{c}0\\ {\stackrel{?}{x}}_y\end{array}\right],$

which can be rewritten as

[00005]${\stackrel{?}{x}}_{\mathrm{tele},\mathrm{sp}}=\frac{{\stackrel{.}{x}}_{b\mathrm{oom},\mathrm{sp}}}{{?}_{{\stackrel{\_}{q}}_{1,2}}^{-1}}.Math.{?}_{{\stackrel{\_}{q}}_{2,2}}^{-1}.$

A corresponding modified flow command Q.sub.boom,sp, Q.sub.tele,sp will then be applied to the actuators. The apostrophe in sp stands for the modified/corrected command.

[0071] If a boom raise command is combined with a telescopic extension, so that the unmodified commanded direction ? lies in quadrant I, the control objective is to slow down the telescopic extension (length variation of the variable length boom) according to the telescopic flow limits as the longitudinal load moment increases. The pivoting aspect, however, is not altered. Hence, the following equations apply:

Q.sub.boom,sp=Q.sub.boom,sp

Q.sub.tele,sp=min(Q.sub.tele,sp,Q.sub.tele,ext,max.Math.C.sub.tele,lim).

[0072] In case of a predominantly horizontal movement state of the tool point 16, with no or little lowering of the tool point 16, the control objective is to slow down the tool point 16 velocity {dot over (x)}=({dot over (x)}.sub.x, {dot over (x)}.sub.y) according to the boom/telescopic flow limits C.sub.boom,lim, C.sub.tele,lim as longitudinal load moment increases. Therefore, the following formulae are used:

Q.sub.boom,sp=max(Q.sub.boom,sp,Q.sub.boom,rtr,max.Math.C.sub.boom,lim) and

[00006]$Q_{\mathrm{tele},{\mathrm{sp}}^{}}=\min \left(Q_{\mathrm{tele},\mathrm{sp}}.Math.\frac{Q_{\mathrm{boom},{\mathrm{sp}}^{}}}{Q_{\mathrm{boom},\mathrm{sp}}},\min \left(Q_{\mathrm{tele},\mathrm{ext},\max }.Math.C_{\mathrm{tele},\lim }\right)\right),$

where the index rtr stands for retraction, while the index ext stands for extension.

[0073] To achieve a soft changeover between regions 270?????.sub.IV and ?.sub.IV??<0?, a transition range is present in region ?.sub.IV,ii??<?.sub.IV,i, in which the following formula is used

[00007]${\stackrel{?}{x}}_{x,{\mathrm{sp}}^{}}={\stackrel{?}{x}}_x.Math.\left(\frac{.Math.{?}_{TP}.Math.-\left(.Math.{?}_{\mathrm{IV}}.Math.-{?}_{\mathrm{IV},\mathrm{II}}\right)}{.Math.{?}_{\mathrm{IV}}.Math.-\left(.Math.{?}_{\mathrm{IV}}.Math.-{?}_{\mathrm{IV},\mathrm{II}}\right)}.Math.\left(-1\right)+1\right),$

in an effort to scale x_x from its full value to 0 and vice versa.

[0074] Since this is a transition from predominantly horizontal movement to vertical movement, Q.sub.boom,sp (as specified in the appropriate formula in the last paragraph) is used as a boom command reference, hence:

[00008]$\stackrel{\stackrel{.}{?}}{q}={\stackrel{\stackrel{\_}{\_}}{?}}_{\stackrel{?}{q}}^{-1}\stackrel{\stackrel{.}{?}}{x}.Math.$${\stackrel{?}{x}}_{y,{\mathrm{sp}}^{}}=\frac{{\stackrel{?}{x}}_{b\mathrm{oom},{\mathrm{sp}}^{}}-{\stackrel{?}{x}}_{x,{\mathrm{sp}}^{}}.Math.{?}_{{\stackrel{\_}{q}}_{1,1}}^{-1}}{{?}_{{\stackrel{\_}{q}}_{1,2}}^{-1}},$$\mathrm{and}\mathrm{finally}{\stackrel{?}{x}}_{tele,{\mathrm{sp}}^{}}={?}_{{\stackrel{\_}{q}}_{2,1}}^{-1}.Math.{\stackrel{?}{x}}_{x,{\mathrm{sp}}^{}}+{?}_{{\stackrel{\_}{q}}_{2,2}}^{-1}.Math.\left(\frac{{\stackrel{?}{x}}_{b\mathrm{oom},{\mathrm{sp}}^{}}-{\stackrel{?}{x}}_{x,{\mathrm{sp}}^{}}.Math.{?}_{{\stackrel{\_}{q}}_{1,1}}^{-1}}{{?}_{{\stackrel{\_}{q}}_{1,2}}^{-1}}\right).$

[0075] As a matter of completeness it should be pointed out that the previous formulae apply to the case that the available actuation power for the actuators is sufficient to fulfill the power requirements of the actuators/to realise the above described actuation schemes. As already mentioned, if this should not be the case, a reduction has to be applied to the actuators in an appropriate way that the available actuation power is sufficient.

[0076] Furthermore, in case different types of actuators are used (for example electric actuators), the formulae have to be adopted appropriately. This, however, is a straightforward task for a person skilled in the art. As an example: In case of electric actuators, the actuation speed is dependent on the applied voltage, current and/or frequency (no fluid flux occurring).