Abstract:
The invention relates to a device for controlling the position for work devices ( 41 ) of mobile machines ( 40 ). The inventive device comprises a measuring device ( 1,2 ) for measuring an angle (α) which is formed between a level ( 42 ) that is determined by the position of the work device ( 41 ) and the direction of the gravitational force (g). The inventive device also comprises an angle transmitter ( 5 ) for predetermining an angle (α′) which is formed between a level ( 42 ) that is determined by the position of the work device ( 41 ) and the direction of the gravitational force (g). The inventive device further comprises a controller ( 3, 4, 6–16 ) for controlling the angle (α) between the level ( 42 ) of the work device ( 41 ) and the direction of the gravitational force (g) in such a way that the measured angle (α) matches the predetermined angle (α′).

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a position-regulating device for working mechanisms of mobile machines and a method of regulating the position of working mechanisms of mobile machines. 
   2. Discussion of the Prior Art 
   A micro-mechanical incline sensor, in particular for motor vehicles, is known as such from DE 197 52 439 A1, and has a bearing plate, the inclination of which is determined relative to the horizontal. At least two pressure sensor units are integrated on the bearing plate to determine a pressure applied to the plate at the respective points. An earth plate is connected to the bearing plate via the pressure sensor units. An evaluation unit uses the data produced by the pressure sensor units to determine the inclination of the bearing plate relative to the horizontal. Depending on the inclination of the device in which the inclination sensor is integrated, the earth plate applies a different degree of force to the respective sensor unit. At least two pressure sensors must be provided in order to measure the angle of inclination. In DE 197 52 439 A1, these are provided in the form of piezo-resistive pressure detectors. 
   A level-regulating device for a quay crane is known from DE 39 38 766 A1. In this case, levelling is regulated using a hydraulic control valve to actuate one or more hydraulic actuators for a part which is to be maintained at a specific level, the part being coupled with another part by which it can be adjusted to any position. To ensure a high degree of operating safety without using expensive electronic systems, the control valve is mechanically linked to and actuated by a pendulum, as its operating mechanism, the position of which is determined by gravity. 
   When the device is at an incline, the pendulum effects a damped deflection in a fixed direction in space, which is transmitted via the control valve to the hydraulic actuator. In DE 39 38 766 A1, a loading and unloading crane, particularly one which is suitable for loading and discharging ships, fitted with this feature, is set up so that when the crane boom is raised and lowered, a loading and unloading device disposed thereon remains in a fixed position relative to the rest of the structure. 
   One particular disadvantage of the level-regulating device known from DE 39 38 766 A1 is the one-dimensional orientation. In the embodiment described as an example in the above-mentioned patent specification of providing a levelling means on a loading and unloading crane, preferably used for ships, the device is totally satisfactory but for mobile machinery such as earth moving machines, for example, which preferably have to move around building sites and hence on uneven ground, one-dimensional level correction is not sufficient. 
   SUMMARY OF THE INVENTION 
   Accordingly, the objective of the present invention is to propose a device and a method for regulating the position of working mechanisms of mobile machines, by means of which the working mechanisms can be reliably adapted to both more than one direction and to the ground below on which they are travelling, depending on the respective position of the machine, without losing load on uneven terrain. 
   The invention is based on the knowledge that in preventing load losses, it is not just the orientation of a working mechanism of a mobile machine when it is not moving or when picking up material that is important, but also specifically when transporting the received material in the terrain. Consequently, a device that is to be suitable for this purpose must permit orientation with respect to a defined plane relative to the force of gravity and within a satisfactorily short time. The device proposed by the invention and the corresponding method constitute an arrangement that will enable a position to be corrected relative to a plane perpendicular to the force of gravity and if necessary inverse acceleration. 
   The possibility of designing the comparator device both as a conventional analogue system and as an integrated circuit is an advantage because it allows the special requirements of individual machines to be met. 
   The arrangement is easy to set up and can be readily fitted with standard sensors. 
   The arrangement is suitable for designs operating in one spatial direction and in two spatial directions. Especially with earth-moving machines, it is of advantage to be able to apply a position correction in the longitudinal and transverse directions. In one especially preferred embodiment, natural vibrations and their multiples induced by the control running time are eliminated. 
   By particular preference, the predetermined angle is adjusted so that the plane defined by the position of the working mechanism is perpendicular to the resultants of gravitational force and inverse acceleration force. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Examples of preferred embodiments of the device proposed by the invention are illustrated in the drawings and will be explained in more detail below with reference to the drawings. They allow the working mechanism to be positioned so as to prevent load loss, even when the working mechanism is being accelerated, e.g. during travel motion. 
     Of the drawings: 
       FIG. 1  is a first circuit diagram of a first embodiment of the device proposed by the invention as a means of controlling and activating hydraulic actuators to regulate the position of displaceable working mechanisms of mobile machines; 
       FIG. 2  is a second circuit diagram of a second embodiment of the device proposed by the invention; 
       FIGS. 3A–3B  illustrate the main structure of a digital filter unit designed as a 2nd order band-stop filter and the associated amplitude response; 
       FIGS. 4A–4B  provide a simplified diagram of the motion of a mobile work machine on the ground as known from the prior art and how the position-regulating device proposed by the invention is applied with a mobile machine as it moves on the ground; 
       FIG. 5  is a perspective illustration showing an example of a working mechanism of a mobile machine with the possible pivot directions; 
       FIG. 6  is a schematic illustration of a mobile machine with the position-regulating device proposed by the invention on uneven terrain; and 
       FIG. 7  is a sketch illustrating load control making allowance for acceleration. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a first circuit diagram of a first embodiment of the position-regulating device proposed by the invention for working mechanisms of mobile machines. The circuit has a first sensor  1 , which measures a first angle in a first spatial direction, hereafter denoted by x. This first angle will be referred to hereafter as α x . Similarly, a second sensor  2  measures a second angle in a second spatial direction y. The second angle is referred to hereafter as α y . The measured angles α x  and α y  are compared by means of a first comparator  3  and a second comparator  4  with an angle α x ′ for the spatial direction x and α y ′ for the spatial direction y fixed by an angle detector  5 , which may be 90° respectively, for example. The comparators  3  and  4  form a comparator unit  6 . The angle detector  5  may provide either a fixed, predetermined or manually variable angle α x ′ or α y ′ using manually controlled detector  5   a.    
   After the first comparator  3 , the signal in x-direction is run through a first band-stop filter  7  whilst the signal in y-direction is run through a second band-stop filter  8  after the second comparator  4 . The purpose of the band-stop filters  7  and  8  is to eliminate the natural vibration f R  and optionally its multiples 2 f R , 3 f R , . . . induced in the system by the control running time τ so that the dynamic behaviour of the system remains controllable, avoiding the occurrence of resonances. 
   Having been run through the band-stop filter  7 , the signal in x-direction is amplified by a first amplifier  9  so as to be able to actuate a first solenoid  10 . The first solenoid  10  is needed to operate a first control valve  11  which in turn actuates a first hydraulic actuator  12  to correct the position in the first spatial direction x. Similarly, after being run through the band-stop filter  8 , the signal in y-direction is amplified by a second amplifier  13  in order to actuate a second solenoid  14  and hence a second control valve  15 . The second control valve  15  operates a second hydraulic actuator  16 . The working mechanism is oriented in the second spatial direction y as a result. 
   In order to operate the hydraulic actuators  12  and  16 , a hydraulic fluid disposed in a tank  17  is compressed by a pump  18  in a front or rear cylinder chamber of a first cylinder  19  of the first hydraulic actuator  12  and in the front or rear cylinder chamber of a second cylinder  20  of the second hydraulic actuator  16 . Consequently, a first piston  21  and a second piston  22  are subjected to a change of position, which in turn regulates the position of the working mechanism  41 . 
   The position continues to be regulated until the comparators  3  and  4  detect no difference between the measured angle α x  and α y  and the pre-set angle α x ′ and α y ′. In terms of amount, the differences α x ′−α x  or α y ′−α y  will be almost zero or will lie at least below a value which is still tolerable for an angular variance Δα, for example ±3°. 
   Once this state is reached, there is no further change in the signal at the control valves  11  and  15 , which then switch back into a neutral position without further altering the position of the actuators  12  and  16  as they do so. The system remains in the neutral position until a modified signal arrives from the comparators  3  and  4  again. 
     FIG. 2  illustrates a second embodiment of a position-regulating device proposed by the invention for working mechanisms of mobile machines. The same reference numbers are used for components described with reference to  FIG. 1  and will not be described again below. Whilst the embodiment of  FIG. 1  is built using analogue technology, the embodiment illustrated in  FIG. 2  is based on digital technology. 
   The device illustrated in  FIG. 2  primarily differs from the device shown in  FIG. 1  due to the use of a digital control unit  34 , which assumes the function both of the band-stop filters  7  and  8  and the comparator unit  6 . 
   Accordingly, the comparator unit  6  is built as follows. The angle α x  emitted by the sensor  1  is pre-amplified in a first pre-amplifier  30  and then converted by a first analogue-to-digital converter  32  from an angular value measured in analogue to a digital value that can be processed by a digital control unit  34 . Similarly, the angle α y  is amplified by a second pre-amplifier  31  and converted by a second analogue-to-digital converter  33  into a digital value. In order to be able to compare the pre-set angle α x ′ or α y ′ with the angles α x  or α y  detected by the sensors  1  and  2 , the pre-set angle α x ′ and α y ′ issued by the angle detector  5  is also converted by a third analogue-to-digital converter  35  and applied to the digital control unit  34 , which may be a microprocessor. 
   In addition to comparing the angular values, the digital control unit  34  also filters the signals. To this end, the filter unit is a digital filter with a band-stop characteristic. As with the embodiment illustrated in  FIG. 1 , the band-stop characteristic correspond to the second order digital band-stop filter illustrated as an example of an embodiment in  FIGS. 3A and 3B , for example, provided by a corresponding programme in the control unit  34 . The digital control unit  34  has a storage  36 , which, for example, offers the possibility of storing the measured and compared data so that it can be made available for subsequent external additional processing. 
   The compared signals from the sensors  1  and  2  are converted into analogue signals by a first digital-to-analogue converter  37  and a second digital-to-analogue converter  38 . The analogue signals are amplified by amplifiers  9  and  13  and forwarded to the solenoids  10  and  14 . Similarly to the first embodiment, hydraulic actuators  12  and  16  are actuated by the control valves  11  and  15 , the pump  18  and the tank  17 . They then correct the position of the working mechanism  41 . 
     FIG. 3A  illustrates the operating principle of a second order digital bandpass filter and  FIG. 3B  the associated frequency response.  FIG. 3A  shows a digital filter which creates a band-stop by means of various delay elements for delaying the sampling values (denoted by z −1  in  FIG. 3A ) and coefficient elements a 0 , a 1 , and a 2  for changing the amplitude of the sampling values, having the resonance frequency f R  shown in  FIG. 3B . As a result, the natural vibration f R  of the system, induced by the control running time τ, and its uneven multiples (3f R , 5f R , etc.) are filtered out. This prevents any build-up in the system. As a result, functioning of the device is highly dynamic on the one hand and extremely accurate on the other. Another digital filter may be provided to filter out the doubled resonance frequency 2f R . 
   How the invention is applied in one dimension will be explained in more detail with reference to a machine  40  schematically illustrated in  FIG. 4  with a bucket as the working mechanism  41 . 
     FIG. 4A  illustrates the existing prior art. When the bucket  41  is in the lower position (left-hand side of the diagram), the bucket  41  is aligned so that an imaginary plane  42  extending across the opening at the top of the bucket  41  is always parallel with the surface of the ground. Standard machines  40  commonly have a lifting mechanism for the working mechanism  41 , which is designed so that the bucket  41  is lifted in such a way that the plane  42  determined by the opening of the bucket  41  always remains parallel with the ground. 
   As long as the machine  40  is travelling on a flat stretch, there are no inherent problems. However, as soon as the machine  40  starts to move up or, as illustrated in  FIG. 4A , down an incline, material  43  is lost because the plane  42  determined by the bucket  41  remains parallel with the ground as before and the material  43  being transported in the bucket  41  falls out with effect from a specific incline. The angle of inclination starting from which the load will be lost depends on the shape of the bucket  41  and how full it is. 
   A different reference plane  42 ′ for aligning the bucket  41  is proposed for the purposes of the invention, as illustrated in  FIG. 4B . As in  FIG. 4A , an imaginary plane  42 ′ extending across the top opening of the bucket  41  is defined on the working mechanism  41  of the machine  40  illustrated in  FIG. 4B . It is no longer necessarily parallel with the ground but is always oriented almost perpendicular to the direction of gravitation, denoted by the vector g in  FIG. 4B . This can be obtained in both the lower and in the upper position of the bucket  41 . The advantage of this is that the bucket  41  proposed by the invention is always additionally controlled when travelling uphill or downhill and when travelling on uneven terrain so that the plane  42  extending through the bucket  41  is always oriented perpendicular to the direction of gravitational acceleration g. This avoids transport losses from the bucket  41 . 
   The one-dimensional correction to the position of the bucket  41  illustrated in  FIG. 4  can also be applied without problem in two directions perpendicular to one another, for example longitudinally and transversely to the direction of displacement. 
     FIG. 5  provides a schematic illustration of a bucket  41  for this purpose, in perspective. The bucket  41  can be pivoted up and down through the axes A and B parallel with and perpendicular to the direction of displacement, both transversely to the travel direction and in the travel direction. Consequently load losses from the front and to the side of the bucket  41  can be prevented during travel on uneven terrain. 
     FIG. 6  is a schematic illustration of a machine  40  travelling on uneven terrain, where the position of the working mechanism  41  is again controlled by means of its position relative to gravitation g. In this connection, it is of practical advantage for the angle α between the plane  42  defined by the bucket  41  and the direction of gravitation g to assume a threshold value for the angular variance Δα with effect from which position regulation can be dispensed with. Consequently, a practical balance can be struck between uninterrupted position correction, which requires a lot of energy and can be impractical because of the delay in regulation, and loading loss due to lack of position correction. Resonant rises, which might occur if the control excitation induced by the unevenness of the ground coincides with the resonance frequency f R  of the system, can be suppressed by the described filter. 
   Whilst the plane  42  defined by the orientation of the bucket  41  is perpendicular to the direction of gravitational force g in the embodiment illustrated in  FIG. 6 , another improved position correction can be applied if the plane  42  defined by the bucket  41  is not perpendicular to the gravitational force g but is oriented perpendicular to the resultants r of the gravitational force g and the inverses b′ of the acceleration force b. The bucket  41  is illustrated on a larger scale in  FIG. 7 . It is assumed that the mobile machine  40  is subject to a delay due to a braking procedure. Consequently, the delaying acceleration force b acts on the bucket  41 . Relative to the reference system of the bucket  41 , an inverse acceleration force b′ acts in the inverse direction to the acceleration force b delaying the bucket  41  due to the mass inertia, and acts on the bulk material introduced into the bucket  41 , i.e. the acceleration force b′ acting on the bulk material in the reference system of the bucket  41  has the same value as the acceleration force b acting on the bucket  41  in the delaying direction but rotated by 180°. 
   Consequently, the resultant r of the gravitational force g and the inverse acceleration force b′ act on the bulk material disposed in the bucket  41 . It is therefore of advantage if the plane  42  is incorporated in the position regulation proposed by the invention in such a way that the plane  42  is perpendicular to the resultant r. To this end, another measuring system  29  is provided with the embodiments illustrated in  FIGS. 1 and 2  for measuring the acceleration or delay of the mobile machine  40 . The acceleration or delay may also be measured separately in the dimensions x and y. Whilst the measuring system  29  for measuring acceleration is connected directly to the angle detector  5  in the embodiment illustrated in  FIG. 1  using analogue technology and the pre-set angle α x ′ in the x-direction and the pre-set angle α y ′ in the y-direction of the angle detector  5  are over-controlled, the measuring system  29  for measuring acceleration in the embodiment of  FIG. 2  based on digital technology is connected to the control unit  34  via an analogue-to-digital converter  28 , which computes a correction of the pre-set angles α x ′ and α y ′ depending on the measured acceleration. 
   This additional feature ensures that the position of the bucket or generally the working mechanism  41  is regulated so that bulk material does not fall out even in the event of higher accelerations or delays of the mobile machine  40 . 
   The invention is not restricted to the embodiments illustrated as examples here but may be applied to any machines using different sensors or filter systems.