Patent Publication Number: US-2011062695-A1

Title: Mobile work device with stability monitoring system

Description:
The invention relates to a mobile work device, particularly a mobile concrete pump, having a chassis, having two front and two rear support outriggers that can be moved out from a travel position into at least one support position, and can be supported on a subsurface by means of a telescoping support leg, in each instance, while raising the chassis, and having a measuring element, in each instance, for determining the supporting force in the support legs, whereby the support legs have an upper telescoping element, in each instance, connected with the related support outrigger at an upper connection point, and a lower telescoping element, in each instance, connected with a support foot that can be supported on the subsurface, at a lower connection point, at its lower end, which lower element is displaceable relative to the upper element. 
     Mobile work devices of this type are provided with extendable support outriggers that are supposed to improve the stability of the work device at the connection point of use. In this connection, the support outriggers have the task, on the one hand, of eliminating the vehicle suspension and raising the wheels from the subsurface. For another thing, the support outriggers are supposed to reduce the risk of tipping, which results if high tipping moments occur by way of a work boom. The support legs of the support outriggers form the corners of a quadrangle, the side lines of which circumscribe an area within which the overall center of gravity of the work device must lie, in order to guarantee its stability. Since the extending work boom can rotate, the overall center of gravity describes a full circle during a rotation, which circle must lie within the quadrilateral area, in the work range of the work boom. Since space conditions on construction sites are limited, full support is often waived. This limits the pivot range of the work boom. 
     In order to guarantee tipping safety, a monitoring device has already been proposed (“Beton” [Concrete] magazine, 6/96, pages 362, 364). There, the pressures that prevail in the four hydraulically activated telescopes of the support legs are monitored. If the pressure in two support leg cylinders decreases, the mast movements and the concrete pump are shut off. This technique can also be used in the event that a machine is not fully supported for space reasons. However, studies have shown that pressure measurements in the telescoping cylinders of the support legs are not sufficient for reliable support leg monitoring. This particularly holds true if one of the support cylinders has been moved to its end position. Dynamic support effects also cannot be detected using this monitoring system. 
     In order to avoid these disadvantages, it has already been proposed (DE-A 101 10 176) that a pair of force sensors is disposed in the foot part of every support leg. Each force sensor there is disposed in an electrical measurement circuit for giving off a support-load-dependent measurement signal, whereby the monitoring device comprises evaluation electronics that can have the support-foot-related support load measurement values and, for a comparison, at least one predetermined stability-determining threshold value applied to them. The evaluation electronics comprise a software routine for determining the second-lowest support-foot-related support load measurement value of each scanning cycle, and for comparing it with a stability-determining threshold value. 
     Furthermore, it is known, in the case of a mobile work device of the type indicated initially (DE-A 103 49 234), that in the case of support outriggers in which the telescoping support legs are articulated onto a support leg box with a telescoping element that is fixed in place on the outrigger, by means of a wrist pin, the wrist pin is configured as a measuring element for determining the support load. In this connection, the elastic bending of the wrist pin can be used as a measure for the support-leg-related support load, for one thing. In this case, the wrist pin carries at least one strain gauge for determining the pin bending. Another possibility consists in that the elastic shear deformation that occurs in the region of the bearing points of the wrist pin is used as a measure for the support-leg-related support load. In this case, the wrist pin carries at least one strain gauge in the region of its bearing points, to determine the shear deformation. Comparison measurements with force measurements that were recorded directly at the foot plate have shown that in the case of supporting force measurement using the arrangements described, systematic incorrect measurements can occur, which oppose reliable stability monitoring. 
     Proceeding from this, the invention is based on the task of improving the support design of the known work devices, to the effect that a precise measurement of supporting force is possible. 
     In order to accomplish this task, the combination of characteristics indicated in claims  1  and  8  is proposed. Advantageous embodiments and further developments of the invention are evident from the dependent claims. The solution according to the invention is based on the recognition that in the case of the force transfer systems for supporting force measurement that are disposed within the support legs, friction forces occur, which lead to a distortion of the measurement at the measurement location. In other words, force paths for the force transfer occur there, which paths do not run by way of the actual measurement location. It is therefore the goal of the invention to eliminate friction forces within the force transfer system, in that the parts of the force transfer system that move relative to one another are mounted to float relative to one another. 
     In order to make this possible, it is proposed, according to the invention, in an embodiment variant in which the measuring element is disposed in the region of the upper connection point between the support outrigger and the upper telescoping element, that the upper telescoping element lies axially against a force introduction location of the measuring element with radially centered play, by means of a pressure piece in a sleeve-shaped accommodation that is disposed on the support outrigger and faces downward, under the effect of the supporting force. It is particularly advantageous, in this connection, if the accommodation has a sheathing pipe that is rigidly connected with the support outrigger, in which pipe the upper telescoping element is axially displaceable, in unhindered manner, with radially centered play. A preferred embodiment of the invention provides that the radial play between sheathing pipe and upper telescoping element is bridged by means of at least two elastically deformable support rings disposed at an axial distance from one another, which bring about the centering. 
     It is particularly advantageous if the telescoping element lies against the force introduction location with spring-centered play, by way of the pressure piece in the sleeve-shaped accommodation. In this connection, the support rings can be spring-elastically deformable. It is advantageous if the spring-elastically deformable support rings are shaped in the manner of a zigzag, a lamella, or a meander, and/or are slit, in the circumference direction. 
     It is advantageous if the upper telescoping element is articulated onto the support outrigger, with its pressure piece disposed on its upper face side, by means of a wrist pin that passes through the accommodation or the sheathing pipe transverse to the telescope axis, whereby the wrist pin is configured as a measuring element. For this purpose, the wrist pin has at least one strain gauge for determining the pin bending or the shear deformation as a measure for the supporting force. 
     A further improvement in the friction-free supporting force transfer system is achieved in that the pressure piece and the upper telescoping element are axially coupled with one another at face-side coupling surfaces that are complementary to one another and curved in spherical shape. A further improvement in this regard is achieved if the lower telescoping element carries a support foot ball that projects downward, while the foot part has a bearing socket to accommodate the support foot ball. Alternatively to this, in the sense of a kinematic inversion, the foot part can carry a support foot ball that projects upward, while the lower telescoping element has a bearing socket to accommodate the support foot ball. 
     According to a second preferred embodiment variant of the invention, in which the measuring element is disposed in the region of the lower connection point between the lower telescoping element and the support foot, it is proposed, according to the invention, that the support foot lies axially against a force introduction location of the measuring element, with radially centered play, with a pressure piece in an accommodation disposed on the lower telescoping element, under the effect of the supporting force. In this connection, it is advantageous if the accommodation has a measuring bell that is rigidly connected with the lower telescoping element, while the foot part has a support foot ball mounted in a bearing socket, whereby the pressure piece is formed onto either the support foot ball or the bearing socket. The pressure piece engages into the measuring bell from below, with radial play, and there lies axially against the measuring element under the effect of the supporting force, and is secured to prevent it from falling out. The radial play between pressure piece and measuring bell is bridged, in this embodiment, as well, by means of at least two elastically deformable support rings disposed at an axial distance from one another, which bring about the centering. In this connection, it is practical if the support rings are spring-elastically deformable, for example in that they are shaped in the manner of a zigzag, a lamella, or a meander, and/or are slit, in the circumference direction. In order to prevent the pressure piece from falling out of the measuring bell, in undesirable manner, the pressure piece has a circumferential groove that is partly penetrated by two securing pins that lie diametrically opposite one another and are supported on the measuring bell. The force measurement takes place using a measuring element that has at least one force sensor to which the supporting force is applied by way of the pressure piece. 
     In order to achieve a compact method of construction, it is proposed, according to a preferred embodiment of the invention, that the measuring element additionally has internal and/or external measurement electronics, which are either connected with power supply and signal lines that are passed to the outside, or that have a transmitter or a transmission receiver for wireless measurement value transmission. In order to protect the lower telescoping element from contamination, it is advantageous if this element is covered by a spiral-shaped folded bellows in which the lines for the power supply and/or the signal transmission can be integrated. Fundamentally, however, a wireless power supply, for example an inductive power supply, is also possible. 
     Another preferred embodiment of the invention provides that each measuring element has two redundant force sensors with measurement electronics and transmitter(s) for data transmission. In order to avoid an external power supply, each measuring element or each redundant force sensor with measurement electronics can have a rechargeable battery assigned to it. Simple charging of the battery is made possible in that an inductive power supply segment connected with an alternating current source on the primary side and with the battery, by way of a charging circuit, on the secondary side, is disposed between the telescoping elements of the support legs, which segment has a primary and a secondary coil that is disposed on one of the telescoping elements, in each instance, and is activated only in the retracted state of the telescoping elements. 
     The telescoping cylinder of the support leg is preferably configured as a cylinder part of a dual-action hydrocylinder, the piston of which is connected with a piston rod that forms the other telescoping element. It is advantageous if the upper telescoping element forms the cylinder part and the lower telescoping element forms the piston rod of the hydrocylinder. 
    
    
     
       In the following, the invention will be explained in greater detail using an exemplary embodiment shown schematically in the drawing. This shows: 
         FIG. 1  a view of a mobile concrete pump parked at the edge of a road, with support outriggers providing narrow support on the road side; 
         FIGS. 2   a  and  b  a top view of the support construction of the mobile concrete pump according to  FIG. 1 , in the state of full support and one-sided narrow support; 
         FIG. 3   a  a detail of a support foot of a support outrigger with a first embodiment variant of a measuring element, in a sectional representation; 
         FIG. 3   b  a diagrammatic representation of a support ring; 
         FIG. 4   a  to  c  two longitudinal sections through the measuring element part of an exemplary embodiment of a support foot, modified as compared with  FIG. 3   a , with integrated measurement electronics, as well as a cross-section through the measurement electronics housing according to  FIG. 4   a;    
         FIG. 5  a longitudinal section through the measuring element part of an exemplary embodiment of a support leg with integrated measurement electronics and power supply unit, modified as compared with  FIGS. 3   a  and  4   a  to  c;    
         FIG. 6  a side view of a support outrigger with a second embodiment variant of a measuring element for the supporting force measurement; 
         FIG. 7   a  a longitudinal section through the support leg of the support outrigger according to  FIG. 6 ; 
         FIGS. 7   b  and  c  enlarged details from  FIG. 7   a.    
     
    
    
     The mobile concrete pump shown in  FIG. 1  essentially consists of a multi-axle chassis  10 , a concrete distributor mast  14  mounted to rotate about a vertical axle  13 , which is fixed in place on the chassis, on a mast base  12  located close to the front axle, and a support construction  15  that has a support frame  16  fixed in place on the chassis, two front support outriggers  20  that can be displaced on the support frame  16 , each in a telescoping segment  18  configured as an extension box, and two rear support outriggers  24  that can pivot about a vertical axis  22 . The support outriggers  20 ,  24 , at their support legs  23 ,  25 , can each be supported on the subsurface  28  with a support foot  26  that can be moved out downward. The front and rear support outriggers  20 ,  24  can be moved out using hydraulic means, from a driving position close to the chassis, to a support position. In the example shown in  FIG. 1 , a narrow support was chosen on the road side. The narrow support, which can be used to take space problems on construction sites into account, necessarily leads to restrictions in the angle of rotation of the work boom  14 . 
     The four support feet  26  that are standing on the ground, namely VL (front left), VR (front right), HL (back left), and HR (back right), span a quadrangle, the sides l, r, v, h (left, right, front, back) of which form a tipping edge, in each instance (see  FIGS. 2   a  and  b ). In order to guarantee stability, the quadrangle sides are not allowed to be exceeded toward the outside by the overall center of gravity of the system when the work boom  14  is moved. The invention makes use of the recognition that the location of the overall center of gravity within the tipping quadrangle can be monitored by means of support load sensors at the corners of the tipping quadrangle. Accordingly, a measuring element  30 ′,  30 ″ is disposed in each support leg  23 ,  25 , which element comprises four strain gauges with a related electrical measurement circuit and operation amplifier, for example. Each measurement circuit issues a support-load-dependent measurement signal that can be sampled in predetermined time cycles, which signal is processed in computer-assisted evaluation electronics. For reasons of reliability, two redundant measuring elements with the related measurement circuit are disposed in each support leg. 
     In the support leg  23  shown in detail representations in  FIGS. 3   a  and  4   a  to  c  and  5 , the measuring element  30 ′ is situated in the region of the lower connection point  36  between the lower telescoping element  42  and the support foot  26 . The telescoping element  42  is the hollow piston rod of a hydraulic piston/cylinder unit  44 . At the lower end of the telescoping element  42 , an accommodation  46  configured as a measuring bell is rigidly disposed, in which accommodation the measuring element  30 ′ configured as a force sensor is disposed, with a pressure piece  50  that faces upward on the support foot  26  axially acting on the force introduction location  48  of the element. The pressure piece  50  is mounted, with radial spring-centered play, in the accommodation  46  by means of two support rings  52 ′,  52 ″, which are disposed at an axial distance from one another, are shaped in meander shape in the circumference direction, and are spring-elastically deformable. Furthermore, the pressure piece  50  has an oval circumference groove  54  through part of which two hollow securing pins  56  that lie diametrically opposite one another and are supported on the accommodation  46  pass. The pressure piece  50  is formed onto a support foot ball  58  that is mounted in a ball-shaped bearing socket  60  of the support foot  26  that can be supported on the ground. Fundamentally, it is possible, in the sense of a kinematic inversion, to substitute the support foot ball  58  and the bearing socket  60  for one another. In this case, the pressure piece is formed onto a part that carries the bearing socket, while the support foot ball is formed onto the foot part  26  so as to project upward, and engages into the bearing socket from below. 
     In the exemplary embodiment shown in  FIG. 3   a , the measuring element  30 ′ is connected with externally disposed measurement electronics by way of a cable  62  that is passed to the outside through a gap region between the lower telescoping element  42  and the support foot  26 . In the exemplary embodiment shown in  FIG. 4   a  to  c , the accommodation  46  is followed by a housing  63  that reaches into the cavity of the lower telescoping element  42 , in which housing the boards of measurement electronics  64  connected with the force sensor of the measuring element  30 ′ are disposed. The data evaluated in the measurement electronics  64 , which have already been digitalized, if necessary, are passed to the outside by way of a data line  66  or by way of a radio link. In addition, a power supply line  68  that is connected with the measurement electronics and comes from the outside is connected with the housing  63 . The power lines and data lines  62 ,  66 ,  68  can be integrated in a folded bellows, not shown, on the outside of the support leg  23 , which bellows protects the support leg from dirt that might enter. 
     In the exemplary embodiment according to  FIG. 5 , the measuring element  30 ′ situated in the accommodation  46 , which element contains two redundant force sensors, stands in connection with amplifier and transformer electronics  64 ′,  64 ″ and a transmission unit  90 ′,  90 ″ situated in the lower telescoping element  42 . Here, the power supply is provided by way of batteries  92 ′,  92 ″, which are present in double form, just like the force sensors of the measuring element  30 ′, the amplifier and transformer electronics  64 ′,  64 ″, and the transmission unit  90 ′,  90 ″. The transmission antennas  94 ′,  94 ″ supplied by way of the transmission unit  90 ′,  90 ″ are disposed on the outside of the lower telescoping element  42 , in the form of wire loops, in the exemplary embodiment shown. The transmission antennas  94 ′,  94 ″ are also configured in double form, for reasons of redundancy. Charging of the batteries  92 ′,  92 ″ in the lower telescoping element  42  takes place by way of an induction section, the primary coil  96  of which, to which an alternating voltage can be applied, is situated at the lower end of the upper telescoping element  70 , and the secondary coil  98  of which, facing the primary coil  96 , is situated on the lower telescoping element  46 . The two coils  96 ,  98  of the induction section lie against one another, by way of a small axial air gap, only when the lower telescoping element  42  is retracted, so that charging of the batteries  92 ′,  92 ″ can take place only in this state of the telescoping element  42 . In this connection, the measurement electronics are not in operation, so that undisturbed charging is possible. 
     In the exemplary embodiment shown in  FIGS. 6 and 7   a  to  c , the measuring element  30 ″ is disposed in the region of the upper connection point  38  between the support outrigger  20 ,  24  and the upper telescoping element  70  of the support leg  25 . In this connection, the upper telescoping element  70  lies axially against a force introduction location  76  on the measuring element  30 ″ with a pressure piece  72  in a sleeve-shaped accommodation  74  that is disposed on the support outrigger  20 ,  24  and faces downward, under the effect of the supporting force. The accommodation  74  has a sheathing pipe  78  rigidly connected with the support outrigger  20 ,  24 , in which pipe the upper telescoping element  70  can be displaced axially, without hindrance, with radially spring-centered play. In this connection, the radial play between sheathing pipe  78  and upper telescoping element  70  is bridged by two spring-elastically deformable support rings  82 ′,  82 ″ that are disposed at an axial distance from one another, and shaped in zigzag manner or meander shape in the circumference direction. As can be particularly seen in  FIGS. 7   a  and  b , the upper telescoping element  70 , with the pressure piece  72  that projects on its upper face side, is articulated onto the support outrigger  20 ,  24  by means of a wrist pin  86  that passes through the accommodation  74 , transverse to the telescope axis  84 , while the pressure piece  72  and the upper telescoping element  70  lie axially against one another on face-side coupling surfaces  88  that are complementary to one another and curved spherically. In this exemplary embodiment, the wrist pin  86  is simultaneously configured as a measuring element  30 ′. For this purpose, the wrist pin has at least one strain gauge, not shown, for determining the pin bending or the shear deformation as a measure of the supporting force (DE-A 103 49 234). The support rings  82 ′,  82 ″ that engage into circumference grooves of the upper telescoping element  70  and of the accommodation  74  ensure that the cylinder/piston unit of the support leg  25  cannot fall out of the accommodation  74 , downward. 
     In the exemplary embodiments shown, the upper telescoping element  70  is configured as the cylinder part of a dual-action hydrocylinder, the piston of which is connected with a piston rod that forms the lower telescoping element  42 . 
     In the exemplary embodiments according to  FIGS. 3   a  and  7   a  to  c , spring centering of the pressure piece  50 ,  72  in the accommodation  46  takes place using meander-shaped and spring-elastically deformable support rings  52 ′,  52 ″ or  82 ′,  82 ″, respectively, one of which is shown diagrammatically in  FIG. 3   b , as an example. The support rings having the shape of a flat cone, which are also called star springs, have a characteristic meander-like slit configuration that gives them particularly great elasticity. An activation force exerted axially on the support ring brings about an elastic change in the cone angle and thus in the diameter of the support ring. If the inside diameter of the support ring is supported, when this happens, the outside diameter increases. If, on the other hand, the outside diameter is supported, the inside diameter decreases. At the same time, an axial activation force leads to a tipping movement of the support ring. This movement is utilized to press a work piece against a longitudinal stop during bracing. An axial activation force that has been introduced is converted, without friction, into a radial force that is multiple times greater, and is used for bracing. In the exemplary embodiments shown in  FIGS. 3   a  and  6   a  to  c , two axial rings are combined into a spring package, in each instance. 
     In summary, the following should be stated: The invention relates to a mobile work device, particularly a mobile concrete pump with stability monitoring. The work device essentially consists of a chassis  10  that can be supported on a subsurface  28  with two front and two rear support outriggers  20 ,  24 . A measuring element  30 ′,  30 ″ for determining the supporting force is disposed in the telescoping support legs  23 ,  25  of the support outriggers  20 ,  24 , in each instance. For this purpose, the support legs  23 ,  25  have an upper telescoping element  70 , in each instance, connected with the related support outrigger  20 ,  24  at an upper connection point  38 , and, in each instance, a support foot  26  that can be supported on the subsurface  28 , at a lower connection point  36 , at its lower end, that can be displaced relative to the upper telescoping element. In this connection, the measuring element  30 ′,  30 ″ that is configured as a force sensor is disposed either directly at the upper connection point  38  between the support outrigger  20 ,  24  and the upper telescoping element  70 , or in the region of the lower connection point  36  between the lower telescoping element  42  and the support foot  26 . In the former case, the upper telescoping element  70  lies axially against a force introduction location  76  of the measuring element  30 ″ with radially spring-centered play, by means of a pressure piece  72 , in a sleeve-shaped accommodation  74  that is disposed on the support outrigger  20 ,  24  and faces downward, under the effect of the supporting force, while in the latter case, the support foot  26  lies axially against a force introduction location  48  of the measuring element  30 ′, with radially spring-centered play, with a pressure piece  50  in an accommodation  46  disposed on the lower telescoping element  42 , under the effect of the supporting force.