Abstract:
An improved gondola assembly for receiving harvested crops in the field from a crop harvester has a lightweight molded drop in tank held in place by a tank framework on the gondola assembly. The drop in tank lowers the gondola center of gravity as it replaces stainless steel or painted mild steel tanks and requires no periodic maintenance. A built in scale for continuous in the field monitoring of the weight of received harvested crop is constructed to be viewable by a tow tractor operator whether towed from one end of the gondola or the other. The towable gondola obtains power for operation of a pair of tank framework lift cylinders from the tow tractor so that the tank is movable between an elevated dump position and a lowered crop collection position. The gondola has a reversible towing tongue for towing in either direction so it may be configured to be towed on either side of a crop harvester.

Description:
BACKGROUND OF THE INVENTION 
     Farmers use bulk material trailers, referred to as “gondolas”, to transport harvested crops, such as grapes, from a field harvester to the edge of the field. The gondolas are then dumped into tanks on highway traveling trailers for transport to a processing facility, such as a winery. The gondola consists of an open top tank mounted on a trailer that has a tongue used to connect the trailer to a towing tractor. The gondola is also referred to as a bulk material trailer. The tractor tows the gondola alongside a crop harvester, having a crop dispensing conveyer that directs the harvested crop into the open top in the gondola. Such a gondola for harvesting wine grapes typically holds five to seven tons of grapes when it is filled. After the gondola is filled, the tractor tows it alongside the highway traveling trailer and the gondola is pivoted about a point on the crop collection trailer until the harvested contents are dumped into the highway traveling trailer. To provide clearance for dumping the harvested crop into the highway-traveling trailer the gondola pivot point is necessarily a considerable distance off of the ground and to one side of the gondola trailer. The gondola-towing tractor provides power, typically hydraulic power, for positioning the crop collection tank thereon between a lowered crop collecting position and a raised dumping position. 
     Current gondola designs tend to tip during the dumping process, because of the necessity for lifting the crop collection tank to a position six to seven feet above the ground and thereafter dumping the collected crop over the side of the bulk material trailer. Currently, stainless steel and painted mild steel tanks are used to collect crops. Mild steel tanks tend to rust because the collected crops, such as wine grapes, can be acidic. Further, stainless steel tanks are quite expensive, difficult to fabricate and also difficult to repair. Painted, mild steel tanks need to be stripped of their paint and repainted approximately every four to six years. This is also an expensive process. 
     Highway traveling trailers must have controlled transport weight. If the highway traveling trailer is under loaded, money is lost in the transport phase of the process. If the highway traveling trailer is over loaded, the hauler towing the highway trailer is subject to fines and delays at highway weight checkpoints. Simply controlling the fill volume in the highway traveling trailer is not an accurate way to control the weight of the crop being hauled, because crop weight per unit volume varies widely. With many crops, such as grapes, the water and sugar content of the crop varies. Scales in the field are not a practical solution, because harvesting takes place over such wide areas of farmland and because most scales for weighing heavy weights are not transportable. 
     SUMMARY OF THE INVENTION 
     This invention relates to a mobile gondola assembly for receiving a harvested crop wherein the gondola assembly includes a removable tank having an open top, a tank support framework for carrying the removable tank, and means for defining a pivot axis on the tank support framework. A mobile trailer is also provided for receiving and supporting the tank support framework for rotation about the pivot axis. Means is mounted between the trailer and the tank support framework for moving the tank support framework about the pivot axis between a raised dumping position and a lowered crop receiving position. Further, means is provided for continuously measuring the weight of the harvested crop in the removable tank in the lowered crop receiving position. 
     In another aspect of the invention a towable gondola assembly for receiving a crop as the crop is harvested includes a thin walled crop receiving tank having an open top and a framework for supporting and holding the thin walled crop receiving tank. A trailer is configured to support the framework for movement over an underlying surface and means is disposed between the trailer and the framework for pivotally supporting the framework for movement about the pivot axis. Further, means is provided for moving the framework about the pivot axis between a raised dumping position and a lowered crop receiving position. The means for moving has one end thereof floating relative to the pivot axis. Additionally, a scale is provided for indicating the weight of the crop within the receiving tank in the lowered crop receiving position. 
     In yet another aspect of the invention a towable gondola assembly for collecting a crop from a crop harvester as the crop is harvested includes a lightweight thin wall crop collecting vessel having an open top and a framework for securely holding and supporting the lightweight thin wall vessel. A trailer supports the framework. Means is provided for mounting the framework on the trailer for pivoting movement about a pivot axis. Means is also provided for moving the framework about the pivot axis between an elevated crop dump position and a lowered crop collecting position. The means for moving has one end thereof floating in the crop collecting position relative to the pivot axis. Additionally, means is provided for sensing and indicating the weight of the collected crop in the lowered crop collecting position during crop collection so that known weight of harvested crop is transferred when the framework is elevated to the dump position. 
     The invention includes a method of collecting a harvested crop from a crop harvester wherein the steps of towing a crop collection gondola along one side of the crop harvester and pivoting a removable open top tank about a pivot axis to a lowered crop collection position are included. The step of collecting the harvested crop in the removable open top tank is performed while the tank is in the lowered collecting position. The removable open top tank is floated relative to the gondola pivot axis during crop collection and the weight of the collected crop is continuously monitored as it is deposited into the removable tank. The removable tank is then raised about the pivot axis to a raised dump position for transferring the collected crop after obtaining a predetermined weight of crop. 
     In another aspect of the invention a crop collection gondola assembly for receiving a crop in the field from a crop harvester includes a tank having an open top and a tank support framework for receiving the tank. Further, a mobile trailer is included for carrying the tank support framework and means is provided for moving the tank support framework between a crop collection position and a crop dumping position. The means for moving assumes a floating condition in the crop collection position. Additionally, a weight measuring means is included for providing in the field measurement of weight of received crop within the tank. 
     A crop collection gondola for receiving crops in the field from a crop harvester has a mobile trailer and a crop receiving tank mounted for pivotal movement on the mobile trailer. Means is provided for pivoting the crop receiving tank between a crop collection position and a crop dumping position. Weight measuring means is disposed between the mobile trailer and the crop receiving tank for providing in the field measurement of the weight of received crop in the tank. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a perspective of one embodiment of the crop collection gondola of the present invention. 
     FIG. 1B is a partial view showing the crop collection gondola of the present invention in a crop collecting lowered position and a crop dumping raised position. 
     FIG. 2 is a perspective of a crop collection tank used in the present invention. 
     FIG. 3 is a perspective of a tank support framework used in the present invention. 
     FIG. 4 is a perspective of a mobile trailer used in the present invention. 
     FIG. 5A is a partial view of the mobile trailer of FIG. 4 depicting details of a mechanical weight measuring structure. 
     FIG. 5B is a diagram of a mechanical weight measuring structure. 
     FIG. 5C is a diagram of an electrical weight measuring structure. 
     FIG. 5D is a diagram of a hydraulic weight measuring structure. 
     FIG. 6 is a front elevation of the crop collection gondola of the present invention. 
     FIG. 7 is a detail view of the mechanical weight measurement structure. 
     FIG. 8 is a detail showing a calibration fixture for the weight measuring structure of FIG.  7 . 
     FIG. 9 is a detail showing a portion of the calibration fixture of FIG.  8 . 
     FIG. 10 is another detail showing another portion of the calibration fixture of FIG.  8 . 
     FIG. 11A is a detail showing one aspect of the floating feature in the structure of the present invention. 
     FIG. 11B is another detail showing another aspect of the floating feature in the structure of the present invention. 
     FIG. 12A is a detail showing alternative structure for weighing collected crop according to the present invention. 
     FIG. 12B is a further detail showing another structure for weighing collected crop according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 1A in the drawings a gondola assembly incorporating the present invention is shown generally at  10 . A molded, drop-in tank  11  is held in a tank support weldment  12 , wherein the tank  11  is held within the weldment  12  by means of a number of clips  13 . A trailer frame  14  is seen in FIG. 1A having a pair of wheels  16  (one shown) attached by an axle (not shown in FIG.  1 A). A tongue  17  extends forwardly from one end of the frame  14  having structure thereon adapting it for connection to a towing tractor (not shown). A hydraulic lift cylinder  18  is shown in FIG. 1A at the forward end of the trailer frame  14  as depicted in the Figure. A second lift cylinder  19  (FIG. 4) is not visible in FIG. 1A, but is mounted in a fashion similar to that shown for lift cylinder  18 . The lift cylinders  18  and  19  are not referred to as forward and rearward lift cylinders, because the tongue  17  may be removed and reassembled on the opposing end of the trailer frame  14  as will be hereinafter explained. An upstanding member  21  is attached to the frame  14  for carrying a weight scale as will also be hereinafter described. A scale pointer  22  shown in FIG.  1 A and is used in one embodiment of the structure described herein for measuring weight contained within the removable tank  11 . 
     FIG. 1B shows the combination of the removable tank  11  and the tank support weldment  12  together with one of the lift cylinders  19 . One end of the hydraulic lift cylinder  19  is pivotally attached to the trailer frame  14  (shown schematically in FIG. 1B) and the other end is pivotally attached to a point  28  on the tank support weldment  12  as shown. The combination of the removable tank  11  and the tank weldment  12  held together by the clips  13  is pivotable about a pivot axis  23  shown in both FIGS. 1A and 1B. Thus, the assembly of the removable tank and the tank support weldment is pivotable about the axis  23  relative to the frame  14  by extension of the hydraulic lift cylinder  19  (in conjunction with lift cylinder  18 ) which places the combination tank and weldment in a raised dump position as shown in ghost line in FIG.  1 B. The solid line depiction in FIG. 1B of the tank and weldment is shown in the lowered crop collection position. 
     FIG. 2 illustrates the removable or drop-in tank  11 . The drop-in tank is fabricated from high density polyethylene material and has a relatively thin tank wall in the range of {fraction (3/16)} to ⅜ of an inch in a preferred embodiment. The removable or drop-in tank  11  is therefore of relatively light weight, but too flimsy to support by itself the weight of collected crop loads envisioned by this invention. The removable tank has a pair of reinforcing ribs  24  extending from an upper edge through the bottom and continuing to an opposite upper edge of the tank. The portions of the ribs  24  that are hidden from view by the structure of the tank  11  are shown in hidden line throughout the contour of the tank from upper edge to opposite upper edge. A lip portion  26  is shown on the tank  11  for enlarging the upper opening shown in the tank of FIG.  2 . The higher edge of the tank shown toward the left side of the depiction of FIG. 2 is the edge of the tank over which a collected crop is dumped following collection of a predetermined weight of harvested crop in the field. 
     FIG. 3 shows the tank support weldment  12  having a pivot  27  (one shown) on each side thereof on the pivot axis  23 . Further, the tank support weldment  12  has the additional pivots  28  (one shown) mentioned in conjunction with FIG. 1B on each side thereof. The pivots  28  serve as attachment points for the upper ends of the hydraulic lift cylinders  18  and  19 . A main spar  29  runs across the bottom of the tank support weldment serving as the lowermost member of the weldment for purposes to be hereinafter described in conjunction with the weight measuring feature of the present invention. The remainder of the tank support weldment is configured with an array of stress absorbing cross members and braces to properly support the aforementioned relatively flimsy removable tank  11  shown in FIG.  2 . 
     Turning now to FIG. 4, the trailer frame  14  is shown, with hydraulic lift members  18  and  19  thereon. An upper end  18   a  and  19   a  on the two hydraulic lift cylinders is configured to be engaged at the pivots  28  on the tank support weldment  12  described previously. Lower ends  18   b  and  19   b  on the hydraulic lift cylinders  18  and  19  respectively, are engaged by pivots  31  situated on the trailer frame. Pivot axis  23  is shown in FIG. 4 extending through receiving holes  32  on opposing ends of the trailer frame  14 . The receiving holes  32  receive the pivots  27  on the tank support weldment  12  so that the weldment and the removable tank combination rotates about the pivot axis  23  relative to the trailer frame  14  when hydraulic lift members  18  and  19  are operated as shown in FIG.  1 B. The trailer frame has a left end member  33  as seen in FIG. 4 on one end of the frame and a right end member  34 . The tongue member  17  is shown extending away from the frame, bolted to the underside of the left end member  33  and having a fixed end attached by appropriate means to a tongue holding bracket  36  that is fixed to a central cross member  35  in the trailer frame. The tongue member  17  may be released from trailer  14  by removing the bolts attaching it to the underside of end member  13  and the fasteners attaching it to towing tongue bracket  36  and reversing the extension of the towing tongue member  17  so that it assumes a position similar to that of FIG. 4, but extending outwardly from the right side of the trailer frame as seen in the Figure. This is accomplished by bolting the towing tongue member  17  to the underside of the end member  34  of FIG.  4  and then fixing the inner end of the towing tongue to the towing tongue bracket  36 . The purpose of this reversal of the extension direction of the towing tongue member is so that the trailer frame  14  can be towed in one direction or in the opposite direction for purposes to be described hereinafter. 
     It should be noted that a stop  37  protrudes from the end member  34  as shown. A similar stop member  34  is fixed in the end member  33  also for purposes to be hereinafter described. 
     Guide members  38  are mounted on the end members  33  and  34  of the trailer frame to position the combination of the removable tank  11  and tank support weldment  12  on the trailer frame. 
     A torsion bar  39  is shown extending between the central cross member  35  on the trailer frame  14  and end member  34  in FIG.  4 . The torsion bar  39  extends through a lever member  41  and is pinned to the lever member so that it cannot rotate relative thereto. The torsion bar extends through the lever member and into a hole (not shown) within the end member  34 . The end of the lever member  41  opposite the end to which the torsion bar  39  is pinned is bolted to the end member  34 . A flange bearing  42  is mounted in the central cross member  35  in the trailer frame and allows the torsion bar  39  to pass therethrough. The end of the torsion bar  39  within the flange bearing  42  is therefore free to rotate. Another lever arm  43  is fixed to the freely rotating end of the torsion bar  39  and extends laterally therefrom having a roller  44  at the end thereof. The free end of the torsion bar  39  has an extension rod  46  attached thereto that extends through a hole in end member  33 . The end of the rod  46  that emerges toward the outside of the end member  33  has attached thereto a pointer  47  that sweeps across the scale plate  21  as rod  46  rotates about its long axis to provide a weight measurement in one embodiment to be described hereinafter. 
     Referring now to FIG. 5A, the structure previously described in conjunction with FIG. 4 is shown in a more detailed fashion. The stop  37  is shown extending from the inside surface of the end member  34  and one of the lower side guides  38  for positioning the combination of the removable tank  11  and tank support weldment  12  is shown attached to the upper surface of the cross member  34 . Torsion bar  39  is shown engaged in one end of lever  41  by means of a previously mentioned pin  48 . The end of the lever  41  spaced from the torsion bar  39  has a bolt  49  extending therethrough to attach that end of the lever arm to the end member  34  on the trailer frame. As previously described the torsion bar  39  extends through the lever  41  and through the end member  34  to be fixed rigidly (rotationally and axially) at that end. The opposing end of the torsion bar  39 , as previously described, extends through the flange bearing  42  exposing an end that is free to rotate upon which is mounted the laterally extending lever  43 . The roller  44  is more clearly seen in FIG. 5A at the free end of the lever  43 . A coupling  51  attaches the rod  46  to the end of the torsion bar  49  so that torsional movement of the torsion bar  39  sweeps the pointer  47  across the scale face  21 . The tongue holding bracket  36  is also seen in FIG. 5A affixed to the fixed end of the tongue member  17 . The main spar  29  seen in FIGS. 1B and 3 contacts the roller  44  to induce torsion in the torsion bar  39  for weight measuring purposes to be hereinafter described. 
     Various ways of measuring weight continuously as a crop is deposited in the removable tank  11  are envisioned by the invention described herein. FIG. 5B displays diagrammatically the weight measuring configuration described in conjunction with FIGS. 4 and 5A. Weight in the removable tank  11  produces a force that is exerted by the main spar  29  in the tank support weldment  12  on the roller  44  positioned at the end of the lever  43 , whereby torque is induced in the torsion bar  39 . The torque is sensed either mechanically, as described in FIGS. 4 and 5A, or by strain gauges or the like  52  to produce a signal transmitted to a gauge  53  for indicating weight on the contained indicator scale. Alternatively, the force induced by the weight of a collected crop within the removable tank  11  induces a force transmitted by the lower spar  29  on the tank support weldment  12  that is transferred to a load cell  54  as seen in FIG.  5 C. The load cell is mounted on the trailer frame  14  as seen in FIG.  5 C and in turn produces a weight proportional output signal that is transmitted to the gauge  53  having a scale graduated in units of weight as described hereinbefore. 
     As illustrated in FIG. 5D, force induced by the weight of a collected crop within the removable tank  11  exerts a force on a piston rod  56  attached to the tank support weldment  12  at a free end and to an internal piston within a hydraulic cylinder  57  at the other end. The lower end of the cylinder  57  is attached to the trailer frame  14 . The cylinder  57  is filled with fluid. The pressure produced by the force within the hydraulic fluid in the cylinder  57  is measured by a pressure transducer  58  that produces a signal connected to the aforementioned gauge  53  having a scale graduated in units of weight. It should be noted that the aforementioned methods of measuring the weight of the collected crop in the removable tank  11  depend on the support for the combination of the tank  11  and the tank support weldment  12  being in a floating condition while the tank and weldment combination is in the lowered crop collection position shown in solid lines in FIG.  1 B. 
     The manner in which the support for the combination of the collection tank and the tank support weldment is floated will be described by first referring to FIG.  7 . The pivot pin  31 , to which reference was made in the description of FIG. 4, is shown in FIG. 7 extending through a hole in the lower portion  18 B of the hydraulic lift cylinder  18 . A bracket member  61  is shown fixed as by welding to the upper surface of the end member  33  on the trailer frame  14 . Turning briefly to FIG. 8, it is shown that the bracket member  61  is an outside bracket member and that a cooperating bracket member  59  is also fixed as by welding to the end member  33 . The bracket members  61  and  59  shown in FIG. 8 are attached to the upper surface of the opposing end member  34  on the trailer frame. It is clear from the figures that the bracket members  61  and  59  mounted on the end members  33  and  34  are for the purpose of retaining the lower ends  18 B and  19 B of the hydraulic lift cylinders  18  and  19 , respectively. A detail of the bracket member  61  is shown in FIG. 9 wherein an elongated opening  62  is formed in an upper portion of the bracket and a round hole  63  is formed in a lower portion of the bracket. The base of the bracket as seen in FIG. 9 is, as mentioned hereinbefore, fastened as by welding to the upper surface of each of the end members  33  and  34  on the trailer frame. Bracket members  59  and  61  are formed identically. 
     FIG. 7 also shows an axle  64  extending beneath the center frame member  35  between the round engaging wheels  16 . End member  33  in FIG. 7 is cut away to the left of the cylinder bracket member  61  so that central cross member  35  on the trailer frame is visible. As a consequence, the lever  43  having roller  44  on the end thereof, is shown wherein the roller  44  is bearing against the main spar  29  on the tank support weldment  12 . The pointer  47  on the end of extension rod  46  may be seen to move with the lever  43  as torsion rod  39  is subjected to more or less torque as the weight of a collected crop within the removable tank  11  produces force through the main spar  29  against the roller  44  on the lever  43 . The tank support weldment  12  is said to be floating, because the pivot pin  31  is allowed to move along the long length of the elongate opening  62 . Thus, the hydraulic lift cylinders  18  and  19  float at the lower ends  18 B and  19 B thereof relative to the trailer frame  14 . As described herein, the combination of the removable tank  11  and the tank support weldment  12  is described as floating about the pivot axis  23 . The pointer  47  sweeps across a scale  66  inscribed on the scale face  21  in accordance with the weight of a collected crop within the removable tank  11 . 
     In FIG. 7, the scale is shown mounted adjacent end member  33  on the trailer frame because the trailer frame  14  and tongue member  17  are configured in FIG. 4 for towing by an operator driven tractor with end member  33  at the forward end of the tow direction for trailer frame  14 . As previously mentioned, the tongue anchor bracket  36  is configured to accept the towing tongue  17  in a fashion such that it extends outwardly from the opposing end member  34 . In such a case the gondola assembly is towed with end member  34  at the forward end in the direction of towing. This feature facilitates towing the gondola assembly on an opposing side of a crop harvester that may dispense the harvested crop on the opposing side of the harvester. It further provides for viewing of the weight scale  66  by an operator of the tractor towing the gondola assembly when the towing is accomplished in either direction with end member  34  or end member  33  in a forward position. 
     Note that in FIG. 11A the pointer  47  is shown indicating zero weight in the removable tank  11 . The pin  31  is shown in FIG. 11A near the top end of the elongated slot  62  in the mounting bracket member  61  for the hydraulic lift cylinder  19 . In contrast, FIG. 11B shows the pointer  47  at the upper portion of the scale  66  when the removable tank  11  is carrying a load of collected crop. In such a case the pivot pin  31  is seen near the bottom of the elongated slot  62  in the bracket member  61 . Note that in either one of the cases of FIG. 11A or FIG. 11B, pivot pin  31  is not butted against either the upper or lower edge of the elongate slot  62 . In these instances the hydraulic lift cylinders  18  and  19  are in condition with the piston rods fully retracted within the lift cylinders. The operator of the towing tractor having control over the hydraulic lift cylinders  18  and  19  therefore fully retracts the rods in the hydraulic lift cylinders for the crop collection operation as the gondola assembly is towed alongside a crop harvester to collect the crop therein. It should be noted that while the description herein has been directed toward a floating lower end of the hydraulic lift cylinders  18  and  19 , that a floating upper end of the lift cylinders would accomplish the same purpose and is considered to be within the scope of the disclosed invention. At this point it should also be mentioned that when the removable tank is fully loaded and the pivot pin  31  is approaching the bottom of the elongate slot  62 , the main spar  29  on the tank support weldment  12  contacts the stop  37  protruding from the inner surfaces of the frame end members  33  and  34  to prevent over load on the weighing structure seen in FIGS. 5A-5D. The stop  37  is best seen in FIGS. 4 and 5A. From the foregoing it may be seen that within the limits of the inscribed scale  66  a true weight within the removable tank  11  is measured because none of the force induced by the weight is absorbed by the cylinders themselves or by any resident friction in the cylinder packings. 
     With reference again to FIG. 8 of the drawings, a description of the manner in which the weighing structure of FIG. 5A is calibrated will be discussed. First, the pivot pin  31  that engages the lower ends  18 B and  19 B of the hydraulic lift cylinders and extends through the elongated hole  62  in the lift cylinder bracket members  59  and  61  is removed. A shackle assembly shown generally at  68  in FIG. 10 has as its component parts a shackle ear  69  for positioning adjacent bracket member  59  and a shackle ear  71  for positioning adjacent bracket member  61  during calibration of the weighing scale. The calibration shackle also includes an upper pin  72  extending through mating holes in shackle ears  69  and  71  and a lower pin  73  extending through another pair of mating holes in shackle ears  69  and  71 . The shackle assembly  68  is installed at the lower end of each of the hydraulic lift cylinders  18  and  19  during calibration. The upper pin  72  is installed through a bore in the lower end  18 B and  19 B of the lift cylinders and the lower pin  73  is installed through the lower holes  63  in the cylinder brackets  59  and  61 . To insert the pin  72  through the mating holes in the shackle ears and the lower end bores in the lift cylinders, the lift cylinders must be slightly extended. When the shackle assembly  68  of FIG. 10 is installed as shown in FIG. 8, the lower ends of the lift cylinders  18  and  19  are fixed relative to the trailer flame  14  so that they no longer float relative to the trailer frame and the pivot axis  23  on the trailer frame. The lift cylinders  18  and  19  are now pressurized at port  74  (FIG. 6) to force the cylinder rods downwardly as seen in the drawings, for example FIG.  4 . With the cylinder rod end so pressurized it is possible to simulate a chosen load, for example a 10,000 lb. (5 ton) calibrating load. While maintaining the pressure for calibration at the rod end of the lift cylinders, coupling  51  (FIG. 5A) is loosened and the pointer  47  is moved to line up with the 5 ton mark on the inscribed scale  66 . Coupling  51  is now tightened to maintain the pointer  47  in the calibrated 5 ton position and the pressure at the rod end of the hydraulic lift cylinders is relieved. The shackle assembly  68  of FIG. 10 is removed and the lower cylinder pivot pins  31  are replaced. Both cylinders are placed in fully retracted position which places the pivot pins  31  near the upper end of the elongate slot  62 . With no collected crop within the removable tank  11 , the pointer  47  will now point to a position on the inscribed scale  66  indicating zero load. As crop is collected within the removable tank  11  and assuming approximate linearity in the torsion rod  39 , the additional weight of the collected crop pushes the roller  44  down against the torsional resistance of the torsion bar  39  causing the pointer  47  to traverse the inscribed scale  66  and to indicate the weight of the collected crop. The torsion spring  39  will continue to move in torsion until the main spar  29  bottoms out on the stops  37  as previously described. Cylinders  18  and  19  are still floating at this point. This continued floating prevents excessive stress from being applied at the upper ends  18   a  and  19   a  of the hydraulic lift cylinders caused, for example, by the gondola assembly bouncing over rough terrain. 
     Referring now to FIG. 6 of the drawings, an example of the aforementioned calibration procedure is described. An end view of the gondola assembly  10  is shown wherein the calibration shackle assembly  68  is installed in place of the normal operating pivot pins  31  as previously described. Hydraulic pressure is applied to a rod end port  74  while a lower end port  76  in the hydraulic lift cylinder  19  is vented to tank. A center of gravity  77  is calculated for the assembly of the removable tank  11  and the tank support weldment  12 . Considering the physical dimensions of the hydraulic lift cylinders  18  and  19 , a hydraulic pressure for calibration is calculated to be introduced at the upper port  74  seen in FIG.  6 . The pressure to be introduced at port  74  may simulate, for example, the ten thousand pound or five-ton load referred to in the previous paragraph. For the physical characteristics of the hydraulic lift cylinders  18  and  19  used in the preferred embodiment, the calibration pressure at port  74  for producing such a load is 1127 psi. Taking into consideration the dimensional characteristics of the removable tank and the tank weldment support and summing the moments about the axis  23  the calibration pressure induces a five-ton force against the weight measurement assemblies described herein. In this example the force generated by the hydraulic lift cylinders  18  and  19  is approximately 28,770 lbs. displaced approximately 18.3 inches from the axis  27 . The force sustained through the center of gravity  77  of the combination of the removable tank  11  and the tank support framework  12  is five tons at about 52.6 inches from the axis  27 . These two moments being equal and summing to zero, the five-ton force is present at the weighing structure represented by any of the weighing schemes depicted in FIGS. 5A-5D. As mentioned previously, the pointer  47  is loosened from the weight sensing structure and fixed to point at the five-ton mark on the inscribed scale  66 . If the scale measurement apparatus is linear, the remaining graduations in the inscribed scale  66  are determined. In the event of non-linearity in the measuring structure, various graduations on the inscribed scale  66  may be determined in the same fashion as described herein for the determination of the five-ton mark on the scale. 
     Looking back at FIG. 1B, detail views of the areas around lower pivots  31  are shown in FIGS. 12A and 12B. These Figures depict apparatus for weighing contents of the tank  11  wherein the tank  11  and the tank weldment  12  are not floating relative to trailer frame  14 , but are filly supported on trailer  14  at the lowered crop collecting position. For example, support may be provided by contact between the lower spar  29  on the tank support weldment and the stops  37  in the trailer frame end members  33  and  34 . Other means for supporting the tank weldment on the trailer frame are envisioned. FIG. 12A shows a load cell  81 , similar to load cell  54  in FIG. 5C, fixed between an end member (in this case end member  34 ) and the lower portions of bracket members  59  and  61 . As described in FIG. 5C, force exerted by the weight of a collected crop within tank  11  creates an output signal from the load cell that is coupled to a gauge (similar to gauge  53 ) that converts the signal to weight. The weight indication can be observed in the field during crop collection by a tractor operator towing gondola  10 . 
     FIG. 12B shows alternative structure for weighing collected crop in tank  11  during harvesting in the field. At any point in the crop collection the hydraulic lift cylinders  18  and  19  are operated to lift the tank  11  and the tank support frame off of the structure on the trailer frame  14 . Pressure at port  76  in FIG. 12B is sensed and converted to weight at a gauge  53  much as in the case addressed in conjunction with FIG.  5 D. Collected crop in tank  11  is thereby weighed without the need for floating the tank and tank support assembly about the pivot axis  23 . 
     Although the best mode contemplated for carrying out the present invention has been shown and described herein, it will be understood that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.