This invention relates to a force measurement device for controlling the position of an implement for towing by an agricultural machine.
Said devices are known to enable the force acting on the implement connection to be measured in order to allow the position of the implement to be controlled automatically. This control enabling the performance of the agricultural machine to be optimized and, more specifically, enables the power of the machine to be distributed in an optimum manner between its implement towing or conveying function and that function involving the positioning of the implement at the required depth in the earth furrow being worked.
The devices presently in use comprise a flexure bar mounted on the agricultural machine and connected by two arms to said implement. Under the action of the force transmitted by the implement when in operation, said bar deforms, and this deformation is determined by mechanical members which transmit their movement to a generally hydraulic control system as the function of the deformation of the flexure bar. The control system is able to cause raising or lowering of the implement, and thus control its position in relation to the working depth required, to the earth quality and to the agricultural machine power.
A force measurement device is also known, which instead of said mechanical members, uses an electronic member able to determine the deformation of the flexure bar by suitable sensors, and to feed a corresponding electrical signal to said control system.
The aforesaid devices have certain serious drawbacks.
In particular, the devices comprising mechanical members for determining the deformation of the flexure bar have limited sensitivity because said mechanical members do no detect small deformations of the flexure bar. Thus, as the flexure bar has to deform in a manner which can be appreciated by said mechanical members, it is subject to considerable wear. To prevent any possible breakage, it must be constructed of a suitably treated and thus high-cost material. Moreover, such devices have a low speed of action on said control system, due to the complexity of the constituent elements of the mechanical members. Finally, because of the aforegoing, the aforesaid devices are complicated from the design and construction aspect, and are of high production cost.
Although the devices comprising said electronic member for determining the deformation of the flexure bar have certain advantages over the aforesaid devices in terms, for example, of constructional simplicity and speed of action, they are difficult to maintain because they are sensitive to the environmental conditions, such as the presence of moisture and mud, in which the agricultural machine often finds itself. In addition, such devices are influenced by the vibration and jolting of the agricultural machine, and electromagnetic interference between the electronic member and the agricultural machine engine. Again, as said electronic member determines deformation of a resilient element (flexure bar), the electrical signal corresponding to the deformation is subject to errors due to friction at the supports of the flexure bar and to the non-linearity thereof. Finally, with such devices it is not possible to obtain data on the different components of the force in a plane parallel to the travel direction of the implement.