Device and Method for Controlling Distributive Feeding Device

This invention relates to a device and method for automatically controlling the feed from a distributive feeding device of the type used for feeding product to each weighing unit of an automatic combination weighing machine having circularly arranged weighing units.

A typical combination weighing machine of the circular array type includes, as shown in FIG. 1, a centrally disposed conical dispersion feeder 1, a plurality of linear conveyer troughs 2 (only two of which are shown) arranged radially therearound, a feed hopper 3 under each conveyer trough, a weigh hopper 4 under each feed hopper, a weight sensor 5 associated with each weigh hopper, a collection chute 6 common to all of the weigh hoppers, and a combination control device 7 for effecting arithmetic of the weight signals from the weight sensors 5 to discharge product from selected weigh hoppers 4, to the collection chute 6. The dispersion feeder 1 and the conveyer troughs 2 are independently supported on a common machine frame (not shown) through their own vibrating mechanisms 8 and 9, respectively. Generally, during the operation of this combination weighing machine in full-automatic fashion, the product to be weighed is lifted above the combination weighing machine by a carrying device 10, such as a bucket conveyer, and thrown through a horizontal feeder 11 into a funnel chute 12 disposed directly above the dispersion feeder 1. The product is dispersed radially over the dispersion feeder 1 by its vibration, and is fed onto each of the surrounding conveyer troughs 2 as a continuous layer of thickness h as shown. The product on these conveyer troughs 2 moves by the aid of independent vibration of each conveyer trough falls into its respective underlying feed hopper 3. Accordingly, it can be understood that the amount of product fed to each feed hopper 3 is generally a function of the vibration time of the corresponding conveyer trough 2 and the thickness h of the product layer on this trough. As is well known to those skilled in this field, it is important to control the weight of the product fed to the respective weigh hoppers 4 or to the corresponding feed hoppers 3, so these weights are as uniform as possible in order to improve the accuracy of the weight of product weighed out every time with respect to a predetermined target weight. However, even if the vibration time of each conveyer trough 2 is kept constant, it is very difficult to provide a uniform amount of feed because of variations in the thickness and apparent density of the product layer due to variations in the state of product caused by aggregation and entanglement, and there has been no way for adjusting the amount of feed other than time-consuming manual work of a skilled operator.

Japanese patent opening gazette No. 60-196626, discloses an attempt at a solution to the above-mentioned problem. According to this system, the horizontal displacement of the center of gravity of the product in the weigh hoppers is arithmetically determined by analyzing the weight signals from the respective weight sensors. The funnel chute 12 is then moved in the direction opposite from the direction of displacement of the center of gravity from the central axis of the above-mentioned dispersion feeder 1 to compensate for the deviation in the amount of feed in the respective hoppers. Although this system has exhibited a substantial effect in obtaining uniformity of the weight signals from the weighing units, it does not compensate for the accuracy of the combined weight of product whose weights were used as the bases of compensation, since this product is already in the weigh hoppers. In other words, this system has a fundamental shortcoming in that it does not completely eliminate inaccuracy and non-uniformity of the weight of the product to the weigh hoppers.

Accordingly, an object of this invention is to provide an improved control device and method which controls the weight of the product delivered to each weigh hopper.

In contrast of the above-cited system in which the displacement of the center of gravity of the product contained in the weigh hoppers is detected, the system of this invention is adapted to detect the displacement of the center of gravity of the product being carried on the above-mentioned dispersion feeder and conveyer troughs and to move the above-mentioned funnel chute in a direction opposite from the direction of displacement.

According to this invention, therefore, there is provided a control device comprising means for detecting the horizontal displacement of the center of gravity of all product being carried by the dispersion feeder and all the surrounding conveyer troughs of a combination weighing machine, and means for moving the position at which product is fed to the dispersion feeder in a direction opposite from the direction of displacement of the center of gravity from the central axis of the dispersion feeder.

It should be apparent that the above-mentioned disadvantages of the prior art are avoided by the system of this invention, since the amount of feed is corrected before the product to be weighed leaves the conveyer troughs.

These and other objects and features of this invention will be described in more detail below in conjunction with a preferred embodiment thereof, with reference to the accompanying drawings.

In the drawings:

FIG. 1 is a schematic view of a prior art automatic combination weighing machine with which the system of this invention is adapted for use;

FIG. 2 is a schematic vertical cross-sectional view of a weighing machine incorporating a feed control device according to this invention;

FIG. 3 is a partial cross-sectional plan view of the system of FIG. 2;

FIG. 4 is a plan view showing the load detecting structure of the center-of-gravity detecting device of the system of FIG. 2;

FIG. 5 is a block diagram showing the arithmetic and control units of the center-of-gravity detecting device of the system of FIG. 2;

FIG. 6 is a plan view of a first alternative construction of the load detecting structure shown in FIG. 4;

FIG. 7 is a cross-sectional view along the X-axis of the structure of FIG. 6;

FIG. 8 is an enlarged perspective view of the central flexure in FIG. 6;

FIG. 9 is a plan view of a second alternative construction of the load detecting structure of FIG. 4;

FIG. 10 is a cross-sectional view along the X-axis of the structure of FIG. 9, and

FIGS. 11(a) and (b) are enlarged front and side views, respectively, representing a load sensor in FIG. 9.

Throughout the drawings, same reference numerals are given to mutually corresponding structural components.

Referring to FIG. 2 there is shown a combination weighing machine of the same general type as that of FIG. 1, but which includes a device for controlling a distributive feeding device constructed according to the principles of this invention and in which the central dispersion feeding device, or feeder 1, the linear conveyer troughs 2, the feed hoppers 3, the weigh hoppers 4, the weight sensors 5, the collection chute 6, the horizontal feeder 11, and the funnel chute 12 have the same structure and arrangement as those in FIG. 1, and operate in the same fashion as described above with reference to FIG. 1. In this embodiment, however, the dispersion feeder 1 and the linear conveyer troughs 2 are supported by the load detecting structure 14 of a center-of-gravity detecting device on a platform 15 which is fixed on a machine frame 13, as shown. The feed hoppers 3, the weigh hoppers 4, weight sensors 5, and the collection chute 6 are fixedly supported directly on the machine frame 13. In addition, the funnel chute 12 is not fixed directly to the machine frame 13, but is supported by a feeding position moving device indicated generally as 16.

The feeding position moving device 16 includes, as shown in FIGS. 2 and 3, a stationary support frame 18 supported by the machine frame 13 through a pair of vertical support rods 17, with its vertical Position being adjustable. A movable Y frame 20y is slidably supported by the stationary frame 18 on a pair of guide rods 19 so that Y frame 20y is slidable in the Y direction as shown. A movable X frame 20x is slidably supported on the Y frame 20y so that X frame 20x is slidable in the Y drive mechanism 22y is supported on the stationary frame 18. An X drive mechanism 22x is support on the Y frame 20y. The funnel chute 12 is fixedly supported by the X frame 20x.

The drive mechanisms 22x and 22y include gears 24x and 24y, respectively, mounted on stationary frame 18 and Y frame 20y, respectively. The gears 24x and 24y each have a threaded hole in their centers for receiving a threaded rod 25x and 25y, respectively. The threaded rod 25x is secured at one end to the X frame 20x. The threaded rod 25y is secured at one end to the Y frame 22y. The gears 24x and 24y are driven by pinions 26x and 26y, respectively, on motors 27x and 27y. The motors 27x and 27y of the respective drive mechanisms are driven by a control device (described below) to drive the corresponding movable frames in X and Y directions, thereby moving the funnel chute 12 in any horizontal direction.

As shown in FIG. 4, the load detecting structure 14 includes a circular support base 28 on which the dispersion feeder 1 and conveyer troughs 2 are fixed through suitable buffer members, such as springs. Three load sensors 29a, 29b and 29c, such as load cells, are fixed at equal intervals on the bottom face of the support base 28, as shown, to support base 28 over the platform 15. Force points 30a, 30b and 30c of the load sensors 29a, 29b and 29c are all positioned on a common circle. The load sensors 29a, 29b and 29c generate load signals Fa, Fb and Fc, respectively, and supply them to a vector arithmetic unit 31 of the control device 33, described below. Here, it is assumed that the structure of FIG. 4 is arranged to have the vector direction of its load signal Fa coinciding with Y axis of the structure of FIG. 3.

The load signals Fa, Fb and Fc from the load sensors 29a, 29b and 29c of the load detecting structure 14 are supplied to the vector arithmetic unit 31 of the control device, as shown in FIG. 5, which sums up the X and Y components of these load signals as follows. ##EQU1## Therefore, the magnitude of displacement of the center of gravity is proportional to ##EQU2## and its direction 0 is represented as follows.

The numerical values Fx and Fy calculated by the vector arithmetic unit 31 are supplied to a control unit 33. When there is no product on either dispersion feeder 1 or conveyer troughs 2, the center of gravity ideally should be on the central axis or the origin in FIG. 4. However, this is not usually the case, and an initial value adjuster 32 is coupled to the vector arithmetic unit 31 for adjusting the values of Fx and Fy to zero in such a no-load condition, thereby positioning the apparent center of gravity at the origin.

A pulse generator 34 is coupled to the control unit 33 for supplying pulses to indicate successive discharge operation of the combination weighing machine. An interval presetter 35 and a movement presetter 36 are also coupled to the control unit 33 through a change-over switch 37. The interval presetter 35 is adapted to establish in the control unit 33 a pre-set time interval at which the center-of-gravity displacement detecting and compensating operation is to take place on account of the discharge operations. The movement presetter 36 is adapted to specify an arbitrary distance movement of the funnel chute 12 regardless of the magnitude of the output of the vector arithmetic unit 31 as occasion demands. When the movement has not been set by the movement presetter 36, the control unit 33 counts the input pulses from the pulse generator 34 and supplies the output of the vector arithmetic unit 31 to the drive control unit 38 every time it counts the preset value from the interval presetter 35. The drive control unit 38 multiplies the inputs F.sub.x and F.sub.y by a predetermined coefficient to calculate corresponding driving time periods and drives the motors 27x and 27y for these time periods. Thus, the funnel chute 12 is moved in a direction opposite to the direction of the composite force F of FIG. 4 to shift the product feeding position to a position opposite to the displaced center of gravity, thereby drawing back the center of gravity to the origin. When the distance of movement has been set by the movement presetter 36, the control unit 33 multiplies or divides F.sub.x and F.sub.y so that the composite force F corresponds to the preset distance of movement and supplies them to the drive control unit 38. Accordingly, the funnel chute 12 moves to a direction opposite to the composite force F by a preset amount. The above-mentioned preset interval and movement may be determined experientially in accordance with conditions such as properties of the handled product, variance of the weights, and the practical amount of displacement of the center of gravity.

While three load sensors are used in the load detecting structure 14 of FIG. 4, a first alternative construction employing two load sensors 29 arranged on rectangular coordinates is shown in FIG. 6. In this case, a flexure 40, such as that shown in FIG. 8, is inserted between the platform 15 and the support base 28 for supporting the latter at its center. The flexure 40 is an elastic member having mutually orthogonaI thin wall portions 41 and 42, and is fixed to face these thin wall portions with the respective load sensors as shown, so as to accommodate any inclination of the support base 28. With this structure, the vector arithmetic unit 31 need not have the above-described operation ability and may be omitted since the outputs of the load sensors 29 can be used directly as the values for F.sub.x and F.sub.y.

FIGS. 9 and 10 show a second alternative construction in which the load sensors 29 of FIGS. 6 and 7 are omitted, and the central flexure 40 is used as a load In this case, as shown in FIGS. 11(a) and (b), strain gauges 43a and 43b and 44a and 44b are adhered on opposite sides of the thin wall portions 41 and 42 of the flexure 40. The output of the strain gauges providing bending moment values M.sub.x and M.sub.y about both axes, which can be reused in lieu of the above-mentioned F.sub.x and F.sub.y to obtain the same effect.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.