Conveyors: power-driven – Conveyor section – Reciprocating conveying surface
Utility Patent
1996-12-24
2001-01-02
Olszewski, Robert P. (Department: 3652)
Conveyors: power-driven
Conveyor section
Reciprocating conveying surface
19, 19
Utility Patent
active
06168010
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibrating feeder, and more particularly, to controlling a vibrating feeder for feeding articles in weighing equipment.
2. Description of the Related Art
In conventional weighing equipment for weighing articles, a vibrating feeder is used to feed the articles to a weighing mechanism. The vibrating feeder is connected to a vibrating mechanism composed of an electromagnet to which power is fed from an AC power supply, a movable part, leaf springs and the like. The vibrating feeder is vibrated by the vibrating mechanism. An AC power supply is selectively applied to the electromagnet. When current passes through the electromagnet, an attractive force is applied to the movable part. By controlling the firing angle of the applied voltage, the vibrating feeder is vibrated to feed the articles on the feeder.
In this case, the vibrating feeder obtains a large vibration force with less energy by the utilization of resonance. Referring to
FIG. 3B
, however, because the prior art vibrating feeder utilizes resonance, overshoots in which the amplitude of vibration exceeds a target amplitude W can occur.
FIG. 3B
illustrates such overshoots during a drive period AT which occurs between a start time t
0
and a stop time t
1
. These overshoots are due to a transient response at the start time t
0
. Due to the occurrence of the overshoots, there has been a problem that the mechanical strength of the vibrating components has to be increased.
Although it is conceivable to detect the amplitude of the vibrating feeder to control it within the target amplitude W, a unit for that end has to be added, which complicates the structure and increases the cost.
On the other hand, a control method in which the overshoot is suppressed by gradually increasing the amount of power fed to the vibrating mechanism when it is started is known (Japanese Utility Model Publication No. 58-16970). However, this method has the problem that the target amplitude W is reached some time after the start time.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a vibrating feeder which suppresses overshoots.
It is a further object of the present invention to provide a vibrating feeder having an excellent response at a start time of operations.
Yet another object of the present invention is to provide a vibrating feeder with a simple structure and reasonable cost.
The above objects are achieved in accordance with a first aspect of the present invention by providing a method of controlling a vibrating feeder including the steps of applying a drive signal to a vibrating mechanism connected to the vibrating feeder at a first predetermined power level; and subsequently applying a drive signal to the vibrating mechanism at a second predetermined power level which is greater than zero and lower than the first predetermined power level whereby the amplitude of vibration of the vibrating feeder converges towards a target amplitude.
The first aspect of the present invention provides an efficient and a simple method of controlling a vibrating feeder such that the amplitude of vibration is controlled to converge towards a target amplitude.
The method according to the present invention may be carried out at any time in a control procedure. For instance, the method may be employed during a drive period to change the target amplitude. Alternatively, the method may be employed at the end of a drive period. Preferably, however, the method is carried out at the start of a drive period, typically to control transient response at the start of the drive period. Typically, the drive signal is applied to the vibrating feeder in a series of drive periods, and the method is carried out at the start of each drive period.
The vibrating feeder may be controlled with feedback, but preferably, the method comprises an open-loop correction method, i.e., the first and second power levels are determined independently of the response of the vibrating mechanism to the applied drive signal.
Typically, the first power level corresponds to a steady-state amplitude of vibration of the vibrating feeder at or above the target amplitude. That is, if the vibrating feeder was driven at the first power level for a long period until it reaches a steady-state amplitude, then that amplitude would be at or above the target amplitude. This ensures that the amplitude of vibration converges rapidly towards the target amplitude. Typically, the second power level corresponds to a steady-state amplitude of vibration of the vibrating feeder below the target amplitude. This ensures that the amplitude of vibration of the vibrating feeder does not overshoot the target amplitude.
The drive signal may be generated in any suitable manner. In a preferable embodiment, the drive signal is generated by switching a power supply signal. Typically, the drive signal is cyclical, and is applied to the vibrating mechanism at the first and/or second power level over a predetermined number of cycles.
In accordance with a second aspect of the present invention, there is provided an apparatus for controlling a vibrating feeder connected to a vibrating mechanism. The apparatus includes a device for applying a drive signal to the vibrating mechanism at a first predetermined power level, and a device for subsequently applying the drive signal to the vibrating mechanism at a second predetermined power level which is greater than zero and lower than the first predetermined power level whereby the amplitude of vibration of the vibrating feeder converges towards a target amplitude.
Any suitable means for generating the drive signal may be employed. However, in a preferable embodiment, the apparatus further comprises a switching element for switching a power supply signal to generate the drive signal; and a firing angle control device for controlling the power level by controlling the firing angle of the switching element. Typically, the apparatus further comprises a control pattern storage device for storing a control pattern, wherein the firing angle control device controls the switching element in accordance with the control pattern.
In accordance with a third aspect of the present invention there is provided a method of controlling a vibrating feeder including the steps of applying a drive signal having a phase to a vibrating mechanism connected to the vibrating feeder at a first phase; and subsequently applying the drive signal to the vibrating mechanism at a second phase which is different to the first phase, whereby the amplitude of vibration of the vibrating feeder converges towards a target amplitude.
The third aspect of the present invention provides an alternative method of controlling a vibrating feeder, i.e., by varying the phase of the drive signal. The method may be carried out at any time in a control procedure. For instance, the method may be employed during a drive period to change the target amplitude. Alternatively, the method may be employed at the start of a drive period. Preferably, however, the method is carried out when the vibrating feeder is to be stopped. In this case the target amplitude is zero. This ensures a rapid reduction of amplitude when the vibrating feeder is to be stopped.
A feedback method may be employed, but preferably, the method comprises an open-loop correction method, i.e., the first and second phases are determined independently of the response of the vibrating mechanism to the applied drive signal. Typically, the power supply signal is applied to the vibrating mechanism in a series of drive periods, and the method is carried out at the end of each drive period.
The first and second phases may be offset by any chosen amount, but preferably the second phase is offset from the first phase by half a cycle. This ensures that the vibration is rapidly stopped.
Typically, the drive signal is generated by switching a power supply signal. Typically, the drive signal is applied to the vibrating feeder at the second phase over a predetermined number o
Ishida Co. Ltd.
McAllister Steven B.
Olszewski Robert P.
Staas & Halsey , LLP
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