Self tuning vibratory control means

Details Self tuning vibratory control means Self tuning vibratory control means

2001-12-10

2004-01-13

Hess, Douglas (Department: 3651)

Conveyors: power-driven

Conveyor section

Reciprocating conveying surface

C198S766000

Reexamination Certificate

active

06675955

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to conveyors and more particularly vibratory conveyors used to move products between two locations or points.
BACKGROUND OF THE INVENTION
Vibratory conveyors are the common and preferred method of transferring product from a collection point to an individual weigh head in a scale system. In order to understand the modifications made to the conventional systems to significantly improve the performance of these systems by the present invention, a complete understanding of the operation of these vibrators and of the shortfalls of existing systems is believed necessary. Therefore, a detailed description, with reference to the drawings will be provided.
A cross sectional view of a typical linear feeder vibrator
50
used to transfer product from a source to a scale head is illustrated in FIG.
1
. The vibrator
50
consists of a magnetic coil
52
which is wound on a core
54
. The vibrator
50
includes a product conveying member or pan
56
, which holds the product for transfer, and is mounted to the vibrator frame
58
by a front flexture
60
and a rear flexture
62
. The flexures
60
,
62
act as support members as well as springs to return the pan
56
to the rest position after it has been deflected by the magnetic force from the coil
52
. In order to achieve maximum efficiency, the pan
56
is attached to the vibrator base
58
using the flexures
62
and
60
and mounting bolts
64
. The assembly
50
is mounted to the main frame using springs
68
to isolate the vibration of the vibrator assembly
50
from the main frame, which is not specifically shown.
These flexures
60
,
62
are generally flat sheets with mounting holes drilled in the ends and are made from fiberglass and can be obtained in varying thickness. The thickness generally determines the stiffness or spring constant, with the thicker flexures being more rigid than the thinner flexures. The thinner the flexture, the greater the amplitude of displacement at a lower frequency and vice versa. The amplitude must be kept within a specific range for each mechanical set-up. For fixed amount of energy applied to the core, if the amplitude is kept too small by using flexures which are too thick, the product will not flow through the pan
56
at the desired rate. If the amplitude is too high because of using flexures which are too thin, the armature plate
66
can come into contact with the winding core
54
, thus resulting in excessive noise and interruptions in the flow of product in the pan
56
.
The motion imparted to the product in the pan
56
is due to two components of the design.
1) The first component is imparted by the magnetic field influenced by the ampere turns in the core
54
. The vibrator displacement is measured from a rest position to the point at which the magnetic force from the coil
52
pulls the armature plate
66
as close as possible to the coil core
54
without contact. The motion traveled by the rear of the pan is back and down because of the mounting orientation of the rear flexture
62
. The coil force imparts potential energy to the flexures
60
and
62
during this movement.
2) The second component of this motion is the release of the potential energy stored in the flexures
60
and
62
when the magnetic field of the coil
52
collapses. At this time, the rear of the pan
56
is moved up and forward thus launching the product in the pan in a similar upward and forward motion.
To check the amplitude of the vibration (pan displacement), an amplitude indicator
80
is attached to the pan
56
. Further detail of the indicator is shown in FIG.
2
. This is a very simple device that takes the form of a stick-on label in the form of a “V”. The “V” consists of a left side
72
and a right side
74
. The distance across the “V” is indicated by the amplitude numbers
76
and
78
, These numbers have the even millimeter numbers
76
shown on the right side and the odd millimeter numbers
78
shown on the left side of the “V”.
An observer looking at the “V” while the pan
56
is vibrating can see a peak as an optical illusion when the side lines cross each other as illustrated in
FIG. 2
a
. This peak indicates the amplitude of the pan vibration and the numeric value in millimeters can be read during the testing process as the vibrator is energized. This simple amplitude indicator has been used to tune these vibrators for years.
The tuning procedure heretofore utilized involves adjusting the spring constant of the flexures by changing the flexure thickness to provide a maximum amount of deflection at a given frequency of 50 or 60 Hz (AC power frequency) with a fixed amount of energy applied to the coil
52
. More specifically, this traditional tuning process involves:
1) Inputting a fixed amount of power into the coil;
2) Observing the amplitude indicator “V”;
3) If the movement detected by the amplitude indicator is less than the desired value, the thickness of the flexures is decreased;
4) If the movement detected by the amplitude indicator is greater than the desired value, the thickness of the flexures is increased; and
5) Often several flexures piled on top of each other are used to provide the desired spring constant and therefore to obtain the desired amplitude. It is readily apparent that this traditional tuning process can only be performed with no product on the pan
56
.
The vibrator illustrated in
FIG. 1
typically operates on ½ wave AC supply. In operation, when the coil
52
is energized with a supply current, a magnetic field is established at the end of the winding core
54
. This magnetic field attracts the armature plate
66
which pulls the vibrator pan
56
back. The distance pulled will depend on the following parameters:
1) The power applied to the coil
52
;
2) The design of the solenoid consisting of the coil
52
and the winding core
54
;
3) The proximity of the solenoid core
54
to the armature
66
;
4) The stiffness of the flexures
62
and
60
; and
5) The mass of the pan
56
and the mounting hardware
70
.
The return is accomplished with the energy stored in the deflection of the flexures
60
and
62
. Because the vibrator is driven by a half wave rectified sine wave, as illustrated in
FIG. 3
a
, this, in theory, means that the pan
56
is moving back for one half of the total cycle of the mains and forward for the remaining half cycle. In fact, this is not true for several reasons.
Looking at
FIG. 3
a
, the half wave rectified sine wave is shown driving the vibrator coil
52
. This is typically a sine wave, which is derived from the line voltage, which means it has a frequency component of either 50 or 60 Hz. At 50 Hz, the cycle to go forward and back takes 20 ms and for 60 Hz, the period is 16.67 ms. Therefore, the tuning of flexure thickness is generally different for a 50 Hz voltage source than for a 60 Hz source.
FIG. 3
b
generally illustrates the displacement as a function of excitation voltage. It should be noted that at time=0, the displacement is 0. When the voltage is applied, there is no movement for a period of time. This is due to the low initial voltage level, as well as the relatively large gap between the armature plate
66
and the coil core
54
. Once the voltage is sufficient to cause a magnetic flux large enough to begin attracting the armature
66
, the armature advances relatively rapidly, as indicated by the exponential form of the displacement curve. This displacement continues to increase so long as the voltage is present, since the voltage required to hold the armature
66
decreases as the gap decreases. If the armature plate
66
was allowed to touch the coil frame
54
, it would be found that the power required in the coil
52
to maintain this condition would be approximately ⅓ of the power required to bring the armature plate
66
into contact with the coil core
54
.
It should be noted that at this point if a different waveform were used, which would cause more power to enter the coil in less time, the response of this coil
52
could be dramatically i

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