Note: Descriptions are shown in the official language in which they were submitted.
VERTICAL DESCENT RATE DETECTOR SWITCH
BACKGRO~ND OF THE INVENTION
_
This inventlon relates to a switch which is actu-
ated when it senses a rate of descent which exceeds a set
amount.
The switch of the instant invention is used to
detect when the device to which it is attached is descending
vertically at or above a set rate. An example of where a
vertical descent rate detector switch can be employed is in
an emergency brake control syst:em for an aircraft passenger
loading bridge. The distal end of such a bridge is raised
or lowered in order to properly posi-tion a cab at the end
of the bridge with respect to the door of an aircraft.
If, in the event of an emergency, the distal end of the
bridge descends too rapidly, the brake control system
applies a brake on the bridge drive mechanism to slow the
descent of the bridge. The rate detector switch of the
instant invention actuates the control,system to apply the
brake when it senses a rate of descent of the bridge in e~-
cess of a set amount.
When attempting to use a commercially available
switch in the brake control system of a passenger loading
bridge, it was found that the switch was actuated and the
brake applied when the bridge was moved horizontally as well
as when it was moved vertically. This adversely affected
the ability of an operator to move the bridge horizontally
to engage an aircraft. Consequently, it was necessary to
develop a switch which detected and was actuated when it
sensed a vertical rate of descent which equalled or exceeded
a set amount but was relatively insensitive to horizontal
forces. It was also necessary to make a switch which did
not require an external power supply or other circuitry.
SUMMARY O~ THE INVENTION
The instant invention provides a vertical descent
rate detector switch having a pair of contacts which are
actuated when the rate of vertical descent of the switch
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exceeds a set amount. The rate detector switch includes
a first magnet mounted at one end of a non-magnetic guide.
The guide passes through a bore in a second magnet which
is positioned above the first magnet such that the lines
of the magnetic field of the first magnet are opposite in
direction to the lines of the magnetic field of the second
magnet, and the second magnet is suspended above the first
magnet by the opposing magnetic fields. The contacts of
the switch are mounted in the guide between the first and
second magnets. The second magnet is movable with respect
to the first magnet between a first position in which the
lines of the magnetic fields of the first and second magnets
pass through the first and second contacts, respectively,
such that the contacts have the same polarity and the con-
tacts are opened, and a second position in which -the lines
of the magnetic fields of one of the first and second mag-
nets pass through the first and second magnets such that
the contacts have opposite polarity and the contacts are
closed. The second magnet is in one of the first or second
positions when the switch senses a rate of descent which is
below a set amount and is in the other of the first and se-
cond positions when the switch senses a rate of descent
which exceeds a set amount.
DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of the vertical de-
scent rate detector switch of the instant invention;
Fig. 2 is a side view of the~ instant switch;
Fig. 3 is a top view of the instant switch;
Fig. 4 is a view along line 4-4- of Fig. 3;
Fig. 5 is a view of the instant switch showing
~he lines of the magnetic fields of the magnets when the
switch contacts are opened; and
Fig. 6 is a view of the instant switch showing
the lines of the magnetic fields of the magnets when the
switch contacts are closed.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figs. 1-3 of the drawings, the verti-
cal descent rate detector switch 10 of the instant invention
has a cylindrical base 12 which has a threaded axial bore 14
and a lateral slot 16 formed in the bottom surface 18 which
extends radially outward from the bore 14 to the side 20.
A hollow shaft 22, which is threaded at each end 24, 26, is
vertically mounted on base 12 by having end 24 threaded into
bore 14. Shaft 22 is constructed of a non-ferrous material,
such as stainless steel, aluminum or plastic, and has a
smooth, central, exterior surface 28.
A first cylindrical ceramic magnet 30, which has a
central bore 2, is mounted on a shoulder 34 of a cylindrical
support 36 which is constructed from a non-ferrous material.
Support 36 has a threaded bore 38 and is threaded onto the
end 24 of shaft 22 adjacent base 12 to thereby fix the magnet
30 to one end of the shaft 22. A second cylindrical ceramic
magnet 40, which has a central bore 42, is mounted in a holder
44 which has a smooth axial bore 46 and is constructed from a
non-ferrous material. A bearing 48, which is constructed of
a non-ferrous material, such as plastic, glass or Teflon~,
and has a smooth central bore 50, is pressed into bore 46
The outside diameter of shaft 22 is slightly less than the
diameter of bore 50 and shaft 22 projects th~ough the bore 50
of bearing 48 in holder 44. Magnet 40 can move parallel
with respect to shaft 22 but cannot move sideways relative to
shaft 22. Holder 44 is oriented such that the bottom sur-
face of magnet 40 has the same polarity as the top surface
of magnet 30. Since the polarity of the top and bottom sur-
faces of the magnets 30, 40 is the same, the lines of force
of the magnetic fields of the two magnets 30, 40 run in oppo-
site directions, the magnets 30, 40 repel each other and the
movable magnet 40 is suspended above the fixed magnet 30.
A third cylindrical ceramic magnet 52, having a centra~ bore
54, is mounted on a shoulder 56 of a cylindrical support 58.
Cylindrical support 58 has a threaded bore 60 which is
threaded onto the top end 26 of shaft 22 to thereby affix
the magnet to one end 26 of the shaft 22. Magnet 52 is
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mounted such that the polarity of the bottom surface of the
magnet 52 is opposite to the polarity of the top surface of
the movable magnet 40.
A stop 62 i5 mounted on shaft 22 to prevent down-
ward movement of the ma~net 40, and a stop 63 is mounted on
shaft 22 approximately one-quarter inch above magnet 40 to
prevent magnet 40 from moving out of its operate/non-operate
region, as described her~inafter.
Referriny to Figs. 4-6, a reed switch 64 having a
pair of contacts 66, 68 surrounded by an inert gas and enclosed
in a sealed glass envelope, is mounted in a central bore 74 of
shaft 22, such that the contact:s 66, 68 are positioned between
the stationary magnet 30 and the movable magnet 40. The con-
tacts 66, 68 are connected to wires 70, 72, respectively,
which are connected to a circuit which functions when the
switch 10 is actuated.
Operation of the rate detector switch 10 is as fol-
lows. Referring to Fig. 5, when the device -to which the
switch 10 is attached, such as an aircraft passenger loading
bridge, is at rest, the movable magnet 40 is suspended a~ove
the stationary magnet 30 by the opposing lines of force of
the magnetic fields of the magnets 40, 30. The weight of
the movable magnet 40 is zero, since its weight i5 cancelled
by the repulsion of the magnetic fields. Although its weight
is zero, the mass of magnet 40 is several ounces and inertial
forces act on this mass as described below.
In the area 76 between the magnetic fields of the
stationary magnet 30 and movable magnet 40, there is a magnetic
void. In the magnetic void area 76 the lines of force of the
magnetic fields run perpendicular to the axis of the shaft 22.
If the reed switch 64 is positioned within bore 74 of the
shaft 22 such that the area where the switch contacts 66, 68
come together is adjacent the area 76 of the magnetic void,
the switch contacts will remain open. The reason for this is
that the lines of the field of the stationary magnet 30 pass
through one contact 68 and the lines of force of the magnetic
field of movable magnet 40 pass through the other contact 66.
Since the lines of force of the two fields run in opposite
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directions with respect to each other, the contacts 66, 68
have the same polarity which causes the contacts to repel
each other and remain open.
When the device to which the rate detector switch 10
is attached descends vertically at or above a set rate, the
reed switch contacts 66, 68 are closed as shown in Fig. 6.
As previously mentioned, the weight of the movable magnet 40
is zero since its weight is cancelled by the repelling force
of the magnetic fields of the stationary and movable magnets
30, 40, respectively. The mass of magnet 52 is on the order
of a few ounces. When the rate of descent of the device ex-
ceeds a set amount, the movable magnet 40 tends to move up
shaft 22 towards the third magnet 52. As the movable magnet
40 moves upward the magnetic void area 76 also moves up.
When this happens, the contacts 66, 68 of the switch 64 close.
They close because the lines of force of the magnetic field
of the first magnet 30 flow through both contacts 66, 68 which
causes the contacts to have opposite polarity and hence be
attracted to each other. In this case, the lines of force of
the field of the first magnet 30 are running generally parallel
to the contacts 66, 68.
When the switch 10 is stationary, the position of the
magnetic void area 76 can be changed such that the area 76 is
directly opposite the switch contacts 66, 68 by rotating sta-
tionary magnet 30 on the threaded portion 24 of shaft 22 until
the contacts 66, 68 are open with respect to each other.
Since, as mentioned above, the stationary magnet 52
is positioned above the movable magnet 40 such that its mag-
netic field runs in the same direction as that of the movable
magnet 40, the movable magnet 40 is somewhat attracted to it.
The function of the third magnet 52 is to linearize the move-
ment of the movable magnet 40. As magnet 40 moves up the
shaft 22, the repulsive force between the opposing field of
the stationary magnet 30 and the movable magnet 40 tends to
weaken. The loss of this repulsive force is made up by the
increase in the attractive force between the magnetic fields
of the movable magnet 40 and the stationary magnet 52.
The process of calibrating the switch 10, i.e.,
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setting it to operate in response to different rates of
vertical descent, is as follows. When shaft 22 is in the
vertical position, the entire weight of movable magnet 40
is supported by the repelling force of the magnetic fields
of the stationary and movable magnets 30, 40, respectively.
When the rate detector switch 10 is at rest, the gravity
force acting on the movable magnet 40 is 1Ø When a body
is in a state of free-fall, the force of gravity acting on
the body is zero. In order for the mo~able magnet 40 to
move upward with respect to the shaft 22, it must be sub-
jected to a gravity force of less than 1Ø The instant
rate detector switch 10 is designed to sense a rate of de-
scent havin~ a force of gravity, or "G" force, between zero
and 1Ø
On the aforementioned aircraft passenger loading
bridge it was found desirable to set the switch 10 to actu-
ate when it senses a rate of descent having a gravity, or
"G" force, approximately equal to .9.
It was found that when the switch 10 is moved off
the vertical, the movable magnet 40 starts to move up the
shaft 22. This occurs because a portion of the weight of
the magnet 40 is taken by the shaft 22 and the repelling
force between the fields of the stationary and movable mag-
nets 30, 40, respectively, can further move the two mag-
nets 30, 40 apart. As the magnet 40 moves up the shaft 22,
the area 76 of the magnetic void is changed. The position
in the central bore of shaft 22 in which the contacts 66, 68
are actuated can be found in the following manner. The
switch 10 is tilted so that the axis of shaft 22 is tilted
from the vertical at an angle whose cosine is equal to the
gravity force at which it is desired to have the swi.tch 10
actuate. While the switch 10 is at this angle, the reed
switch 64 is inserted in the central bore 74 of shaft 22 un-
til the switch is actuated, When the reed switch is pro-
perly positioned, it is secured by means of pouring a potting
material, such as an epoxy or silicon rubber, into the bore
74. After the material has hardened, the switch 10 is placed
in a vertical position. The cylindrical support 36 for the
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~ stationary magnet 30 is moved until the area 76 of the mag~
netic void is properly positioned with respect to the con-
tacts 66, 68, stop 62 is moved adjacent the bottom of movable
magnet 40 and stop 63 is positioned approximately one-~uarter
inch above magnet 40 to prevent the magnet 40 from moving
out o~ the operate/non-operate :region.
Although a preferred embodiment of the invention
has been illustrated and described, it will be apparent to
those skilled in the art that various modifications may be
made without departing from the spirit and scope of the
present invention.
I CLAIM:
