Note: Descriptions are shown in the official language in which they were submitted.
114~30g
Field of the Invention
= _
This invention is concerned with improvements in or
relating to dockboards, and especially to dockboards of the
type comprising a main plate having a lip plate pivotally
connected to its front edge for movement between stored and
operative extended positions. More particularly the invention
is concerned with dockboards of the type specified which are
powered hydraulically, using one hydraulic motor to elevate the
main plate and another hydraulic motor to elevate the lip plate
relative to the mai-n plate.
Review of the Prior Art
Hydraulically-powered dockboards are now well-established
commercially and have the advantages of very positive operation
while requiring the absolute minimum of physical effort of the
operator even with a heavy board; these advantages frequently
outweigh the hi-gher cost of the hydraulic motors and their
accompanying controls over a spring-operated board. In known
constructions, for example those shown in U.S. patent Nos:
3,345,665; 4,010,571 and 4,110,860
respective piston and cylinder hydraulic motors are used for
elevating the main and lip plates and the weights of the plates
employed for returning them to their respective stored positions.
It is now almost universal practice with such boards that when
not in use they are returned to a so-called "dock-level position"
in which the main plate is horizontal and level with the surface
of the dock in which it is mounted, while the lip plate is
vertical with its front edge located behind a pair of solid stops,
114~3~g
so that the board is positively retained in that position.
It is of course important for reasons of safety alone
that the board be properly stored when not in use, since the
operators will assume that this is the case and move heavy
equipment, such as loaded fork trucks, over the main plate as if
it were part of the dock floor. A serious accident can result
if the board is above or below~do~k level, and if the lip plate
edge is not securely behind its stops, when the weight on the main
plate may be sufficient for it to move suddenly dow~ward~
Theoretically such accidents should not be possible, but
this usually pre-supposes that the main and lip plate pivots are
well lubricated regularly and move freely over their full ranges
of movement. In practice in this industry the quality and
regularity of maintenance frequently leave much to be desired.
Moreover the constant heavy traffic to which the boards are
subjected can over a period of time produce warping and misalign-
ment that results in difficult and erratic operation.
Definition of the Invention
_
It is therefore an object of the invention to provide a
new hydraulic powered dockboard adapted for automatic control.
It is a more specific object to provide a new dockboard
in which movement of the board through a complete cycle of
operations is obtainable with push button control.
In accordance with the present invention there is provided
5 a dockboard comprising frame means;
a main plate having front and rear edges;
4~309
means pivotally connecting the main plate with said frame
means adjacent said rear edge for pivoting movement about a
respective first pivot axis between a lowered position and an
elevated position;
a lip plate;
means pivotally connecting the lip plate with the main
plate front edge for pivoting movement relative to the main plate
about a respective second pivot axis between a dependent positon
and an extended position;
first motor means operatively connected between the main
plate and the frame means for moving the main plate relative
to the frame means;
second motor means operatively connected between the main
and lip plates for moving the lip plate relative to the main plate;
and
-~ontrol means for operating the said first and second
motor means whereby during operation of the first motor means
to elevate the main plate while it is between predetermined lower
and upper elevated positions the second motor means is also
operated to move the lip plate to the said dependent posit~on.
Description of the Dr-awings
A dockboard which.is a particular preferred embodiment
of the invention will now be described, by way of example, with
reference to the accompanying drawings wherein:
FIGURE 1 is a plane longitudinal cross-section through the
board with its main plate in an elevated position and its lip
plate in a dependent position,
.
1~63~9
FIGURE 2 is a partial cross-section similar to Figure 1
and showing the lip plate in a fully extended position,
FIGURE 3 is a cross-section similar to Figure 1 and showing
both the main and lip plates in a so-called stored position,
FIGURE 4 is a section taken on the line 4-4 of Figure 1,
FIGURE 5 is a schematic diagram of the dockboard electrical
system, and
FIGURE 6 is a schematic diagram of the dockboard hydraulic
system.
Description of the Preferred Embodiments
The particular form of dockboard shown herein is adapted
to be mounted as an integral unit into a prepared recess in a
loading dock or platf-orm (not shown) so that with the dockboard
in the-position shown in Figure 3 (called herein its stored
position), the main plate 10 thereof is approximately horizontal
and level with the top surface of the dock, while its lip plate
12 is folded down to a dependent stored position, in which it
is approximately flush with the front face of the dock. It will
be understood that the term "stored position" is used for
convenience in terminology, and under some conditions the board
will be used for loading and unloading while in the so-called
stored position.
This particular dockboard has a box-like frame means
comprising a bottom 14, side walls 16 and a rear wall 18,
formed of welded sheet metal and made sufficiently rigid for
transport, installation and subsequent use. When installed this
particular frame means is supported by the surrounding concrete
30~
of the dock and a minimum of additional strengthening means, such
as cross braces and specially thickened edges, is required. The
invention is however also applicable to other forms of dockboard,
such as a free-standing unit without a surrounding dock, which
will require such additional strengthening means and a unit of the
type especially adapted for use with a "step-down" dock.
The term !~ frame means" is used herein for convenience in
terminology, and in the embodiment illustrated comprise the said
box-like frame assembly, in other embodiments the frame means
may instead comprise, for example, only the fastening means by
which the main plate and its associated elevating mechanism are
fastened to a suitable supporting structure, which may be the
dock.
The main plate 10 has its rear edge pivotally connected
to the frame assembly about a first pivot 20, the axis of the
pivot being shown as horizontal. The pivot means normally are
arranged to permit some side to side tilting of the main plate,
but such arrangements are well known in the art and are not
illustrated since they form no part of this invention. The lip
plate 12 is pivotally connected to the front edge of the main
plate about a second pivot 22 having its axis parallel to the
first axis. In the stored position with the lip plate in what
is called herein its dependent position, the lip plate front
edge is engaged inside stop means comprising a pair of spaced
stops 24. It is also possible to move the board to a position
in which the main plate is below dock level, in which case the
lip plate front ed~e is en~aged inside lower stop means 26.
-- 5
1~63V9
Elevating means for both the main and lip plates consist
of hydraulic motor means. Such means for the main plate are
constituted by a single-acting cylinger 28 pivotally connected
at 30 to brackets 32 mounted on longitudinal reinforcing member 34,
and a piston 36 pivotally connected at 38 to a bracket 40 mounted
on the underside of t~e plate 10. Motor means for elevating
the lip plate relative to the main plate consist of a double-
acting cylinder 42 pivotally connected at 44 to a bracket 46
fixed to the underside of the main plate 10 and a piston 48
pivotally connected at 50 to a bracket 52 fixed to the underside
of the lip plate.
Electric switches 54 and 56 fixed to the underside of
the main plate are operated, as will be described below, by an
actuating arm 58 fixed to the piston 48, while an electric switch
6Q fixed to the cylinder 28 and movable therewith is operated
with a lost motion by engagement of an arm 62 thereof with the
upper and lower horizontal walls of channel member 64 fixed
to the reinforcing member 34.
The operation of the dockboard, including the functioning
of the hydraulic and electric circuits will now be described.
In the most usual docking operation a transport backs up to the
dock while the board is in the stored position of Figure 3. The
operator ensures that selector switch 66 is in the "auto" position
in which its contacts 66a and 66c are closed, while contacts 66b
and 66d are open, and then pushes the "start" button 68. Electric
power is then suppled from lines 70 and 72 to relay 74, closing
its contacts 74a and 74b; at this time both switches 54 and 56
3~
are closed while switch 6Q is open. The relay 74 is therefore
latched closed by its contacts 74a, while the motor of pump 76 is
energised through contacts 74b and safety overload switch O/L.
A timing relay 78 ls also energised and its contacts 78a closed,
5 but it has no function in this "auto" mode.
Pump 76 draws hydraulic fluid from reservoir 80 via
filter 82 and feeds it through pilot valve 84 and normally-open
solenoid valve 86 to the bottom end of main plate ~ylinder 28
and also to the top end of lip cylinder 42. Pilot valve 84
10 is piloted to the necessary state against its spring by the liquid
under pressure from the pump. The pressurised liquid is also fed
to a transfer valve 88, but at this stage is insufficient to
overcome the bias of its adjustable spring and it therefore
remains in the condition illustrated, in which the lower end of
15 the lip cylinder 42 is connected via a check valve 90 to return
hydraulic liquid to the reservoir. The check valve is piloted
by the pressurised liquid to open condition so that the liquid
from the lip cylinder returns freely to the reservoir. The main
plate motor is therefore operated to lift the main plate, while
20 at the same time the lip plate motor is operated to move the lip
plate fully to the stored dependent position, if it is not in that
position, and to hold it firmly in that position while the main
plate is elevated.
When the main plate reaches its uppermost position the
25 main cylinder will not accept any more liquid and the liquid
pressure therefore increases until it reaches a value, e.g. about
38 Kg. sq. cm~500 p.s.i.~, at which transfer valve 88 is piloted
1~4~3~9
to shift, whereupon liquid is now fed to both ends of the lip
cylinder. The area o~ the lip piston face is greater at the bottom
end than at the top end because of the presence of the piston rod,
so that the force is greater and the motor therefore operates to
pivot the lip plate to the extended position; when the lip plate
reaches the fully extended position the arm 58 opens switch 54,
deenergising relay 74 and stopping motor 76. With the piloting
liquid pressure removed the pilot valve 84 now moves to the
condition specifically illustrated, in which it permits the main
cylinder 28 to drain via an adjustable orifice 92 and low-pressure
relief valve 94 to the reservoir 8Q; the main plate therefore
floats downward under its own weight until the extended lip engages
the back of the truck. The transfer valve ~8 also reverts to the
condition illustrated when the pump stops and the lip plate is held
in elevated position since the liquid at the piston side is re-
tained by the check valve 90, which is no longer piloted open
by the pressurised liquid. It may be noted that if the extended
lip is subjected to a sudden unexpected force, such as by a truck
backing into it, the liguid in the cylinder 42 can escape through
the check valve 90 to permit the lip to fold and avoid being damaged.
If for any reason the hydraulic pressure be~omes excessive relief
valve 95 operates to return the liquid to reservoir 80.
The dockboard lip plate xemains resting on the back of
the truck under the weight of both plates during the loading/
unloading operation; at its conclusion the truck may simply drive
away whereupon the plates will resume their downward movement~ At
a predetermined lowermost position (not illustrated~ below the
-- 8
3~P~
horizontal position of Figure 3 the switch 60 is closed and motor
76 is again energised, whereupon liquid is fed simultaneously to
the main and lip cylinders folding the lip to the dependent
position and raising the main plate. As described above~ the
operating arm 62 of the switch 60 is engaged in channel of member
64 and, after the main plate has lifted to a position just above
the horizontal, as set ~y the switch 60, t~e switch is again opened,
stopping the motor 76; the entire board now lowers under its own
weight. The cooperation between the switch arm 62 and channel
member 64 provides the necessary lost motion for the required
operation of the switch. The lip plate was positively moved to
its folded position during the upward movement of the main plate,
and it is now held positively in the folded position by the action
of relief valve 92, which ensures that there will always be a
positive pressure at the rod side of the lip cylinder. This positive
folding of the lip plate ~ill always take place, even if the pivot
joint between the plates is stiff due to some misalignment or due
to poor maintenance and consequent lack of lubrication. The ramp
therefore settles automatically into the position of Figure 3
with the free end of the lip engaged behind the stops 24, and such
action must always occur unless there has been some catastrophic
accident to the board.
It will be seen therefore that a board of the invention
is able to execute a complete cycle of operation automatically
upon a single push of the start ~utton, whereupon it will lift
the main plate, extend the llp and lower, and subsequently will
1~4~i3~P9
automatically return to stored position. This may be contrasted
with the prior art boards of which I am aware in which an operation
must hold the operating switch closed while the board executes
the raising and lip extending part of the cycle. It sometimes
happens w;th a docklng operation that the level of the transport
platform is below dock level, or the body of the truck is completely
full at the start or end of ~he operation, so that it is not
possible to rest the lip plate on the transport platform. In such
cases the board must be brought ~elow dock level with the lip
slightly extended until the hinges 22 rest on an upward-extending
top member 25; a fork-lift truck can now be employed in the usual
manner and engage its fork beneath the load. To operate in this
manner it must be possible for the board to drop below dock level
without the above-described automatic functioning of switch 60 to
restore the main plate to dock level. If this is required the
selector switch 66 is set to BDLC (bel,ow,dock level control)
whereupon contacts 66a and 66c open, while contacts 66b and 66d
close. If start switch, 68 is now closed relay 74 operates via
contacts 66b and switch 56; motor 76 and timing relay 78 are then
actuated via relay contacts 74b, so that the main piate rises
with the lip plate urged to the dependent position. After a
predetermined period long enough to ensure that the bottom edge
of the lip plate has lifted out of the keepers 24, contacts 78a
of the timing relay close and solenoid valve 86 is operated to
the alternative position now shown in Figure 6, whereupon the
supply of pressurised liquid to the main plate cylinder is cut
off, while the supply ~o lip c~linder 42 continues via shuttle
-- 10
63(19
valve 88; the lip plate therefore begins to elevate, after a
relatively small but sufficient movement of the lip plate the arm
58 leaves switch 56 which opens, deenergising relay 74 and
thereby the motor 76 and tim~ng relay 78 with the motor off the
main plate drifts downward under its own weight with the lip
partly elevated as descri~e~. The sw~tch 60 is no longer operative
since the contacts 66c.are open, so that the board can proceed down-
wards below dock level, until it engages the stop 25.
To restore the board to normal operation the selector
switch 66 is set again to."auto"; since the switch 60 is closed
the motor 76 will operate and take the board through its cycle of
elevating, bringing the lip to depending position and storing the
board as before with the lip plate behind the ~tops 24~
With the selector switch 66 in the "off" position all
contacts are open. At any time the movement of the board can be
stopped by pressing a switch 96; switch contacts 96c.stop
operation of relay 74 as though both switches 54 and 56 were open
and therefor the motor 76 is stopped, while contacts 96b close to
cause energisation of hydraulic relay 86, whereupon return of liquid
from the bottom end of main plate cylinder 28 and the top end of
lip plate cylinder 42 to the reser-~oir is stopped and the plates
remain stationary in the position they were in when the switch 96
was closed. Operation will start agai~ by pressing start switch
68. If at any time the lip is to be extended without passing
through the automatic sequence described a lip extend switch 98 is
pressed, whereupon cont~cts 98a are closed and permits operation
-- 11 --
1~630~
operation of motor 76, while~contacts 98b are closed to energize
solenoid relay 86 so that liquid is fed only to the lip plate
cylinder 42; this is a useful feature in that cycling of the board
will always take an appreciable period of time- It will be seen
therefore that at all times the operator has full control over
any of the functions that normally are performed with this
type of board.
