U.S. patent number 3,817,346 [Application Number 05/282,157] was granted by the patent office on 1974-06-18 for mobile scaffolding.
Invention is credited to Donald T. Wehmeyer.
United States Patent |
3,817,346 |
Wehmeyer |
June 18, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
MOBILE SCAFFOLDING
Abstract
There is disclosed a mobile scaffolding which is powered by self
contained electrical storage batteries. The electric drive is
mechanically linked to the lift mechanism of the scaffolding by
mechanical means comprising screw means and a mating nut means
interconnected by rolling means to provide a high efficiency
coupling. The lift mechanism employs very compact spring means
which is biased to extend the lift mechanism from its contracted
position to provide a force that supplements the electric drive
when the mechanism has the most unfavorable lever moment for
extension of the scaffolding. The unit has a self contained power
means for mobility and a self contained directional control means
with remote control means whereby the entire unit can be controlled
from the scaffolding platform with a single lever that actuates the
lift, drive and steering motors.
Inventors: |
Wehmeyer; Donald T. (Fountain
Valley, CA) |
Family
ID: |
23080336 |
Appl.
No.: |
05/282,157 |
Filed: |
August 21, 1972 |
Current U.S.
Class: |
182/14; 182/16;
182/69.5; 182/148 |
Current CPC
Class: |
B66F
11/042 (20130101); E04G 1/22 (20130101); E04G
2001/244 (20130101) |
Current International
Class: |
E04G
1/22 (20060101); E04G 1/18 (20060101); B66F
11/04 (20060101); E04g 001/22 () |
Field of
Search: |
;182/141,148,63,69,16,13,14 ;254/122 ;52/109 ;60/6,7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Machado; Reinaldo P.
Attorney, Agent or Firm: Strauss; Robert E.
Claims
What is claimed is:
1. A mobile scaffolding machine having:
a platform;
a base, axle means carried thereon, wheels on said axle means
whereby said scaffolding is mobile;
an extendible assembly mechanically interlinking said platform and
base and comprising at least one pair of arm members joined
together in a pivotable connection at an intermediate point of
their length;
platform attachment means securing a pair of free ends of said
extendible assembly to said platform;
base attachment means securing the opposite pair of free ends of
said extendible assembly to said base;
said attachment means including longitudinal channel means carried
on each of said platform and base and wheeled means engaged therein
and carried by at least one of each of the pairs of free ends of
said assembly to permit its sliding engagement with its respective
platform or base;
lift means operatively attached to at least one end of said
extendible assembly comprising screw means positioned transversely
to the direction of extension of said assembly, screw engagement
means cooperative therewith, electric lift motor means,
interconnecting means linking said motor in rotational driving
relationship to one of said screw and screw engagement means and
means securing at least one of said pair of free ends at said one
end of said extendible assembly to at least one of said screw and
screw engagement means whereby rotational movement of said motor
effects the extension and retraction of said assembly;
resilient means comprising compression coil spring means carried on
said scaffolding coaxially with said screw means to engage said
extendible assembly between its retracted position and a partially
extended position having said arm members at an angle no greater
than about 45 degrees to the horizontal and to urge extension of
said assembly from said retracted position to said partially
extended position whereby the force stored in said resilient means
by retraction of said assembly is available for supplementing the
force of said motor means through the positions of said assembly
having the most disadvantageous lever moments to said screw
means.
2. The scaffolding machine of claim 1 wherein said base carries:
electric power means, means linking said power means to at least
one of said wheels to drive said scaffolding, directional control
power means, means linking said control power means to at leat one
of said wheels to steer said scaffolding, and a source of
electrical energy with connector means to said electric power
means.
3. The scaffolding machine of claim 1 wherein said extendible
assembly comprises two assemblies of arms located at each side
thereof.
4. The scaffolding machine of claim 3 wherein each of the
extendible assemblies of arms comprises four arms pivotably
interconnected.
5. The scaffolding machine of claim 4 wherein each of said platform
and base attachment means includes a set of fixed brackets at one
end of said scaffolding.
6. The scaffolding machine of claim 5 wherein screw and screw
engagement means are positioned at each side of the scaffolding
base.
7. The mobile scaffolding machine of claim 1 wherein said screw
means comprises at least one screw rod longitudinally carried by
said base with one end thereof secured to said one end of said
extendible assembly and the opposite end thereof extending to said
interconnecting means, the latter comprising a rotating nut drive
member engaged by said screw rod in a thread drive housing.
8. The mobile scaffolding machine of claim 7 wherein said free end
of said screw rod extends past said threaded drive housing and into
sliding engagement with a tubular member having a flanged abutment
and coxially supporting said compression coil spring means between
said abutment and said threaded drive housing.
9. A mobile scaffolding machine comprising:
a rectangular mobile base with dirigible wheels;
a pair of spaced-apart parallel channel means located on opposite
sides of said base, each of said channel means having a pivot
fixture located at one end thereof;
a separate dolly means reciprocally confined in each of said
channel means;
a first screw rod having one end connected to one of said dolly
means and extending coasially therefrom in its associated channel
means toward its pivot fixture;
a second screw rod having one end connected to the other of said
dolly means and extending coaxially therefrom in its associated
channel means toward its pivot fixture;
a first thread drive housing fixedly mounted intermediately of one
of said channel means and having a rotating nut drive member
engaging the threads of said first screw rod;
a second thread drive housing fixedly mounted intermediately of the
other of said channel means and having a rotating nut drive member
engaging the threads of said second screw rod;
drive means in each of said housing for rotating its drive nut
member;
a rigid cross shaft interconnecting said drive means of said
housings for simultaneous rotation thereof;
an electric drive motor drivingly connected to said cross shaft
where said dolly means can be simultaneously advanced and retracted
relative to their respective pivot fixtures;
a pair of vertically oriented scissor-type lift arms, one of said
pair connected between one of said dolly means and its pivot
fixture and the other of said pair connected between the other of
said dolly means and its pivot fixture whereby a work platform
connected to said pair of vertically oriented lift arms is raised
and lowered as said dolly means are simultaneously reciprocated in
their associated channel means.
10. The mobile scaffolding machine as defined in claim 9 wherein a
compression spring is coaxially mounted between each threaded drive
housing and the end of its screw rod extending therefrom toward its
associated pivot fixture whereby said compression spring will be
compressed as its associated dolly moves away from its pivot
fixture.
11. The mobile scaffolding machine of claim 10 wherein said
compression springs are operative only to bias their associated
screw rods when said scissor-type lift arms are between their most
retracted position and a partially extended position having said
arms at an angle no greater than about 45 degrees to the horizontal
and to urge extension of said lift arms from their retracted
position to said partially extended position whereby the force
stored in said compression springs by retraction of said lift arms
is available for supplementing the force of said motor through the
positions of said lift arms having the most disadvantageous lever
moments to said screw rods.
12. The mobile scaffolding machine as defined in claim 9 wherein
the electric drive motor is a variable speed drive motor so the
speed of simultaneous movement of said dolly means in their
associated channels can be controlled.
13. The mobile scaffolding machine defined in claim 12 wherein the
electric drive motor is a DC drive motor and its speed is
controlled with a control circuit employing a SCR operable to pulse
the drive motor at different frequencies to selectively change its
speed.
14. The mobile scaffolding machine defined in claim 13 wherein a
control circuit is provided to change the pulse rate of the SCR,
said control circuit having a manually operated device for changing
the pulse rate of the SCR circuit.
15. The mobile scaffolding machine defined in claim 14 wherein the
manually controlled device includes a lever means which includes a
reversing switch and a potentiometer whereby advancing the lever
from a neutral position in one direction will cause the motor to
drive clockwise at a rate proportional to the displacement of said
lever from a neutral position and the advance of said lever from
said neutral position in the other direction will cause said motor
to rotate in a counter-clockwise manner proportional to the
distance said lever is moved from said neutral position.
16. The mobile scaffolding machine as defined in claim 15 wherein
the lever means is mounted on the work platform whereby the ascent
and descent of the platform can be controlled directly
therefrom.
17. The mobile scaffolding machine as defined in claim 15 wherein
the rectangular mobile base with dirigible wheels includes an
electric drive motor and the control circuit can be switched so the
lever means can be utilized to control the movement of said mobile
base in speed and direction.
Description
DESCRIPTION OF THE INVENTION
This invention relates to mobile scaffolding and, in particular, to
a mobile unit having an electric drive and a mechanical lift
mechanism.
The construction industry, particularly that of tilt up wall
construction employs scaffolding to a large extent for installation
of ceilings and overhead utility facilities. This construction is
used largely for warehouse and industrial building construction.
The foundation and floor are generally poured concrete and the
walls are formed as concrete panels which are cast on the floor and
are then tilted upright and secured in place. These walls can be
from about 8 to 30 feet in height. Generally, all the utility
facilities, electrical wiring or water or gas plumbing, etc., are
installed overhead, directly beneath the roof.
Fixed or immobile scaffolding has been used to support workmen near
the roof, however, workmen are needed at many different locations
under the roof and the construction of fixed scaffolding at each of
these locations is time consuming and costly.. Mobile scaffolding
which can be moved about the building without dismantling has been
used. This scaffolding comprises a mobile base with a work platform
that can be elevated by jacks carried by the unit. These jacks
have, without exception, been hydraulically actuated and generally
have been powered by a gasoline engine that is mounted on the unit.
Gasoline engines are objectionable for indoor work and require a
substantial ventilation of the building when in use. While electric
motors would be more desirable as a power source, their use has
been limited by the inefficiency of the hydraulic mechanism used
with the conventional mobile scaffolding.
Mechanical lifting mechanisms, however, have not been used for this
service because of the large lifting force that is required during
the initial actuation of the lift when the lift mechanism provides
the least favorable lever arm for the lifting force. Consequently,
the direct use of a mechanical drive lift mechansim has
necessitated a compromise in lift design, e.g., either the
scaffolding must be too high in the collapsed position or it fails
to extend as high as desirable.
An extremely efficient mechanical drive means for use in the lift
unit is a screw with mating screw engagement means having rolling
contact with the screw. The screw means can be combined with
electric motive power means in a highly efficient, portable or
mobile scaffolding unit having a minimum collapsed height and
maximum extended height. I have found that such a mechanical drive
mechansim can be used with a portable scaffolding device provided
that compact resilient means are provided to bias against the
platform or any of the members of the extendible assembly linking
the platform to the base when the platform is in its retracted
position. The compact resilient means comprises at least one
massive compression spring which is coaxially placed about the lift
screw so that it is compressed when the platform is collapsed and
is operative to release its stored force to supplement the lift
power means when the platform is extended.
The mobile scaffolding of this invention comprises: a base, wheels
carried thereon, electric power means linked to at least one of the
wheels to provide mobility to the base, directional control means
to pivot at least one of the wheels and provide steering of the
base, a platform, an extendible assembly mechanically
interconnecting said platform and base and comprising at least one
pair of arm members joined together in a pivotable connection at an
intermediate point of their length, platform attachment means
securing a pair of free ends of the extendible assembly to the
platform and base attachment means securing the free ends of the
opposite end of the assembly to the base, while permitting the
sliding engagement of at least one of either or both of said pairs
of free ends with its respective platform or base, lift means
operatively attached to at least one end of the extendible assembly
comprising screw means transversely positioned to the direction of
extension of the assembly, screw engagement means cooperative
therewith, electrical lift motor means, interconnecting means
linking said motor in rotational driving connection to one of said
screw and screw engaging means to one of said pair of free ends
whereby rotational movement of said motor effects extension and
retraction of the assembly, and resilient means coaxial with the
screw means and operative to engage the extendible assembly in its
retracted position and to resiliently urge movement of said
assembly from its retracted position whereby the force stored in
the resilient means by retraction of the assembly is available for
supplementing the force of said electric lift motor means to extend
the assembly through the positions having the most disadvantageous
lever moments. In its preferred embodiments, the scaffolding has
remote control means carried on the platform to control the
actuation of the lift mechanism and the movement of the unit about
the building. The entire operation of the unit can be controlled by
a single hand control that actuates switches in the respective
circuits for the drive power means, the directional control power
means or the lift motor means.
The invention will now be described with reference to the FIGURES,
of which:
FIG. 1 illustrates the mobile scaffolding unit in its most extended
position;
FIG. 2 is a plan view of the base of the unit;
FIG. 3 is a sectional view along the line 3--3' of FIG. 2;
FIG. 4 illustrates the slidable connection of the extendible
assembly;
FIG. 5 illustrates the electrical circuit of the unit; and
FIGS. 6 and 7 illustrate the hand control of the unit.
Referring now to FIG. 1, the mobile scaffolding unit comprises a
base 10, a platform 20 and an extendible assembly 30 mechanically
interlinking the platform and the base.
Base 10 has a protective cover 12 with sidewalls. The unit has a
pair of rear wheels 14 and a pair of forward wheels 16. The rear of
base 10 is covered by a plurality of cover plates 18. The forward
pair of wheels 16 are steerable and are mounted on base 10 with
means permitting their axes to be turned to the right or left of
the base.
The platform 20 has a floor 21 with a protective railing 22 about
its periphery and an open section for access at its rear end. If
desired, the railing can fold away from the platform or a gate can
be furnished for the open section. At its front end, the platform
preferably carries a control console or pedestal 9 which supports
an instrument and control box 24 for operation of the unit.
The extendible assembly 30 comprises at least one and, preferably,
two pairs of arm members 31, 32, 33 and 34 which are pivotably
interconnected at points intermediate their lengths, at hubs 35 and
36. For maximum stability, these pairs of arm members are
duplicated at each side of the scaffolding unit and are identified
by common numbers. Each assembly has one pair of its free ends,
e.g., the upper ends of arm members 31 and 32, attached to the
platform and, at its opposite end, has the free ends of its arm
members, e.g., the lower ends of arm members 33 and 34 attached to
the base 10. The attachment means at the front of the base can be
bracket members 37 which are supported on the frame of the base. A
similar pair of bracket members can be provided on the forward edge
of the undersurface of platform 20.
The extendible assemblies 30 are vertically extendible and,
accordingly, at least one of each pair of free ends of the
assemblies is attached to either the base or platform by means
permitting its sliding engagement therewith. While the free ends of
both arm members 31 and 32 can slidably attach to the platform and
the free ends of both arm members 33 and 34 can slidably attach to
the base, it is preferred that only one of each of these pairs be
slidably attached to its respective base or platform. This is shown
in FIG. 1 where the lower end of the arm members 33 of each of the
assemblies is slidably attached to the base 10. The ends of these
members are secured to curved flange plates 38 and 37 which extend
through grooves 40 and 41 and into the housing of base 10. The
upper ends of members 32 bear rollers which are free to move in
channels on the underside of the platform. The remaining member of
each pair of free ends is secured to its respective platform or
base by brackets.
All the power and drive mechanisms for the unit can be contained
within the housing of base 10, including the electrical energy
storage means, motive power means for propulsion of the unit, its
directional control and extension of the platform.
FIGS. 2 and 3 illustrate the construction and assembly of base 10.
The base is formed by a pair of longitudinal beams 50 and 51 that
run the length of the base. These can be formed of sheet metal
welded to provide an upright, open channel. Two transverse beams
are provided; 52 at the front of and 53 intermediate the lengths of
the longitudinal beams. A sheet 67 also extends transversely across
the base a short distance behind beam 52 and has an offset pocket
68 at the midline of base 10. The front of base 10 is covered by
plate 54 while the rear portion is covered by plates 18 which
extend between beams 50 and 51. The plates have a short lip that
overhangs the inside wall of these beams to hold them in place. A
narrow plate, 55, is secured over the channel and provides open
slots 40 and 41 along each beam.
Cover plate 54 extends to about 12 inches of both edges of the
unit. The remainder of the top comprises a hinged cover 56 at each
side of the unit as shown in FIG. 1. Beneath the hinged cover are
compartments for the control circuit components 57, battery charger
74 and the electrical batteries 129 which are placed six at each
side.
The longitudinal beams have apertures near their rear ends and
support outboard brackets 58 in line with the apertures. The rear
axles 59 extend through the apertures and through a bearing support
carried by bracket 58. A conventional differential 60 is supported
on the midline of the base 10 with its axles extending to universal
joints 61 that connect to axles 59. Other means such as flexible
couplings can also be used in lieu of the universal joints. The
power drive to the differential comprises electric motor 62, a
conventional direct current motor of suitable voltage, e.g., 6 to
42 volts, that is linked by sprockets and chain 63 to the
differential input shaft.
The forward wheels 16 are mounted on axles having upright spindles
that are journaled at 64 by a sleeve carried at the outboard end of
beam 52. A trailing arm 65 projects from the wheel spindle and is
pivotably secured to a tie rod 66. The inboard end of rod 66 is
secured to shaft 72 by a ball joint coupling 73. The steering motor
and its mechanical linkage are mounted at the front center of base
10. The motor 10 fits into the pocket or housing 68 in transverse
sheet 67 and is supported by bracket 69 that is carried by beam 52.
The shaft of motor 70 is connected to gear box 71. Shaft 72
projects through gear box 71 and has a mid section bearing screw
threads which engage a mating nut in gear box 71. The nut is
secured to a pinion gear that is meshed with a worm gear which is
connected to the motor shaft so that rotation of the motor effects
side to side movement of rod 66.
The lift assembly, as previously described, comprises two pairs of
interconnected arms at each side of the unit. The arms are
preferably formed by welding together the edges of two channels to
form a hollow beam having the illustrated shape. The lower ends of
arms 34 are pivotably secured on base 10 by brackets 37 which are
secured to the forward ends of the longitudinal beams 50 and 51.
The lower end of arm 33 is secured to plates 38 and 39 which
project into base 10 and are mounted therein in sliding engagement
with wheels such as 75 that are contained within channel beams 50
and 51 and that roll on the inside bottom of these channel
beams.
FIG. 4 illustrates the construction of the lower end of the arms
33. Plates 38 and 39 are secured, preferably by welding to the
opposite sides of the arms 33. The plates are bored at 76 and
collar 77 is fitted into each bore. The collar has an annular
flange 78 which fits against the outer side of the plate and can be
secured thereto by welding or other suitable means. A bronze
bushing 79 is placed within collar 77. Mounted between the plates
38 and 39 is cylindrical block 80. This block has trunions 81 at
each end and a central bore 82 to accomodate shaft 83. The bosses
81 fit in bearing relationship to bushing 79. Bore 85 is tapped
transversely through block 80 and set screw 84 is provided to lock
shaft 83 in the block after assembly of the elements. The wheels 75
are similarly carried on shaft 83 with a bushing. Block 80 is bored
at 86 and and the end of shaft 87 is threaded into one end of
clevis 64 which is free to pivot with its opposite end having a
bore for shaft 83.
Each of the shafts 87 bears screw means, threads 88, as shown in
FIGS. 2 and 3 for the right side shaft. These shafts lie within the
channel beams 50 or 51. Each shaft 87 projects through a gear
housing 89 and a flange plate 99 which extends across the channel
directly forward of gear housing 88. The end of shaft 87 which is
opposite block 80 projects into tubular member 90 and bears a
collar 91 that is secured thereto by threads, welding or the like.
Tubular member 90 has an end plate which is bored to receive shaft
87 in a sliding fit and which serves as a stop to collar 91. The
opposite end of member 90 is open and bears annular collar 92 about
its outer periphery.
Resilient means comprising compression spring 93 is mounted about
member 90 and is biased between flange 99 and collar 92. The
retraction of the extendible assembly into the position shown in
FIG. 3 compresses resilient springs 93. The springs are selected so
that the dead weight of the platform and extendible assembly is
sufficient to compress the springs, thereby insuring that in the
event of failure of the lift motor, the unit can still be
retracted.
The gear housings 89 comprise conventional units wherein screw
threads 88 engage in rolling contact at a nut that is driven by a
worm gear on shaft 98. While other gear drives could be used, the
drive with rolling contact is preferred for its high efficiency. A
commercially available gear drive that can be used for this is a
ball screw "Jactuator" described in U.S. Pat. No. 3,178,958 and
manufactured by the Duff-Norton Company, North Carolina. The nut of
this unit, which is driven by screw threads on shaft 98 has a
helical race for ball bearings to provide a recirculating, rolling
contact with the threads on shaft 98. This gear drive is preferred
for its high efficiency. Other gear drives, e.g., a direct worm
gear be used, if desired. The shafts 98 are coupled through
flexible couplings 100 to shaft 101 that is mechanically linked by
chain 103 to electric motor 102. The outboard end of shaft 98
extends through gear housing 89 and bears brake means 104. Any
conventional brake means can be used, preferably the brake has a
solenoid which is biased to lock the brake and is unlocked by the
application of a direct current voltage to the solenoid coil. The
brake should also have manual means for its release and at least
one of shafts 98 is extended, as shown, so that a crank can be
attached to the shaft to permit manual lowering of the lift
platform.
Resilient spring means 93 are effective throughout the initial
movement of the arms of the extendible assemblies from their
positions shown in FIG. 3. The springs should be compressed against
the assembly during translation of the arms through an arc from
their compressed position, shown in FIG. 3. to an angle of about
45.degree., preferably about 40.degree. to the axis of the screw
shaft 87. The arms in the embodiment shown in FIG. 3 have an angle
to this axis when in the compressed position of about 7.degree..
Consequently, the springs are under compression when the arms are
at an inclined angle to the axis of shafts 87 of from 7.degree. to
40.degree.. Other embodiments can have varied minimum angles of
inclination from 2.degree. to about 15.degree., however, with most
embodiments, the maximum angle of about 45.degree., for compression
of the springs would be applicable.
During the initial movement of the assemblies from their retracted
position, the vertical component of force applied to the assemblies
from the motor 102 and through gear housings 89 is at a minimum
value. In the absence of the springs, a considerable force would
need to be exerted to lift even the unloaded platform because of
the unfavorable lever moment provided to the lift motor. Springs
93, however, elastically release their stored force to supplement
the force of motor 102 and permit substantially the entire force of
motor 102 to be applied to lifting of any load on platform 20.
The resilient spring means are coaxial with the screw means to form
a very compact power unit. Placement of these compression springs
in the indicated position avoids expanding the structure to any
significant degree and insures a minimum collapsed height to the
unit.
As the extendible assemblies are advanced to full extension, shafts
87 are moved forward in their channels 50 and 51. The position of
the forward end of these shafts is shown by the broken lines in
FIGS. 2 and 3. The forward ends project past flanges 105 which are
transversely positioned in the channels and which have a central
bore through which the shafts project.
In a typical embodiment of the portable scaffolding as illustrated
herein, the unit has a lift capacity of 2,000 pounds with a lift
motor of 3.25 horsepower, a drive motor of 2.25 horsepower and a
steering motor of 0.5 horsepower, all at 36 volts. The unit has
twelve six volt batteries and has a useful work period of 10 hours
continuous use between recharging cycles. This is sufficient for
about 5 days of normal use. The extendible height of the
scaffolding platform 20 above the floor surface is 20 feet and the
collapsed or retracted height is 4.5 feet. The unit has a maximum
ground speed of 7 miles per hour and a minimum lift time of from 30
to 40 seconds at the rated capacity load of 2,000 pounds.
The entire unit can be controlled with a single hand lever which is
mounted in a control box 24. The control box is illustrated in FIG.
6 and the control circuit for the unit, including that of the
control box, is shown by FIG. 5. The circuit of the control box is
shown at the left of FIG. 5 within the box defined by the broken
lines.
The control box 24 has a hinged cover panel 152 that supports a key
switch 154 and a manual four pole, double throw selector switch
156. The two throw positions of this switch are identified as Lift
and Drive on FIG. 5. The cover is slotted at 158 and a T-bar handle
160 protrudes through this slot. The handle has a threaded shaft
162 that is turned into a tapped bore of tube 164. The latter tube
is slidably mounted in a larger diameter tube 166, the base of
which bears journal 168 that is mounted on and secured to shaft
170. Shaft 170 is the shaft extension from the accelerator master
switch, not shown. The shaft has a segment gear mounted on it that
drives a pinion gear which in turn rotates the wiper of
potentiometer 174, shown in FIG. 5. The shaft also bears cams which
move the levers of each of switches 176 and 178 also shown in FIG.
5. When the handle is pushed forward in slot 158 and pivots shaft
170, the cams of switch 176 are actuated. Depending upon the
position of selector switch 156, this will close the contacts to
the up relay of the contactor panel 132 or the forward relay of
contactor panel 133. When the handle is pulled back in slot 158, it
pivots shaft 170 and actuates the cam of switch 178. Again,
depending upon the position of selector switch 156, this either
closes the contacts of the down relay of panel 132 or the contacts
of the reverse relay of panel 133. The operation of these relays
will be described in greater deail hereinafter.
A compression spring, not shown, is in tube 166 and seats against
journal 168. The spring is biased against the lower end of tube 164
and this tube is retained in tube 166 by pin 180 that extends from
a transverse bore in tube 164 outwardly and into an inverted
T-groove 182. The spring urges the handle assembly of tube 164 and
handle 160 upwardly so that pin 180 seats in the upright leg of
groove 182, thereby locking the handle assembly against rotation
about its axis. When the handle is depressed against the tension of
the spring, it can then be rotated left or right, the pin 180
following the horizontal legs of the groove 182.
The upper end of tube 164 bears a bracket 184 to which are secured
two normally open microswitches 186 and 188. These switches have
spring arms which support rollers 190 and 192 that bear against the
side of the control box 150. A view of the bracket and switches
appears in FIG. 7. As the handle 160 is rotated clockwise about its
axis, the switch lever of switch 188 is moved into contact with its
spring arm and is depressed against this arm sufficiently to close
its contacts. Switch 188 actuates the relays of the steering motor
124 to cause the motor to turn the forward wheels towards the
right. Switch 186 actuates other relays to reverse the current
through motor 124 and turn the wheels to the left.
The steering motor 70 and its normally open relays 190, 191, 192
and 193 are shown at the upper right of FIG. 5. The positive lead
130 is connected to the coils of the relays and to the contacts of
relay 193 and 190 while negative lead 140 is connected to the
contacts of relays 191 and 192. When switch 186 is closed by
clockwise rotation of handle 160 and when selector switch 156 is in
the Drive position, the coils of relays 192 and 193 are grounded to
the negative lead 140 through normally closed left limit switch
194. The limit switch is mounted on the unit near gear box 71 so
that when the wheels have turned the maximum degree the contacts of
this switch are opened by engagement with the left end of shaft 72
or by left tie rod 66. Closing of the contacts of relays 192 and
193 permits current to flow from lead 130 through the relay
contacts, the windings of motor 70 to negative lead 140. When the
wheels have turned the maximum degree to the left, the contacts of
limit switch 194 will be forced open, breaking the circuit to the
relay coils. Closing of the contacts of microswitch 188 by
counterclockwise movement of handle 160 will close the contacts of
relays 190 and 191 and cause current to flow through relay 190, the
windings of motor 70 in an opposite direction than previously
described, the contacts of relay 191 and through limit switch 195
whichch will open when the wheels have turned the maximum degree to
the right. which
The control circuits for the lift and drive motors are based on
commercially available circuit components which have silicon
controlled rectifiers, SCRs. Each motor control circuit employs a
silicon controlled rectifier panel, a contactor panel and a pulse
monitoring trip card. Both motors are controlled with a single
accelerator master switch, which as previously mentioned is
actuated by handle 160.
The silicon controlled rectifier circuit employs a SCR to provide a
pulsed input to the motor contacts at a frequency of 50 to 300
times per second. The duration of the closed motor contact period
is a fixed value determined by the rate of charge of a fixed
capacitor in the silicon controlled rectifier panel while the
duration of the open motor contact period is variable and is
determined by the rate of charge of a capacitor which is in series
with a potentiometer in the accelerator master control circuit. The
wiper of the potentiometer is mechanically linked to the
accelerator control so that the resistance can be varied; high
resistance limiting the current flow to charge the turn-on
capacitor and thereby limiting the frequency of on cycles to the
motor and low resistance, conversely, increasing the number of on
cycles and increasing the duration of the on time to the motor. The
potentiometer, previously mentioned, is shown at 174 in FIG. 5.
The motors operate on the average voltage supplied to them. A low
frequency of on cycles is the same as a steady state low voltage so
that the motors turn slowly and their speed increase with
increasing frequency of on cycles, i.e., increasing average
voltage. Some refinements of the circuit, as it is commercially
available, include placing a diode across the motor terminals so
that induced current can flow through the motor windings during the
off cycles, greatly increasing the efficiency of the motor
operation.
The components for the lift and drive motor control circuits are
available from the General Electric Company and are described in
detail in the General Electric publication RKE-151, Static Control
for Electric Vehicles. These components are illustrated in FIG. 5
in the integrated circuit for the scaffolding unit.
The lift motor is shown at 102 and the drive motor at 62. The
armature contacts of these motors are shown at 119 and 121 and 123
and 125 for motors 102 and 62 respectively. The field or stator
contacts are 115 and 116 and 117 and 118. The terminals of the
armatures and fields of the motors are connected through magnetic
contactor panels 132 and 133. These panels each have three relays,
two of which are opposite acting double throw relays and are
identified as D and U on panel 132 and R and F on panel 133. The
connections to the switch contacts of these relays are shown while
the relay actuating coils are omitted to simplify the drawing.
The positive lead 130 from batteries 129 is connected, through
circuit breaker 131, to an armature contact of each motor, 119 and
123. The other armature contact of the lift motor 102 is connected
to the normally open switch terminals of down relay D and up relay
U in the magnetic contactor panel 132. The armature contact 125 of
motor 62 is similarly connected to the normally open terminals of
the reverse relay R and the forward relay F of the magnetic
contactor panel 133. One of the stator contacts of each motor, 115
and 117, is connected to the switch pole terminal of the up relay U
and the forward relay F of its respective panel 132 or 133. The
opposite stator contacts 116 and 118 are connected to the switch
pole terminal of the down relay D and reverse relay R of their
respective panels 132 and 133. The normally closed terminals of the
relays are commonly connected to terminal T2 of their respective
SCR control circuit.
The circuit through the motor and its contactor panel is described
herein with regard to lift motor 102. The current flows from
positive lead 130 through the armature of the motor, the closed
contacts of the up relay U, to stator contacts 115, through the
field of the motor 102 to line 181 through the normally closed
contacts of the down relay D to contact T2 of the SCR panel and, in
a controlled pulsing, through SCR panel to the negative contact of
the panel. When the up and down relay switches are reversed, the
current flows through the armature, through the down relay D to
stator contact 116, through the field of motor 102 in an opposite
direction to that previously described to line 181 through the
normally closed contacts of the up relay U.
The actuating coils for the relays of the magnetic contactor panels
are not shown, however, the connecting leads to these coils are
shown in FIG. 5 as line 110 from terminal 8 and line 111 from
terminal 6 of terminal connector strip 134 which lead to the coils
of the down relay D and up relay U, respectively. The opposite
terminals of the relay coils have a common lead 112 which extends
to terminal 13A of the terminal connector strip 134.
The selector switch 156 connects switches 176 and 178 into the
control circuit for the drive motor 62. With the selector switch in
the lift position, closing of switch 176 by moving lever 160
forward will permit current to flow from the positive lead 130,
through lead 113 and the lift up limit switch 198 to contact 6 of
the terminal connector strip 134. This contact is connected to the
coil of the up relay U, the opposite terminal of which is connected
to terminal 13A of terminal connector strip 134. Lead 115 connects
13A to contact 5 of the safety card 136. Contact 5 of this card is
internally connected to the negative terminal 1 by a safety circuit
which disconnects the internal connection in the event that
excessive voltage appears across terminals 2 and 3 of the card.
Terminals 4 and 6 of the card are connected to the positive lead
and are connected to an internal circuit which requires that the
external circuit to terminal 5 be opened to reset the card in the
event that the internal connection is opened by an overload
condition.
When the hand control lever 160 is moved fully forward, the cam on
shaft 170 closes switch 109 and current flows to the coil of relay
1A of the magnetic contactor panel through lead 117 and terminal 45
of the terminal connector strip 134. The common connector on the
normally closed terminals of the down and up relays is connected
through relay 1A to negative lead 139, bypassing lead 181 and the
SCR control circuit and permitting full voltage operation of the
motor.
Whenever the lift motor circuit is actuated, current flows from
terminal 27 of terminal connector strip 134, through the coil 119
of the solenoid of brake 104, releasing this brake.
The limit switches for the lift motor 102 are located on the unit
so that the up limit switch 198 is opened when the assembly is
fully extended and the down limit switch 197 is opened when the
assembly is fully retracted.
While the preceding discussion has been directed to actuation and
operation of the lift motor in the up mode, the operation of the
closely related circuit to actuate the down mode and the related
circuits to actuate the drive motor in forward and reverse are
substantially identical. The actuating switch for the drive motor
comparable to 109 is not illustrated; its employment, as well as
switch 109 and the 1A relay bypass circuit for the lift motor, is
optional.
The invention has been described with regard to the illustrated and
presently preferred mode of practice. It is not intended that this
specific illustration be unduly limiting of the invention. Instead,
it is intended that the invention be defined by the means and their
obvious equivalents set forth in the following claims.
* * * * *