Lift mask carriage mounting arrangement

A lift mask carriage mounting arrangement is disclosed including a support assembly having an upright pair of laterally spaced and inwardly facing channular beams forming rail surfaces and interconnecting web surfaces at substantially right angles thereto, and a carriage assembly having an upright pair of elongated legs disposed between the channular beams for movement longitudinally along them, an upper pair of guide rollers and a lower pair of guide rollers mounted on the legs for in use rolling engagement with the rail surfaces of their respectively associated channular beams in planes substantially perpendicular thereto, and a pair of canted guide rollers mounted on the legs elevationally intermediate the upper and lower guide rollers for in use rolling engagement with the rail surfaces and with the web surfaces of their respectively associated channular beams in planes angularly related to the perpendicular planes of the upper and lower guide rollers for corneringly transmitting loads from the carriage assembly to the channular beams. Preferably, a side thrust roller is mounted on each of the legs elevationally between the upper and canted guide rollers.

BACKGROUND OF THE INVENTION 
In the usual fork-type lift truck, the forks are raised by a vertically 
extensible lift mast arrangement located at the forward end of the truck. 
The forks are placed beneath a load, are initially raised a limited amount 
for transportation purposes, and are thereafter raised to a desired 
elevation for depositing the load on a stack, shelf or the like. Such a 
mast arrangement usually includes a rearwardly disposed support assembly 
having at least one pair of upright channular beams, a forwardly disposed 
carriage assembly mounted by a plurality of rollers for rolling engagement 
longitudinally within the beams, and a motor or lifting device to cause 
relative vertical dispacement therebetween. Exemplifying the prior art in 
this area are the following U.S. Pat. Nos.: 
2,759,562 issued to B. I. Ulinski on Aug. 21, 1956. 
3,213,967 issued to R. Hastings, Jr et al. on Oct. 26, 1965. 
3,556,247 issued to A. Shinoda et al. on Jan. 19, 1971. 
3,768,595 issued to W. H. Kelley, Jr. on Oct. 30, 1973. 
For the most part, the aforementioned lift mast constructions have 
experienced distortion of the channular beams due to the loading of the 
rollers under typically adverse circumstances and severe flaking of the 
beams by the rollers after extended service due to high contact stresses. 
A considerable portion of these problems is caused by offset loads on the 
forks which tends to cock or rotate the carriage assembly relative to the 
channular beams which guides it. To solve this, many arrangements of 
rollers have been adopted, including the addition of side thrust rollers 
which serve to transmit lateral forces and to relieve the longitudinally 
oriented rollers of this function. Upper and lower pairs of guide rollers, 
as well as another intermediately elevational spaced pair of guide rollers 
are being used with separate side thrust rollers disposed in various 
locations in the limited space often found in these lift masts. 
More recently, canted rollers have been commercially introduced on lift 
mast carriage arrangements whereby the upper rollers are canted to contact 
the inside corner angles adjacent the front rail surfaces and webs of the 
channular beams and the lower rollers are oppositely canted to contact the 
corner angles adjacent the rear surfaces of the channular beams. In this 
way it is possible to omit one or two pairs of side thrust rollers in 
certain lift masts. However, the roller engaging surfaces of the beams 
then experience a reduced wear life because the canted guide rollers do 
not transmit direct in-line forces. Moreover, the service life of the 
canted guide rollers is reduced over straight guide rollers because more 
side thrust is absorbed thereby. 
It is to be appreciated that it is difficult to accurately and positively 
adjust the position of the usual longitudinally oriented rollers and the 
position of the side thrust rollers in order to distribute the loads 
evenly and to stabilize the carriage assembly as it is positioned in the 
channular beams. Moreover, this adjustment problem becomes more complex 
when canted guide rollers are used, and the accurate shimming and 
manufacturing thereof is considerably more expensive to undertake. 
Still another major factor relates to the advantages associated with a six 
roller carriage assembly, wherein the carriage assembly can advantageously 
be elevated beyond that of a four roller assembly because the upper pair 
of rollers are allowed to travel upwardly beyond the extremities of the 
channular beams. This complicates the roller arrangement at the upper 
portion of the carriage assembly since both longitudinal and transverse 
guiding must still be retained. 
Another factor involves the tendency of certain side thrust roller 
arrangements to laterally spread the beams, so that it is further 
considered to be desirable to transmit offset loads on the carriage 
assembly solely into one of the beams. 
SUMMARY AND OBJECTS OF THE INVENTION 
Accordingly, an object of the invention is to provide an improved lift mast 
carriage mounting arrangement having a plurality of rollers thereon which 
are so positioned and arranged as to more effectively transfer both 
longitudinal and transverse forces on the carriage assembly into the 
guiding channular beams. 
Another object of the invention is to provide such a roller and carriage 
mounting arrangement which will better resist distortion of the channular 
beams by transferring offset loads on the carriage assembly to a single 
one of the beams. 
Another object of the invention is to provide a carriage mounting 
arrangement of the aforementioned type which will have a limited number of 
guide rollers and a minimum of close tolerance adjustment thereof. 
Another object of the invention is to extend the service life of the guide 
rollers. 
Another object of the invention is to minimize wear and/or flaking problems 
on the rolling surfaces of the channular beams. 
Another object of the invention is to provide a carriage mounting 
arrangement of the character set forth wherein an elevationally 
intermediate pair of rollers are so positioned and oriented on the 
carriage assembly as to favorably transfer longitudinal and transverse 
forces to the guiding channular beams when the carriage assembly is raised 
to extend the upper rollers beyond the channular beams. 
Other objects and advantages of the present invention will become more 
readily apparent upon reference to the accompanying drawings and the 
following description.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring initially to FIG. 1, a fork-type lift truck 10 is shown as having 
a body portion 12 mounted on driving and steerable wheels 14, and an 
operator's station 16 bounded by a protection canopy 18. A lift mast 
carriage mounting arrangement 20 constructed in accordance with the 
present invention is mounted on the front of the lift truck body portion, 
and is so arranged as to allow vertical lowering and raising of a pair of 
load-carrying forks 22. 
Basically, the lift mast carriage mounting arrangement 20 includes a front 
carriage assembly 24, a rearwardly disposed support assembly 26, and an 
extendable lifting apparatus 28 operationally connected therebetween. 
Preferably, the support assembly consists of two major components, namely, 
a rear stationary upright 30 which is appropriately secured to the body 
portion 12, and an inner upright 32 nested for vertical rolling movement 
within it. 
More specifically, and as best shown in FIGS. 1 and 3, the rear stationary 
upright 30 includes an upright pair of laterally inwardly facing C-shaped 
channels 34 which are integrally secured to a sturdy base 36, and at least 
one laterally connecting tie bar 38 secured to the channels at the upper 
ends thereof. The tie bar is positioned for maximum operator visibility 
and maintains the channels in parallel relation. In addition, a pair of 
longitudinally oriented guide rollers 40 are mounted on the laterally 
inner face of each of the channels at the upper extremity thereof. In this 
connection, the term "longitudinally oriented" and similar phrases 
hereinafter used relates to those elements which are arranged in planes 
parallel to an upright and centrally disposed longitudinal plane 39. 
With reference now to the construction of the inner upright 32 illustrated 
in FIGS. 1, 2 and 3, it is clearly seen to include an upright pair of 
inwardly facing J-shaped channular beams 41. These beams are preferably of 
hot rolled alloy steel to resist deflection, and which also provide good 
wear resistance. Each of these beams has a laterally inwardly disposed and 
longitudinally oriented roller-engaging web surface 42, and a front rail 
surface 43 and a rear rail surface 44 substantially normal thereto 
bordering the ends thereof and forming internal corners therewith. In 
order to provide a rigid frame-like inner upright structure, at least two 
vertically spaced apart and distortion resistant support bars 45 extend 
transversely between the rear portions of the beams. These support bars 
are also positioned for maximum visibility and maintain the beams in 
parallel. Moreover, a cantilevered arm 46 extends horizontally and 
forwardly at the top of the upper support bar for operational cooperation 
with the lifting apparatus 28, and at the lower extremity of each of the 
beams a longitudinally oriented guide roller 48 extends outwardly and 
longitudinally rearwardly to engage the C-shaped channels 34 of the 
stationary upright 30. While the lower guide rollers 48 are partially 
obscured by the upper rollers 40 in FIG. 3, it is nevertheless apparent 
that both sets cooperate to allow the inner upright to be moved vertically 
and closely laterally within the stationary channels in the usual manner. 
In accordance with the present invention, and as clearly illustrated in 
FIGS. 4 and 5, the carriage assembly 24 includes an upright pair of 
elongated legs 50 which are weldably secured in laterally spaced relation 
to a pair of vertically separated and transversely elongated steel back-up 
plates 52. The legs are also steel plates which are longitudinally 
oriented in the normal travel direction of the lift truck 10 and are 
disposed in symmetrical facing relation. Each of the legs has an upper pin 
bore 54, a central pin bore 56 and a lower pin bore 58 formed therein 
which are adapted to respectively receive a stepped pin 60, a stepped pin 
62 and a stepped pin 64. These pins are cylindrically stepped and extend 
laterally outwardly from the legs to serve as support mounts for an upper 
pair of guide rollers 66, an intermediate pair of canted guide rollers 68, 
and a lower pair of guide rollers 70, respectively. Preferably, the 
intermediate guide rollers are disposed above a horizontally oriented 
mid-plane 71 spaced elevationally equidistantly from the upper and lower 
pairs of guide rollers. 
In keeping with one of the principle features of the invention the upper 
guide rollers 66 and lower guide rollers 70 are longitudinally oriented, 
while the intermediate guide rollers 68 disposed substantially centrally 
between them are advantageously inclined. Particularly, the intermediate 
guide rollers are cantably oriented to rotate in a pair of symmetrically 
angularly related vertical planes 72 and 74 which diverge in the forward 
direction at an angle of 3.degree. to the normal longitudinal direction of 
vehicle travel as diagrammatically illustrated in FIG. 3 by the angle 
identified by the reference letter A. Thus, in certain modes of operation, 
to be hereinafter described, the canted guide rollers 68 serve to transfer 
side loads as well as longitudinal loads from the carriage assembly 24 
corneringly into the channular beams 41 of the inner upright 32. 
In order to further transfer side loads, however, the legs 50 of the 
carriage assembly 24 are each provided with a window 76 transversely 
therethrough and disposed elevationally closely below the upper carriage 
guide rollers 66. As best shown in FIG. 5, a pair of capscrews 78 are 
adapted to be screw threadably received in the laterally outwardly facing 
surface of each leg on either side of the windows for securing a 
longitudinally oriented and appropriately shimmed stepped mounting pin 80 
thereto. An upper side thrust roller 82 is rotatably mounted on each of 
these pins for selective engagement with the laterally inner web surfaces 
42 of the channular beams 41. 
In addition to the upper side thrust rollers 82, the carriage assembly 24 
includes a pair of lower side thrust rollers 84 which are mounted on 
longitudinally oriented pivot joints 86 secured in a rearwardly extending 
manner from the lower back-up plate 52. These lower side thrust rollers 
are adapted to bear perpendicularly against the front portion of the 
laterally outer sides of the beams 41. Moreover, a pair of laterally 
spaced chain anchor pin joints 88 are also secured to the rear of the 
lower back-up plate between the legs 50. 
In order to elevate the carriage assembly 24 and inner upright 32 to the 
desired position, the extendable lifting apparatus 28 is secured to the 
base 36 of the stationary upright 30 as may be visualized with reference 
to FIG. 3. As is also shown in FIGS. 1 and 2, the lifting apparatus 
includes a hydraulically actuated lift cylinder 90 with a vertically 
extemdable cross head 92 disposed on the upper extremity thereof. A pair 
of anti-friction bearing mounted chain rollers 94 are mounted on the 
opposite sides of the cross head and a pair of chains 96 are looped over 
them. The rearwardly disposed and depending ends of the chains, not shown, 
are suitably secured to the stationary upright in a conventional manner, 
while the forwardly disposed and opposite ends of the chains extend 
downwardly where they are secured to the carriage assembly 24 at the 
anchor pin joints 88. 
Thus, the initial extension of the lift cylinder 90 will cause the cross 
head 92 and the chain rollers 94 to be elevated to raise only the carriage 
assembly 24 including the lift forks 22 and load carried thereby above the 
ground. Since the stationary upright 30 and the inner upright 32 are not 
initially raised, the overall height of the lift truck 10 is maintained at 
an advantageously low value to enable it to go through doorways, for 
example. 
However, upon upward extension of the cross head 92 the "free lift" 
distance identified by the reference letter B in FIG. 1, it makes abutting 
contact with the cantilevered arm 46 and further raising thereof will 
result in upward travel of the inner upright 32 also. In the embodiment 
illustrated, the carriage assembly 25 is raised relatively more rapidly 
than the inner upright to thereafter allow a load carried by the forks 22 
to be deposited on a shelf, truck bed or the like. 
OPERATION 
While the construction and operation of the present invention is believed 
clearly apparent from the foregoing description, further amplification 
will subsequently be made in the following brief summary of the operation 
thereof. When the carriage upper guide rollers 66 and lower guide rollers 
70 are elevationally disposed within the channular beams 41 of the inner 
upright 32, and with the forks 22 carrying a load, they respectively make 
rolling engagement with the front rail surfaces 43 and rear rail surfaces 
44 of their associated channular beams in planes substantially 
perpendicular thereto as may be best visualized with reference to FIG. 3. 
Under these conditions the canted guide rollers 68 do not normally make 
rolling contact with the beams. This can also be appreciated by making 
reference to FIG. 2 and assuming that the upper guide rollers are 
elevationally lowered from the position shown to engage the beams, and 
that an offset load is acting on the forks which tends to rotate the 
carriage assembly 24 in a clockwise direction when viewing the drawing. In 
this circumstance, the lower right side thrust roller 84 transmits loads 
to the laterally outer side surface of the right beam 41. At the same time 
the upper right window side thrust roller 82 transmits loads to the 
laterally inner web surface 42 of the right beam. Thus, in accordance with 
one aspect of the invention, the clockwise-acting load results in a 
lateral resisting reaction on a single one of the channular beams so that 
spreading thereof is minimized. It is to be appreciated that the guide 
rollers 66 and 70 are desirably relieved from transmitting side loads 
under these conditions. 
Pursuant to the present invention, provision is made to fully utilize the 
load transferring and guiding function of the canted guide rollers 68 upon 
extending the forks 22 to a substantially fully raised condition. Such 
condition is illustrated in FIG. 2, wherein it is clear that the upper 
guide rollers 66 and the window side thrust rollers 82 are extended 
upwardly beyond the beams 41. While this desirably permits maximum 
elevation of the carriage assembly 24, it is clearly apparent that the 
canted guide rollers must subsequently assume the dual function of 
transferring longitudinal and lateral stabilizing loads at the top of the 
channular beams. Note is also made that the canted guide rollers extend to 
within an extremely limited distance "H" from the top of the beams. 
Specifically, if it is again assumed that a clockwise load is applied to 
the carriage assembly 24, a reaction is transmitted by the lower right 
side thrust roller 84 against the laterally outer surface of the right 
beam 41 when viewing FIG. 2. On the upper portion of the carriage assembly 
the lateral reaction is transmitted by the upper right canted guide roller 
68 corneringly against the web surface 42 of the right beam. Again, the 
side thrust reaction is desirably on only one of the beams, which tends to 
reduce distortion of the oppositely associated rolling surfaces. 
The canted guide rollers 68 also transmit longitudinal forces under the 
aforementioned FIG. 2 conditions by bearing corneringly against the front 
rail surfaces 43 of the beams 41, while the lower guide rollers 70 bear 
rearwardly and perpendicularly against the rear rail surfaces 44 of the 
beams. Advantageously, the canted guide rollers 68 exhibit a substantial 
vertical moment arm or spacing elevationally above the lower guide rollers 
since they are located above the mid-plane 71. This improves the transfer 
of forces upon the supporting beams and increases the service life of the 
mast carriage mounting arrangement 20. 
While the canted guide rollers 68 may be positioned just below the upper 
extremity of the beams 41 for maximum elevational extension of the 
carriage assembly 24, it is to be appreciated that upon initial lowering 
thereof the window side thrust rollers 82 will engage the beams to relieve 
any side thrust loading on the canted guide rollers. Moreover, upon 
further lowering of the upper guide rollers 66 into the beams, the canted 
guide rollers are substantially isolated from longitudinal loads as well. 
In view of the foregoing, it is readily apparent that the lift mast 
carriage mounting arrangement 20 of the present invention provides a 
carriage assembly with six guide rollers and four side thrust rollers 
thereon for selective optimum rolling engagement against the guiding 
channular beams. The intermediately disposed and canted guide rollers 68 
progressively assume the job of transferring longitudinal loads when the 
upper guide rollers 66 extend upwardly beyond the beams, and then the 
additional job of transferring lateral loads when the window side thrust 
rollers 82 extend beyond them. On the other hand, when the carriage 
assembly is not so extended, the upper guide rollers 66 and the lower 
guide rollers 70 do not have such a dual responsibility and so solely make 
perpendicular contact with the rail surfaces 43 and 44 of the beams. In 
the latter case the side thrust rollers 82 and the side thrust rollers 84 
also solely make lateral rolling contact with the beams to provide an 
extended service life thereof. Because these rollers transmit forces 
substantially only normal to their axes the bearing life thereof is 
effectively extended and the degree of beam flaking is substantially 
reduced. 
While the invention has been described and shown with particular reference 
to a preferred embodiment, it will be apparent that variations might be 
possible that would fall within the scope of the present invention, which 
is not intended to be limited except as defined in the following claims.