Anti-two block system

A new and improved anti-two block system adapted to be used with a crane for the prevention of damage to the boom tip of the boom of the crane by the travelling member wherein the two block system of the present invention includes an engaging mechanism movably mounted with the boom tip for engaging the travelling member when the travelling member moves into close proximity to the boom tip during lifting operations of the travelling member with the crane for the prevention of damage thereto.

TECHNICAL FIELD OF THE INVENTION 
The field of this invention relates to anti-two block systems for 
preventing damage to the boom tip of a crane should a travelling member be 
inadvertently drawn into the boom tip of the crane. 
PRIOR ART 
For lifting devices, such as all types of cranes, two blocking, as it is 
called, provides a very significant health and safety factor for those 
working about such lifting operations. Two blocking is the lifting by the 
lifting line of a travelling member up into the boom tip of a crane 
resulting in damage to the boom tip and sheaving mechanisms therewith, 
with attendant damage to the travelling member and/or the load. Such a two 
blocking situation typically occurs when the lifting line is hoisted too 
rapidly by an operator not paying proper attention to the proximity of the 
travelling member to the supporting member, such as the boom tip of a 
crane, resulting in the travelling member colliding with the boom tip 
structure. Not only is there a substantial risk that the lifting or 
hoisting line may snap due to such instantaneous high load situations 
resulting in a free falling load with the potential danger to those below, 
also the line, upon snapping, may whip into proximity of the operator 
resulting in substantial risk of injury thereto. 
Attempts to solve these problems have included those such as detailed in U. 
S. Pat. No. 4,067,447 wherein a hydraulically actuated sensing mechanism 
is used to sense the movement of the travelling member when in proximity 
to the boom tip with an attendant communication with a hoisting actuator 
mechanism such that sensing device effects movement of the hoisting lever 
of the crane. This movement caused by the travelling member engaging such 
a sensing device results in discontinuance of the lifting force exerted on 
the lifting line. U.S. Pat. No. 4,019,852 discloses the use of a 
protective plate rigidly affixed to the boom tip to prevent damage to the 
sheaves adjacent the boom tip. However, no maintenance free, strictly 
mechanical device is known that ensures an effective anti-two blocking 
system capable of preventing two blocking at substantially all boom angles 
of operation of the crane. 
SUMMARY OF THE INVENTION 
The present invention relates to a new and improved anti-two block system 
adapted to be used with a crane adjacent the boom tip thereof and 
including engaging members mounted with the boom tip for engaging the 
travelling member when the travelling member moves into close proximity to 
the boom tip during lifting operations of the travelling member with the 
crane.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the drawings, the letter B designates the anti-two block system of the 
present invention. The anti-two block system B is adapted to be used in 
any type of lifting device such as crane assembly C. Unless otherwise 
noted, the components of this invention are made of steel capable of 
taking heavy stresses and strains without failure, although other 
suitable, high-strength materials may be used if desired. 
As shown in FIG. 1, the crane assembly C, which may include a pedestal 
crane as shown or any other type of suitable crane, may preferably include 
a boom designated generally as 10 being movably affixed to the upper 
works, designated generally as 12, which is adapted to be disposed about a 
pedestal P. The pedestal P may be mounted with an offshore platform, 
permanently embedded in the ground, mounted with a movable vehicular frame 
or in any other way rigidly affixed to a supporting structure (not shown). 
The upper works 12 generally includes a platform 14 adapted to be disposed 
about the pedestal P. A revolving turntable R is in turn mounted for 
movement about the pedestal P. 
The upper works 12 provides an appropriate boom support 18 wherein the boom 
10 may be pivotally mounted therewith by means of pin joint 20. Preferably 
as shown in FIG. 1, the main hoist 22 and auxiliary hoist 24 are mounted 
with an appropriate shelter 25 mounted on platform 14. As discussed more 
fully hereinbelow preferably hoists 22, 24 are hydraulically actuated. The 
main hoist line 26 and auxiliary hoist line 28 extend from the main hoist 
22 and auxiliary hoist 24, respectively, up and into sheave 30 supported 
by boom tower 32 adjacent upper end 32d thereof. Hoist lines 26, 28 extend 
from the sheave 30 over idler sheave 34, preferably mounted with the 
shelter 25, from idler sheave 34 to idler sheave 36 which is preferably 
mounted with the platform 14 adjacent pin joint 20. From sheave 36, the 
hoist lines 26, 28 are located along the length and therethrough the 
central portion of the boom 10 to sheaves 38 and 40, respectively. 
As is known, the boom 10 may be made up of multiple sections such as boom 
sections 10a, 10b or any number of additional sections in addition thereto 
(not shown) that would be appropriate for the given job to be done. As 
shown in FIG. 1, boom section 10a is pivotally mounted with platform 14 
adjacent pin joint 20, with sections 10a, 10b being appropriately fastened 
together at the mid point of the boom 10. The sheaves 38, 40 are 
appropriately affixed to the boom adjacent the boom tip designated 
generally as 10c. Preferably, the boom tower 32 is appropriately affixed 
to the platform 14 of the upper works 12 with the boom tower 32 having 
appropriate support members 32a, 32b and appropriate bracing 32c 
therebetween to provide the necessary structural strength therefor. 
As noted hereinabove, the boom tower 32 supports sheave 30 adjacent the 
upper end 32d and also provides a support for the mechanism necessary for 
changing the boom angle of the boom 10 with respect to the platform 14 and 
pedestal P. A connector 42 pivotally affixes the boom tip 10c to an 
appropriate cable 44 which in turn has clevis 46 attached thereto. Clevis 
46 is pinned to housing 48 by pin 50, with the housing 48 having sheave 52 
mounted therein. Support arms 54 are pivotally mounted with the upper end 
32d of the boom tower 32 by pin 56, with the support arms 54 supporting 
sheave 58. Boom stop 60 is further mounted with the upper end 32d of the 
boom tower by pin 56 with end 60a adapted to engage sheave 52 upon 
vertical disposition of the boom 10. Boom stop 62 mounted with the shelter 
25 also provides a positive, fail-safe metal-to-metal type boom stop for 
limiting movement of the boom 10 to a vertical disposition. 
Elevation of the boom 10 is controlled by boom hoist 64, preferably mounted 
with shelter 25, with the boom hoist 64 having boom hoist line 66 
extending from hoist 64 to sheave 58 and thereafter threaded between 
sheaves 52 and 58. Withdrawal of boom hoist line 66 by boom hoist 64 
results in the boom being appropriately elevated while conversely, if the 
boom hoist 64 reels out boom hoist line 66, then boom 10 is appropriately 
lowered, changing the relative boom angle of the boom 10. 
Loads (not shown) are adapted to be picked up and moved about by the crane 
assembly C by travelling means T which includes the travelling block 68 
operatively connected to the main hoist line 26 or the ball-hook assembly 
70 operatively connected with the auxiliary hoist line 28. It will be 
appreciated that the routing of the main hoist line 26 and auxiliary hoist 
line 28 about sheave 36 and through the length of the boom 10, allows the 
boom 10 to be raised and/or lowered with a corresponding change in 
relative boom angle while the relative distance of the travelling members 
T, such as travelling block 68 and/or ball-hook assembly 70, from the boom 
tip 10c remains substantially constant, preventing two blocking of the 
travelling block 68 or ball-hook assembly 70 when the boom 10 is lowered. 
As is known, two blocking occurs when the travelling block 68 or ball-hook 
assembly 70 actually engages the boom tip 10c causing damage thereto, 
typically occurring while the boom 10 is being lowered. 
The platform 14 preferably provides adequate space for the heavy equipment 
necessary for crane operation. This includes as noted hereinabove, the 
various hoists such as hoists 22, 24, 64. Other equipment, for example, as 
an appropriate engine (not shown) may be mounted on platform 14 to provide 
motive power for a hydraulic pump (not shown) which may provide fluid 
power for the operation of hoists 22, 24, 64, which is preferred. The 
platform 14 provides an appropriate location for the controls necessary 
for the operator to manipulate and control the crane assembly C. 
Preferably, the controls may be located within the shelter 25 adjacent a 
location designated as 72. Still further, the platform 14 provides the 
support for equipment necessary for rotating the crane assembly C about 
the pedestal P. This, by way of example, may include power means such as a 
hydraulic motor (not shown) mounted with platform 14 for powering an 
appropriate bull gear 74, with the power of the bull gear 74 being 
transferred through power transfer means such as an appropriately sized 
chain 76, which in turn engages gears 78 which are permanently affixed 
with the pedestal P. Action of the power means causes movement of the 
platform 14 about the pedestal P. A bearing assembly (not shown) is 
adapted to be disposed between the revolving turntable R of the crane 
assembly C and the pedestal P, the specific structural details of which 
are the subject of our co-pending United States Patent application Ser. 
No. 892,018, filed Mar. 31, 1978. 
As noted hereinabove, sheaves 38, 40 are mounted with the bottom tip 10c of 
the boom 10 of the crane assembly C. Preferably, sheave 38 is of a 
multiple sheave assembly as shown in FIG. 3 and includes sheaves 38a, 38b, 
38c, 38d, 38e, 38f. Sheave assembly 38 is preferably mounted with the boom 
tip 10c by means of sheave carrier designated generally as 80 (FIGS. 3, 4, 
5). The sheave carrier 80 preferably includes a pair of axially aligned 
tubular members 80a, 80b that are mounted with boom sections 10s, 10t 
adjacent boom tip 10c and adapted to receive sheave axle 80c that is 
adapted to extend therebetween tubular members 80a, 80b, having sheave 
assembly 38 mounted therewith. Furthermore, supports 80d, 80e are 
preferably mounted with boom sections 10u, 10v for providing interior 
support for the sheave axle 80c and the anti-two block system B of the 
present invention as discussed more fully hereinbelow. Supports 80d, 80e 
are formed with appropriately formed openings 80f, 80g, respectively, and 
are capable of receiving the sheave axle 80c for appropriate rotational 
movement therein. The sheave axle 80c is adapted to support the sheave 
assembly 38 in addition to the anti-two block system B of the present 
invention. 
Generally speaking, the anti-two block system B includes engaging means F 
which may include a frame member F, abutting means A, guide member G and 
stop means S. The anti-two block system B includes engaging means E 
movably mounted with the boom tip 10c for engaging the travelling member T 
when the travelling member T moves into close proximity to the boom tip 
10c during lifting operations of the travelling member T with the crane C. 
As noted hereinabove, the travelling member T may include a travelling 
block 68 and a ball-hook assembly 70. The travelling block 68 includes 
side supports 68a, 68b which provide support for sheave axle 68c. Side 
supports 68a, 68b are rigidly affixed to base support 68d which preferably 
affixes the side supports 68a, a proper distance thereapart. The sheave 
axle 68c supports sheaves 68e, 68f, 38g. Base support 68d further mounts 
hook 68h therewith with the hook 68h adapted to receive and carry the load 
to be hoisted by a travelling member T in response to action of the crane 
assembly C. Preferably, the side supports 68a, 68b are formed with 
abutting means A of the present invention which includes abutting detents 
such as abutting detent 68a (FIG. 2) formed with the travelling member T 
for abutting the engaging means E when the travelling member T is moved 
into close proximity of the boom tip 10c to prevent damage thereto. 
The anti-two block system B includes a frame member F pivotally mounted 
with the sheave carrier 80 for unencumbered rotation about the sheave 
carrier 80 as the boom tip 10c moves during lifting operations. The frame 
member F, as shown in FIG. 3, includes a singular support member 82 having 
a suitably formed opening therein (not numbered) for receiving the sheave 
axle 80c therein to allow the support member 82 to rotate freely 
thereabout. Alternatively, the frame member F may include plural support 
members 84, 86 (FIG. 5), with each of such support members 84, 86 also 
having suitably formed openings therein to receive the sheave axle 80c for 
rotation of the frame member F about the sheave axle 80c of the sheave 
carrier 80. 
The engaging means E of the present invention is preferably mounted with 
the frame member F for engaging the travelling member T as necessary. The 
engaging means E may include engaging member 88 mounted with the lower end 
of the singular support member 82 or an engaging member 90 mounted with 
the lower ends of the support members 84, 86. Engaging members 88, 90 may 
be of any suitable configuration. For example, as shown in FIG. 2, the 
engaging member 88 is of a circular cross section; however, any suitable 
cross section of engaging means E may be used as is necessary. Preferably, 
the engaging members 88, 90 and the abutting means A are formed having 
compatible engaging surfaces such as the abutting detent 68i being 
compatible with the engaging member 88 as shown in FIG. 2. The engaging 
members 88, 90 must be of a sufficient length such that the abutting means 
A with both side supports 68a, 68b of the travelling block 68 may come 
into contact with the engaging member 88 with frame member F. Thus, the 
engaging members 88, 90 are mounted with the frame member F for engaging 
the travelling member T adjacent the abutting means A which is formed with 
the travelling member T for abutting the engaging members 88, 90 when the 
travelling member T is moved into close proximity of the boom tip 10c. 
Since the frame member F is pivotally mounted on the sheave axle 80c of the 
sheave carrier 80, the frame member F is adapted to pivot about an arc 
designated generally as 92 as the boom 10 of the crane assembly C is 
raised and lowered during lifting operations. Similarly, the travelling 
member T is adapted to pivot about an arc described generally as 94 as the 
boom tip 10c of the boom 10 is raised and lowered during lifting 
operations. Because the frame member F and travelling member T rotate 
about the same axis, namely the sheave axle 80c of the sheave carrier 80, 
irrespective of the boom angle with respect to the ground, the frame 
member F having the engaging means E therewith will be aligned with the 
abutting means A with the travelling member T. Accordingly, during lifting 
operations, should the travelling member T be inadvertently lifted to the 
point where the travelling member T actually engages the engaging means E 
of the anti-two block system B of the present invention, the travelling 
member T will be prevented from doing actual damage to the boom tip 10c of 
the pedestal crane assembly C. 
As noted hereinabove, the main hoist line 26 is preferably hydraulically 
actuated by main hoist 22 such that when the abutting means A engages the 
engaging means E, an increase in hydraulic pressure will be registered 
adjacent the upper works 12 of the crane assembly C. An appropriate 
pressure relief valve (not shown) incorporated into the hydraulic system, 
will prevent undue stretching and possible snapping of the main hoist line 
26 and also act as an indicator of engagement between the engaging means E 
and abutting means A. Thus, the frame member F having the engaging means E 
therewith and the travelling member T both pivot about the sheave carrier 
80 such that the frame member F and travelling member T are at 
substantially the same angle with respect to the boom 10 during lifting 
operations. 
The anti-two block system B of the present invention may also be 
incorporated with the ball-hook assembly designated generally as 70. The 
ball-hook assembly 70 includes a typically weighted ball 70a having 
appropriate hook 70b attached therewith, with the hook 70b being adapted 
for lifting loads by the crane assembly C. Preferably, a collar 70c is 
mounted with the ball 70a in a position opposed to that of the hook 70b. 
Abutting means A is mounted with the collar 70c and includes an arcuate 
abutting member 70d fixed with collar 70c as discussed more fully 
hereinbelow. 
The guide member G includes a guide member generally designated as 96 and 
is preferably mounted with the crane assembly C adjacent boom tip 10c of 
the boom 10. The guide member G includes preferably at least two 
substantially parallel guide plates 96a, 96b mounted with guide support 
plate 96c which in turn is mounted with the boom tip 10c of the crane 
assembly C. Preferably, the guide plates 96a, 96b are formed having 
engaging surfaces 96d, 96e, respectively, at least a portion of which are 
circular. A sheave carrier 98 is supported by the guide plates 96a, 96b 
and is adapted to receive sheave 40 between such guide plates 96a, 96b for 
support by the sheave carrier 98. 
Stop means S is preferably mounted with and between the guide plates 96a, 
96b of the guide member 96 and with the travelling member T for preventing 
the travelling member T from damaging the boom tip 10c of the crane 
assembly C as necessary. The stop means S includes a stop bar 100 mounted 
with the guide member 96 between guide plates 96a, 96b in a substantially 
parallel relation to the sheave carrier 98. The stop means S further 
includes a portion 28a of the auxiliary hoist line 28 that may be adjacent 
the stop bar 100. When lifting a load with the ball-hook assembly 70 
during raising and/or lowering operations of the crane assembly C, should 
the ball-hook assembly 70 come into close proximity with the guide member 
G, the abutting means A including arcuate abutting member 70d may contact 
the correspondingly formed exterior engaging surfaces 96d, 96e of the 
guide members 96, while the auxiliary hoist line 28 causes the ball-hook 
assembly 70 to be drawn about the guide member G as it is retracted. The 
ball-hook assembly 70 may swing about the guide member G for substantially 
a maximum of 180.degree. until such time that the portion 28a of the 
auxiliary hoist line 28 engages stop means S when the abutting means A 
including the arcuate abutting member 70d engages engaging surfaces 96d, 
96e of the guide member 96 adjacent to the stop bar 100. 
Thus, the ball-hook assembly 70 comes to rest in the position best seen in 
FIG. 2. Due to the engagement between the travelling member T and the 
guide member G, the hoist line 28 experiences a stretching or tensioning 
force, which is transmitted by the hoist line 28 to the auxiliary hoist 
24. As a consequence, the auxiliary hoist 24 stalls when the maximum hoist 
line tension is reached, with the point at which stalling occurs being 
regulated by a pressure relief valve having an appropriate relief valve 
setting. Thus, the portion 28a of the auxiliary hoisting line 28 engages 
the stop bar 100 when the arcuate abutting member 70d engages the circular 
engaging surfaces 96d, 96e of the guide member 96 of the guide member G 
adjacent the stop bar 100 of the stop means S to protect the boom tip 10c, 
as necessary. The substantially circular engaging surfaces 96d, 96e act to 
guide the arcuate abutting member 70d of the ball-hook assembly 70 about 
the guide member G to allow the auxiliary hoist line 28 of the crane 
assembly C to engage the stop bar 100 to protect the boom tip 10c of the 
crane assembly C. Furthermore, during operations of the crane assembly C 
wherein the ball-hook assembly 70 is not needed, the ball-hook assembly 70 
may be parked in the position substantially as shown in FIG. 2 to 
effectuate and prevent the interference of the ball-hook assembly 70 of 
the travelling member T with that of the travelling block 68 of the 
travelling member T. In its parked position, the ball-hook assembly 70 
cannot interfere with operation of the travelling block 68 and eliminates 
the risk of entanglement of the auxiliary hoist line 28 with that of the 
main hoist line 26. 
Therefore, the anti-two block system B of the present invention provides a 
new and useful mechanism for preventing two blocking of travelling members 
T adjacent the boom tip 10c of a crane assembly C. Furthermore, the 
anti-two block system B of the present invention is effective at all boom 
angles because the system is capable of pivoting and/or rotating as the 
boom 10 of the crane assembly C is either raised and/or lowered during 
lifting operations and at worst, results in the travelling members T 
standing off from the boom tip 10c for the prevention of damage thereto. 
The foregoing disclosure and description of the invention are illustrative 
and explanatory thereof, and various changes in the size, shape and 
materials as well as in the details of the illustrated construction may be 
made without departing from the spirit of the invention.