Revolving block for high place working vehicle

A revolving block having an inclination correcting mechanism housed therein is adapted to revolvably support a working implement, such as a ladder or boom, mounted on a high place working vehicle.

BACKGROUND OF THE INVENTION 
This invention relates to a revolving block for use in a high place working 
vehicle such as a ladder truck. 
RELATED ART 
In a high place working vehicle, such as a ladder truck, in order to secure 
safety of operation where the vehicle is placed on the inclined ground, it 
is necessary that the inclination of the working implement such as a 
ladder tiltably supported on the revolving block, which inclination is due 
to the inclination of the vehicle, be corrected somehow so as to allow 
said working implement to be angularly raised and lowered in a vertical 
plane. 
As for the method of correcting the inclination so that the raising and 
lowering operation of the ladder on the revolving block may be effected in 
a vertical plane, it is known to provide an attitude correcting device 
adapted to ensure that the ladder is always in a vertical plane, or to 
utilize the outrigger to make the vehicle horizontal. 
The aforesaid two conventional method have problems; in the former method 
using an attitude correcting device, since the revolving block remains 
inclined while the inclination of the ladder is corrected, it is necessary 
that each time the position of revolution changes, a correcting operation 
be made, a fact which is irrational and which, moreover, means that the 
attitude correcting device must be built in the vehicle body tilting 
device, thus complicating the mechanism. 
In the latter method utilizing the outrigger, the vehicle wheels must be 
separated from the ground in order to make the vehicle body horizontal and 
the outrigger must have a particularly great support capability and a 
sufficient vehicle body raising stroke. Further, from the standpoint of 
safety of operation when the wheels are lifted in the air, the attaching 
position of the outrigger is limited, imposing restrictions on the design 
of the vehicle body. 
The aforesaid inclination correcting operation would be complicated if it 
is to be effected manually, such manual operation being inconvenient 
particularly where the high place operation is emergent as in fire 
extinguishment. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a revolving block which is 
free from the problems in the aforesaid conventional inclination 
correcting methods. 
Another object of the invention is to provide a revolving block adapted for 
automatic correction of inclination. 
A revolving block for a high place working vehicle according to an 
embodiment of the invention comprises a first wheel fixed on the body of 
the high place working vehicle at the center of revolution of the vehicle, 
a second wheel supported for rotation by said first wheel through a first 
rolling contact bearing, a third wheel supported for rotation by said 
second wheel through a second rolling contact bearing having an axis 
obliquely crossing the axis of said first rolling contact bearing, a 
fourth wheel supported for rotation by said third wheel through a third 
rolling contact bearing which has an axis obliquely crossing the axis of 
said second rolling contact bearing and which is positioned parallel to 
the first rolling contact bearing when not in inclination correcting 
action, a turntable fixed on said fourth wheel, a device for preventing 
said turntable from rotating relative to the vehicle body, a first fixing 
device for fixing said first and second wheels to prevent their relative 
rotation, a second fixing device for fixing said second and third wheels 
to prevent their relative rotation, a first driving device for causing 
relative rotation between said first and second wheels, and a second 
driving device for causing relative rotation between said turntable and 
said third wheel. 
A revolving block for a high place working vehicle according to another 
embodiment of the invention comprises a first wheel fixed on the body of 
the high place working vehicle at the center of revolution of the vehicle, 
a second wheel supported for rotation by said first wheel through a first 
rolling contact bearing, a third wheel supported for rotation by said 
second wheel through a second rolling contact bearing having an axis 
obliquely crossing the axis of said first rolling contact bearing, a 
fourth wheel supported for rotation by said third wheel through a third 
rolling contact bearing which has an axis obliquely crossing the axis of 
said second rolling contact bearing and which is positioned parallel to 
the first rolling contact bearing when not in inclination correcting 
action, a turntable fixed on said fourth wheel, a device for preventing 
the turntable from rotating relative to the vehicle body, a first fixing 
device for fixing said first and second wheels to prevent their relative 
rotation, a second fixing device for fixing said second and third wheels 
to prevent their relative rotation, a rotative drive motor for causing 
relative rotation between said third and fourth wheels, first rotative 
angle detecting means for detecting the angle of rotation of the second 
wheel, second rotative angle detecting means for detecting the angle of 
rotation of the third wheel, inclination detecting means for detecting the 
angle and direction of inclination of the turntable, present rotative 
angle position signal generating means for generating present rotative 
position signals for the second and third wheels on the basis of the 
rotative angles detected by the first and second rotative angle detecting 
means, target rotative position signal generating means for generating 
target rotative position signals for the second and third wheels for 
making the turntable horizontal on the basis of the angle and direction of 
inclination of the turntable detected by the inclination detecting means, 
control means which compares the present rotative position signals for 
said second and third wheels with said target rotative position signals to 
generate fixing and releasing signals for the first and second fixing 
devices and rotative drive signals for the second and third wheels, first 
fixing device drivind means for driving the first fixing device in 
response to fixing and releasing signals for the first fixing device, 
second fixing device driving means for driving the second fixing device in 
response to fixing and releasing signals for the second fixing device, and 
rotative drive motor driving means for operating the rotative drive motor 
in response to rotative drive signals. 
According to the invention, in the case where high place working vehicle is 
stopped on an inclined ground, the turntable having a working implement 
such as a ladder attached thereto can be corrected horizontal without 
having to correct the vehicle horizontal by means of the outrigger. 
Further, in the apparatus of the present invention, since the turntable 
itself is corrected horizontal, it is possible to eliminate the 
inconvenience of having to make a positional correction each time the 
direction of the ladder or other working implement is changed as in the 
case where an attitude correcting device is attached to the device of 
raising and lowering the working implement on the turntable.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1 showing a high place working vehicle on which a 
revolving block 2 according to the present invention is mounted, the 
revolving block 2 is installed on the rear portion of a vehicle body 1. A 
ladder 4 pivotally mounted at its base on the revolving block 2 through a 
support frame 3 is adapted to be angularly raised and lowered by a 
piston-cylinder mechanism 5. The numeral 6 denotes outriggers, and 7 
denotes a ladder support. 
The construction of the revolving block 2 is as shown in FIG. 2A. In this 
figure, the numeral 8 denotes a first wheel attached to the vehicle body 1 
by bolts 9; 10 denotes a second wheel supported for rotation by the first 
wheel 8 through a first rolling contact bearing 11; 12 denotes a third 
wheel supported for rotation by the second wheel 10 through a second 
rolling contact bearing having an axis b obliquely crossing the axis a of 
said first rolling contact bearing 11; 14 denotes a fourth wheel supported 
for rotation by the third wheel through a third rolling contact bearing 15 
which has an axis c obliquely crossing the axis b of said second rolling 
contact bearing 13 and which is positioned parallel to the first rolling 
contact bearing 11 when not in inclination correcting condition; 16 
denotes a turntable attached to the fourth wheel 14 by attaching bolts 9; 
and the numeral 17 denotes a rotation preventing device for preventing the 
turntable from rotating relative to the vehicle body 1, said device 17 
including a pin 19 extending through a sleeve 18 extending integrally from 
the lower surface of the turntable 16, the lower end portion of said pin 
19 projecting beyond the sleeve 18 being loosely fitted in an elongated 
opening 20 formed in the vehicle body 1 (FIG. 3). The numeral 21 denotes a 
first fixing device for fixing the first and second wheels 8 and 10 
together, including a fixing bolt 22 threadedly inserted in the first 
wheel 8 for advance and retraction relative to the axis a of the first 
rolling contact bearing 11, the front end of said fixing bolt 22 pressing 
a friction plate or lining 23 against the outer peripheral surface of the 
second wheel 10 to thereby fix the first and second wheels. The numeral 24 
denotes a second fixing device for fixing the second and third wheels 10 
and 12 together, including a fixing bolt 25 threadedly inserted in the 
third wheel 13 for advance and retraction relative to the axis b of the 
second rolling contact bearing 13, the front end of said fixing bolt 25 
pressing a friction plate or lining 26 against the outer peripheral 
surface of the second rolling contact bearing 12 to thereby fix the second 
and third wheels. The numeral 27 denotes a driving device installed on the 
vehicle body 1, wherein a small gear 31 connected to a handle 28 through a 
gear box 29 and fixed on the upper end of a rotary shaft 30 extending 
upward through the vehicle body 1 meshes with a large gear 32 formed 
integrally on the lower end portion of the inner peripheral surface of the 
second wheel 10. The numeral 33 denotes a driving device installed on the 
turntable 16, wherein a small gear 37 connected to a handle 34 through a 
gear box 35 and fixed on the lower end of a rotary shaft 36 extending 
downward through the turntable 16 meshes with a large gear 38 formed 
integrally on the upper end portion of the outer peripheral surface of the 
third wheel 14. 
The inclination correcting operation of the revolving block 2 will now be 
described by taking, as an example, a case where the vehicle body 1 is 
placed on a ground which is lower at left as shown in FIGS. 1 and 2A. 
First, in the state of FIG. 2A, the operator loosens the fixing bolts 22 
and 25 of the first and second fixing devices 21 and 24, respectively, 
thereby canceling the fixation between the first and second wheels 8 and 
10 and between the second and third wheels 10 and 12. Subsequently, he 
rotates the handle 28 of the first driving device 27 to rotate the rotary 
shaft 30, thereby turning the second wheel 10 through the aid of the 
meshing between the small and large gears 31 and 32. Thus, the second 
wheel 10 is turned relative to the vehicle body 1 and turntable 16, so 
that the direction of inclination of the second rolling contact bearing 13 
changes to the one shown in FIG. 2B. In this state, the operator tightens 
the first fixing bolt 22 of the first fixing device 21 so as to fix the 
second wheel 10 to the first wheel 8. Subsequently, he turns the handle 34 
of the second driving device 33 to rotate the rotary shaft 36 so as to 
turn only the third wheel 12 through the aid of the meshing between the 
small and large gears 37 and 38. Then, since the third wheel 13 is 
supported by the second wheel 10 through the second rolling contact 
bearing 13 which is inclined, the left or lower sides of the fourth wheel 
14 and turntable 16 are raised. This operation is continued until the 
turntable 16 becomes horizontal, and when the inclination of the turntable 
16 is corrected horizontal as shown in FIG. 2B, the operator tightens the 
fixing bolt 25 of the second fixing device 24, thereby fixing the third 
wheel 12 to the second wheel 10. In this state, he extracts the pin 19 of 
the rotation preventing device 17 so as to cancel the prevention of 
rotation of the turntable 16. Thus, by turning the handle 34 of the second 
driving device 33, the turntable 16 can be revolved in a horizontal plane 
through the aid of the meshing between the small and large gears 37 and 
38. 
In the above desoription of the operation, the first driving device 27 is 
first used to turn the second wheel 10 and then the second driving device 
33 is used to rotate the turntable 16. However, which of the second and 
third wheels 10 and 12 is to be turned first may be arbitrarily decided. 
It is also possible to use the first driving device 27 to turn the second 
and third wheels 10 and 12 while using the second driving device 33 
exclusively for turning the turntable 16. In addition, if the third wheel 
12 is to be turned earlier than the second wheel 10, a third fixing device 
(not shown) for fixing the third wheel 12 to the fourth wheel 14 or to the 
turntable 16 will be required to ensure that the third wheel 12 once 
positioned will not move when the second wheel 10 is turned. This third 
fixing device may be constructed in the same way as the first or second 
fixing device 21 or 24. Alternatively, a worm gear or the like may be used 
as the power transmission mechanism for transmitting power from the second 
driving device 33 to the third wheel 12, or said power transmission 
mechanism may be provided with a locking mechanism to make it impossible 
to operate the second driving device 33 from the side associated with the 
third wheel 12, so that the power transmission mechanism itself will serve 
as said third fixing device. Further, as in the aforesaid power 
transmission mechanism for the first driving device 33, the power 
transmission mechanism for the first driving device 27 may be arranged to 
have the capability of fixing the second wheel 10 so as to serve as the 
first fixing device. In this case, the first fixing device 21 shown would 
be unnecessary. 
Referring to FIG. 4A showing an embodiment adapted for automatic correction 
of inclination, the numeral 39 denotes a first wheel fixed on a vehicle 
body 1; 40 denotes a second wheel supported by the first wheel 39 through 
a first rolling contact bearing 41; 42 denotes a third wheel supported for 
rotation by the second wheel 40 through a second rolling contact bearing 
43 having an axis b obliquely crossing the axis a of the first rolling 
contact bearing 41; 44 denotes a fourth wheel supported for rotation by 
the third wheel 42 through a third rolling contact bearing 45 which has an 
axis c obliquely crossing the axis b of the second rolling contact bearing 
43 and which is positioned parallel to the first rolling contact bearing 
41 when not in inclination correcting action; 46 denotes a turntable fixed 
on the fourth wheel 45; 47 denotes a device for preventing rotation of the 
turntable 46, including a pin 47a inserted in a sleeve 46a extending 
downward from the turntable 46, the lower end of said pin being inserted 
in an elongated opening 1a formed in the vehicle body 1 when in 
inclination correcting action; and the numeral 48 denotes a rotative drive 
motor installed on the turntable 46, with its output shaft 49 extending 
downward through the turntable 46 and having fixed thereon at the lower 
end a small gear 50 meshing with a large gear 51 formed integrally on the 
outer peripheral surface of the third wheel 42. The numeral 52 denotes a 
first fixing device for fixing the first and second wheels 39 and 40 
together, including a first solenoid 53 attached to a portion of the outer 
peripheral surface of the first wheel 39 and having an actuating rod 54 
adapted to press a first friction plate 55 against the outer periphery of 
the second wheel 2 to thereby fix the first and second wheels together. 
The numeral 56 denotes a second fixing device for fixing the second and 
third wheels 40 and 42 together, including a second solenoid 57 attached 
to a portion of the outer peripheral surface of the third wheel 42 and 
having an actuating rod 58 adapted to press a friction plate 59 against 
the outer periphery of the second wheel 40 to thereby fix the second and 
third wheels together. The numeral 60 denotes a first rotative angle 
detecting means for detecting the rotative angle of the second wheel 40, 
having a magnetic sensor 63 fixed to the first wheel 39 through an 
attaching bracket 61. The magnetic sensor 63 is positioned in opposed 
relation to projections 62 equispaced around the outer peripheral surface 
of the second wheel 40, said sensor being adapted to detect a change in 
magnetic resistance due to the presence or absence of a projection so as 
to detect the angle of rotation of the second wheel 40 relative to the 
first wheel 39. The numeral 64 denotes a second rotative angle detecting 
means for detecting the rotative angle of the third wheel 42, having a 
magnetic sensor 67 fixed to the second wheel 40 through an attaching 
bracket 65. The magnetic sensor 67 is positioned in opposed relation to 
projections 66 equispaced around the outer peripheral surface of the third 
wheel 42, said sensor being adapted to detect a change in magnetic 
resistance due to the presence or absence of a projection so as to detect 
the angle of rotation of the third wheel relative to the second wheel 40. 
The numeral 68 denotes inclination detecting means fixed to the turntable 
46, including a magnetic resistance type potentiometer using a magnetic 
resistance effect element for detecting the position of a suspended 
permanent magnet. The numeral 69 denotes a control circuit comprising 
present rotative position signal generating means 70 which counts the 
outputs from the first and second rotative angle detecting means 60 and 64 
to successively generate present rotative position signals for the second 
and third wheels, target rotative position signal generating means 71 
which receives signals from the inclination detecting means 68 and 
generates target rotative position signals for the second and third wheels 
40 and 42 so as to make the turntable 46 horizontal, control means 72 
which compares present rotative position signals from the second and third 
wheels with said target rotative position signals to generate fixing and 
releasing signals to the first and second fixing devices 52 and 56 and 
rotative drive signals to the second and third wheels, first fixing device 
driving means 73 which amplifies fixing and releasing signals to the first 
fixing device 52 and delivers the same, second fixing device driving means 
74 which amplifies fixing and releasing signals to the second fixing 
device 56 and delivers the same, and rotative drive motor driving means 75 
which amplifies rotative drive signals to the rotative drive motor 40 and 
delivers the same. 
The control circuit 69 is composed, for example, of a known microcomputer 
as shown in FIG. 5. In this figure, the numeral 70 denotes a CPU; 71 
denotes a RAM; 72 denotes a ROM; 73 and 74 denote first and second A/D 
converters for converting X-direction and Y-direction analog outputs from 
the inclination detecting means 68 into digital values, respectively; 75 
denotes an input port for receiving outputs from said first and second A/D 
converters 73 and 74 and outputs from said first and second rotative angle 
detecting means 60 and 64; 76 and 77 denote first and second amplifying 
circuits for driving the first and second fixing devices 52 and 56, 
respectively; 78 denotes a third amplifying circuit for driving the 
rotative drive motor 48; and the numeral 79 denotes an output port for 
delivering fixing and releasing signals and rotative drive signals to the 
first through third amplifying circuits 76, 77 and 78. 
A series of inclination correcting operations of the apparatus of the 
aforesaid arrangement will now be described. 
As shown in the flowchart of FIG. 6, an X-direction inclination signal from 
the inclination detecting means 68 is read into the target rotative 
position signal generating means 71 (step (1)). Similarly, a Y-direction 
inclination signal is read (step (2)). These two input signals are 
referred to target rotative position tables 69a and 69b for the second and 
third wheels, respectively, and on the basis of a combination of the 
X-direction and Y-direction inclinations, the target rotative positions 
for the second and third wheels 40 and 42 to be positioned to eliminate 
these inclinations are decided (step (3)). The target rotative position 
signal generating means 44 delivers target rotative position signals for 
the second and third wheels 40 and 42, respectively, (step (4)). Then, as 
shown in the flowchart of FIG. 7, inputted into the control means 72 are 
target rotative position signals for the second and third wheels, which 
are the outputs from the target rotative position signal generating means 
71 (step (5)). Then, the present rotative position signal for the second 
wheel 40 from the present rotative position signal generating means 70 is 
inputted into the control means 72 (step (6)). 
If the target rotative position is to the left of the present rotative 
position, the procedure goes to step (8); if it is to the right, the 
procedure goes to step (8'); and if it is equal thereto, the procedure 
goes to step (10). Suppose that the target rotative position is to the 
left of the present rotative position, when the first fixing device 52 
receives a releasing signal through the first fixing device driving means 
73 (step (8)). At this time, the fixing device 56 is maintained in its 
fixing state. Thus, the second and third wheels 40 and 42 are in the 
interconnected state ready to turn relative to the first wheel 39. In 
addition, at this time, the turntable 46 fixed to the fourth wheel 44 is 
fixed by the rotation preventing device 47. At this stage, an instruction 
for clockwise rotation is sent to the rotative drive motor 48 through the 
rotative drive motor driving means 75 (step (9)). The rotation of the 
rotative drive motor 48 is transmitted to the small gear 50 attached to 
the output shaft 49 to turn the third and second wheels 43 and 40 in a 
unit counter-clockwise through the aid of the meshing between the small 
gear 50 and the large gear 51 formed on the outer peripheral surface of 
the third wheel 43, with the procedure goes back to step (5). 
Then, in the same manner as described above, the target rotative position 
for the second wheel 2 is compared with the present rotative position, and 
if it is found to the left, the steps (6), (7), (8) and (9) will be 
repeated so log as it is to the left. By and by the target rotative 
position of the second wheel 40 comes to coincide with the present 
rotative position thereof, whereupon a stoppage output is sent to the 
rotative drive motor 48 through the rotative drive motor driving means 75 
(step (10)) to stop its rotation. Thereafter, a fixing output is sent to 
the first fixing device 52 through the first fixing device driving means 
73 (step (11)) to fixedly connect the first and second wheels 39 and 40. 
In the case where the target rotative position of the second wheel 40 is to 
the right of the present rotative position thereof, the only difference is 
that the direction of rotation is opposite; with the same operation as 
that described above, the steps (6), (7), (8') and (9') are repeated until 
the target rotative position of the second wheel is equal to the present 
rotative position thereof, whereupon the procedure goes to steps (10) and 
(11). 
Then, the target rotative position of the third wheel 42 is inputted into 
the control means 72 from the present rotative position signal generating 
means 70 (step (12)). The target rotative position of the third wheel 42 
is compared with its present rotative position (step 13)), and if it is to 
the left of the latter, the procedure goes to step (14); if it is to the 
right, the procedure goes to step (14'); and if it is equal to the present 
rotative position, the procedure goes to step (14). Suppose that the 
target rotative position is to the left of the present rotative position, 
then a releasing output is sent to the second fixing device 56 through the 
second fixing device driving means 74 (step (14)). At this time, the first 
fixing device 52 is maintained in its fixing state. Thus, only the third 
wheel 42 is ready to turn relative to the second wheel 40 fixedly 
connected to the first wheel 39. In this case, the turntable 46 having the 
fourth wheel 44 fixed thereto has been fixed by the rotation preventing 
device 47. Then, a clockwise rotation output is sent to the rotative drive 
motor 48 through the rotative drive motor driving means 75, the rotation 
of the rotative drive motor 48 being transmitted to the small gear 50 
attached to the output shaft 49, so that the third wheel 42 is turned 
clockwise through the aid of the meshing between the small gear 50 and the 
large gear 51 formed on the outer peripheral surface of the third wheel 
42, the procedure going back to step (12). Thereafter, a comparison is 
made between the target rotative position of the third wheel 42 and its 
present rotative position in the same manner as described above, and steps 
(12), (13), (14) and (15) are repeated so long as it is to the left. By 
and by the target rotative position as eaqual to the present rotative 
position, whereupon a stoppage output is sent to the rotative drive motor 
48 through the rotative drive motor driving means 75 (step (16)) to stop 
the rotation. Thereafter, a fixing output is sent to the second fixing 
device 56 through the second fixing device driving means 74 (step (17)) so 
as to fixedly connect the second and third wheels 40 and 42. 
If the target rotative position of the third wheel 42 is to the right of 
its present rotative position, the only difference is that the direction 
of rotation is opposite; thus, with the same operation as described above, 
the steps (12), (13), (14') and (15') are repeated until the target 
rotative position of the third wheel 42 is equal to its present rotative 
position, whereupon the procedure goes to steps (16) and (17). 
As a result of the aforesaid operation, the turntable 46 is corrected 
horizontal with the second and third wheels 40 and 42 overlapping each 
other to form an angle of inclination of predetermined direction and 
predetermined size relative to the vehicle body 1. 
The above description refers to an embodiment wherein the second wheel 40 
is first positioned and fixed at the target rotative position and then the 
third wheel 42 is positioned and fixed at the target rotative position. 
However, this order may be reversed. 
In the reverse case, the target rotative position of the third wheel 42, 
which is to be positioned and fixed first, will be deviated by an amount 
corresponding to the target rotative position of the second wheel 42 from 
that rotative position of the first wheel 39 which is found when the third 
wheel 42 has been finally positioned and fixed. 
Thereafter, the rotation preventing device 47 which has fixed the turntable 
45 and vehicle body 1 with respect to the direction of rotation thereof is 
released, and the rotative drive motor 48 is rotated to turn the fourth 
wheel 44 relative to the vehicle body 1 and the first, second and third 
wheels 39, 40 and 42 which have been fixedly connected together by the 
first and second fixing devices 52 and 56, thereby revolving the turntable 
46, whose inclination has been corrected, so as to direct the ladder 4 or 
other working implement in any desired direction. 
A modification of the embodiment whown in FIG. 4A will now be described. In 
this modification, two rotative drive motore are provide, one on the side 
associated with the turntable and the other on the side associated with 
the vehicle body, to separately effect the revolution of the turntable 46 
and the rotation of the second and third wheels 40 and 42. Thus, as shown 
in FIG. 8A, a first rotative drive motor 100 is attached to the vehicle 
body 1, with its output shaft 101 extending through the vehicle body 1 and 
having attached thereto at the front end a small gear 102 meshing with a 
large gear 103 formed on the inner peripheral surface of the second wheel 
40, while a second rotative drive motor 104 is attached to the turntable 
45, with its output shaft 105 extending through the turntable 46 and 
having attached thereto at the front end a small gear 106 meshing with a 
large gear 51 formed on the outer peripheral surface of the third wheel 
42. Further, as a result of the provision of an increased number of 
additional rotative drive motors, first and second rotative drive motor 
driving means 107 and 108 are provided in the control circuit 69' as drive 
means for driving said first and second rotative drive motors 100 and 104 
in response to signals from the control means 72. Further, in FIG. 9 
showing a concrete example of the arrangements of the control circuit 69' 
in the second embodiment, there are provided third and fourth amplifying 
circuits 109 and 110 for driving the first and second rotative drive 
motors 100 and 104. The only difference from the arrangement of the 
embodiment shown in FIG. 4A is the addition of the first rotative drive 
motor 100 and its accessories, the other components being the same. Thus, 
in FIGS. 8A, 8B and 9, the same components are marked with the same 
reference characters as those used in FIGS. 4A, 4B and 5 and a description 
thereof is omitted. 
The inclination correcting operation in this modification is performed in 
the same manner as previously described using the flowcharts of FIGS. 6 
and 7. In this case, the turning of the second wheel 40 is effected by the 
first rotative drive motor 100 attached to the side associated with the 
vehicle, and the turning of the third wheel 42 is effected by the rotative 
drive motor 104 attached to the side associated with the turntable. As 
shown in FIG. 8B, the turntable is corrected horizontal. 
Thereafter, the second rotative drive motor 104 is used to revolve the 
turntable 46 to direct the ladder or other working implement in any 
desired direction. 
In addition, the order in which the second and third wheels 40 and 42 are 
rotated for correction of inclination is arbitrary. For example, the 
rotative positioning of the third wheel 42 may be effected first by the 
first rotative drive motor 100 attached to the side associated with the 
vehicle body and then the rotative positioning of the second wheel 40 by 
the first rotative drive motor 100. In the case where the rotative 
positioning of the third wheel 42 is effected first, a third fixing device 
(not shown) will be necessary in order to fix the third wheel 42 against 
rotation relative to the turntable 46. 
If the power transmission means for transmitting the rotation of the first 
rotative drive motor 100 to the second wheel 40 uses a worm gear or 
incorporates a locking mechanism to make it impossible to rotate the first 
rotative drive motor 100 from the side associated with the second wheel 
40, then this power transmission means serves as the first locking device; 
in this case, the first locking device 52 shown becomes unnecessary. 
While particular embodiments of the present invention have been described 
so far, other various embodiments may be contemplated wherein some 
components are replaced by their counterparts having like functions. 
The turntable (16, 46) has been constructed with the second wheel (10, 40) 
placed inside the first wheel (8, 39), the third wheel (12, 42) placed 
outside the second wheel (10, 40) and the fourth wheel (14, 44) placed 
inside the third wheel (13, 42). However, the manner in which the wheels 
are combined may be changed as desired. 
Besides the rotative drive motors 48, 100 and 104 being electric motors, 
they may be any desired rotative means, such as a combination of a 
hydraulic motor, solenoid valves and a hydraulic fluid source or a 
combination of a pneumatic motor, solenoid valves and an air pressure 
source. Further, the method of transmitting power from the rotative drive 
motors 48, 100 and 104 to the second and third wheels 40 and 42 has been 
shown as using external and internal gears as in the embodiments, but 
besides this, worm gear drive, belt drive and chain drive systems may be 
used. 
In the embodiments shown in FIGS. 4A and 8A, the solenoids 53 and 57 have 
been used to press the friction plates 55 and 59. However, hydraulic or 
pneumatic cylinders may be used as the drive means, and any desired fixing 
system may be employed, such as one in which a locking pin is used as the 
locking means adapted to fit in holes formed in the second or third wheel 
40 or 42. 
As for the rotation preventing device (17, 47), there may be employed any 
other desired means than the system in which the pin (19, 47a) is inserted 
into the vehicle body 1 from the turntable (16, 46), as in the 
embodiments. For example, by making use of the fact that the ladder 4 of 
the high place working vehicle is locked by the ladder support 7, as shown 
in FIG. 1, it is possible to use the ladder support 7 as the rotation 
preventing device. 
As for the inclination detecting means 68, besides using a magnetic 
resistance effect element for detection separately in X- and Y-directions, 
it is possible to use any other desired arrangement. For example, 
detection may be made separately as to the direction of inclination and 
the angle of inclination. As for the detecting means, there may be 
employed arrangements using a plurality of pendulum switches, or utilizing 
a change in resistance to fluid, or using a U-shaped tube to use a change 
in the level of the fluid in the tube. 
As for the first and second rotative angle detecting means 60 and 64, in 
the embodiments, use has been made of the magnetic sensors 63 and 67 to 
detect changes in the magnetic resistance of the gear-like projections 62 
and 66 opposed thereto, but the gear-like projections 62 and 66 may be 
replaced by holes formed in the second and third wheels 40 and 42. 
Further, the magnetic sensors may be replaced by elements adapted to 
detect a change in electrostatic capacity or in the intensity of light or 
it is possible to use a potentiometer or rotary encoder which rotates with 
the second or third wheel 40 or 42. 
As a concrete example of the control circuits 69 and 69' in the 
embodiments, a system using a microcomputer has been shown (FIGS. 5 and 
9), but other arrangements may be used so long as they have the function 
of said control circuits 69 and 69'. For example, a sequence circuit using 
relays or an electronic circuit using a combination of logic ICs may be 
used.