Hydraulic valve for a camera dolly

An improved hydraulic valve for a camera dolly includes Teflon inserts around a valve pin to reduce vibration and noise. The ratio of movement between the boom control, which controls the up and down movement of the arm on the camera dolly, and opening and closing of the hydraulic valve, is increased to reduce the sensitivity of the valve to boom control movement. The boom control includes ready up and ready down detents which provide the user a tactile indication of where to position the boom control for immediate up or down movement.

FIELD OF THE INVENTION 
The field of the invention is hydraulic valves. More particularly, the 
invention relates to hydraulic valves used in camera dollies, to raise and 
lower a camera. 
Camera dollies are used in the television and motion picture industries to 
support and maneuver a camera. Typically, the camera dolly is on wheels 
and has an arm to raise and lower the camera. The camera dolly is 
generally moved by dolly operators or "grips", to properly position the 
camera, to follow the film or video sequence. 
Various designs have been used to raise and lower a camera on a camera 
dolly. For example, U.S. Pat. No. 4,360,187 describes a two piece arm 
design for use in a camera dolly. The arm is raised and lowered via a 
hydraulic actuator and a control valve. Other camera dollies use a 
straight single piece beam arm or a telescoping pedestal lifted by a 
hydraulic or pneumatic actuator, such as described in U.S. Pat. No. 
5,516,070. 
The valves used to control a hydraulically driven camera dolly arm should 
meet certain design objectives. For example, the opening and closing 
characteristics of the valve should allow the camera dolly operator to 
accurately and easily control the speed and direction of the arm movement. 
The valve should also allow the arm to be accurately stopped at a selected 
elevation. In addition, the valve should operate silently, so as not to 
interfere with the sound track being recorded for the motion picture or 
video sequence. 
U.S. Pat. Nos. 4,747,424 and 4,109,678, incorporated herein by reference, 
describe hydraulic valves which have been successfully used in camera 
cranes and dollies for many years. However, the valve described in U.S. 
Pat. No. 4,109,678 will occasionally generate fluid rushing or whistling 
sounds, especially on the "down" side, as hydraulic fluid rapidly flows 
through the valve, when the camera dolly arm is quickly lowered. In 
addition, controlling this valve to begin movement of the camera dolly arm 
at a precise time can require a level of skill and experience, as the 
control handle must be turned by a certain amount before the camera dolly 
arm actually begins to move. The delay between control handle movement and 
arm movement results because the swash plate in the valve must turn 
sufficiently, before the valve cracks open. This characteristic can make 
precise control of the movement of the camera dolly arm more difficult. As 
split second timing is often needed to position a camera, the delay in arm 
movement can be a disadvantage. The delay may also induce less experienced 
grips to over-compensate by turning the control handle too far. This 
results in arm movement that is too fast, or that overshoots the desired 
camera lens height. 
Accordingly, there remains a need for an improved hydraulic valve to 
control movement of a hydraulically actuated camera dolly arm. 
SUMMARY OF THE INVENTION 
To these ends, in a first aspect of the invention, an improved hydraulic 
valve has a head bushing positioned around the head of the valve pin on 
the down side of the valve. 
In a second aspect of the invention, a shaft bushing is located around the 
shaft of the pin on the down side of the valve. 
In a third aspect of the invention, a detent provides for instant down 
movement, closed, and instant up movement positions for the valve control. 
In another separate aspect of the invention, the ratio of movement between 
the valve control and the valve is selected to provide desensitized 
control of the valve, and therefore of the camera dolly arm, thereby 
making the arm easier to precisely control. Accordingly, it is an object 
of the invention to provide an improved hydraulic valve for a camera dolly 
.

DETAILED DESCRIPTION OF THE DRAWINGS 
Turning now in detail to the drawings, as shown in FIGS. 1 and 2, a camera 
dolly 10 has an arm 12 supporting a motion picture or video camera 14. A 
boom or arm control 16 at the back of the camera dolly 10 is turned to 
open and close a hydraulic valve 60, to raise and lower the arm 12. The 
hydraulic valve 60 controls the flow of hydraulic fluid to a hydraulic 
actuator 18 extending from the chassis 20 of the dolly 10 to the arm 12. A 
steering bar 15 at the back end of the dolly 10 is used to steer the 
wheels of the dolly, and to shift between different steering modes. 
Referring to FIGS. 3, 4 and 5, a receiver tube 50 is rotatably mounted at 
the back end of the chassis 20 on bearings 52. The boom control 16 is 
irrotatably secured to the upper end of the receiving tube 50. A boom 
sprocket 54, preferably having 20 teeth is irrotatably attached to the 
bottom end of the receiver tube 50. 
A hydraulic valve 60 is mounted within the chassis 20 in front of the 
receiver tube 50. A valve sprocket 58, preferably having 32 teeth, is 
attached on top of the valve 60. The valve sprocket 58 is linked to the 
boom sprocket 54 via a roller chain 56. 
Referring to FIGS. 5 and 6, the receiver tube 50 has three detent grooves 
or dimples: a down groove 64, a stop groove 66, and an up groove 68. A 
ball detent 62 on the chassis is positioned to engage these grooves. 
Referring to FIGS. 5 and 7, the hydraulic valve 60 has a valve body 22 
generally divided into an up side 70 and a down side 72. A valve base 23 
is bolted onto the valve body 22. A port 40 extending into the valve base 
23 connects to a passageway 24 leading into an up bore 45, which connects 
to an up outlet 30 extending out of the valve body 22. 
Similarly, on the down side 72 of the valve 60, the port 40 extends through 
the passageway 24 to a down bore 47 in the down valve body 21. A return 
port 28 extends through the down valve body 21 and joins into the down 
bore 47. The junctions between the passageway 24 in the valve base 23 and 
the up bore 45 and down bore 47 in the down valve bodies 21 and 22 are 
sealed by O rings 42, compressed by bolts 25 clamping the valve body and 
valve base together. 
An up pin 74 is centered in position within the up bore 45 via a steel 
bushing 76 (which is preferably pressed into the up bore 45.) The bushing 
76 and the shaft 77 of the up pin 74 are dimensioned to create a small 
annular opening around the shaft for hydraulic fluid passage. The upper 
end of the shaft 77 of the up pin 74 is threaded into a piston 26 which 
bears against a swash plate 65 which reacts against a Teflon washer 69 
over the swash plate 65. The valve sprocket 58 is attached to and rotates 
with a cam 67. The Teflon washer 69 is sandwiched between the swash plate 
65 and the eccentric bottom surface 73 of the cam 67. As the cam turns, it 
depresses either of the pistons 26 and 27. Alternatively, a glass filled 
Teflon washer or a needle bearing plate may be used in place of the Teflon 
washer 69, for faster valve response. The swash plate 65 generally does 
not turn with the valve sprocket 58. The lower end of a compression spring 
46 rests on the bushing 76 with the upper end of the compression spring 46 
pushing on the piston 26. A steel valve seat 79 in the valve body 22 seals 
the up bore 45 closed when the head 75 of the up pin 74 engages the seat 
79. 
On the down side 72 of the hydraulic valve 60, a head insert 86, as shown 
in FIGS. 8 and 9, is pressed into the valve base 23. A head bore 90 
extends through the head insert 86. The head bore 90 connects to the 
passageway 24 through a cutout 94 in the side cylindrical surface of the 
head insert 86. As shown in FIG. 8, side channels 92 extend through the 
head insert 86. The head bore 90 is dimensioned to closely fit around the 
head 84 of the down pin 82. A steel valve seat 83 is positioned in the 
valve body 22 above the head insert 86. 
Referring to FIG. 7, a shaft insert 88 is pressed into the down bore 47, 
above the valve seat 83. The shaft insert 88, as shown in FIGS. 10 and 1, 
has a through bore 96, dimensioned to closely fit around the shaft 85 of 
the down pin 82. Grooves 98 on the outside of the shaft insert 88 allow 
hydraulic fluid to flow through the down bore 80 past the shaft insert 88. 
A piston 27 is threaded onto the upper end of the shaft 85 of the down pin 
82. A spring 89 biases the down pin 82 upwardly with the piston 27 bearing 
against the swash plate 65. 
As best shown in FIG. 5, the boom sprocket 54 is smaller than the valve 
sprocket 58. In the preferred embodiment, the boom sprocket 54 has 20 
teeth and the valve sprocket 58 has 32 teeth. This provides a 1:1.6 ratio 
between turning movement of the boom control 16 and turning movement of 
the valve sprocket 58 and the cam 67. In prior designs, a 1:1 ratio was 
used, making the valve highly sensitive to movement of the boom control 
16, so that even a slight movement of the boom control 16 would result in 
a rapid movement of the arm 12. The design shown in FIG. 5 makes operation 
of the dolly easier because more turning movement of the boom control 16 
is needed to actuate the valve 60 and cause the arm 12 to move. As a 
result, the operator can more easily avoid camera positioning errors 
caused by the arm moving too fast or too slow. The design shown in FIG. 5 
provides about 72.degree. of boom control movement from the full speed up 
or down position to the stop position, in contrast to about a 45.degree. 
range of movement in previous camera dollies. 
In use, hydraulic lines are connected to the down outlet 28, up outlet 30 
and to the port 40, to connect the valve 60 into the hydraulic system of 
the camera dolly 10. To raise the arm 12 of the camera dolly 10, the boom 
or arm control 16 is turned counterclockwise (when viewed from above as in 
FIG. 6). The boom control turns the receiver tube 50, and the boom 
sprocket 54 on the receiver tube 50. Consequently, the valve sprocket 58 
turns in the same direction, and by about 62% (20 teeth/32 teeth=62%) of 
the amount as the boom control 16, driven by the chain 56 connecting the 
valve sprocket 58 to the boom sprocket 54. As the valve sprocket 58 turns, 
the swash plate pushes down on the piston 26 causing the head 75 of the up 
pin 74 to move away from the seat 79. The up side 70 of the hydraulic 
valve 60 is then opened, allowing hydraulic fluid to flow through the port 
40, the passageway 24, through the annular space between the bushing 76 
and shaft 77 of the up pin 74, through the up bore 78, and out through the 
up outlet 30, to drive the hydraulic actuator 18 up and raise the arm 12. 
Lowering the arm is performed by turning the boom control clockwise, 
opening the down side of the valve, and allowing hydraulic fluid to return 
from the actuator, through the down bore 47, through the side channels 92 
in the head insert 86, through the grooves 98 on the shaft insert 88, out 
of the return port 28, to a sump or reservoir. 
Referring to FIGS. 2, 5-7, when the boom control 16 is turned to a position 
so that the detent 62 engages the stop groove 66, the swash plate 65 is 
positioned so that both pistons are up and both sides of the valve 60 are 
closed. Consequently, no hydraulic fluid can flow through the valve 60 and 
the arm 12 remains in a fixed position. When the boom control 16 is turned 
so that the detent 62 engages the up groove 68, the swash plate 65 is 
positioned so that the up side 70 of the hydraulic valve 60 is on the 
verge of opening. Further counter-clockwise turning of the boom control 
16, even by a small amount, causes the up side 70 of the valve 60 to open, 
so that the arm 12 moves virtually simultaneously with the further turning 
movement of the boom control 16. 
Similarly, when the boom control 16 is turned so that the detent 62 engages 
the down groove 68 in the receiver tube 50, the down side 72 of the 
hydraulic valve 60 is on the verge of opening. As the boom control 16 is 
turned further counter-clockwise, as shown in FIG. 6 the downside 72 of 
the valve 60 opens virtually simultaneously with the further turning 
movement. Accordingly, turning the boom control to engage the up groove 64 
or down groove 68 provides a "up ready" and an "down ready" position, from 
which the operator knows that further movement of the boom control 16 will 
result in instantaneous movement of the arm 12. 
In contrast, in previous camera dolly designs, substantial turning movement 
of the boom control was required to move the swash plate 65 to open the up 
or down side of the valve. This delay in the prior designs between turning 
the boom control and achieving arm movement made precise timing of arm 
movements difficult. The grooves 64-68 and detent 62 eliminate the delay 
and make precise timing of arm movements easier to achieve for the dolly 
operator. 
When the receiver tube 50 is positioned with the detent 62 engaged into the 
down groove 68 or the up groove 64, no hydraulic fluid flows through the 
valve 60. The stop groove 66 is provided in between the up groove 64 and 
the down groove 68 as an additional tactile point of reference. The valve 
60 remains closed at all angular positions of the receiver tube 50 between 
(and including) the down groove 68 and the up groove 64. 
The arm 12 can move down rapidly, when the valve 60 is fully opened and the 
arm is carrying a heavy load. In existing designs, the down pin 82 will 
frequently vibrate due to the turbulent and rapid flow of hydraulic fluid 
around the down pin. This vibration creates unwanted noise. The head 
insert 86 and the shaft insert 88, preferably made of Teflon, largely 
prevent vibration of the down pin 82 and associated noise. Consequently, 
the valve 60 operates silently under virtually all conditions. 
If a needle bearing 69 is used in place of a Teflon washer 69 between the 
swash plate 65 and the cam 67, the valve 60 may tend to close itself, when 
the operator releases the boom control knob, depending on the friction in 
the mechanical position, hydraulic pressure, and valve position. The up 
force on the pistons generated by hydraulic pressure and the springs 46 
and 89, creates a certain level of closing torque on the cam 67 and 
sprocket 58. This torque will close the valve unless it is exceeded by the 
piston/swash plate; chain/sprocket; bearings; and o-ring friction forces. 
This self-closing can be prevented by increasing tension in the chain 56 
which will increase the friction acting to prevent the cam 67 from 
turning. A viscous fluid 80 dampener may optionally also be linked to the 
swash plate, to provide a smooth and controlled closing movement of the 
valve. 
Thus, a novel hydraulic valve for a camera dolly has been shown and 
described. Various modifications and substitutions of equivalents may of 
course be made without departing from the spirit and scope of the 
invention. The invention, therefore, should not be restricted, except by 
the following claims and their equivalents.