Pivotal mounting system

The cathode ray tube assembly of a visual display unit is suspended over the static base in a cradle, the suspension pivots being as close as possible to the center of gravity of the moving section. Attached to the underside of the cradle is a bracket with forked arms. The forks engage with a spindle carrying a pair of friction pads and a helical compression spring. The spindle runs in a curved slot in a bracket attached to the static base. The friction pads are situated one on each side of the bracket and are maintained in intimate contact with it by the helical spring generating a friction force. Thus a force of sufficient magnitude applied to the moving part of the visual display unit will overcome the friction force and permit it to move, although normally the friction force will hold it in the required position.

BACKGROUND OF THE INVENTION 
This invention relates to assemblies with a movable part and more 
particularly to an assembly in which the movable part can readily be moved 
from one position to another and is retained in that position. 
More particularly the invention relates to a mounting system for a 
relatively heavy pivoted member which is regularly pivoted from one 
position to another whilst in use, such as a visual display unit, which 
may be pivoted from one position to another by one user or a number of 
different users. 
A common method of permitting such regular pivoting of a relatively heavy 
member is to have a friction bearing or a handwheel on the pivot. A 
friction bearing however must have relatively high friction for a heavy 
member, particularly at high angles of pivot when the centre of gravity of 
the member is considerably displaced laterally of the pivot. Such high 
friction can make movement of the member difficult, and regular use can 
cause wear in the friction member necessitating regular adjustment or 
renewal of friction pads, washers etc. The use of a handwheel to tighten 
the pivot after every movement of the member is time consuming and 
undesirable for the users of a Visual Display unit as variable tightening 
torque are required with the unit in different positions. A high torques 
is required, for example, when the unit is at high angles of pivot. 
This torque can be reduced by providing a lever extending from the pivot 
with an arcuate slot at the end of the lever which is engaged by a fixed 
tightening wheel or nut. Whilst this method does in fact reduce the 
tightening torque the method is still time consuming and can be dangerous, 
as too rapid loosening of the wheel or nut can cause the unit to swing 
rapidly down under its own weight. 
Various other methods have been tried to overcome this problem such as the 
TV camera pivot disclosed in U.S. Pat. No. 4,225,105. This discloses a 
system of levers and slides arranged so that the camera is moved along a 
slide as it is pivoted so that the centre of gravity of the camera is 
always in a position to restore the camera to a horizontal position. A 
pivot tightening nut is provided to hold the camera in any described 
position, which again for a visual display unit is undesirable. The 
arrangement is also quite complex and expensive to produce. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a mounting system for a 
relatively heavy member which does not have a locking wheel or nut, and is 
fairly simple and cheap to manufacture. 
The present invention therefore comprises a base member and a mounting 
member pivoted thereon, the pivot being substantially in alignment with 
the centre of gravity of the relatively heavy member when it is mounted on 
the mounting member, the mounting member having a lever extending to a 
position in which the end of the lever is adjacent to a bracket formed on 
the base member, the bracket being located remote from the pivot axis of 
the mounting member and having a slot which is engaged by the end of the 
lever, friction means being provided between the end of the lever and the 
slot whereby the mounting member can pivot and is retained in a 
predetermined position by the friction means. 
Thus, since the relatively heavy member is pivoted substantially about its 
centre of gravity there is virtually no force to cause the member to swing 
from one position to another under its own weight and the force required 
on the end of the lever to hold the member in any angular position is very 
low and virtually constant. Thus, simple spring loaded friction washers 
are provided on the end of the lever which engage both sides of the 
slotted bracket. 
The assembly is simple and therefore inexpensive, and the force required on 
the friction washers is low so they will not need regular adjustment or 
replacement.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The visual display unit comprises a cathode ray tube 10 which is supported 
on a cradle 12 which can pivot relative to the base 14 of the unit so as 
to facilitate use by the operator of the visual display unit. Both the 
cathode ray tube and the base unit are normally enclosed within stylised 
housings, but these have not been shown in the interests of clarity. 
The base 14 is provided with two upstanding supports 16, at the upper ends 
of which the cradle 12 is pivoted on pivot pins 18. Also provided on the 
base 14 is a vertically extending bracket 20 between the supports 16, the 
bracket 20 having an arcuate slot 22 formed therein with its centre on or 
substantially on the pivot axis of the cradle 12. When the cathode ray 
tube 10 and the enclosing housing is mounted on the cradle 12 the pivot 
axis of the cradle 12 is adjacent to or passes through the centre of 
gravity of the whole cathode ray tube assembly so that there is no or 
virtually no tendency for the cathode ray tube assembly to pivot about the 
pivot pins 18. 
Secured to the underside of the cradle 12 are two arms 24 the lower ends of 
which are forked to loosely accommodate a spindle 26 which engages the 
forked portion of each of the arms 24. The spindle 26 has a diameter which 
permits it to pass through the arcuate slot 22 with a small clearance 
only. Rigidly secured to the spindle 26 is a stop 29 and against the stop 
abuts is a disc 28 formed of high friction material, the diameter of the 
disc 28 being large enough to present a fairly large surface area to one 
side of the bracket 20 above and below the arcuate slot 22. Axially 
movably mounted on the spindle 26 on the opposite side of the bracket 20 
is a further disc 30 of high friction material and this disc is urged 
towards the bracket 20 by a helical compression spring 32. The opposite 
end of the spring 32 abuts a stop 34 formed on the spindle 26. 
Since the spindle is free to move within the forked ends of the arms 24 the 
spring 32 has the effect of axially adjusting the position of the spindle 
26 until the two friction discs 28 and 30 apply substantially equal 
pressures to opposite sides of the bracket 20 and thus act as a brake. 
Thus normally the discs 28 and 30 hold the cradle in any desired position, 
but by manually pivoting the whole cathode ray tube assembly the discs 28 
and 30 move along the slot until the required position for the assembly is 
reached. Since the discs 28 and 30 are remote from the pivot pins 18 a 
mechanical advantage exists and the spring 32 needs only to apply a 
relatively low force, even if the centre of gravity of the cathode ray 
tube assembly is not exactly on the pivot axis of the cradle 12. 
Many modifications to the arrangement may be made without departing from 
the spirit of the invention. Thus, for example, only one friction disc may 
be used or the bracket 20 may be located in a different position although 
still remote from the pivot axis. Alternatively friction members may be 
secured to a portion of the base and act on one or both of the arms 24, or 
only a single arm may be provided.