EP0082898A1

EP0082898A1 - Improvements in and relating to HF slip rings

Info

Publication number: EP0082898A1
Application number: EP81306175A
Authority: EP
Inventors: Ernest Henry Birch; H. Labato
Original assignee: IDM Electronics Ltd
Current assignee: IDM Electronics Ltd
Priority date: 1980-12-16
Filing date: 1981-12-30
Publication date: 1983-07-06
Also published as: GB2090074A

Abstract

The destructive effect on the amplitude of an input signal of a single input/single output (3,12) HF slip ring assembly is reduced by dividing the input signal path (3) into a number of paths (6, 7, 8, 9) at the slip ring-brush interface X and recombining the paths to form the required single output (12). This has the effect of reducing the length of stubs thereby reducing the destructive effect on the amplitude of the input signal.

Description

This invention relates to HF Slip Rings and to a method and means for improving the waveform of output signals from the slip ring.
An object of the present invention is to improve the waveform of output signals from the slip ring by reducing the destructive effect of stub lines on the signal transmission.
A further object of the present invention is to improve the frequency bandwidth of the slip ring without correspondingly increasing the slip ring diameter.
For HF slip rings having a single input and a single output, the stub length is a maximum and where the stub length is greater that
a considerable loss occurs between the amplitude of . the input signal and that of the output signal and a still further object of the invention is to-obtain more constancy between the amplitude of the input signal and that of the output signal of the slip ring, particularly at those frequencies where virtual cutoff of the signal occurs when the combination of stubs is particularly destructive to signal transmission.
Thus, according to the invention there is provided a high frequency slip ring assembly having a single input and a single output, characterised in that the normally destructive effect on the amplitude of the input signal on the single input by the effect of stubs is reduced by dividing the input signal path at the brush-slip ring interface into a number of paths followed by recombination of the divided signal paths from the interface to produce an output signal on said single output having an amplitude corresponding substantially to the amplitude of the input signal.
The electrical effect of the division of the electrical signal input into a number of branches to the slip ring-brush interface followed by the recombination to a single output, is to divide the slip ring circumference by
where n is the number of sub divisions of the input signal at the slip ring-brush interface. This effect is illustrated by way of example only in the accompanying drawings wherein:

Figure 1 is a diagrammatic representation of a known RF transmission line showing the signal paths when the input and output are displaced by 180°;
Figure 2 is a diagrammatic representation similar to that of Figure 1 but showing the signal paths when the input and output are in phase;
Figure 3 is an equivalent circuit network for an RF slip ring of the present invention showing the signal paths when the input and output are displaced by 180°;
Figure 4 is a network similar to that of Figure 3 but with the input and output in phase and
Figure 5 is a sectional view through a slip ring assembly of the present invention and where the slip ring circumference is divided by
.

In the equivalent circuit network of Figure 1, the stub length of each parallel branch is indicated as π
, the characteristic impedance being indicated at Zo and the slip ring impedance through each parallel stub, as Z_SR, for a single input displaced 180° from the output.
In Figure 2, the input and output are in phase given open circuit stub lengths of π
as shown. Figure 1 and 2 thus illustrate the two extremes in an RF slip ring during rotation.
Referring to Figure 3, for the best position where the input and output are displaced by 180⁰, the number of inputs has been increased by initially dividing the initial characteristic impedance Zo into two branches, each of characteristic impedance 2Zo and then subdividing each of the 2Zo characteristic impedance branches into two parallel branches indicated as Zs_R. The brush-slip ring interface is shown dotted in Figure 3 and at the output side, each of the two sub-branches of impedance Z_SR are recombined to form two branches of impedance 2Zo and combined again to give a single output of impedance Zo. The stub length of each sub-branch is shown as π
i.e. half the stub length of that shown in Figure 1.
Similarly in Figure 4, the input characteristic impedance Zo is divided into two branches each of impedance 2Zo and sub-divided to give the slip ring impedance ZSR for each stub line. The stub line impedances ZSR are recombined into two branches each of impedance 2Zo and combined again to give an output of impedance Zo. The diagram shown in Figure 4 is for the worst position during rotation where the input and output are in phase. The open circuit stub length of each of the sub-branches of Figure 4 is indicated as π
; again half the stub 4 length of that shown for Figure 2.
Thus it is seen that increasing the number of inputs has the effect of reducing the 'electrical diameter' and reduces the open circuit stub length, thereby improving the characteristics of the slip ring by reducing the normally destructive effect of the stubs on the amplitude of the input signal. -In Figures 1 -and 2 for a single input/single output RF transmission line, the stub length is a maximum. By dividing the stub length by a factor of 4, the effect of the stub on signal amplitude is reduced, the destructive effect of the stub being particularly apparent when the stub. length is greater than
.
In order for the sub-division to be effective and to operate satisfactorily in practice, the inputs should be matched to the line and must also be symmetrical to produce inputs of equal magnitude and phase.
The maximum number of-inputs for the system of the present invention is four, since it is impractical to produce a line impedance of >4Zo.
A typical RF slip ring assembly is shown in Figure 5 and comprises a slip ring housing 1, and high frequency slip ring 2. A single input conductor 3 is divided into two branches 4, 5, and each branch is sub-divided into two further branches 6, 7, 8, 9 at the brush-slip ring interface X, the sub-branches being recombined at Y to form two output branches 10, 11, combined to form a single output 12.
It will be appreciated that the invention is susceptible to considerable modification and is not to be deemed limited to the particular features shown by way of example only in the accompanying drawings.

Claims

1. A high frequency slip ring assembly having a single input (3) and a single output (12), characterised in that the normally destructive effect on the amplitude of the input signal on the single input (3) by the effect of stubs is reduced by dividing the input signal path at the brush-slip ring interface into a number of paths (4, 5, 6, 7, 8, 9) followed by recombination of the divided signal paths from the interface to produce an output signal on said single output (12) having an amplitude corresponding substantially to the amplitude of the input signal.

2. A high frequency slip ring assembly as claimed in claim 1 wherein the single input signal path (Zo) is initially divided into a pair of branches (2Zo) and each branch sub-divided at the slip ring-brush interface, the sub-divided branches (Z_SR) being recombined into two branches (2Zo) and further combined at the output to form the single output path (Zo).

3. A high frequency slip ring assembly as claimed in claim 1 or 2 wherein the length of each stub is reduced from π

to π

.

4. A high frequency slip ring assembly as claimed in claim 1 or 2 wherein the length of each stub is reduced by a factor of 4.

5. A high frequency slip ring as claimed in any preceding claim wherein the divided inputs are matched to the line and are symmetrical to produce inputs of equal magnitude and phase.