Renishaw TONiC T20 1 Series Installation Manual page 9

Ring orientation for partial arc applications
The partial arc DSi is based on a ring with two reference marks opposite each other.
The ring must be installed so that when the ring rotates only H1 can see R1 and only H2 can see R2.
Small angular movements
To allow the DSi to operate with very small angular movements the ring must be mounted in a certain
way in relation to the two readheads. Figure 1(a) shows how the ring must be initially mounted with
reference mark R1 to the left of readhead H1. This position could be the maximum travel the ring can
be rotated in an anti-clockwise direction (limited by the user).
The angle Ф determines the minimum amount of angular movement the ring can be rotated for the
DSI to become initialised. With optimum readhead and ring positioning, the minimum angle of rotation
required to initialise a system is 3°. This is to make sure that there is enough rotational travel for both
readheads to see a reference mark. The ring will now be rotated clockwise so that H1 will see R1 and
H2 will see R2, at this point the DSI will become initialised (Figure 1(b)).
H1
1. Ф
H2
(a)
Figure 1 : Small angular movements
Large angular movements (<357°)
When the DSi is used in applications where large amounts of rotation are required the ring must be
installed correctly. Figure 2(a) shows the maximum position the ring can be rotated in an anti-clockwise
direction. Reference mark R1 must be positioned to the left of H2 so H2 will never see R1 upon
initialisation. The angular position Ф of R1 to H2 must again be greater than 1.5°, therefore the maximum
amount of angular movement of the ring, this being 357°.
Figure 2(b) shows the ring after it has been fully rotated in a clockwise direction to its maximum travel.
During this rotation H1 would have seen R1 and H2 would of seen R2. The DSI is now initialised.
H1
H2
(b)
H1
2. Ф
H2
(a)
Figure 2 : Large angular movements
H1
H2
(b)