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T h e g o a l of the
T a p e
Tension
Servo
S y s t e m
is
:
T o maintain constant tension
t h r o u g h o u t
the l e n g t h
of the
t a p e r e g a r d l e s s
of
t a p e p o s i t i o n
(
reel
radius )
o r s p e e d
.
T o
p r o v i d e
the
a c c u r a c y n e c e s s a r y
t o
fulfill this
g o a l
,
the
APR
- 5000
utilizes
a m i c r o p r o c e s s o r
controlled look
-
u p
table
( ROM
table )
.
T h e CPU board
m i c r o p r o c e s s o r
c o m m u n i c a t e s
with
the TIB board
v i a
the 16
-
bit
p a r a l l e l
data bus
.
This data
bus p r o v i d e s t h e
control and drive data to the TIB for
t e n s i o n
servo
control
.
T h e
TIB (
T r a n s p o r t
Interface Board )
serves as the bi
-
directional data interface between the CPU
and the
t r a n s p o r t
electro
-
mechanical drivers (
o n
the Reel
Motor Driver Board ) and the sensors
( Reel Tach
Sensor
Board
,
T a p e
Tach Sensor Board
,
and Hall Effect Sensor Board )
.
As
the CPU is
t o
be
in control of the
t r a n s p o r t
,
it
(
the CPU )
must be a w a r e of the c h a n g e s
in reel
motor motion
,
tension
a r m p o s i t i o n
,
and absolute
t a p e s p e e d
.
T h i s reel m o t o r motion
information is
p r o v i d e d t o
the CPU
from RTS boards ( mounted o n each reel motor ) via the
TIB
.
T h e four tach
s i g n a l s
(
t w o for each motor
) are created
a s
each reel motor r o t a t e s
.
To
a c c o m p l i s h
this there is
a
m a g n e t i c r i n g
mounted
o n
each reel motor shaft that is
p o l a r i z e d a l t e r n a t e l y
North
to South
.
As the
p o l e s
p a s s
over
the hall effect sensors
o n
the R T S boards
,
a f r e q u e n c y
of
p u l s e s i n v e r s e l y proportional
to the radius of the
t a p e o n
the reel is created
.
These
p u l s e s are s h a p e d b y p u l s e
t i m i n g
circuits
o n
the TIB board in
p r e p a r a t i o n
for
r e a d i n g b y
the
CPU
.
T h e TTS board has two
o u t p u t s i g n a l s
to the CPU board
( via
the
TIB board )
.
To
a c c o m p l i s h
this there is
a m a g n e t i c r i n g
mounted o n timer roller
g u i d e
shaft that is
p o l a r i z e d
a l t e r n a t e l y
North to South
.
This board also
u s e s a
hall
efect
s e n s o r to
detect the
c h a n g e s
in flux as the
c o u n t e r
roller
g u i d e
rotates
.
As the p o l e s
p a s s
over the hall effect
s e n s o r s o n
the TTS board
,
a f r e q u e n c y
of
p u l s e s d i r e c t l y
p r o p o r t i o n a l
to the absolute s p e e d of the
t a p e
is created
.
These
p u l s e s are s h a p e d b y p u l s e t i m i n g
circuits
o n
the
TIB
board
in
p r e p a r a t i o n
for r e a d i n g
b y
the CPU
.
The CPU
u s e s
this f r e q u e n c y t o determine absolute t a p e
s p e e d
of the reel
s e r v o s y s t e m
.
T h e H E S
board
also utilizes
a
hall efect sensor circuit w h i c h
p r o v i d e s a n e r r o r v o l t a g e
to the CPU board ( via the
TIB
board )
.
This
a n a l o g v o l t a g e
is converted to
a d i g i t a l
data
word at the TIB board
.
This data word
i s
used
b y
the CPU
board t o minimize the flutter content of the tension
s e r v o
.
4
-
20
P
^
$
tH
-
JVcMri
0
&
£
.
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