In the other case the user must define the maximum deviation accepted along with the
maximum acceleration of the system. Whenever the estimator uncertainty exceeds the
maximum deviation, the dev_thr_err signal will be raised to “1”. The remainder of
this chapter will provide the necessary information to set up these values.
To set the maximum position deviation allowed for the estimator calculation the MAXDEV
registers are used (see chapter 6.3.26). The resolution of this value is the same as the
resolution of the fast position.
The maximum acceleration needs to be calculated for each individual application.
Some margin should also be given to the maximum limit in order to account for noise,
inaccuracy and so on.
The maximum absolute value of the acceleration must be written to the MAXACC regis‐
ter in a floating point format (see chapter 6.3.25). The resolution is stored in bits 7 and
6, and a positive integer mantissa on the remaining part of the register. The resulting
value can be calculated as follows:
acc
max
= mantissa
·
resolution
Here, mantissa is the value stored in bits 5…0 and resolution is defined as per the fol‐
lowing table:
Table 30: Resolution of fast position acceleration boundary
Bit 7,6 Resolution
00 256
01 64
10 16
11 4
The ACC
LSB
value is the resolution of the DSL fast position channel which can be calcu‐
lated as:
ACC
LSB
=
2�
2
Pres
T
2
hframe
[rad/s
2
]
with Pres as position resolution per turn in number of bits and T
hframe
as DSL frame
duration in s (see chapter 3)
Example:
If the DSL frame lasts 15.625 µs, an 18 bit resolution encoder is used, and a limit of
10.000 rad/s² is foreseen:
ACC
LSB
=
= 98174.77 rad/s
2
2�
2
18
(15.625 10
-6
)
2
The finest possible resolution for ACC
max
is ACC
LSB
/256 = 383.5 rad/s². Accordingly,
ACC
max
can be set to
acc
max
=
27 383.5 rad/s
2
=10355 rad/s
2
with a setting of 0x1B in the MAXACC register.
Values greater than 24.000 rad /s² can be achieved by using different resolutions: on
the same system as above, a limit of 30.000 rad /s² can be set using ACC
LSB
/64 =
1534 rad /s².
Therefore:
acc
max
=
20 1534 rad/s
2
=30680 rad/s
2
In this case the data to be written to the MAXACC register would be 0x54.
CENTRAL FUNCTIONS
7
8017595/ZTW6/2018-01-15 | SICK T E C H N I C A L I N F O R M A T I O N | HIPERFACE DSL
®
63
Subject to change without notice
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