Truck & Off-Highway Engineering - August 2022 - 22

Positioning to centimeter-level improves agriculture
Comparison of IMU/INS application, performance, size and cost.
James Fennelly,
product manager of
Inertial Measurement
Systems, ACEINNA Inc.
" Today, high
performance
MEMS IMUs can
weigh and measure
as little as a
quarter or a euro
coin and can cost
less than $30. "
and attitude. Accelerometers in the IMU measure linear
acceleration in all three dimensions, while IMU gyroscopes
measure angular (rotational) rate about the x, y
and z axes. In this way, the changes in an autonomous
tractor's velocity, position and attitude, for instance, can
be determined.
Higher-performance micro electro-mechanical systems
(MEMS) sensors are now available at a cost and size
smaller than the gimbal and fiber-optic gyroscopes once
used for IMUs. The arrival of MEMS on the scene is making
precision navigation more practical for agriculture.
High-performance MEMS IMUs have steadily improved
the cost-to-performance ratio. Once they
weighed in at a hefty 500 grams (17.6 oz) and measured
100 x 100 x 100 mm (3.9 x 3.9 x 3.9 in.) at costs
exceeding $500 each. Today, high-performance IMUs
can weigh and measure as little as a quarter or a euro
coin and can cost less than $30.
22 August 2022
INS meets off-highway challenges
Machinery in agricultural environments face navigation challenges
that on-road vehicles do not. Besides the absence of marked lanes,
HD maps and directional signs, there are also equipment characteristics
to consider. For example, solutions for safe navigation and movement
by farm equipment must take vibration into account.
In the presence of vibration, an IMU's signal chain must be on its
toes. It must protect the integrity of the signal needed to steer a vehicle
or safely operate an implement such as an automated seeder or
hay baler. Rejecting and eliminating vibration-related acceleration
and vibration-induced error is vital.
The most effective IMUs are calibrated on precision rate tables and
in temperature chambers. This approach preserves accuracy and consistency
over input range and temperature.
Meeting ISO 13849 with backward compatibility
Safety is a common factor that is critical for all agricultural machinery.
The need for safety runs through autonomous applications as
diverse and sophisticated as weed killing to increase crop yield,
avoiding over- or under-fertilization or boosting irrigation efficiency.
As automation grows, machine safety must keep pace. This is why
systems and subsystems that meet the ISO 13849 safety standard
have begun to arrive on the market.
One example of a subsystem used in autonomous farm machinery,
and which meets ISO 13849 Category 2, Performance level d (PLd), is
the MTLT335D Dynamic Tilt Sensor Module from ACEINNA. From the
ground up, MTLT335D development followed the design and safety
requirements detailed in ISO 13849.
Keeping the same form factor, electrical interface and connector as
the previous-generation (MTLT305D) preserved backward compatibility
even as key performance parameters improved. For example,
without changing the form factor, two key parameters related to gyro
TRUCK & OFF-HIGHWAY ENGINEERING
BOTH IMAGES: ACEINNA
Truck & Off-Highway Engineering - August 2022

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