Transcript Document

Inertial Measurement Unit
Image Acquisition and Processing of Remote Sensing Data
Monitoring crop heath via aerial photography is a proper technique used to
maximize agricultural productivity. ImAP RSD was initiated to develop a more
efficient and cost effective method of determining crop health. An automated
system is being developed that will acquire crop images as it is flown by a high
altitude weather balloon.
Problem Statement:
Due to the spinning and swaying of a payload in flight, it is difficult to identify a
particular field based on its acquired image during a flight mission. Precise
knowledge of the payload flight path and attitude is required to acquire and identify
desired targets.
Develop an Inertial Measurement Unit to sense angular and linear motion to
determine flight path and payload attitude.
Project Requirements
Functional Requirements:
• IMU shall measure balloon oscillation frequency and angular rotation rate to one
degree per second
• IMU shall measure to 0.01g for each of the three principle axes
• Data logging system shall be able to log at a 100 Hz rate with 10 bit or greater
• IMU shall receive power from a 11.1 V nominal lithium-ion battery
• IMU shall function for a minimum of 2 hours using a 4 Amp-hour battery pack
• IMU shall operate over a temperature range from -40˚ C to 85˚ C
Concept Sketch Diagram:
The inertial measurement unit will be
used in conjunction with a GPS unit
and a horizon detection system for
precise flight path and payload attitude
determination. This data is used by an
on-board computer and control system
to accurately point the on-board
camera to a desired point on earth.
System Block Diagram:
The IMU system consists of one
MMA7261QT triple-axis
accelerometer and three MLX90609
single-axis rate gyros. The analog
sensor outputs are fed into an Atmel
ATMega128 microcontroller. The
microcontroller outputs identical
digital signals to a Logomatic
universal data logging device and to
the primary processor of the total
ImAP system. Additionally, a
temperature signal is received by
the microcontroller from a rate gyro.
The IMU has been tested to ensure it is operational and meets the functional
requirements. Testing apparatuses included a rotational test platform with angle
measurement encoder and a controllable temperature chamber.
Non-Functional Requirements
• IMU may measure temperature and voltage levels during flight
Component Testing:
•Null-point static calibration procedure developed to zero sensor outputs prior
to a mission
•Tilt angle measurements conducted with test platform to verify accelerometer
•Rate gyros subjected to known angular motion with test platform to verify
•Sensors subjected to required operating temperature range to observe
induced error
•Look-up tables developed to compensate in coding for temperature induced
Operational Environment / Design Constraints
• ImAP payload shall operate at altitudes from 20,000 to 30,000 feet
• IMU must be shielded from electromagnetic interference (EMI)
MATLAB Simulink Results:
To aid in choosing suitable sensors for the project the
balloon and payload system was modeled as a simple,
two-dimensional, ridged pendulum in MATLAB Simulink.
The simulation results from this model aided in selecting
appropriate accelerometers and rate gyros. Below are a
few major results.
System Testing:
•IMU subjected to expected EMI to ensure aluminum Faraday cage properly
shields system
•Microcontroller and data logging operation validated by examining collected
data and checking against functional requirements
•Test flight conducted to ensure system functions properly for duration of a
mission while experiencing flight conditions
The figure on the right is a Simulink simulation of rotational
rates that can be expected on-board the payload. From
the simulation, the payload can be expected to experience
rotational rates up to 55 degrees per second.
The two Simulink figures to the right
correspond to the normal and
tangential accelerations that are
expected to be experienced by the
payload. The simulations indicate that
1.5g is the maximum acceleration
expected to be experienced by the
Estimated Personal Effort
Estimated Cost
Prototype IMU
Closing Summary
Temperature Chamber
Test Platform with Angle
Measurement Encoder
Labor ($10/hr)
Faculty Advisor:
The Dec08-01 senior design team has successfully designed, tested, and
implemented a 6-degrees of freedom IMU. The ImAP project will continue to
develop an improved data acquisition technique for maximizing agricultural
productivity until completion.
Dr. John P. Basart
Matthew Nelson
ISU Space Systems and Controls Lab
Dec 08-01
Team Members:
Julian Currie
Luis Alberto Garcia
Amardeep Singh Jawandha