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Image Acquisition and Processing of Remotely Sensed Data (ImAP RSD). Dec08-01: Inertial Measurement Unit (IMU) Team: Luis, Julian, Amar , Matt Client: Matthew Nelson - Space Systems and Controls Lab (SSCL) Advisor: Dr. Basart. Presentation Outline. Background/History

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image acquisition and processing of remotely sensed data imap rsd

Image Acquisition and Processing of Remotely Sensed Data (ImAP RSD)

Dec08-01: Inertial Measurement Unit (IMU)

Team: Luis, Julian, Amar, Matt

Client: Matthew Nelson - Space Systems and Controls Lab (SSCL)

Advisor: Dr. Basart

presentation outline
Presentation Outline
  • Background/History
  • Requirements Specification
  • Project Plan
  • Design
  • Testing/Verification on IMU system
  • Project Evaluation
imap rsd motivation
ImAP RSD Motivation
  • Methods of monitoring crop health over large areas are currently cost and labor intensive
    • Airplane
    • Manual Inspection
  • ImAP RSD initiated by SSCL HABET program to develop an improved method of monitoring crop health
    • Automated photography via high-altitude weather balloon
      • Accomplished by integrating multiple subsystems including:
        • Horizon Detection, Inertial Measurement Unit, GPS, Processing, and Camera systems
imap system description
ImAP System Description
  • The ImAP RSD system will be mounted as a payload attached to a high-altitude weather balloon.
  • The onboard sensor systems will be used to determine payload flight path and orientation
  • This system will capture images at predetermined waypoints using flight prediction software
  • Collected field images will be analyzed to extract image intensities and make geometric corrections
  • The corrected images will be transferred to a plant pathology team who will interpret the images
horizon detection system
Horizon Detection System
  • Developed by previous team to determine pitch and roll
  • Thermopile System
    • Compares sky and ground temperatures to determine horizon
  • Image System
    • Aquires images and uses DSP to determine horizon
  • Completed in Spring of 2008
dec08 01 problem statement
Dec08-01 Problem Statement

The ISU SSCL requires an Inertial Measurement Unit (IMU) and data logging system for the ImAP RSD project.

operating environment
Operating Environment
  • The payload will operate at altitudes from 20,000 – 30,000+ feet
  • The payload will experience temperatures ranging from -40° to 80°C
user interface
User Interface
  • RCA power jack
    • 11V
  • Serial Port
    • RS-232
      • BCD to primary processor
  • Logomatic universal data logger
    • SD Card
      • Post Flight Analysis
system requirements
System Requirements

Functional Requirements

  • FR01: IMU shall measure balloon oscillation frequency and angular rotation rate to 1.215 degree per second.
  • FR02: IMU shall measure linear acceleration to 0.01g for each of the three principle axes.
  • FR03: Data logging system shall log at a 100HZ+ rate with 10 bit or greater precision.
  • FR04: IMU shall operate over a temperature range of -25˚ C to +85˚ C

Non-functional Requirements

  • NR01: IMU shall receive power from a 11.1V nominal lithium-ion battery
  • NR02: IMU shall function for a minimum of 2 hours using a 4 Amp-hour battery
  • NR03: IMU may measure temperature and voltage levels during flight.
market survey imu
Market Survey: IMU
  • Commercial IMUs
    • SEN-00839 IMU with 2 degrees of freedom for $99.95
    • Inertia-Link-2400-SK1 IMU for $2795.00
    • Military grade IMUs
    • Buying an IMU would defeat the purpose of a student project
deliverables
Deliverables
  • Project Plan √
  • Design Report √
  • Final Report
  • Project Poster √
  • IRP Presentation
  • IMU √
  • IMU User Manual √
resource requirements
Resource Requirements

Estimated Hours

Estimated Cost

***Insert Parts list cost

risks
Risks
  • Unfavorable weather
    • Continue or cancel mission
  • Power Failure
    • Schedule another flight
theory of operation
Theory of Operation

An accelerometer coupled with a rate gyro can efficiently be used for attitude determination purposes. Rate gyros measure angular rotation rates. By subtracting out known linear accelerations, an accelerometer can be use as a tilt measurement device. These two angles can be combined in an optimal fashion to accurately determine attitude.

pendulum model of habet system
Pendulum Model of HABET system

The HABET balloon and payload system has been modeled as a simple, 2-D rigid pendulum. From this model we can determine angular rates, as well as the normal and tangential components of acceleration that the payload will experience.

rate gyro model
Rate Gyro Model

The equation of motion on the left can be numerically integrated to obtain rotational rates. This model is only for roll/pitch rates.

These rotational rates will help us choose the appropriate rate gyro for our project. We have simulated this model on Simulink. The results follow.

Fig. Model for determining roll/pitch rates.

rate gyro simulink results
Rate Gyro Simulink Results

Results:

Roll/pitch rates under 75°/sec.

From past data, we have determined that yaw rates typically range from 20°- 50°.

FFT results suggest a sampling rate greater than 90Hz.

Conclusion:

Rotational rates and sampling rate obtained from math model meet functional requirements. Rate gyro used in this project, MLX90906, measures 300deg/sec, which satisfies both functional requirements and math model.

accelerometer model
Accelerometer Model

By assuming a simple pendulum, the acceleration equation reduces to the one boxed in red. This equation measures tangential and normal components of acceleration.

These acceleration values will help us choose the appropriate accelerometer for our project. We have simulated this model on Simulink. The results follow.

accelerometer simulink results
Accelerometer Simulink Results

Results:

Greatest magnitude of acceleration expected is under 1.5g.

FFT results suggest a sampling rate greater than 80Hz.

Conclusion:

Acceleration and sampling rate obtained from math model agree with our functional requirements. Accelerometer used in this project, MMA7260Q, measures ±2g’s, which satisfies both functional requirements and math model.

data storage space and
Data Storage Space and

We are required to log for a maximum of 3 hours. A 1 GB SD Card will be used for data storage

Using a baud rate of 19200 symbols/sec, we can log for approximately 28 hrs (maximum) at this rate

power budget
Power Budget

The power budget for the IMU components totals at .5034 Amp-Hours and will be powered by a 4.8 Amp-Hour battery leaving 4.2966 Amp-Hours for other systems.

rate gyro testing calibration
Rate Gyro Testing/Calibration
  • Calibration:
  • EMI effects: Electromagnetic interference degrades or obstructs the performance of the circuit.
  • Output verification using test platform:

Encoder test platform 

Rate gyro  angular rate

We compare it by differentiate and angular rate

accelerometer testing calibration
Accelerometer Testing/Calibration
  • Calibration:
  • EMI Shielding: Electromagnetic interference degrades or obstructs the performance of the circuit.
  • Tilt measurement using test platform:
test platform rotations
Test PlatformRotations

Maximum 400deg/s

conclusion lessons learned
Conclusion/Lessons Learned
  • We spent more hours on the project than anticipated.
  • The system integration and debugging consumed most of our time.
  • We tried to make the system as simple as possible.
  • The assumptions can be wrong for the same component made by different supplier and buffers for this should be accounted.
  • Ask for expert help sooner.
references
References
  • Dynamics of Flight, Stability and Control; B. Etkin, L. Reid. John Wiley and Sons, 1996
  • Aurzkai et al. ImAP Fall 2007
slide53

Euler angle rates:

p,q,r are angular rates measured by the rate gyro in the body frame. To transform into the inertial frame, we utilize the transformation matrix, T. We run this through RK4 and produce the desired angles, and thus the payload attitude.

tilt calculations
Tilt Calculations

Vout = Output of Accelerometer

Voffset = 0g offset of Accelerometer

1g = Earths Gravity

= Angle of tilt

hardware
Hardware
  • 3 MLX90609 1-axis Gyroscope
  • 1 ADXL330 3-axis Accelerometer
  • 1 GB SD Card
  • 1 Atmel Mega 128 Processor
  • 1 Logomatic SD Data Logger
  • Various Electrical components (resistors, capacitors, etc)
hardware mlx90609 gyroscope
Hardware:MLX90609: Gyroscope

Requirement:

  • Measure angular rotation to 300 degrees per second for each of the three principle axes(FR:01). Operational temperature: -40°-85°C(FR:06).

Reasons for choosing this part:

  • The MLX90609 is a 1 axes gyro that includes a breakout board for

evaluation purposes.

  • Measures 300 °/s which is not excessive and will not have resolution issues,

but also measures more than the required specifications.

  • Low Price: $59.95
  • The selling point of this gyro is the angular rate measurement and the temperature

range.

hardware adxl330 accelerometer
Hardware:ADXL330 (Accelerometer)

Requirements:

  • Measures linear acceleration to 0.01g for each of the three principle axes(FR:02). Operational temperature: -40°-85°C(FR:06).

Reasons for choosing this part:

  • Includes a breakout board which will make the evaluation process easier.
  • Very low noise density: 280μg/√Hz rms
  • Very good sensitivity change due to temperature: ± 0.015%/°C
  • Non-linearity: ±0.3
  • Low Price: $34.95
hardware atmel mega 128 microprocessor
Hardware:Atmel Mega 128 Microprocessor

Requirements:

Power and weight

Reasons for choosing the part:

light weight

price

hardware logomatic serial sd data logger
Hardware:Logomatic Serial SD Data Logger

Requirements:

  • We needed some system that had the FAT system ready to use. There is a lot of code that has to be written to be able read anything legible from the SD card

Reasons for Choosing this Part:

  • Automatically logs incoming data from the UART (saves time, and power)
  • Comes with a lot of FAT16/32 code for free on Sparkfun.com (saves a lot more time)
  • Has a place holder for the SD card which saves spaces
  • An alternative was the DosOnChip ($44.95) board which also utilizes a FAT system , but it has really poor documentation and is unavailable indefinitely.
  • Price: $59.95
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