imu620_engineering_specifications

Inertial Measurement Unit Engineering Specifications

Rev. G 2013.1.5

General Description The IMU620 is a high reliable, vibration-rejecting solid state Inertial Measurement Unit. It consists of three vibrating ring gyroscopes and three internal damping accelerometers mounted orthogonally in each axis of space. Each device is factory calibrated over the working temperature range. The fusion of the sensors is performed with an extended Kalman filter to provide the optimal estimation of dynamic roll and pitch angles. The IMU620 is available in standard and high range sensor configurations.

The IMU620 is featured with a high performance vibration isolation mechanism to provide excellent reliability under vibration and shock conditions.

The IMU620 can accept external electronic compass (module number TBD) to provide optimized heading angle. GPS aided version is also available upon request.

Applications Unmanned helicopters and light helicopters UAV and AGV Platform stabilization Vessel applications Inertial navigation systems

Features Consistent performance under high vibration environment. Internal vibration isolation mechanism. Fully Calibrated for offset, scale factor, cross-axis sensitivity and misalignment of each axis of sensors.

Temperature compensated for improved bias and sensitivity stability. Double precision extended Kalman filter running at 500 cycles per second with synchronous sampling rate

at 128kSPS of each sensor. Data rate up to 250 packets per second. User-friendly RS232 digital interface. Low power consumption, typical 0.25A @ 12V. Complete against Crossbow VG440.

CNSENS INC. 1160 BRICKYARD COVE RD STE 200, RICHMOND CA 94801-4173

CNSENS IMU/ VG/ AHRS62 0

Add:Room B-1120 No.15-1 Jian Guo Road, Chao Yang District, Beijing, China.100024Tel:+86 10-52875407 Fax:+86 10-85376704 E-mail:[email protected] www.cgs-tech.com

Table. 1 SpecificationsNote

Terms Values Remark

Heading (Pending)

Range (°) ±180

Accuracy (°) < 1° With compass aiding or GPS aiding

Resolution (°) 0.01 Attitude

Range: Roll, Pitch (°) ±180, ±90 Accuracy (°) <0.3° Helicopter steady flight or hovering Resolution (°) 0.01

Angular rate Range: Roll, Pitch, Yaw (°/sec)

±150, ±300 Standard configuration

±900 High range configuration Bias absolute error (°/sec) < 0.5deg/s Over working temperature, without Kalman Filter <0.02 deg/s Kalman Filter stable Bias stability in-run((°/hr) 6 Typical, Allan Deviation

Resolution (°/sec) <0.01

Angle random walk (°/√hr) 0.1 Typical Noise density(°/s/√Hz) 0.002

Acceleration Range: X,Y,Z(g) ±12g ±4 for low range version

Bias stability(m/s2) 4×10-4 Typical, Allan Deviation

Resolution (mg) <1mg

Noise density(mg/√Hz) 0.08

Bandwidth

Sensor Bandwidth 20Hz With internal filtering

Environments

Shock survival in run 750g@1ms Shock survival power off [email protected] Vibration Operational 6g rms 20Hz-20kHz, random Operating temperature -20°C ~85°C -40°C ~105°C with reduced spec

Enclosure level IP66 Compliant

Electrical Input Voltage (DC V) 11-13 Surge clamping above 15.0V

Size (mm) 74×60×56 Weight (g) <400

Connector Micro-DB9 Note: Subject to change without notice, unless requested. Warning: placing the IMU beyond the specifications may damage the device temporarily or permanently.



FLIGHT TEST PERFORMANCE Test results vs. Crossbow VG440 in dual cylindeer gasoline combustion engine (80cc volume total) unmanned helicopter, high dynamic flight. (VG440 is installed with external dampers, IMU620 is installed with screws only, without any external dampers)

Fig.1 Photo of flight tests

Fig. 2a Pitch comparison

Fig. 2b Pitch comparison in zoomed detail



Fig. 2c Roll comparison

Fig.2d Roll comparison in zoomed detail

Sensor Allan Deviation Following plots are static sensor Allan Deviation plots in 25°C constant temperature. Data was collected during 10 hour’s period. Angular rate’s bandwidth is 20Hz, acceleration’s bandwidth is 5Hz.

Fig.3 Typical Allan Deviation of angular rate (left) and acceleration (right)



Electrical connections The IMU620 is supposed to be powered with 12V typical (range 9-12.5V) stable DC voltage. The connector is J30J-9TJ 9-pin female provided with the IMU620. Pin definitions are listed below:

Table 2. Pin definitions

Pin Number Function

1 Positive power supply

2 Ground power supply

3 RS-232 transmit

4 RS-232 Receive

5 Auxiliary RS232 Transmit

6 Auxiliary RS232 Receive

7 PP1S input for time alignment

8 Heart beat signal output (toggle every second)

9 Signal ground

Orientation IMU620 is designed according to NED right hand rule coordinate system. The angle around x axis is defined as roll, around y is defined as pitch and around z is defined as yaw.

Fig.4 Axes orientation

Tips for having best performance Inertial sensors are extremely sensitive to environment conditions like temperature change, vibrations, shocks, power supply instabilities etc. Although these conditions have been taken care in the design and fabrication process of IMU620 to eliminate negative impacts from environment, it is highly recommended that the users have the following attentions when applying the IMU620. 1. Power supply should be as stable and low noise as possible. When using long cables, place capacitors or

EMI filters near the IMU side. Use external voltage regulator if necessary. 2. Avoid mounting the IMU near vibration sources like motor rotors and engines. If performance is degraded

by vibration, proper external vibration isolators may be required. Also be cautious that external vibration isolators may cause unwanted resonance in certain conditions, which should be avoided.

3. Avoid large and frequent temperature variation during operation.

X axis

Y axis

Z axis


4. Align the IMU to the body axes as accurate as possible. 5. Try to mount the IMU as close as possible to the center of gravity of the machine.

User protocols Command for Vertical Gyro mode:

Table 3. Command: VG mode Byte No. Content Description

1 0xBD First header byte 2 0xDB Second header byte 3 0x65 Attitude (with Sensor) Output command byte 4 0x03 Checksum: Byte-wise XOR of byte 1 to 3.

The output packet format is type VG 0x04. Refer to Table 3 for detailed format.

Table 4. User packet format Byte No. Content Description

0 0xBD First header byte 1 0xDB Second header byte 2 Status 0x04 3

Roll LSB of Roll

4 MSB of Roll 5

Pitch LSB of Pitch

6 MSB of Pitch 7

Yaw LSB of Yaw

8 MSB of Yaw 9 DEBUG0 LSB of DEBUG0

10 MSB of DEBUG0 11 DEBUG1 LSB of DEBUG1 12 MSB of DEBUG1 13 GX LSB of x-axis gyroscope 14 MSB of x-axis gyroscope 15 GY LSB of y-axis gyroscope 16 MSB of y-axis gyroscope 17 GZ LSB of z-axis gyroscope 18 MSB of z-axis gyroscope 19 AX LSB of x-axis accelerometer 20 MSB of x-axis accelerometer 21 AY LSB of y-axis accelerometer 22 MSB of y-axis accelerometer 23 AZ LSB of z-axis accelerometer 24 MSB of z-axis accelerometer 25 Temp LSB of temperature sensor 26 MSB of temperature sensor 27 Timestamp LSB of timestamp 28 Mid1 of timestamp 29 Mid2 of timestamp 30 MSB of timestamp 31 Info LSB of INFO 32 MSB of INFO 33 Checksum Byte-wise XOR of byte 0 to 32

Default 2D AHRS mode protocol

Table 5. Command: 2D AHRS mode Byte No.

Content Description

1 0xBD First header byte 2 0xDB Second header byte


3 0x45 AHRS mode (2D compass)

4 0x23 Check sum Table 6. Command: 2D AHRS packet

Byte No.

Content Description

0 0xBD First header byte 1 0xDB Second header byte

2 Status 0x05(2D compass) 0x08 (3D compass)

3 Roll

LSB of Roll

4 MSB of Roll

5 Pitch

LSB of Pitch

6 MSB of Pitch

7 Yaw

LSB of Yaw

8 MSB of Yaw

9 DEBUG0 LSB of DEBUG0

10 MSB of DEBUG0

11 DEBUG1 LSB of DEBUG1

12 MSB of DEBUG1

13 GX LSB of x-axis gyroscope

14 MSB of x-axis gyroscope

15 GY LSB of y-axis gyroscope

16 MSB of y-axis gyroscope

17 GZ LSB of z-axis gyroscope

18 MSB of z-axis gyroscope

19 AX LSB of x-axis accelerometer

20 MSB of x-axis accelerometer

21 AY LSB of y-axis accelerometer

22 MSB of y-axis accelerometer

23 AZ LSB of z-axis accelerometer

24 MSB of z-axis accelerometer

25 MX LSB of x-axis magnetic field

26 MSB of x-axis magnetic field

27 MY LSB of y-axis magnetic field

28 MSB of y axis magnetic field

29 MZ LSB of z-axis magnetic field

30 MSB of z-axis magnetic field

31 Temp LSB of temperature sensor

32 MSB of temperature sensor

33 Timestamp LSB of timestamp

34 Mid1 of timestamp

35 Mid2 of timestamp

36 MSB of timestamp

37 Info LSB of Info

38 MSB of Info

39 Checksum Byte-wise XOR of byte 0 to 38 Angle and sensor output data are 16-bit scaled integers. To scale into degrees, multiply Roll, Pitch or Yaw by this factor: 360/215. To scale into degrees per second, multiply angular rates by this factor: GRange/215. To scale into g, multiply accelerations by this factor: ARange/215. The ARange and GRange can be found in the Info word:


Table 7. Info word definition

15 14 13 12 11 10 9 8 Model2 Model1 Model0 SW ver2 SW ver1 SW ver0 HW

ver1 HW ver0

7 6 5 4 3 2 1 0

GRange2 GRange1 GRange0 ARange1 ARange0 Sys warning

Sys Err

Over range Err

Model <2..0> 000 IMU810 001 IMU620 010 WS602 011 MiniIMU 1xx Future models SW ver <2..0> Software main version HW ver<1..0> Hardware main version GRange<2..0> Gyro measurement range 000 75deg/s 001 150deg/s 010 200deg/s 011 300deg/s 100 573deg/s 101 900deg/s ARange<1..0> 00 2g 01 3g 10 5g 11 12g

Sys warning: System warning Sys Err: System initial or in-run error Sensor Saturation warning: sensor Saturation warning. Warnings will be cleared if no new warnings come up for 1 sec.

Using IMU62 0 Assistant Software The IMU620 Assistant Software (current version 1.2) is designed for the user’s easy configuration and viewing the status of the IMU. The software interface is shown in Fig.5.



Fig.5 IMU620 Assistant Software

Serial Port area: includes baud rate and COM port settings of PC side. Binary Operations area: Operations under binary protocol. Binary Data area: shows attitude and/or sensor data real time under binary protocol mode. ASCII Operations area: Operations under ASCII protocol. Artificial Horizon area: Graphical viewer of attitude Heading Area: Graphical viewer of attitude Message Window area: shows messages from IMU or PC software.

Disclaimer: CNSENS Sense Inc. does not responsible for any damage, injury and deaths caused by applying this product or technology to aircrafts, weapons, or other life maintaining and any other systems.




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imu620_engineering_specifications