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Summary of Contents for Shimmer Shimmer3
- Page 1 Copyright © Shimmer Research 2013 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.1 IMU User Guide Revision 1.4...
- Page 2 Neither the name of Shimmer Research, or Realtime Technologies Ltd. nor the names of its contributors may be used to endorse or promote products derived from this document without specific prior written permission.
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Page 3: Table Of Contents
Safety Considerations ....................... 22 6.4. Firmware ......................... 22 FAQs ............................23 References ..........................24 Appendix ..........................26 9.1. Legacy hardware: Shimmer2/Shimmer2r ................. 26 9.2. Legacy Hardware: Shimmer IMU daughterboards............. 31 9.3. Legacy sensor axis directions .................... 34 9.4. Errata and Updates ......................35... -
Page 4: Introduction
The Shimmer 9DoF IMU daughterboard has a both a gyroscope to measure angular velocity and a magnetometer to measure magnetic field, which, combined with the accelerometer on the baseboard, can give a kinematics solution with 9 degrees of freedom (DoF). -
Page 5: General Information
A Shimmer 3, Shimmer 2, Shimmer 2r* device programmed with appropriate firmware. For example for Shimmer 3, LogAndStream (v0.6.0 or greater) can be used to log data or stream data over Bluetooth while SD Log (v0.12.0 or greater) can be used to log data to the SD card;... -
Page 6: Inertial Measurement Units
Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 3. Inertial Measurement Units This sections provides a brief introduction to IMUs (sometimes known as kinematic sensors) and the signals that they measure. 3.1. Accelerometer... - Page 7 Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 A good way to understand why the measured acceleration due to gravity points in an upward direction is to imagine that an accelerometer is a hollow cube with a ball inside, as illustrated in Figure 3-1.
- Page 8 Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 Figure 3-2 Acceleration in positive Y-direction Now, let’s lift the assumption that the ball is weightless and include the effect of gravity. If the accelerometer is motionless, the ball will rest on the bottom face of the hollow cube. Just as you...
- Page 9 The Shimmer3 is equipped with tri-axial accelerometers (as is the Shimmer2r). The default representation of its reference axes, as assumed in Shimmer applications, is arranged as shown in Figure 9-2. Thus, the acceleration measured by the Shimmer device has three components, one in...
- Page 10 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 Figure 3-4 Shimmer3 default axis directions To understand how the acceleration is distributed across the axes, we consider, first, a single axis (uni-axial) accelerometer. Uni-axial accelerometer A uni-axial accelerometer measures the sum of the inertial acceleration component and gravitational acceleration component acting along its single measuring axis.
- Page 11 Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 In the insert at the left side of the figure, the sum of the inertial and gravitational acceleration vectors is illustrated by a dashed arrow, .
- Page 12 Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 Figure 3-6: Bi-axial accelerometer attached to a leg segment The insert at the left side of the figure shows the vector sum of the inertial and gravitational acceleration components, as in Figure 3-5.
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Page 13: Angular Rate Gyroscope
A rate gyroscope can be used to measure angular velocity. The Shimmer3 is equipped with a tri-axial rate gyroscope to measure angular velocity in three dimensions. (For Shimmer2r, the 9DoF IMU daughterboard or Gyro IMU daughterboard is required.) -
Page 14: Magnetometer
Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 Figure 3-7: Uni-axial rate gyroscope attached to a rotating plate The angular velocity measured by the gyroscope, whose measurement axis, , makes an angle, ,... - Page 15 For example, in Dublin, Ireland, the angle is approximately 68°. The Shimmer3 is equipped with a tri-axial magnetometer to measure the local magnetic field in three-dimensions. (For Shimmer2r, the 9DoF IMU daughterboard is required,) To understand how the magnetic field measurement is distributed over the three sensing axes, it is useful to, first, consider a uni-axial magnetometer.
- Page 16 Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 where is the magnitude of the magnetic field vector component along the measuring axis of the magnetometer, is the angle between the magnetometer measuring axis and the magnetic field vector, is the magnitude of the magnetic field acting on the sensor.
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Page 17: Inertial Sensor Signals
For a tri-axial sensor, if the value of the sensed phenomenon vector is , then the sensor output, , can be described by: where For more detailed information on the calibration of kinematic sensors, please refer to the Shimmer 9Dof Calibration Application and the associated User Manual and Tutorial videos, available from www.shimmersensing.com. -
Page 18: Kinematic Parameters
), is the offset bias vector, and is the noise vector. The average noise affecting the kinematic sensors on the Shimmer3, Shimmer2r, Gyro IMU daughterboard and 9DoF IMU daughterboard is summarised in Section 6.1 and Appendix 9.1. 4.2. Kinematic Parameters... -
Page 19: Coordinate Systems
Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 magnetometer, as outlined in Sections 3.1 and 3.3, whilst sensor fusion of at least accelerometer and gyroscope is required to accurately estimate continuous angular displacement for moving bodies. -
Page 20: Applications Of Imus
Please note that solutions to these applications are not directly supported by Shimmer and the information below is intended as a starting point for the new user, unfamiliar with the relevant literature. -
Page 21: Fall Detection
Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 5.4. Fall detection Fall detection is a common application of IMUs in healthcare, with concerns about an ageing population generating significant research interest in recent years. A basic but over-simplistic method for detecting falls using an accelerometer alone, would be to calculate the magnitude of the measured acceleration and compare this to a threshold to detect a large spike due to an impact. -
Page 22: Practical Usage Considerations
Please refer to the manufacturer's datasheets for detailed information. Gyroscope The output of the gyroscope device on the Shimmer3 is digital. The gyroscope on the MPU-9150 chip from Invensense is used. The following approximate values apply to these devices: ... -
Page 23: Noise Specifications
Table 1 shows the noise performance that can be expected at varying signal bandwidths for the IMU devices on a Shimmer3 unit. The sampling rate in each case was 500 Hz and a low-pass filter was used to vary the bandwidth. -
Page 24: Faqs
Ensure that you have attached a Shimmer 9DoF IMU daughterboard to the Shimmer baseboard before you try to stream or log magnetometer data and that you have attached either a 9DoF IMU daughterboard or a Gyro IMU daughterboard to the Shimmer baseboard before you try to stream or log gyroscope data. -
Page 25: References
Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 8. References Bourke, A. K., O'Donovan, K. J., & O Laighin, G. (2008). The identification of vertical velocity profiles using an inertial sensor to investigate pre-impact detection of falls. Medical Engineering & Physics , 30 (7), 937-946. - Page 26 Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 Won, S. H., Melek, W. W., & Golnaraghi, F. (2010). A Kalman/Particle Filter-Based Position and Orientation Estimation Method Using a Position Sensor/Inertial Measurement Unit Hybrid System.
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Page 27: Appendix
3. 3-axis Magnetic Sensor and 3-axis Gyroscope with User Interaction controls All of the configurations extend the capabilities of the Shimmer platform. Note that Figure 9-1 and the notes in this section refer to current production hardware only, i.e. SR16-6 or later. For older hardware, please refer to Section 9.2 Legacy Hardware: Shimmer IMU daughterboards. - Page 28 Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 Figure 9-1: Board layout If the locations marked U1 and U2 are empty, then there is no gyroscope capability on your device. If the location marked U5 is empty, then there is no magnetometer capability on your device.
- Page 29 A highly integrated MEMs sensor provides 3-axis magnetic field sensing capabilities (digital compassing) on the Shimmer 9DoF IMU daughterboard. A HMC5883L device from Honeywell is used. The Shimmer's I2C interface is used to configure and communicate with the sensor. The key features are listed below: ...
- Page 30 The indicator, D1, is active low and tied to USER_LED/SER0_RXD on the Shimmer baseboard. The LED should not be confused with the coloured indicators on the Shimmer baseboard (which are exercised by the sample program blink). Possible uses for the UI components on the board, in a logging or streaming application, are: ...
- Page 31 Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 User Button press: Start/Stop logging or data transmission. LED: On when logging or streaming data. Noise Specifications Table 3 shows the noise performance that can be expected at varying signal bandwidths for the accelerometer on a Shimmer2r unit and the gyroscope and magnetometer on an SR16-6 daughterboard (illustrated in Figure 9-1).
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Page 32: Legacy Hardware: Shimmer Imu Daughterboards
No Connect Table 4: Expansion Connector Pin-Out Firmware Developers should leverage the driver and test application code in the TinyOS and Shimmer github repositories for Shimmer2r. The Shimmer User Manual also includes tutorial information in the embedded firmware section. The I2C interface used for magnetic sensing is on USART0, a shared resource with the microSD card on Shimmer, Shimmer2 and Shimmer2r platforms. - Page 33 Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4 magnetometer device from Honeywell and IDG-500 and ISZ-500 MEMs gyroscope devices from Invensense, with hardware configurable gyroscope signal range and optional user interaction controls. The following information is provided as legacy support for these devices.
- Page 34 Please refer to the manufacturer's datasheets for detailed information. Gyro Signal Range The output of the Gyro MEMs devices is analog. The Shimmer 9DoF IMU daughterboard has a fixed reference output and runs off of a secondary LDO for improved power-supply noise rejection. Zero-...
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Page 35: Legacy Sensor Axis Directions
2mV/°/sec. In 110°/sec that value is 9.1 mv/°/sec. In both cases, the full scale range is .35V-2.35V, well within the range of the Shimmer's ADC. IDG-500 and ISZ-500 MEMs devices from Invensense are used. Please refer to the manufacturer's datasheets for detailed information. -
Page 36: Errata And Updates
IMU User Manual All rights reserved Rev 1.4 Figure 9-2: Shimmer accelerometer axis directions - Shimmer baseboard only enclosure (left) and Shimmer IMU enclosure (right) 9.4. Errata and Updates The accelerometer RMS noise values quoted in Table 6.2 of v1.0 of this User Guide were erroneously... - Page 37 Copyright © Shimmer 2016 Realtime Technologies Ltd IMU User Manual All rights reserved Rev 1.4...
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