This portable data acquisition system is a viable alternative to first developing a fully instrumented test vehicle.
The study of driver behavior can provide a wealth of information that can be useful in the design of automobiles including active safety features and functions. There may be differences in driver behavior, as reflected in driver state, and these differences may be confounded by a driver’s condition. Much can be learned from studies that look at driver state and condition to answer questions such as how vehicle features and functionality could be designed to complement the driver’s capabilities and limitations in the vehicle. Also, a better understanding could be gained to determine how, or if at all, a safety feature’s characteristics should be modified to accommodate a driver’s condition.
Whereas driver state can often change during the course of a drive, driver condition is generally not a transient, e.g. a driver with asthma or hypertension. A record of the variation of driver state during the course of a drive and a corresponding record of a driver’s condition can be maintained for analysis. A transportable instrumentation package (TIP) has been developed for in-vehicle data acquisition. The TIP is designed to be portable from vehicle to vehicle, and can acquire a full range of signals for driver state monitoring without interference with normal driving.
The TIP system consists of four modules: a physiological module (P-M) to record physiological measures of interest; a video and audio module (VA-M) that can record four video and one audio channel; a vehicle module (V-M) to record vehicle parameters during real-time driving; and a positioning sensors signals module (PS-M). These four modules are integrated through a commercially available data-logging device, which synchronizes all signals and has powerful onboard processing (see Figure 1). The real-time data can be viewed live (on a display or video).
The most commonly used physiological signals include an electromyogram (EMG), electrocardiogram (ECG), galvanic skin response or skin conductivity level (GSR), and respiration (RSP) through chest cavity expansion. In TIP, devices were used to record these physiological signals. The ECG signal provides a record of the changes occurring in the electrical potentials between different sites on the skin as a result of cardiac activity.
The GSR, also known as the electro dermal response (EDR), measures the activity of the eccrine sweat glands. The two electrodes of the GSR device should be wrapped around two fingertips. The transducer provides a small constant current between the electrode sites, and the measured resistance between the two electrodes constitutes the electro dermal response.
Respiratory signal is recorded as a measure of the change in thoracic circumference. The transducer is a silicone rubber strain assembly that connects to a fully adjustable nylon strap to allow the transducer to fit any circumference. The transducer is placed around the area of maximal expansion when the subject breathes, and was fitted so that it is snug.
The three physiological sensors are connected to a transmitter that includes operations such as filtering, offset, and gain control for each of its three signal channels. The signal data are transmitted to wireless receivers. The receiver is connected to an amplifier, which is connected to a laptop by a LAN cable. From the three primary signals, heart rate, heart beat interval, respiration rate, respiration interval, and skin conductivity can be calculated.
A high-resolution camera of 540+ TV lines was used for driver face image, and one video camera was used to capture the driver’s foot movement. A steering wheel sensor measured the grip pressure. A microphone with optimized gain control and frequency response (considering in-vehicle noise) recorded vocal comments while driving.
Six video cameras are used in TIP. The driving environment is captured with four video cameras: one provides the front view, and two provide the left and right side views. One camera provides the facial view of the driver, and the sixth camera is used to record the driver’s braking/foot action (see Figure 2).
In addition, a steering wheel pressure sensor and an ambient light sensor were built. The steering wheel sensor is composed of an end device and an access point. The end device is connected to a strip force sensor that picks up the pressure made by the driver when the steering wheel is grabbed.
The TIP system can be installed in a given vehicle in less than 30 minutes. It is only necessary to attach the video cameras and steering wheel sensors to predefined places, connect the data-logging device to all the video cameras and the OBD port, attach the physiological sensors to the driver, and connect the receiver to the laptop.
This work was done by Dev Kochhar of Ford Motor Co.; and Yi L. Murphey, Fang Chen, Yinghao Huang, and Yong Wang of the University of Michigan-Dearborn. The full technical paper on this technology is available for purchase through SAE International at http://papers.sae.org/2013-01-0202.