VEHICLE OPERATOR SAFETY:THE ADVANTAGES OF USING ELECTRONIC SENSORS IN OFF-ROAD VEHICLES


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Abstract:

In extreme outdoor conditions, vehicles are designed to perform arduous tasks .Vehicles must navigate on uneven surfaces while lifting and moving heavy loads in areas like industries such as construction, agriculture and forestry. For vehicle operators, the chances of tipping or rolling over are high, and safety is a concern. Operator’s safety is increased by installing preventative measures such as electronic sensors to detect the vehicle’s operating condition and alignment. The sensor families which are used in off-road vehicles include tilt sensors, inductive position sensors and pressure sensors. This paper will describe the advantages of using these three distinct sensor types in off-road vehicles to ensure the safety of operator.

Introduction:

To prevent vehicle operator injury, electronic sensors can be used in off-road vehicles to warn the operator if the vehicle or its load is in danger. The technologies behind each sensor family will be examined as well as application examples presented.
Environmental exposure is also a safety factor. As virtual "plants-on-wheels," off-road vehicles are exposed to extreme shock and vibration, harsh chemicals, dirt and electrical interference. The sensors used on these vehicles must be able to withstand these same extreme conditions to prevent mechanical damage and downtime.
Tilt Sensors Monitor the Safe Horizontal Alignment of Vehicles
Rugged terrain and moving machine parts can quickly shift the balance of a vehicle. A dangerous alignment can cause hazardous conditions for a vehicle operator. To assist operators in monitoring the horizontal alignment of vehicles, tilt sensors precisely detect slight angle variations. Tilt sensors can report, for example, the exact road-grade angle, boom angle, platform angle and crane-level angle. Upon receiving these signals, an operator can take action to avoid an unsafe situation.
Tilt sensors must be able to withstand the extreme shock, vibration, and harsh elements associated with outdoor use. Direct exposure to chemicals, dirt, moisture, sunlight, and electrical interference is common. Design features that enable tilt sensors to resist the elements and perform in extreme environments include:
• Compact housings - rated for IP67 protection - encase and protect the electronics from chemicals and liquid ingress,
• UV-resistant plastic and metal housings prevent damage from exposure to sunlight,
• Noise-immune technology enables the sensors to ignore conducted and radiated electrical noise.
• Outputs protected from short-circuits and overloads eliminate damage during installation,
• Highly flexible cables, jacketed to resist chemicals and perform at temperatures as low as -40 °F.
Two very different, yet highly effective sensing technologies can be applied to verify horizontal alignment.

Electrolytic tilt sensing

The first technology is referred to as electrolytic tilt sensing1. Sensors filled with electrically conductive liquid are fitted with two internal measuring cells. By applying an alternating voltage between the cells’ electrodes, current flows through the liquid and generates an electrical field. If the sensor tilts, the fluid surface remains level, so the electrical field changes - as well as the fluid’s level-dependent resistance. The measuring cells monitor any change in the liquid’s conductivity and thus detect angle variations of the X and Y axes with precision. Sensors using this technology are appropriate for platform leveling (narrow tilt angle ±15°) or where high precision (0.025°) and a flexible network connection are advantageous.


Electrolytic tilt sensing technology: measuring cells monitor any change in the liquid’s conductivity to detect angle variations.

MEMS sensing technology

The second technology is micro electromechanical sensing (MEMS)2. A silicon mass is suspended in the sensor body by two resilient beams between two stationary capacitor plates. When the body tilts, the movement is transferred to the beams. The beams deflect to take the inertial forces of the mass. The deflection changes the relative position of the mass between two plates. Because each of the above plates is part of two separate capacitors, the deflection creates a reciprocal change in capacitance in each of the two.

Micro electromechanical sensing (MEMS) technology:

When the vehicle tilts, the movement is transferred to the beams that deflect to take the inertial forces of the mass. Any change in capacitance is proportional to the tilt of the sensor.
Any change in capacitance is proportional to the tilt of the sensor, which then is converted to a change of voltage and transferred as an analog value to the vehicle controller. Sensors incorporating this technology are better suited to applications where a single-axis wide tilt angle (±90°) and lower precision (±1°) are needed.

Inductive Position Sensors Monitor the Position of Moving Parts on a Vehicle

Inductive position sensors are designed to detect the position of moving parts on an off-road vehicle. Multiple sensors can be used on one machine to maximize the operation of the vehicle and to protect the vehicle’s operator. For example, a position sensor can be used on an industrial crane’s cable drum to detect the end of its cable, protecting the crane against machine damage. Position sensors can also monitor the rotational speed of a gear, detect the position of a platform, or sense the open- and closed-position of vehicle cab door. The position sensors provide continual feedback on the operating condition of the machine’s moving parts and send this information to the vehicle operator.
Position sensors are designed to withstand outdoor conditions and can include the following features:
• Long sensing ranges that increase the distance between the target and sensor and reduce the chance of impact and damage to the sensor.
• Flexible electronic circuitry that resists the effects of shock and vibration.
• Stainless steel, zero-leak housings encase and protect the electronics from chemicals and liquid ingress.
• Highly visible LEDs that indicate power and output status that aid in setup and monitoring, especially in direct sunlight.
• Sensing faces made of UV-resistant plastic that won’t break down from exposure to sunlight.
• Noise-immune technology that enables the sensors to ignore conducted and radiated electrical noise.