How Sensors Are Moving Material Handling Towards Safe Automation

Next generation sensing technologies put the smart in robot AGVs.

Industry 4.0 is enabling a new generation of smart manufacturing and distribution facilities, requiring new ways of thinking in all aspects of material handling, especially when it comes to functional safety and reducing accidents in the workplace. Today’s smart manufacturing integrates as much of the process as possible into a single manageable entity.

Such a high level of process integration requires several challenging steps, like eliminating human handling points, connecting the processes of multiple lines, and creating a flow management that follows a part throughout the process. Frequently this requires moving components and/or materials from one conveyor belt to another, often in different buildings.

Taking on these challenges, Automated Guided Vehicles (AGVs) transfer parts and products, working within an intelligent manufacturing system. Each part of a facility can connect to any other for process and inventory control, with top-level oversight and management of the entire system. AGVs can automate the operational link among different systems in a manner not cost-effective using other methods.

Most AGVs automate material handling and packaging logistics, with man and machine working together. A few companies are taking automation to the next level by adding a robot arm to pick the desired object, taking man completely out of the equation. This can also be accomplished by having transfer mechanisms at the start and end of every separate process area.

Integrating production systems with AGVs has been shown to be more efficient and cost-effective than human-controlled material handling, while being intrinsically safer. Despite these benefits barriers to wider adoption exist, even beyond the hefty initial investment. For instance, there is not yet a single navigation technology against which a consistent standard can be set.

Navigation Technologies
There are many types of navigation technologies in the market, but some, like wired guidance, are less frequently used. Although more precise positioning and control requirements play a minor role in causing some technologies to fall out of favor, this is happening mostly due to device integration into modules and the advent of newer technologies like LiDAR.

Magnetic navigation uses a magnetic tape for the guide path. One major advantage of tape over wired guidance is that it can be easily relocated if the course needs to change, removing the expense of restructuring. However, the routes have to be fixed and well-defined by the tape. If any obstacle is detected in front of the AGV, it stops and must wait for the problem to be solved (for example, the obstacle to be removed) before it restarts.

Laser-guided navigation is like an electronic eye, using reflectors on the surrounding walls to triangulate and determine the exact position of the vehicle. The advantage is that it requires no floor work, and route changes can be made easily via software updates.

Vision-guided vehicles use cameras to navigate, using software within the vehicle to build a 3D map of its operating environment. This technology allows the vehicles to operate in automatic or manual mode for maximum flexibility. These vehicles use wheel sensors and other inputs to confirm and collaborate the optical data.

Legacy camera-based vision can be enhanced with improved software for pattern recognition and image identification. And a newer technology, Light Detection and Ranging (LiDAR) shoots laser pulses in very rapid succession and captures the reflections with an optical sensor to create a three-dimensional map of the surroundings.

Figure 1: Sensata-Quanergy’s solid state LiDAR sensors provide a more affordable and reliable navigation solution than traditional mechanical models.

Traditionally, LiDAR sensors have been costly and based on a mechanical scanning design. LiDAR technology is moving forward however, and new, entirely solid-state solutions (i.e. they have no moving parts) require less power and deliver higher resolution at a longer range. Not only is this new generation of LiDAR sensors more reliable than mechanical models, with advances in research and development, and increases in volume, LiDAR technologies are also becoming more affordable. By mounting several small solid-state LiDAR sensors in an array, it’s possible to create a live 3D surround view that can detect and track stationary and moving objects.

Encoders Monitor Speed and Direction
Used to monitor ground speed and direction, highly precise and safety-rated encoders can be certified to industry standards of performance and safety levels. For AGV applications, components that are rated up to Safety Integrity Level 3, or SIL3, are ideal, as this allows for the highest safety level in the system. SIL3-rated encoders can often be more expensive than those of a lower safety rating, but they greatly reduce the risk of costly damage or injury.

Draw-Wire Sensors Ensure Proper Mast Height
When it comes to forklift and pallet truck AGVs, additional encoders and position sensors are required to ensure safe and controlled operation. Controlling the mast or fork height in a lift truck is crucial for proper load positioning, as goods must be safely removed or stored at varying heights and to prevent collisions with overhead items (Figure 2). Also known in the industry as cable transducers, string potentiometers, linear position string pots, and string encoders, draw-wire sensors are used to provide precise linear position feedback of the mast.

Figure 2: Designed for use in warehouses and manufacturing plants, Autonomous Material Handling vehicles rely on a combination of advanced and basic sensing technologies to operate safely and efficiently.

These components utilize a flexible cable, a spring-loaded spool, and a sensor (an optical encoder with incremental, absolute, analog or potentiometric output or, in some cases, a Hall effect sensor) and are ideal for wet, dirty, or outdoor environments. This type of position sensor can also be used in AGVs to monitor lateral fork movements for automatic pre-setting to various pallet sizes.

Rotary Hall Effect Sensors Help Prevent Load Spills
AGVs employ rotary Hall effect sensors for different functions like the fork tilt control in lift truck AGVs (and lift trucks in general). Positioned at the bottom of the mast, this sensor determines the inclination of the fork and prevents the load from being spilled. Pressure sensors help control the load weight in forklifts, and load cells can be used for the same function in unit load carriers; in magnetic navigation systems, specific sensors for track guidance along magnetic tape are used.

AGVs guided by inertial navigation use transponders to verify that the vehicle is on course and a gyroscope to detect the slightest change in the direction of the vehicle. In lift truck applications, compact photoelectronic sensors are integrated into the narrow fork cone ends as well as the metal chassis in order to prevent the AGVs from colliding and to safely load and unload pallet materials.

Steering Control Configurations
AGV steering control comes in a variety of configurations. To determine what method is the best fit for a particular vehicle and application, four factors are usually considered: the ease of building; the steering and driving capabilities; the ability to navigate in confined areas; and the overall cost of the vehicle. The three most commonly used set ups for steering control in AGVs are the three-wheel, differential, and quad configurations.

The three-wheel configuration is the most common solution for lift truck AGVs. They are relatively easy to implement and provide very accurate control. Frequently, this design relies on encoders to monitor and measure the speed and direction of one master wheel that determines the vehicle’s movement.

The differential configuration is a popular solution for unit load carrier and tow-vehicle (or tugger) AGVs, as it is possible to rotate around the center of the vehicle, although with some turning limitations. The steering control is achieved using different speeds in either forwards or backwards directions on the two controlled wheels, where a single motor and an encoder are used on each wheel.

A quad wheel configuration offers the most maneuverability as it permits 360 degrees of movement in any direction, making it the ideal solution for unit load carriers. The ability to steer the vehicle in a sideways or crabbing motion allows for better and more accurate navigation in tighter and more challenging spaces. As there are more wheels that require steering controls and accompanying motion control components such as encoders and sensors, this type of configuration is the most complex.

The material handling sector is one of the most important to designers, manufacturers, and engineers working with sensing and control technologies, and the rise of Automated Guided Vehicles is accelerating the development of new and even more sophisticated sensing solutions.

The increasing interaction between man and machine means that the watchword in material handling remains ‘safety,’ and this in turn means that sensors and controls manufacturers are continuing to raise the bar in innovation and excellence, while at the same time reducing cost and size. Today’s emerging sensing technologies are fast becoming the standard product of tomorrow, as material handling equipment designers, manufacturers, and operators seek greater efficiencies, better performance, and the highest possible levels of safety.

Alessandro Bosio is a Global Segment Manager at Sensata Technologies, one of the world’s leading suppliers of sensing, electrical protection, control and power management solutions with operations and business centers in 12 countries. He is responsible for developing and executing market strategies for various industrial engineering segments such as Material Handling and Industrial Autonomous Vehicles. He has 20 years of experience in industrial automation and process control, with a global view of market needs as a result of his experience working in both Europe and Asia, as well as in the U.S. where he currently lives.





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