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Navigation & Safety Systems that drive Mobile Robots

Navigation & Safety Systems that drive Mobile Robots is the core feature of mobile robots that enables the robot to direct itself from the current position to the desired destination. Navigation of mobile robots has been traditionally understood as solving the problem proposed by these three questions:

  • Where am I?
  • What are the other places related to me?
  • How do I get to other places from here?

These questions involve the determination of a collision-free path from one point to another while minimizing the total cost of the associated path. Depending on the nature of the environment, path planning can be divided into a static and dynamic environment. In a static environment, everything is static except mobile robot where obstacles change their place to time, it is also referred to as static path planning. And if obstacles change their place and orientation to time, then it is referred to as dynamic path planning. Mobile robot in a dynamic environment is finding the shortest possible path from an arbitrary starting point towards a defined goal which needs to be safe (obstacle avoidance) and smooth movement as well as possible.

Popular Mobile Robot Navigation Technologies

With the advent of the Internet of Things (IoT) & Industry 4.0 mobile robots have been used for many applications in various fields such as industry, space, defence, and other social sectors. They have been used for material handling, picking, special applications such as disinfectant robots, etc. Therefore, an intelligent mobile robot is required that could travel autonomously in various static and dynamic environments. Several techniques have been applied for mobile robot navigation and obstacle avoidance. Let’s understand some of them,

LIDAR Based Navigation –

There are several ways for sensors to map and track the environment and estimate mobile robot positioning.

LIDAR – Light Detection and Ranging technology is an essential ingredient in robotic autonomy and navigation. It allows mobile robots to extend outside controlled situations and pre-defined task functions in unpredictable and unfamiliar situations. Lidar sensors provide a constant stream of high-resolution, 3D information about the mobile surroundings, including locating the position of objects and people. Simultaneous Localization and Mapping (SLAM) technology enables the indoor capabilities of a robot with the Lidar data. The benefits provided by SLAM technology include “easy navigation without reliance on external technologies and real-time formation of 3D maps with reduced cost and power requirement”.

Vision-Based Navigation –

Vision system of the robot allows the mobile robot to see its environment as a human sees and interpret the information. Vision-based navigation technique uses a computer algorithm and data from optical sensors calculate the optimal path. The algorithm translates the visual information into concentration surroundings data so that the location of mobile robot can be identified & from there it chooses an optimal path to accomplish its goal. After that, the driving system of the mobile robot will be activated to reach its destination.

Why vision for navigation?

The conventional robot navigation systems, using traditional sensors like ultrasonic, IR, GPS, laser sensors or magnetic tape-based navigation etc, suffer several drawbacks related to either physical limitations of the sensors or being significantly expensive. Vision sensing has emerged as a popular alternative where cameras reduce the overall cost and are flexible.

Safety System

The impact of mobile robots within warehouses and factories is set to accelerate over the next five years. According to research and advisory firm LogisticsIQ, the warehouse automation market will be more than double from $13 billion in 2018 to $27 billion by 2025. With more robots expected in the workplace issues around safety and security will become more important for those working alongside them. According to Lewandowski, “Safety is fundamental”, so to take care of these safety concerns mobile robots are loaded with a 2-level sensory system, 3D cameras, and many other safety protocols. Let’s delve a bit deeper into each of them.

How safety sensors work?

Many of the mobile systems are based on the LIDAR (light datection and ranging) technology so, from a safety standpoint, the point of entry is to make sure you have what is recognized as a capable safety system to detect objects and people and to react appropriately. This also allows the robot to assess appropriate risk behaviour models, which is essential for managing safety in robot-human collaboration.

Mobile robots working outside can depend on geolocation capabilities, such as GPS alongside detecting technologies including LIDAR, to figure out where they are and where they are going to. That isn’t commonly conceivable inside. Mobile robots working inside utilize simultaneous localization and mapping (SLAM) technology that uses LIDAR’s information to build a map of the robot’s environment and find the robot inside that map.

mobile robot saftey    safety sensor_mobile robot

Mobile robots safer than conventional or manual vehicles, as they are equipped with components that help them to become more autonomous, find the correct path while in motion, make them more capable to detect and diagnose faults and understand the surrounding environment.

Let’s take a brief look at what these components are and how do they work:

  • 3D Depth Camera: One of the main safety components is the Camera to visualize every time a mobile robot passes through some object.
  • Ultrasonic Sensors & Mechanical bumpers: Apart from LIDAR and depth camera, other sensors like ultrasonic and mechanical bumper (physical contact sensor) have been used in mobile robots. To avoid Collison with unexpected obstacles, these sensors help for detecting and mapping.
  • Warning and Alarm Lights: Waring lights give audible warning signals to mobile robots, when the mobile robot is approaching a turn, the warning lights function as directional signals to alert personnel in the area of the mobile robot’s intention to branch right or left.
  • Audible Warning/Alarm Signals: If any distinct tones such as songs, the noise will occur during the operation of mobile robots – alarm warning tone will get activate.
  • Emergency Stop Buttons: When mobile robots enter an emergency stop state, emergency stop buttons automatically become active and stop the robot to move.

Equipped with the above mentioned critical components and systems, mobile robots are constantly evolving into human-friendly and making the machine-human interaction an everyday reality.

Types of Mobile Robots – What to use where?

Mobile robots are capable of locomotion, they move around their environment and are not fixed to one physical location. They can be classified in two different ways; by the environment wherein they work and by the device, they use to move.

Let’s discuss different examples of different environments wherein mobile robots can work:

  • Underwater robots or autonomous underwater vehicles (AUVs) which can direct themselves and travel through water. AUVs are also called as Swimming Robots.
  • Aerial Robots are autonomous micro air vehicles, specializing in their guidance and control in the air.
  • Land-based robots categorized as wheeled robots, tracked robots, and legged robots. These are more complex types of robots and are autonomous humanoid as it requires many degrees of freedom and synchronization. Also known as unnamed vehicle group (UGVs), they navigate on inside the house or dry land.
  • Delivery & Transportation robots can move materials and supplies through work with the capability of moving around by navigating through an uncontrolled environment with or without the need for the physical or electro-mechanical guidance system.

Mobile robots can be autonomous or non-autonomous, in order to do the achieve motion, it relies either on guidance devices such as sensors or physical devices that allow them to travel a pre-defined navigation route in relatively controlled space.

Hence the two types of mobile robots are:

  1. Non- Autonomous guided mobile robots
  2. Autonomous mobile robots

Non – Autonomous Mobile Robots:  Guided mobile robots or non-autonomous mobile robots require some sort of guidance system or instruction to make a movement that allows them to travel pre-defined navigation maps in a controlled environment. The pre-defined navigation map such as magnetic tape, bar codes, wire or sensors installed on the environment’s floor that creating an inflexible environment.  These are the following types:

  1. Autonomous Guided Vehicle (AGV): This AGV requires the external guidance system in the form of magnetic strips to travel. These follow a rigid form of the preset route. Typical AGV applications incorporate transportation of raw materials, work-in-progress, and finished goods in support of manufacturing production lines, and storage/retrieval or other movements in support of picking in warehousing and distribution applications. AGVs provide automated material movement for a variety of industries including Automotive, Food & Beverage, Chemical, Hospitals, Manufacturing, Pharmaceutical, Paper.
  2. Rail Guided Vehicle/Cart (RGV/RGC): RGV/RGC is a fast, flexible and easily installed material transport system that travels at a predefined path guided by rails or tracks. RGC has separate input/output stations that allow it to perform multiple operations at once. These mobile robots are an efficient, cost-effective and fast option for complex sorting applications.
  3. Guided Fork-lifts: This specific AGV type is inspired by the conventional human manned forklifts. These forklifts are becoming increasingly complex and intelligent full of autonomy for some applications. These could manned/unmanned traveling with the help of external devices such as tablets, human, etc. The forklift AGV is designed to provide both horizontal and vertical movement of the load.

Autonomous Mobile Robots: Autonomous mobile robots (AMR) are just like humans; can make their own decisions and then perform tasks accordingly. Autonomous robots can perceive their environment and remember it. Based on this info they navigate in a controlled environment without any predefined path or electro-magnetic guidance map, that way they offer flexibility to a large extent. AMRs also optimize the travel distance by calculating the shortest path for every mission & drive efficiency in the warehouse.

Let’s look into a few of its applications:

  1. AMR for Good-to-picking: This includes robots bringing mobile shelf units filled with items to a workstation. In this case, pickers remain at their workstations while software-driven AMRs deliver shelves with different materials directly to the order pickers’ workstation.
  2. Picking Assist Autonomous Mobile Robots: In this case, the robots travel to pick locations, where operators deliver (“pick”) goods based on the robot’s needs. They are an AMR base with an operator interface that provides information about picking order. The robot tells the operator “I want this item and here is where you can find it”. The user interface is also interactive, being possible to provide further info about the product or receiving info from the operator such as “picking accomplished”.
  3. Unmanned Aerial Vehicles (UAVs): These are basically drones moving large products through the air in distribution centers with the help of RFID-scanning technology to offer real-time inventory visibility in the warehouse. Guided autonomously by remote control, UAVs can sense their environment and navigate on their own.
  4. Sorting Robots: These robots play an important role in high speed sorting esp in fulfilment centers. These robots work on a mezzanine with chutes/rabbit holes for location or order positions. Sortation is easily achieved by utilizing a fleet of sorting robots that sort the orders by dumping them through chutes/rabbit holes. The dropped orders or parcels are collected in sacks, gaylords or containers, which will be shipped directly to customers.

Now, along with commercial and industrial sectors, mobile robots are a common sight in public sectors such as hospitals and airports as well. With the evolution of advanced navigation systems & enhanced safety features they are only a step away to become human allies in our everyday activities.

Functional Challenges of Mobile Robots

Over the past few years, mobile robots have started emerging as one of the most important assets in industries for material handling and other intra-logistics operations. These robots have minimized the need for manual handling and an increased number of handling tasks. Little do people realize that even though these robots carry heavy loads but still face functional challenges that are not often noticed and have adverse effects on their maneuverability.

Challenges Synoptic

Mechanical Design Overview

The design of mobile robots capable of intelligent motion and action involves the integration of many different bodies of knowledge. The aim of this system is to idealize an existing autonomous mobile robot, on all levels. This includes the mechanics, kinematics, dynamics, perception, sensor fusion, localization, path planning, and navigation. All these aspects must be reviewed and modified to a modular system if necessary new modular modules must be designed and developed. This way a robust and modular autonomous mobile robot, capable of intelligent motion and performing different tasks will arise.

Mechnical Design Overview

The major challenges include mechanical structure, navigation, and human-centred intelligent control, of which navigation is the most challenging functionality required for such autonomous systems. The navigation comprises four dominant blocks of competencies: perception, localization, cognition and motion control.

  • Perception is the ability of a robot to interpret meaningful data from its sensor,
  • Localization defines how good a robot determines its position in the environment,
  • Likewise, Cognition and Motion control helps in extracting a way to achieve its goal and modulating the motor controller to reach the desired trajectory.

Of all the above four competencies in navigation, localization is considered the most challenging area which requires the greatest research attention.

localization-mobile robot

A Pitfall to Mobile Robots

Assuming one could just attach a GPS sensor to a mobile robot that could solve the localization problem informing the robot of its exact position in the environment. Unfortunately, the current GPS system is not practical with accuracy to say several meters which are almost unacceptable for localizing the mobile robot. Furthermore, the current advancements with positioning technologies are not proving any place in the market especially when it comes to indoors or in obstructed areas. Also, localization is not just limited to determining an absolute pose in space, rather a series of collaborative tasks like building a map, then identify the robot’s relative pose with respect to mapping. In other words, one can say that the robot’s sensors play a crucial role in the localization and the sensor’s inaccuracy and incompleteness contributes to major challenges in localization.

In perception, the major contributor lies with sensor noise and aliasing, further aggravating the problem of localization. On the other hand, using a noise-free sensor alone can’t solve these challenges of insufficient information to identify robot’s pose in the world, instead, it also requires robot programming to recover the robot’s position over time based on series of sensor readings.