Enhance Factory Automation with Charging Solution for Mobile Robots

The Fourth Industrial Revolution in Manufacturing

The manufacturing industry has been continuously evolving and changing for the past 200 years. The first revolution (Industry 1.0) started with the mechanization of industrial machines with steam power in the late 18^th century and has now evolved to the fourth generation of industrial revolution (Industry 4.0), which is focused on automation, interconnectivity and real-time data processing. This new revolution in the manufacturing industry is helping manufacturers optimize their cost by automating equipment to stay competitive in the market.

Figure 1: The Evolution of the Manufacturing Industry

Almost all major manufacturers are investing in mobile robots in their factories, assembly lines and warehouses for doing the bulk of the work involving assembly, material transportation and packing. These mobile robots are powered with batteries that require frequent charging and it can be challenging sometimes on a factory floor since wired charging can be messy and may require regular maintenance and manual intervention. Recent improvements in wireless charging have made the wireless charging of these mobile robots possible by bringing the investments down and increasing the efficiency close to wired charging systems.

What is Inductive Wireless Charging?

This charging technique uses the principle of electromagnetic induction. When an alternating current is passed through an induction coil on the transmitter side, an oscillating magnetic field is created. When this oscillating magnetic field couples with an induction coil on the receiver side, an alternating electric current is produced in the receiver side coil.

A full wireless charging system comprises mainly of the following components:

• Transmitter coil
• Tuning capacitors
• Coil driver
• Receiver coil
• Diode rectifiers
• DC-DC converter
• Transmitter and receiver control circuitry and algorithms
• Battery charging circuit

Wireless charging systems on a factory floor use electromagnetic induction to transfer energy from a charging source pad installed on the factory floor to a receiving pad installed on the mobile robot.

Why Wireless Charging in a Factory Floor?

Modern wireless charging systems with increased efficiency and cost-optimized components have proven to be a game changer in a factory setup for the following reasons:

• Improved productivity and reduced manufacturing cost
• Continuous operation with opportunity charging (use idle time to charge)
• Low investment as robots could be multipurposed for different operations
• Low human intervention as the charging process can be automated
• Low maintenance cost (connectors, cables and more can be eliminated, making the solution completely contactless)
• Increased safety and security
• No risk of sparks caused by connectors
• Wireless power eliminates the risk of short circuits due to contamination/moisture in connectors
• Reliable Foreign Object Detection (FOD) to detect any metal debris between the transmitter and receiver coil
• Secure authentication can be easily implemented between charger and robot to avoid unauthorized access
• Data transfer during charging can be used for predictive maintenance to prevent downtime
• Overall, complete automation (especially charging) with minimal human intervention can help prevent spread of communicable diseases amongst workers (e.g., COVID-19)

Challenges of Wireless Charging

Keeping the advantages in mind, the use of wireless charging technology in a factory setup has the potential to take the manufacturing industry to the next level and solve several production challenges faced today by various manufacturers. However, there are some challenges with wireless charging too. Let us try to understand these challenges.

• Relatively higher investment is needed to implement wireless charging infrastructure when compared to traditional wired charging
• Comparatively lower efficiency than traditional wired charging
• Efficiency also depends on distance between transmitter coil and receiving coil as well as alignment
• Safety issue related to overheating in case of a foreign object between the transmitter and receiver coil
• Design can be challenging with respect to Bill of Materials (BOM) selection, tuning of coils and component selection
• Security and Electromagnetic Interference (EMI)

Safe and Secure High-Power Wireless Solutions

Microchip has developed custom fixed-function devices and a reference platform to address the challenges of implementing safe, reliable and efficient wireless power at high power levels.

These fixed-function devices implement the algorithms for communications, power control and FOD, which are based on several years of research and development and several granted patents. The communication in this solution is in-band and hence does not need any out-of-band communications schemes that add to the system cost. The power transfer frequency is in the range of about 100 KHz. Power control is done using variable frequency and the variable duty cycle control of the Pulse-Width Modulation (PWM) that drives the full bridge inverter in the transmitter. FOD is critical at high power levels and a Q-factor based method is implemented. In this method, power transfer is briefly stopped for a few microseconds and the coil voltage is measured using the WP300’s high peripherals and core. The presence (or not) of a foreign object can be detected by calculating the slope of the coil voltage when the output Field-Effect Transistors (FETs) are off.

The components of the solution including the controller, FETs, regulators and coils are chosen such that the total system cost can be optimized to be within the cost of high-end metal contacts that may be needed for reliability in an environment with moisture/dust. The efficiency is maximized by the proprietary power control scheme and an optimal coil design. The efficiency of this solution is greater than 90% at loads above 100 Watts. This efficiency is measured from the DC input to the transmitter to the regulated DC output of the receiver. The solution can operate at an input voltage of 11–36 V_DC and can regulate to a similar voltage range on the receiver side.

Board layout is a critical component of the system solution. Unoptimized board layout will impact the wireless power functionality and result in poor EMI performance that can be crucial in many use cases. The Printed Circuit Board (PCB) should be designed in a way so that the digital, analog and power sections are well isolated to minimize noise coupling. Similarly, the EMI can be mitigated by using appropriate control algorithms and decoupling capacitors, but this can be at an expense of increased switching losses resulting in slightly lower efficiency. These are important tradeoffs that are critical while evaluating a design. For reliable performance, the coil calibration data is written to the WP300TX IC during product testing.

To create a 1:1 pairing between the transmitter and receiver, secure communications can be included in-band to make sure only receiver devices that are authenticated by the transmitter are powered.

As you can see, wireless power functionality at high powers is complex and requires both science and art to design optimally.

Microchip’s WP300TX01 (transmitter controller), WP300RX01 (receiver controller) and 300W wireless power reference design can provide a solid foundation for a design. Below are block diagrams of the transmitter and receiver of the reference solution.

WP300TX01 Transmitter:

WP300RX01 Receiver:

For more information, please visit our wireless power web page.