Amabie - an Affordable and Manufacturable UV Robot

Technical Abstract

Accelerating to introduce robots into sanitizing tasks is strongly required all over the world under the COVID-19 pandemic. Nevertheless, existing robots have a lot of problems, especially they are expensive and hard to mass-produce. This fact is fatal: the former, a problem of cost, prevents consumers from buying robots; the latter, a problem of mass-production, prevents suppliers from deciding to develop and sell robots. These two problems surely delay market development, and the deployment of sanitizing robots in the society would be postponed.

We develop a sanitizing robot named “Amabie, ” whose name comes from a Japanese spirit, which is manufacturable and affordable to tackle these problems. Amabie sanitizes rooms using UV lamps autonomously. Its design is mainly focused on three points: the first point is “manufacturable, ” the second is “affordable, ” and the last is “extendable.”

The first point, “manufacturable, ” means easy to mass-produce. The hardware of Amabie can be divided into some modules, and almost all of the modules are composed of ready-made parts sold by reliable suppliers. Such design makes building and repairing simple. In addition, we do not have to produce complex components (e.g. motor units). Amabie no longer needs to be built, in contrast to traditional robots. The second point “affordable” means we can build Amabie at low cost, while it has sanitizing abilities enough to be used in any institution. Taking a hard look at mass-production consistently, we realize to reduce manufacturing cost, which includes component procurement and assemblage. The last point “extendable” means that users easily customize Amabie for their own environments. As examples, we prepare three types of Amabie: Type-1 is a basic model, Type-2 has more UV lights and a larger battery to work longer time, and Type-3 has a robotic arm. Since all of them are based on the same frame, the three types of Amabie can be built on the same production process.

In the following, we describe the technology that builds Amabie Type-1, a basic model. Our proposal includes not only a robot but also a robot system, i.e. an environmental assistance module to use Amabie safely. The main contribution of our work is integration. Although each elemental technique is not new, our combination of current techniques is the most effective in sanitizing tasks.

Machine: Two actuated wheels drive Amabie, and four casters support it. Suspension units make wheels stable even if Amabie runs on a non-smooth floor. It has six UV lamps: four are fixed to the main frame, and the other (two lamps) tilt in order to face not only walls but also the top of beds, chairs, and desks.

Circuit: A lead-acid battery is equipped Amabie. For a safe emergency stop, a circuit breaker is well designed not to damage any components of Amabie. To maximize the performance of the main computer, a microcontroller communicates with actuators and analog interfaces instead.

Software: All software is implemented on Robot Operating System (ROS), a world-wide used robot platform. A lot of resources running on ROS are published, and they extend Amabie as you desire. Four camera modules enable Amabie to create maps, self-localize, and detect objects and humans.

Safety System: While no one can eliminate blind spots from Amabie, we create a novel system to detect humans for safe operation. We develop a beacon easy to be attached to a door. The beacon has a wireless communication module and an ultrasonic sensor, so it can detect that someone enters the room, then the beacon sends it to Amabie.

1. Concept

Introduction

These days, COVID-19 is prevalent all over the world. Since many infected people and patients with underlying diseases gather in hospitals, virus eradication activities are carried out daily. Of course, even before the global pandemic of COVID-19, these activities have been performed every day. However, employees have been sterilizing using alcohol-based disinfectant sprays or cloths in most hospitals [1]. Then, to reduce human errors and labor costs, the UV robot was developed. For example, UVD Robots ApS developed UVD robot [2], and General Disinfection Service developed “Light Strike” [3]. These robots can eradicate 99.99% of the virus, so some hospitals use these robots.

However, these hospitals are large scale, such as university hospitals, and small hospitals, such as individual hospitals, rarely introduce these robots. The main reason is the high price. These robots are about $150, 000. Comparing the robot introduction cost and the labor cost, hospitals have no choice but to judge that it is not the work to introduce it. Also, considering the battery life and other performance, we cannot deny excessive performance. Hospitals that have not suffered medical disruption will be postponed to introduce it. However, the medical industry is changing day by day. So, if they need UV robots, we need to have them right now. Therefore, we developed the UV robot ”Amabie” that satisfies affordability and can be immediately introduced to the site. The name "Amabie" comes from a Japanese spirit. It is said that Amabie foretells an epidemic and avoids people from it in Japan. We made it possible for users to select the UV robot that suits their situation by making it have minimum required functions and high expandability. This article mainly describes the most basic type.

Concept

This is our UV robot “Amabie”. We developed Amabie based on the following 3 concepts.

• Extendable
• Affordable
• Manufacturable

(1) Extendable

UV robots are needed by various institutions. So, we developed the following 3 types to meet various demands. It is one of the examples. Amabie can custom to suit your situation.

(2) Affordable

As shown in Table1, Amabie is inexpensive. Existing UV robots are almost $150, 000. Amabie is less than one-tenth of existing UV robots.

(3) Manufacturable

Amabie is easy to produce. You can get Amabie within 1 week. So, when you become to want a UV robot, for example pandemics, you can get UV robot “Amabie” sooner than other UV robots. About 80% of Amabie parts are made of ready-made products. So, Amabie is easy to produce.

Sanitization Performance

This is sanitized areas of Type1. As shown in this picture, Amabie has a large sanitizing range.

Existing UV robots sanitize the space. However, it is needed to sanitize the surface in the hospital, and so on[1]. So, Amabie approaches to the target to sanitize properly.

This performance is enough to sanitize almost all areas properly.

2. Operations Instructions

How to Use Amabie

It is very simple to use Amabie. The flow is;

(1) You set the course along the left-side wall.

(2) You push the start button.

(3) Amabie sanitizes the room.

(4) Amabie returns to the start point.

(5) Amabie notifies you.

One example course is this.

How to Maintenance UV lamps

Each UV lamps should be replaced new one when lighting time reaches 6000 hours or the lamp breaks down. Users can change the UV lamp by twisting the lamp 90 degrees when Amabie’s switch is off. Grow starter should be replaced new one when the number of a lamp “on” reaches the designated number of times. Users can change grow starter easily when you remove the Amabie’s outer covering because it is screwed. Users can check the lighting time and the number of a lamp “on”, but an automatic reminder will be displayed in a touch panel.

3. UV Lamp

The Objective of UV Germicidal Irradiation

UV-C light (wavelength is 200-280 nm) have been used to kill or inactivate a bacterium or a virus. UV germicidal irradiation attracts rising attention because COVID-19 (SARS-CoV-2) is spreading worldwide now. According to the latest journal article, UV-C (254 nm) irradiation is highly effective in inactivating and inhibiting SARS-CoV-2 replication [6]. The objective of Amabie is not sanitizing the whole of room space but effective sanitizing necessary surfaces and floor. The reason why the floor is included is that viruses soar in the air when airborne droplets fallen on the floor dried [7].

UV Lamp Specification

Amabie has two types of UV lamps made by Panasonic, a Japanese manufacturer. One is GL 10, 10W lamp power. The other is GL15, 15W lamp power. Other UV robots using more high-power lamps such as a UVD robot uses 180W UV lamps [8]. We consider Amabie has enough UV power because she can get close to the target. Both lamps are very accessible and low cost less than 20 dollars per unit. Besides, the rating life, that is, the time when 80% of the output is maintained is six thousand hours. The power transition of some UV lamps is not clear but that of Amabie’s lamp has been known. Therefore, we use 80% of UV irradiance in the calculation because the degradation of the UV lamp should be considered.

UV Lamp Layout

In Type1, Amabie has six UV lamps consisting of two for floor and four for wall or side object. In Type2 and 3, which is an extended edition of Type1, Amabie has 11 UV lamps consisting of three for floor and eight for wall or side object. UV lamp symmetrical layout and height of Type2 and 3.

Lamp A (A’) has two pieces of UV lamps and it can irradiate a wide area because it is tilted by a servomotor. All lamps have an aluminum reflector, so their rays will concentrate on the center of the front face. We consider lamp A can irradiate efficiently low and high place by tilting. This is a key point of Amabie. Lamp D (D’) and E are for floor sanitizing. Lamp E is only 10W output (GL10), and the others are 15W (GL15).

The UV-C Dose Calculation

We defined 25 mJ/cm2 or more dose in less than 5 minutes as a sanitized condition and calculate the sanitized distance and area of each UV lamp. Define E [µW/cm2] as UV irradiance at 1m and t [s] as exposure time. γ [mJ/cm2] as irradiated energy density at r [m] position from the UV lamp has expressed this equation.

By solving for r, γ=25 mJ/cm2 or more dose-distance is derived like this.

Lamp A (2 pieces) is regarded as a single lamp having twice irradiance for simplification. As previously explained, we use 80% of UV irradiance in the calculation because of degradation. Thus, the irradiance at 1m of GL10 is 23.2 µW/cm2, that of GL15 is 40.8 µW/cm2.

We should consider the effect of a reflector to calculate the correct sanitized area of Amabie by using CAD data of light fixtures because all lamps have an aluminum reflector. Because the wavelength of GL10 and GL15 is 253.7 nm, we use 92% as the reflectance of aluminum reflector in this calculation.

Amabie has five lamps but lamp B and lamp C are the same. So, we analyze the four patterns effects of the reflector. For simplification, we only consider the light ray going straight or reflecting only one time.

Correction factor k expresses how much irradiance is improved by the reflector and derived this equation when α is going straight rays and β is reflecting rays. Actually, the effect of the reflector has a dispersion of angle. However, we use the correction factor for simplification in this calculation.

The dashed lines are ordinary UV lamps and solid lines are including the effect of the reflector. As a result, the sanitized area of Amabie is improved by using the reflector.

These figures show the sanitized area in 1 minute. The floor is covered about 900 mm width. If the distance from Amabie to the wall is 200 mm, the UV lamps cover 1700 mm height. The sanitized area of type 2, 3 is distributed symmetrically. About the axis direction of UV light, the width of the sanitized area is the same as lamp length.

Threshold Limit Value (TLV) Calculation

The threshold limit values TLV_λ equal to 6 mJ/cm2 because the wavelength of the UV lamp is 253.7 nm.[11] So, maximum exposure time at 1m t_max [s] is derived from this equation when E_λ [mW/cm2] is the unfiltered irradiance [11]. The minimum value of t_max is 43.8 seconds. Amabie’s UV lamps are more secure than high power UV lamps like other UV robots.

Design of Upper Part

We use the 30mm square aluminum frame as a structure of Amabie because it is lightweight and easily available. Carbon steel S45C (JIS) is used as a material of lamp A rotating shaft. Lamp A is tilted by a servomotor RS405CB (Futaba, 48kgf･cm) through a timing belt. Because lamp A rotating shaft penetrates a center of gravity, it can rotate by minimum torque. The diameter of the rotation axis d is determined by these equations when T_q=480x9.8=4704 [N･mm] is torque, τ_a=94 [MPa] is allowable torsional stress, M=3863 [N･mm] is bending moment, and σ_a=117 [MPa] is allowable bending stress. As a result, the diameter should be more than 7mm and we decided the diameter equals to 20mm to have a high safety margin.

4. Undercarriage

Undercarriages are parts of moving. The size is W460×D570(mm). It has 2 driving wheels and 4 casters. By reducing the number of motors, we could reduce the cost. UV lamp inside the undercarriage disinfects the floor. When the UV lamp has gone out, users can change it by removing the cover. Driving wheels have suspension, so users don’t mind to spin in the air. In order to climb over steps, for example cables, the diameter of the wheel and caster is large.

Driving Wheel

The driving wheel is a part that moves the robot. Main components are motor, suspension, and wheel. Then, I describe what products I selected.

The motor is MS-94BZB build by MABUCHI MOTOR. The suspension is P513 build by Accurate. The slide bush is SME16GWUU build by NIPPON BEARING. The wheel is heavy duty model of 6” build by Actobotics. Other fix parts are made by MISUMI.

We designed the undercarriage as total weight assumed 100kg. It has 6 grounding points, so the force loaded on a driving wheel is 166N in order not to heart the floor. Then, the suspension must have forced more than 166N. the allowable load of suspension ”P513” is 103.2. It is used two suspension par one driving wheel.

Since to climb over steps, the diameter of wheel is 6”. Then, starting function load torque “T_L” is;

We decided that the maximum speed is the same as human walking speed, 1 m/s, and the acceleration period is 2s. By using trapezoid acceleration, the acceleration torque is;

So, the motor needs torque more than 8.2 kg・m. MS-94BZB has 86 kg・m. So, it meets the requirement. Also, we prioritized ease of assembly. We didn’t want to use Gearbox. Then, the Radial load capacity of this motor’s output shaft is 70 kgf. It meets the requirement.

Next, we considered the moment generated by the force loaded from the ground. The force received from the ground is the same as the force of suspension”206N”. The moment”M” generated from the force”F” is loaded on two slide bushes. So, the moment loaded on one slide bush is 1/2 * M. The length”L” is 119.86mm. So, 1/2 * M is;

The allowable static moment of SME16GWUU is 12600 N・mm. So, it meets requirements.

Caster

The caster is K-420G-50N of TAKIGEN MFG.CO. Since the allowable load is 372N, it meets the requirement. Now, we want to climb over 100mm step. The required moment to climb over the step is M_P. The moment generated by the force of pushing robot, ”F” is M_F. The load is 166N. So, M_P is;

Then, M_F is;

From this formula, amabie can climb over 10mm step by pushing 217N force.

5. Circuit Design

Power Supply

Amabie has two power lines, a DC 24V power line, and an AC 100V power line. The DC 24V power is supplied from the lead-acid battery built into the robot, and the AC 100V power is generated from it with the DC/AC inverter inside the robot. The DC 24V power line drives wheel motors, tilting motors of top UV lamps, the MCU board, and tower indicator lights, and the AC 100V power line drives UV lamps and a main computer. For emergencies, the current supplied to motors and UV lamps can be cut off by a contactor.

Control Signals

Amabie has two control devices, a main computer and a custom micro control unit (MCU) board. The computer handles the advanced controls, e.g., SLAM and image sensing, and the MCU board handles the controls of the internal devices, e.g., driving motors, toggling UV lamps, and receiving switch signals. The computer and the MCU board send and receive control signals by serial communications through the USB cable. The computer transmits the information of the operation status, wheel motor speed, ON/OFF of UV lamps, and the tilting angle of UV lamps to the MCU board. The MCU board transmits an emergency stop signal to the computer. It also transmits a rotation command to the wheel motor controllers and servo motors and driving signals to the UV lamp relay based on the received signal from the computer.

Components

• Battery

Amabie has two 12V Lead-acid batteries. They are connected in series and supply 24V power to the circuit. The capacity of the battery is enough for Amabie's max power operation for 2 hours.

• Circuit Breaker (CB1)

The battery and DC 24V power line are connected via a circuit breaker. It has the role of disconnecting the battery and the circuit when a short the circuit, and the role of the main power switch of the robot.

• DC24V/AC100V Inverter (U4)

The AC 100V power line is generated by DC/AC inverter from the DC 24V power line. The inverter can output 280W power that can sufficiently drive 15W UV lamp x10 and a 15W computer.

• Emergency Stop Button (SW1, U5)

Amabie is equipped with an emergency stop button. When this button is pressed or the Enable signal from the MCU board is cut off, the electrical signal to the contactor is cut off. At the same time, the DC/DC converter also stops.

• Contactor (U6, U7, U10)

The wheel motors and UV lamps are connected to the power supply via a contactor. When the emergency stop button is pressed or the Enable signal from the MCU board is cut off, the contactor shuts off these circuits.

• DC/DC Converter (U3)

Since the nominal voltage of the servo motors is 12V, the DC/DC converter steps down the 24V power line into 12V and supplies power to the servo motor.

• Motor Controller (U1, U2)

This motor controller, which is genuine of the motor manufacturer, receives commands by CAN signal. CAN signals are transmitted from the MCU board.

• Servo Motor (M1)

The servo motors mounted to change the direction of UV lights receives the target angle command by RS485 signal. RS485 signal is transmitted from the microcomputer board.

• UV Lamp Drive Relay (U12, U13, U14)

UV lamps are connected to the 100V power line via the relay. The relay is turned on/off by a signal from the MCU board.

• Tower Lamp (U21)

Amabie is equipped with a tower indicator lamp to inform the operating status of the robot to users. The lamp emits three colors. Green: Standby, Yellow: Running, Red: Error. Note that the yellow lamp blinks.

• Wheel Brake (U18, U19)

The electromagnetic brake mounted on the wheel motor is used to make an emergency stop of the robot. The brakes of all-wheel motors are activated via relays by signals from the MCU board.

• MCU (U20)

The MCU board that communicates with the main computer and sends signals to each device supports serial communication with the main computer, 24V digital I/O, RS485 communication, and CAN communication.

6. Safety Measures

Amabie has an emergency stop function as a safety measure in case of a human error or unexpected situation. When Amabie detects a human intrusion or internal problems, it cuts off the electric power supplied to the electric motor and UV lamps and brakes the wheel motors, which means operating Amabie can safely stop. Once Amabie performs an emergency stop function, the program automatically shifts to the emergency stop state. Then, it cannot restart unless the startup sequence again.

Emergency Stop Button

In case users or other people notice a danger for themselves or an abnormality of the working robot, they can stop Amabie’s operation safely by pushing the kill button mounted on the top of the body. The kill button transmits a kill signal to contactors on the circuit and cuts off the power supply directly without any software. Therefore, even if the software cannot detect unexpected problems, you can safely stop Amabie’s operation.

Circuit Breaker

The circuit breaker can detect the over current on the circuit. In case the short circuit happens, the circuit breaker cuts off all power lines lower from the battery. Therefore, the circuit breaker avoids abnormal heating and fire.

Human detection

The 3D camera mounted on the top front of the body can detect human existence. In case a human comes into in front of the operating Amabie, the camera detects that and stop Amabie’s operation immediately. The details of the detection algorithm are in the software section.

Battery Observer

In case the battery power turns empty in the middle of an operation, there is a risk that Amabie performs unexpected behavior. A battery observer always monitors the voltage of the battery during operations. If the observer judges that the remaining battery level is too low, Amabie stops safely before the battery is empty.

Human Entering Sensing Beacon

Human entering sensing beacon is an external accessory for expanded safety. The beacon is attached to the wall near the door in the room by users, and it monitors people entering the room through the door. It contains an ultrasonic distance sensor and a Bluetooth module and works on the battery. The size is very small that L:60mm, W:60mm, H:25mm. In case someone enters the room during Amabie’s operation, the beacon detects it and transmits the notification to Amabie. Receiving it, Amabie immediately stops the operation safely.

Power Charge

Before starting Amabie, make sure that the battery is already charged. You can check the battery level with the charging port on the lower backside of the body. If the indicator is not full, you need to charge the battery before starting. You can use a general battery charger for a 24V lead-acid battery to charge the robot's battery. Slide the cover of the charging port up, and attach the charger plug according to the +/- mark on the port. Please refer to the instruction manual of each product for how to use the charger.

7. Software

Overview

Amabie software is distributed: there exist two core computing units, i.e. the main computer and the MCU board. the former mainly takes charge of image processing and decision; the latter communicates modules and processes signals.

Computer

The main computer of Amabie is Jetson Xavier NX, which has a high-performance energy-efficient GPU. Ubuntu 18.04 LTS Bionic Beaver is installed as the operating system. All implemented software running on the computer is based on Robot Operating System (ROS) Melodic Morenia, the most popular robotic platform.

MCU

The MCU board on Amabie is the original custom board composed of STM32 Nucleo Board STM32F303RE (STMicroelectronics), X-NUCLEO-PLC01A1 (STMicroelectronics), and RS485 CAN Shield (Waveshare). The firmware is implemented with the Mbed environment. The program is described so that each component of Amabie abstract and realizes expandability. The structure of the program is as shown in the figure.

All the components of Amabie such as wheels and UV lamps are described as classes. In addition, the program has a class for sending and receiving command signals. Supported communication is serial communication using the rosserial protocol, RS485 communication, and CAN communication. And the board own 8ch 24V digital PLC I/O ports for each.

Code on Mbed: https://os.mbed.com/users/yamadola/code/UV_Robot_Nucleo/

Cameras

Amabie has four cameras: three Intel RealSense d435 RGB-D cameras and one Intel RealSense T265 tracking camera. RGB-D cameras can take depth pictures; in other words, they work not only as cameras but also as LiDAR sensors. Two RGB-D cameras are attached to the lower front and the lower rear to detect obstacles that Amabie must avoid. The other RGB-D camera and the tracking camera are attached to the upper front. All cameras are connected to the main computer by high-speed USB 3.1 cables.

ROS-basedSoftware

Since ROS is designed as a distributed computing platform, each software runs independently as a node. The main nodes are described below.

• V-SLAM: Simultaneous localization and mapping (SLAM) is essential technology for autonomous robots. Since small institutions have a lot of movable objects, e.g. chairs and toys, 2D (planar) SLAM algorithms may fail because of their uncertainty. 3D SLAM is necessary inside. On the other hand, 3D LiDAR sensors are generally so expensive. Instead, we use visual SLAM (V-SLAM), camera-based SLAM algorithms. Amabie parallelly uses two different algorithms. One runs on the tracking camera to estimate local displacement [12], and the other runs on the computer to create maps and estimate the global position [13].
• Autonomous driving: Fully autonomous driving and sanitizing are still difficult techniques. We propose imitation to realize it. After a user buys Amabie, he/she controls it as a radio-controlled car and teaches a path and sanitization targets that they want it to replay. In this term, Amabie creates maps while remembering them. When Amabie drives autonomously, it follows the path and sanitizes the targets. If some obstacles are on the path, Amabie tries to avoid them.

Simulation

Although we cannot build a real prototype because of the university shutdown due to the pandemic, we develop a simulation environment with Choreonoid [14]. Since Choreonoid supports light simulation as the following snapshot, we can evaluate sanitized areas that Amabie can light.

Acknowledgement

This project has been carried out with the supports from the following companies.

• Micron Technology

• Mabuchi Motor

Thank you very much for much supports for us.

BOM and Design Requirements Document

https://docs.google.com/spreadsheets/d/1FIv3fazMtrw80iwv6Le36PQSGC0AbXs4U0AWoJZUeUA/edit?usp=sharing

References

[1] 一般病棟における除菌剤を用いた環境表面清拭回数と付着細菌数の減少効果に関する検討 2015年11月11日 伊藤重彦 中川祐子 南博子 橋本治 堀江恭子 樋渡美紀 諸永幸子 元石和世 谷口初美 松本哲郎

[2] http://www.uvd-robots.com/#uvdr-bullets

[3] https://www.medicalexpo.com/ja/prod/xenex/product-78878-577461.html

[4] https://rmda.kulib.kyoto-u.ac.jp/item/rb00000122/explanation/amabie

[5] https://www.r-lease-ds.jp/space/

[6] Andrea Bianco et al., UV-C irradiation is highly effective in inactivating and inhibiting SARS-CoV-2 replication, (2020) https://www.medrxiv.org/content/10.1101/2020.06.05.20123463v2

[7] Tokyo Metropolitan Institute of Public Health http://www.tokyo-eiken.go.jp/k_kenchiku/bldg/yobou/

[8] UVD Robot Model B Technical Specifications https://www.vingmed.dk/wp-content/uploads/sites/3/2020/04/UVD-Robot-Model-B-Technical-Specifications.pdf

[9] Akari Center Germicidal Lamp https://www.akaricenter.com/sakkin.htm

[10] E. Fearon et al., Thermal effects of substrate materials used in the laser curing of particulate silver inks, Laser Assisted Net Shape Engineering 5, (2007) https://www.researchgate.net/publication/233814472_Thermal_effects_of_substrate_materials_used_in_the_laser_curing_of_particulate_silver_inks

[11] Ultraviolet Radiation (2010)

[12] Intel RealSense Tracking Camera T265 https://www.intelrealsense.com/tracking-camera-t265/[13] OpenVSLAM: A Versatile Visual SLAM Framework https://github.com/xdspacelab/openvslam[14] Choreonoid Official Sitehttps://choreonoid.org/en/