Poster Abstract: Enabling a Cloud-Based Logging Service for Ball Screw with an Autonomous Networked Sensor

System Huang-Chen Lee*1, Yu-Chang Chang*, Yen-Shuo Huang*, Wei-Kuan Wang+, and Yuan-Sun Chu+

Department of Communications Engineering*, Department of Electrical Engineering

+, and the

Advanced Institute for Manufacturing with High-tech Innovations (AIM-HI),

National Chung-Cheng University, Taiwan *1

huclee@ccu.edu.tw

ABSTRACT

Precision ball screw assembly (hereafter called "ball screw"), as

shown in Fig. 1, is a mechanical wear out part that widely used in

CNC (computer numerical control) machine tools to control the

movement of processing targets and spindles. Up until now, there

has been no simple way to directly measure ball screw for

knowing the state of wear quantitatively. An indirect approach is

logging all the signals (vibration, temperature, and preload change)

during the operation of ball screw, and to use them to construct

the wear model for estimating its remaining lifetime. To achieve

this goal, we proposed a cloud-based logging system in this study

that emphasizes (1) logging all the signals during operation in a

ball screw’s whole lifetime, and transferring to the data server

without data loss; and (2) saving all the data into the cloud data

storage of the ball screw’s manufacturer. The data collected from

many ball screws can be used to analyze and construct the wear

model of ball screw, allowing the manufacturer to understand the

state of wear and send a warning to the tool machine’s owner

before excessive wear.

Categories and Subject Descriptors C. 3 [Special-Purpose and Application-Based Systems]: Real-time

and Embedded Systems

General Terms

Design, Experimentation, Measurement, Performance

Keywords: ball screw, wireless sensor, factory

1. INTRODUCTION A ball screw is a mechanical device composed of steel balls, a

shaft, and a nut body that is used to convert rotary motions to

linear motions. The rotation of a ball screw’s shaft causes the

metal balls rolling in the threads of the ball screw and nut body

with little friction. The cumulative friction of balls, regardless of

whether it is due to long-time use or improper installation, may

cause the ball screw to wear out, thus controlling the linear

movement inaccurately. In addition, unnoticed wear of ball screws

could cause excessive backlashes, skids, or lock-ups, as well as

deteriorating the quality of processing object, which could

result in loss of time and money. Because the amount being worn

is invisible to the naked eye, we often rely on the judgments of

experienced engineers, who make their judgments based on

unusual sounds and vibrations produced during the movement of

the ball screw, or significant quality changes of processing object.

Recently, several sensor systems [1] were proposed to estimate

the wear of a ball screw. These studies focused on two points: (1)

how to collect signals like vibration, temperature, and the change

of preload force between nut, balls, and shaft during operation by

using a wire or wireless sensor system; and (2) how to

interpret the collected data to estimate the wear condition.

CNC Machine tool

Precision Ball Screw Assembly

Fig. 1 A precision ball screw assembly installed in a CNC

machine tool.

In previous studies, the proposed systems have collected the

signals of the operating ball screw to estimate the state of wear.

The sensing components were attached on the surface of the nut

or shaft of the ball screw and connected by wires to transfer data

to the data server for further analysis. Later studies [2] added

wireless communication capability to the sensor system to transfer

data. Although wireless communication provides the freedom to

install locations, the reliability of data transmission becomes one

of the major challenges in making this system commercially

viable.

Wireless communication in factory environments is generally

degraded and unstable for the following reasons: (1) the metal-

made tool machines and buildings reflect RF signal considerably,

and (2) running motors in machine tools generates significant

radio interferences. In addition, the quality of wireless

communication in factory environments is worsening since the

type of wireless transceiver used in this application (built-in to the

ball screw assembly) must be in low-power and small form-factor.

This limits the antenna design and degrades its communication

performance.

While data cannot be reliably transmitted to the data server over

wireless communication, an expedient solution is that buffers the

unsent data into temporary local storage, and retransmits it once

the wireless channel becomes available. However, the

microprocessor used in this type of application (due to the

Copyright is held by the author/owner(s).

IPSN’13, April 8–11, 2013, Philadelphia, Pennsylvania, USA.

ACM 978-1-4503-1959-1/13/04.

hardware cost and size limitation) has very constrained internal

RAM (typically 2~16 Kbytes), so it is not practical for buffering a

large amount of collected raw data (i.e., sampling 3-axis vibration

at 2 kHz in 16 bits ADC can generate 3×2000×2 bytes=12 Kbytes

per second) into RAM for a long time before it could be sent out.

To our knowledge, in previous studies, some data may have been

discarded before being sent out, or the data transferred over

wireless communication may have been lost and not recovered. In

their designs, data transmission without data loss is not possible.

Moreover, in order to build an accurate wear model, we need to

log as many real signals from numerous ball screws in machine

tools as possible. However, this raises a substantial problem: How

could we collect a large amount of real signals from ball screws

that were sold by their manufacturer and installed in many

machine tools—which could be located anywhere in the world—

and aggregate data for wearing model analysis and construction?

2. PRELIMINARY SYSTEM DESIGN In response to the previous issues, the autonomous networked

sensing system (hereafter called ANSS), a promising system for

logging ball screws, was proposed and implemented in this study.

Referring to Figure 2, ANSS is an embedded system that is used

to log signals of ball screws during operation. The long-term

vision is integrate ANSS into the ball screw (i.e., the circuit

system is embedded into the shaft or nut of the ball screw) as it is

shipped from its manufacturer. The current prototype version of

ANSS consists of an Atmel ATmega328p microprocessor and

several sensing components to measure vibration, temperature,

and preload of the ball screw assembly. All the collected data will

be transferred wirelessly to the ANSS server by Nordic

NRF24L01+ RF transceivers, and be forwarded to the

manufacturer’s cloud storage via the internet for data aggregation

and analysis afterwards.

Factory 3

Machine tool

CNC Machine Tool 1

Precision Ball Screw Assembly 1

ANSS node 1

Factory 1

ANSS Server

CNC Machine Tool 3 ANSS

nodes

CNC Machine Tool 2

Ball Screw Manufacturer's Cloud Storage

internet

ANSS Server

Factory 2

ANSS Server

ANSSnodes

Precision Ball Screw Assembly 2

ANSS node 2

Fig. 2 The system architecture of the proposed cloud-based ball

screw monitoring system.

As shown in Figure 2, in this system, a machine tool may have

several ANSS-enabled ball screw assemblies, and an ANSS data

server (at least one ANSS server in each factory) may control and

collect data from many ANSS nodes in several machine tools.

In contrast to previous studies, our system ensures that all the

data collected by an ANSS node will eventually be sent to the

factory’s ANSS data server without data loss. Referring to Figure

3, the ANSS node saves all the logged data to its local storage (i.e.,

an SD card), and sends out the buffered data while the wireless

channel is clear. As the running electric motors of CNC machine

tools often generate considerable radio interferences, the

expedient solution is to transfer data to the ANSS server only if

the motor has been stopped. Also, the network protocol of the

ANSS node and server ensures the data’s integrity by adapting

transmission acknowledgement and checksum techniques.

Therefore, all the data in the ANSS node can be reliably

transferred wirelessly to the ANSS server and eventually uploaded

to the manufacturer’s cloud storage. So, the manufacturer can use

this huge amount of data to (1) know the usage and correctness of

installation of the ball screw by the tool machine owner; (2) build

the wear model of a ball screw and estimate the state of wear; and

(3) send notifications to remind the owner of the machine tool to

execute maintenance services in time, i.e., adjust, repair, or

replace with the new ball screw assembly.

`

NRF24L01+RF Transceiver

ATmega328PMicroprocessor

SD CardStorage

Battery/Energy Harvester

VibrationTemperature

Preload Sensor

ANSS node

Fig. 3 The prototype of an ANSS node.

3. DISCUSSION AND CONCLUSION As presented in Figure 3, we implemented an ANSS node

prototype and executed a preliminary test to measure the signals

of an operating ball screw in a machine tool and shown that this

idea is feasible. The foreseeable issues are (1) the current version

of ANSS node is powered by batteries. An additional energy

harvester, such as an electromagnetic generator, may help to

supply energy to ANSS; (2) the circuit of ANSS node may be

embedded and enclosed inside the steel-made ball screw shaft or

nut, which may cause RF signals to degrade when going through

metals. A good antenna design is critical for good wireless

communication; and (3) as some ANSS nodes may not be able to

communicate to the local data server directly in factory (i.e., in

single-hop, due to low RF power or obstacles), a multi-hop

networking protocol may be needed. However, this would

complicate the issue of wireless communication regarding bulk

data transmission.

We hope to design a miniature ANSS node in the near future and

integrate it into ball screw assembly. This will make it possible for

machine tool owners to know the state of wear and the time to

execute maintenance, therefore reducing the loss of time and

money due to over-wear ball screw assembly.

4. ACKNOWLEDGMENTS The authors acknowledge support from the National Science

Council, Taiwan, under the grant 100-2218-E-194-006-MY3. The

authors would like to thank Professor Shyh-Leh Chen, Professor

Chin-Chun Cheng, Research Assistant Mr. Pei-Jyi Kuo, and Mrs.

Pin-Chen Kuo for their excellent technical assistance.

5. REFERENCES [1] Guo-Hua Feng; Yi-Lu Pan; , "Embedded temperature and

vibration sensing system for monitoring ball screw

preload," Control Conference (ASCC), 2011 8th Asian , vol.,

no., pp.171-174, 15-18 May 2011

[2] Liqun Hou; Bergmann, N.W.; , "Novel Industrial Wireless Sensor Networks for Machine Condition Monitoring and Fault

Diagnosis," Instrumentation and Measurement, IEEE

Transactions on , vol.61, no.10, pp.2787-2798, Oct. 2012