WIRELESS COMMUNICATION MODULE TO REPLACE RESOLVER CABLE IN WELDING ROBOTS

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1 WIRELESS COMMUNICATION MODULE TO REPLACE RESOLVER CABLE IN WELDING ROBOTS Anagha Jayan PG Scholar, Department of ECE Sri Krishna college of Technology Coimbatore, India M.Sownthara PG Scholar,Depatment of ECE Karpagam University Coimbatore, India M.Sivaram Kumar Asst Professor,Department of EEE, Karpagam University, Coimbatore, India Abstract The main aim of the project is to replace the resolver cable in welding robots by ZIGBEE as wireless communication module. The replacing work is done to avoid wiring damages from the Serial Measurement Board (SMB) to Robot end. The controlling unit used here is PIC Microcontroller which transmits the feedback data from the seventh axis of the robot to the SMB which is in the manipulator of the robot. The welding operation is carried out with a predefined angle of rotation based on the feedback data that is excited. Zigbee communication module can give a maximum range of 76m. This module is connected to the PIC Microcontroller Unit through RS232 cable. Index Terms Serial Measurement Board (SMB), Zigbee, Resolver. I. INTRODUCTION Wireless technologies have been available for decades, and in the last several years wireless technologies have been making their way to the factory floor. This technology has allowed for transferring data efficiently over long distances. When this wireless technology is utilized, a new world of applications is available to designers. Sensors and actuators can be added to many industrial, commercial, and entertainment automation applications. The main advantages for using a wireless solution in industrial applications are greater mobility, possibility to move devices and connect to smart phones and tablets freely without constraining cables, eliminate expensive and heavy transmission media such as flexible cables, swivels, fast and easy installation and commissioning, high flexibility if there is a need to modify an installation, increased personnel safety by not having to be physically close to a device during configuration and maintenance, flexible human interface devices (HID),easy integration of devices into the network. Industrial plants consist of multiple devices interconnected in different ways. These varied types of devices consist of Simple data collection units (I/Os) without built in intelligence, intelligent devices such as sensors with built in intelligence, single-loop controllers or programmable controllers, supervisory systems used as human machine interface (HMI), data logging and supervisory control. All these types of devices are interconnected using different communication protocols that in some cases can be replaced by wireless technologies to achieve the above listed advantages. The aim of this project is to implement a wireless communication system that could replace the current system i.e. the cable connection between the SMB and robot end that has been currently used in Ford India Private Limited Chennai. In Ford flexible tube press and welding system developed by ABB robotics are used for the industrial applications. Welding robots have seven axes, in which the seventh axis is the resolver cable in welding robot. In simple resolver cable is a feedback loop that transmits the data/signal from the robot end to the serial measurement board (SMB). A resolver is a type of rotary electrical transformer used for measuring degrees of rotation, it is considering an analog device, and has a digital counterpart, the rotary (or pulse) encoder. The most common type of resolver is the brushless transmitter resolver. On the outside, this type of resolver may look like a small electrical motor having a stator or rotator. On the inside, the resolver cable has six wires represented as,,,,, here,,, connects the resolver cable and the stator portion and, connects the rotor portion., is the exciter winding used to excite the rotor. The exciter winding is located on the top; it is in fact a coil of turning transformer. This transformer induces current in the rotor without a direct electrical connection, thus there are no wires to the rotor limiting its rotation and no need for brushers. The two other windings are on the bottom, wound on a lamination. They are configured at 90 degrees from each other. The rotor houses a coil, which is transformer and a separate primary winding in a lamination, exciting the two phase windings on the stator. The primary winding of the transformer fixed to the stator is excited and a current is induced in the secondary windings of the two stators which are 90 degree to each other. The output signals from the secondary windings are 90 degree out of phase with each other and hence one of them can be called as sine and the 230

2 other cosine. From this the angle of rotation of the stator is measured and feedback through the resolver cable to the SMB [6]. II. EXISTING SYSTEM In the existing system, communication system of the robot and the Serial Measurement Board is purely a wired system. The wire gets damaged easily due to the fast welding operations. In the proposed system, the damages is avoided to make the system more efficient A. Drawbacks of Existing System Cable gets damaged easily at fast welding operations. Maintenance cost is high. Production cost of cable is high. B. Problem Statement The below table 1 represents the failure logs in production field due to resolver failure. From this case study and maintenance loss a new system is implemented. TABLE 1 FAILURE LOGS Date Model And Shift Failure 14/08/13 B515 A Resolver connector damage 23/08/13 MB80R03 B517 7 th axis resolver B cable connector damage (motor end ) 27/08/13 MB70RO6 7 th axis resolver framing A cable, externally lagged 18/09/13 MB80R02 Gun 2 Resolver and power cable damage. 11/10/13 MB100R03 C Resolver failure B515 12/10/13 MB70R05 A MB70R05 14/11/13 B515 A GUN 19/12/13 MB70R06 B Robot framing Framing, external resolver cable to be removed Servo motor terminal box and resolver connector damage 7 th axis resolver failure while welding III. PROPOSED SYSTEM In this project the aim is to replace the resolver cable present between the SMB board and robot end to a wireless module. Zigbee is used has wireless communication module. The proposed system has two parts i.e., to transmit the generated 5v dc from the SMB to energize the robot s rotor part and to feedback the data collected from robot end to the SMB by means of zigbee as an communication module. Using this module we can transmit and receive the data with the maximum operating voltage of 3.8V. A. INDUCTIVE COUPLING The inductive power coupling technology that allows both signal and power to be sent in an air gap distance without any physical connections or batteries are required. This technology can be used to replace slip rings, connectors, and other mechanical connections where harsh environments create a short life, or in situations where those types of mechanical solutions are impossible to us. Inductive power coupling happens when a current flow in one wire induces a voltage in another wire without any physical connection between the two wires which is also known as electromagnetic induction. In industrial automation and control inductive coupling induces electrical interference or noise. Electrical noise can cause havoc in control wiring and design, the resultant output signal gets corrupted and causes error in the control process [2]. In Ford we cannot implement inductive power coupling technology because the SMB board which produces 5v power and the rotor part is nearly 7m apart. If the work is proceeding further it may leads to power radiation and sparking, induces electrical noise and the whole system gets damaged. B. PHASE 1 The system has two units, transmitter and receiver. The transmitter part is placed at the SMB board and the receiver near the motor. Instead of carrying the 5Vdc from SMB it is supplied as input to the controller at the transmitter section. The controller used is PIC16F877A.When the transmitter part gets the supply an LED at the UART glows. An encoder HT12 E is used at transmitter section. It sends a 4 bit data which represents that at the transmitter part the supply from SMB is received. The encoder encodes the data and transmit the data through an RF 433MHZ module to the receiver part. At the receiver the decoder HT12 D decodes the data and sent to the controller. Decoder is active high. When the decoder status pin is high, it transmits the data as a bias voltage to the base of a transistor. When the transistor is ON, through an 231

external battery the motor gets energized and starts rotating. This part acts as a sensing unit. +90 0 Max.

[8]. C. PHASE 2 The second part is the feedback section i.e., the angle of rotation from motor is sent from the receiver to the transmitter using zigbee.

3 external battery the motor gets energized and starts rotating. This part acts as a sensing unit Max. In phase with feed Fig 1 Block Diagram Of Input Section That is when the SMB Part is off then the whole system is turned off and when the transmitter part receives the supply then only the motor runs [8]. C. PHASE 2 The second part is the feedback section i.e., the angle of rotation from motor is sent from the receiver to the transmitter using zigbee. The output signals on the secondary windings are 90 degree out of phase with each other and hence one of them can be called sine and the other cosine. The information about position and speed of the shaft can be determined. The sign of the sine and cosine signal is used to determine in which the shaft is located. Using analog to digital convertor this information is converted into digital format. Fig 2 Block Diagram Of Output Section From the observed sine and cosine signal the maximum voltage level of the output is 2.5v. According to the voltage level it has to be converted to corresponding digital format. TABLE 2 PHASE REPRESENTATION OF OUTPUT Motor angle X (S1) Y (S4) 0 Max. In phase with feed 0 The most significant bits represent the quadrant the shaft is and the remaining bit represents the angle the shaft is at from the edge of the quadrant. For example for a 16 bit microcontroller the EPRL (equivalent lines per resolution) is The bias voltage of controller is 5v and is 2.56v. According to the design criteria the accuracy of the controller is 10mv. For each division in sin and cosine values it checks the number of counts of 10mv present. If 1v is given to ADC, according to the program in the controller it converts 1v to 1000mv in this it as 100 counts 10mv is present. In this way the analog value is converted to digital and the count value is transmitted through zigbee to the SMB part. At the receiver side DAC convert the 100 count to its corresponding 1v. D. ZIGBEE vs. XBEE The communication layer of Zigbee is at level 3 in the OSI model. Zigbee provides a network topology to let a network of devices communicate among them and to set extra communication features such as authentication, encryption, and association and in the upper layer application services. A reactive adhoc protocol has been implemented to perform the data routing and forwarding process to any node in the network. The main application of zigbee is clustering. Where as in case of Xbee provides communication between two devices. The digital information units are managed and organized to become electromagnetic impulses on the lower level [1], [4]. STACK LAYER TABLE 3 Comparisons between Xbee and Zigbee PROPERTIES XBEE ZIGBEE Layer at level two in OSI model Communication layer at level three and uppers in the OSI model PURPOSE To let Provides an adhoc communication networking between two devices FREQUENCY ISM Band GHz BAND 2.48 GHz BIT RATES 115 kbps 250 kbps Zigbee has a lot to offer in industrial applications such as low cost deployment and redeployment, mesh networking to cover entire industrial plants and factories, open standard with multiple vendors, battery operation. Through this zigbee as 232

communication module the digital value of angle of rotation is transmitted part. For further calculations the converted analog value is sent to the SMB. IV.

4 communication module the digital value of angle of rotation is transmitted part. For further calculations the converted analog value is sent to the SMB. IV. HARDWARE DETAILS EEPROM memory makes it easier to apply microcontrollers to devices where permanent storage of various parameters is needed. Low cost, low consumption, easy handling and flexibility make PIC16877A in automation industries. It has inbuilt CPU, memory and peripherals to make it as a mini computers [9]. A. ZIGBEE For the hardware implementation CC2500 is used. The CC2500 is a true single chip 2.4 GHz IEEE complaint RF transceiver designed for low power and low voltage wireless applications. CC2500 includes an effective data rate of 250 kbps [4]. 1) Key features True single-chip 2.4 GHz IEEE compliant RF transceiver with MAC support. Fig 4 Pin Diagram Of 16F877A For this project the main advantage of using 16f series is that it is fabricated in CMOS that uses separate bus for instruction and data allowing simultaneous access of program and data memory. Fig 3 Zigbee Module C. RF 433 MHz An RF module is a small electronic circuit used to transmit and receive radio signals on one of a number of carrier frequencies. RF modules are widely used in electronic and designing radio circuitry. 250 kbps effective data rate. Low power consumption. Low supply voltage ( v) with integrated voltage regulator. B. PIC16F887A Microcontroller PIC16f877A is one of the PIC micro families in which the most popular that is used in current technologies is 16f877A. Because of very easy using PIC16F877A and the use of flash memory technology so that the write-erase technology can be used thousand times and the data is retained even when the power is switched off. PIC16f877A can be used in many applications such as automotive industries and controlling home applications to industrial instruments, remote sensors, electrical door locks and safety devices. Because of its low consumption, Fig 5.RF 433 Hz Modules This module comprises of an RF transmitter and receiver. The transmitter/receiver pair operates at a frequency of 434 MHZ. It receives serial data and transmits that through the wireless antenna which is connected at pin 4 to the receiver side. The transmitted data is received by a receiver operating at same frequency. The transmission occurs at a rate of 1 kbps to 10 kbps. The RF module is used along with a pair of encoder and decoder. 233

D. Encoder and Decoder The two classes of medium scale integration circuits are Encoders and Decoders. These two are based on binary coded input. Encoders typically have inputs and N outputs.

Each address and data bits can be set to one of the two logic states. The programmed addresses and data are transmitted together with the header bits via an RF with a trigger signal.

The enable input performs no logical operation, but is only responsible for making the decoder Active or Inactive. If the enable pin is zero then all outputs are zero regardless of the input values.

Fig 6. Model of SMB V. RESULT The below Fig.6 represents the transmitter and receiver part. The values from the resolver are further sent to SMB for further calculations.

SERIAL MEASUREMENT BOARD The serial measurement board primarily gathers resolver data from the robots motors. This data is used to measure the speed and position of each axis.

5 D. Encoder and Decoder The two classes of medium scale integration circuits are Encoders and Decoders. These two are based on binary coded input. Encoders typically have inputs and N outputs. Here we are using HT12 E encoder hence it is represented as. They are capable of encoding information which consists of N address and 1N data bits. Each address and data bits can be set to one of the two logic states. The programmed addresses and data are transmitted together with the header bits via an RF with a trigger signal. For the HT12 E encoders, transmission is enabled by applying a low signal to the TE pin. A decoder is a circuit component that decodes an input code. The enable input performs no logical operation, but is only responsible for making the decoder Active or Inactive. If the enable pin is zero then all outputs are zero regardless of the input values. If it is one, the decoder performs its normal operation. For our circuitry it depends on the VT pin. The output of the VT pin is high only when the transmission is valid. Otherwise it is always low. Fig 6. Model of SMB V. RESULT The below Fig.6 represents the transmitter and receiver part. The values from the resolver are further sent to SMB for further calculations. Fig 6 Transmitter Output, Wireless Transmission Of 5v Fig 6 Pin Diagram Of Encoder And Decoder E. SERIAL MEASUREMENT BOARD The serial measurement board primarily gathers resolver data from the robots motors. This data is used to measure the speed and position of each axis. SMB acts as a slave controller. Each SMB is capable of measuring up to 7 axes. It is also stores a number of data pertaining to each robot. This data is used by the controller and can be transferred between the SMB and the controller. Normally, the data is transferred automatically, but it can also be done manually. Fig 6 Receiver Section, Motor End. VI. CONCLUSION The resolver cable in welding robot has been replaced by the wireless communication modules. The replacing is done to avoid wiring damages from SMB to robot end. And to effectively increase its efficiency and speed without any data loss and damage to welding robots used in automobile industry.the communication modules proposed in this paper are zigbee and RF transmitter and receiver. The RF 433 MHZ module is used to transmit the 5v dc from SMB board to the 234

6 robot end. CC2500 zigbee is used to provide feedback. The angle of rotation from the robot end is provided to the SMB board for further calculations. ACKNOWLEDGMENT The authors would like to thank Mr. Murali and Mr. Logesh, Ford India Private Limited, Chennai. REFERENCES [1] Shekhar Mane, R.H.Khade, A zigbee based wireless reconfigurable stepper motor controller using FPGA, UACEE international journal of advances in electronics engineering VOL 2,issue 3. [2] Junji Hirai, Tae-Woong Kim and Atsuo Kawamura, IEEE MEMBERS, Integral motor with driver and wireless transmission of power and information for autonomous subspindle drive, IEEE Transactions of power electronics, VOL 15,issue 1,January [3] Arvind Kumar, Mrs.M.Valarmathi, Dept.of ECE SRM University, High precision stepper motor controller implementation on FPGA with GUI on lab VIEW, International journal of advanced research in electricalelectronics and instrumentation engineering VOL 2,issue 4, April [4] Zigbee/IEEE Summary by Sinem Coleri Ergen September 10, [5] Xbee series 2 datasheet, [6] Application manual, Additional axes robotware os 5.0 [7] Xuewu Dai, Konstantinos Saalolou, Robert Atkinson, John Strong, Isabella Panella, Lim Yun Cai, HanMingding, Ang Chee wei, Wireless communication networks for gas turbin engine testing, Hindawi publishing corporation international journal of distributed sensor networks [8] Sudip K. Mazumder, Senior Member, IEEE, Rongjun Huang, Student Member, IEEE, and Kaustuva Acharya, Rotor position feedback over an rf link for motor speed Control,IEEE Trancation on powerelectronics VOL.25,issue 4,April [9] Muhammad Ali Mazidi, Janice Mazidi and Janice Gillispie Mazidi"A text book of 8051Microcontroller and Embedded Systems" Publication: Prentice Hall; Har/Dsk edition (November 11, 1999), ISBN-13:

Job Sheet 2 Servo Control

Job Sheet 2 Servo Control Electrical actuators are replacing hydraulic actuators in many industrial applications. Electric servomotors and linear actuators can perform many of the same physical displacement