Open Access 
Abstract
In the field of mechanical engineering, the precision and real-time of high-performance manufacturing machine plays an important role. Recently, some solutions for servo system could overcome these drawbacks. Therefore, a design of motion controller to manipulate the highly precise position control and stability. The investigation of both hardware design and software programming is presented in this work. In addition, overall system is created in the real-world application. The use of the seven segments polynomial in motion generator provides an intuitive examination. From these results, it is clarified that the effectiveness and feasibility of our design and control is proper for industrial applications
INTRODUCTION
In the early days of the development of mechanical means, position and velocity control were accomplished by complex, expensive, and time-consuming solutions such as a series of cams 1 , 2 , gears 3 , 4 , and shuttlecocks, and the like. Other devices such as hydraulic and pneumatic cylinders 5 , 6 , electric solenoids 7 , pistons, and grips are often added to these systems. Some examples of these solutions include rudimentary textile machinery, coil manufacturing, and winding equipment.
The automotive and machine tool industries 8 are among those that view motion control as a means of delivering complex profiles and integrating versatile operations. Heavy materials can be moved and handled repetitively, adding value and increasing system productivity. While this dramatically benefits continuously repetitive and unchanged operations, it is not the optimal solution for short-stroke parts for any degree of variety or customization. This is, of course, because early automation systems are very specialized and require resetting the tool and setting up when different products or processes are required.
With the advent of computers and microprocessor technology 9 , other design ideas became possible. In automation electronics-based systems, various parameters can be selected by simply changing the software in the system. This makes work less setup and more efficient. For example, to change the speed of a specific part's operation, a mechanical system might require exchanging an existing piece of equipment for a larger or smaller one. In the modern field of motion control, this can be done by entering a few lines of code or selecting a different velocity profile from the system's memory.
The motion control system is defined as the application of programmable hardware and software (in combination with sensors, actuators, and other feedback devices) to control one or more motions, such as linear motion 10 or rotary motion 11 . Extending this definition into today's concepts of devices used to control motion, motion controllers often take the form of microprocessor-based systems 12 . The system will include the following essential components: controller, amplifier, actuator, and feedback device.
The controller would consist of a device for entering a set of instructions or code into its memory, which is then translated into a sequence of electrical pulses or analog signals and outputs to an amplifier to control some controller. The amplifier receives the signals from the controller and increases or amplifies them to the appropriate levels for the actuator. The actuator provides realistic physical movement and will be closely matched to the design characteristics of the amplifier. Amplifiers or actuators can be one of several different design categories. Typically, these components will be electronic amplifiers and electric motors. Other standard motion actuators are pneumatic or hydraulic actuators. The final element of the system is the feedback device. Nowadays, there are many feedback devices commonly used in motion control systems to provide information about linear or rotational motion.
In general, a motion control system will base and adjust its functions based on the input of any combination of different devices. Multiple motion control systems can be integrated into a more extensive system. Various computer-based devices, such as programmable controllers 13 , PC 14 , stand-alone industrial computers 15 , or remote operating host computers for linkage and coordination of motion control function with other functions. In addition, the operator interface is capable of receiving control logic input, changing an existing program, or providing real-time modification, such as turning the system on or off or changing the schedule.
Networked control systems (NCSs) have been one of the leading research areas focusing on academia and industry for decades and have become a multidisciplinary field 16 . In general, there are three types of networks applied to the controller, including centralized configuration, decentralized configuration, and distributed configuration 17 .
With the strong development of Internet, embedded systems, wireless communication and new control strategies, distributed control network has been increasing its importance in various fields. industrial as well as civil. The authors 18 pointed out that the challenges to be solved in the distributed configuration include: network latency, data loss in transit (dropouts), out-of-order data feeds, and process errors. discretization – digitizing data, different network topologies affecting synchronization times, etc. Eliminating or reducing the problems caused by these challenges is the goal of the suites industrial network control.
In this paper, a novel approach in controlling multi-axes for mechanical system is introduced. The advantages of our method are to release the compact unit, multi-functional device, highly reliability and robust control. The hardware design is presented initially to launch the protentional schematic. Then, the flows of data exchange and communication protocol are illustrated in software design. Later, from the proposed structure, it is verified in many practical scenarios to approve the effectiveness, feasibility and possible applications in the real-world industry. The rest of this work is organized as following. Section METHOD generally describes the overall method. The hardware design in practical platform is depicted in Section HARDWARE DESIGN AND SPECIFICATIONS . The components of firmware and data communication are mentioned in Section SOFTWARE DESIGN AND COMMUNICATION . The results of our research are indicated in Section RESULTS AND DISCUSSIONS so that it could be seen easily the benefits and superior performance in proposed system. Finally, several conclusions in Section CONCLUSION are carried out to concentrate on the powerful specifications.
Method
The overall system could be classified into two sections that the first one contains controller and main computer while servo actuator and peripheral devices locate in the second part as Figure 1 . In the first section, it plays as an important role in distributing user’s command to actuating mechanism as well as delivering the servo status to operators. The second one senses the information and gathers the input data, execute the motion command as desired reference. It might include several measuring sensors, slave controller, power source and so on.
In most cases, one personal computer could be installed more than one slave controller simultaneously. The interface protocol should be usb HID or peripheral component interconnect (PCI) to ensure the rapid communication. The software package in Windows must be allowed to access most libraries. Moreover, the extendable ability of motion controller in multi-axes control is advantageous function which maintain the high performance in industrial application. It should be noticed that the servo system must fully support the network protocol.
Hardware Design and Specifications
In hardware level, a description of the proposed system is visually shown as Figure 2 . The core of motion controller is 32-bit micro-controller PIC32MX360F512L which is available with a variety of memory sizes and processing speeds, along with advanced analog and digital peripherals. It can be used to add functional capabilities to customized design. They also offer a variety of connectivity options including CAN, CAN FD, Hi-Speed/Full-Speed USB and Ethernet. The communication IC MINAS A6 provides the servo cycle up to 0.0833 ms, 32-byte mode with rapid transmit/receive, ring topology and two operating modes such cyclic transmission and non-cyclic transmission. Besides, it could compute the changes in command position during command updating period and generates the movement command. The design of MCX501 is based on the industrial standard, compact size, easy to obtain many signals from external sides, for instance programmable logic controller, desktop, micro-processor or embedded computer. This controller is typically utilized for several solutions in M2M, motion applications, smart transportation and so on. Additionally, several peripheral ICs could be implemented as interface signals to convert the proper standard.
In this design, most of micro-processor is low energy consumption, surface mounted package and small dimension. The power supply for this board is 5V DC which could be delivered by popular adapters.
Software design and Communication
Conventional Ethernet protocol could not satisfy the real-time characteristics of motion control system owing to timing, synchronization, or data transmission. To surpass these limitations, a novel design of modular real-time express which fulfills the industrial communication standard, is recommended. Figure 3 indicates the comparative structure of data frame. Once, the operator manipulates on host personal computer in central control room. The popular USB connection assists easy plug-in, fast data transportation between host and network module. There are two selections in circuit schematic, debug for development and release for commerce. The host controller links with servo pack by two LAN wires (receive and transmit) which could extend up to 100 meters. The servo pack-based system is our target of motion controller. To visualize the feed-back signals, a built-in software installed in host computer interconnects with servo via USB type-B.
For the control loop in servo system as Figure 4 , data from controller feeds to actuator as reference signal and feed-forward signal. There are three main loops in servo pack: position, velocity and torque. While position command is supplied for positioning loop, values of velocity and torque are provided as feed-forward control for velocity loop and torque loop. The feed-back signal that is derived from encoder, is then responded to these loops.
Results and Discussions
To verify the correctness and effectiveness of our approach, the overall platform is launched in practical scenario as Figure 5 . This system is linked with several types of sensing equipment through USB2Serial protocol that needs two pins (Rx, Tx) to proceed. Data is received commonly, nevertheless, it is only kept in local station during each sampling period. The wireless communication is the intermediate connection between centralized station and local station. Later, data is set in cloud for easily accessing if required.
The experimental verification for single axis has been described in Figure 6 . In such S-curve motion profile, the motion command is transmitted from master station to target servo pack. As well, destination and maximum speed are added in the frame of data. Then, these frames are delivered to each station based on the ring topology. In a cycle, master station gathers responses from all slave nodes. When receiving the feed-back frame, the system state of servo drives comprising the messages of servo ready, alarm, warning status or in position signal, supports master station to observe online.
For the polynomial profile from Figure 6 a to Figure 6 d, it requires additional parameters for setting. In the default mode, acceleration and deceleration have been registered in parameter identification (ID) 8.01 and 8.04. Some supplementary parameters such as filters, could produce better performance. Along with the user-defined parameters, different profiles could be reached.
Commonly, the symmetric shape of motion profile must guarantee the same cycling time for phases to accelerate and decelerate whilst the asymmetric profile causes more time slices to slow down. Henceforth, the total period of S-curve profile is smaller than that of AS-curve profile even though the same constraints are input. In addition, the real value of position in AS-curve profile is obviously more superior since it gradually reaches to target. Vibration suppression and flexible profile generation are the most advantageous outcomes of the asymmetrical profile. On the other hand, max velocity and max acceleration of symmetric profile could be precisely obtained because there is no need to lessen so much. Besides, it must come to a climax in the initial period, then it produces the trajectory of deceleration phase. It is well-acknowledged that the valuable benefits of AS-curve profile are better than those of S-curve profile.
Figure 6 . Experimental results using the proposed system of single-axis control with polynomial profile.
Conclusion
In this paper, an effective design of motion controller in machining system is introduced. The hardware platform consists of slave micro-processor, motion control IC and several peripheral devices. The communication of both software and firmware is illustrated so that data exchange is transmitted with high speed and reliable. Several laboratory tests are carried out in the real-world application. It is verified that the feasibility, effectiveness and robustness of this approach are approved.
Acknowledgment
We acknowledge Ho Chi Minh City University of Technology (HCMUT), VNU-HCM for supporting this study.
Conflict of Interest
There is no conflict of interest.
Authors’ Contribution
Minh Tuan Nguyen: hardware, software, validation, formal analysis, writing draft
Ha Quang Thinh Ngo: review and editing.
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