Control and Implementation of Rotary Table Based on Hollow Rotary Platform
Guo Huifang, Chu Zhen
Abstract: This paper introduces a control method for a multi-station rotary indexing table built using a stepping hollow platform. Combined with a human-machine interface, it can easily achieve multi-station processing or inspection with equal or unequal division. The table operates stably and is easy to operate. Combined with an automatic unloading station, it can greatly improve production efficiency and reduce the labor intensity of operators.
Keywords: hollow platform; torque; step angle; pulse equivalent; PLC; ladder diagram
Chinese Library Classification Number: TM301 Document Identification Code: A Article Number:
1. Introduction
This article introduces a rotary table suitable for applications requiring rapid, automated multi-process machining, such as gluing, welding, electronic component assembly, and manufacturing. It includes a tabletop, sensors, a frame, a motor, a reducer, and control and drive devices. The multi-station rotary table performs rotary indexing movements, automatically rotating the tabletop and workpieces by a certain angle, sequentially delivering them to various processing positions to complete the necessary machining or assembly steps. It allows for one-time workpiece installation, and even includes loading and unloading operations. Figure 1 shows a ten-station rotary table.
The hollow rotary platform (Figure 2) is a series of planetary servo reducers, suitable for various rotary motion applications. It integrates high-performance...
Combining efficiency, high precision, and cost-effectiveness, this product features easy motor configuration, stable load-bearing capacity, and can be paired with AC servo motors or stepper motors for arbitrary angle division. The repeatability positioning accuracy can reach about 5 seconds, satisfying the variable position control that traditional cam dividers cannot achieve, while its positioning accuracy is comparable to DD motors. Therefore, it can significantly reduce costs and replace DD motors and cam dividers in factory applications.
Hollow rotary platforms driving multi-station rotary worktables are used in automated production lines to avoid the drawbacks of traditional horizontal assembly lines, such as long inter-station transfer times, inaccurate positioning, and large space requirements.
It can overcome the shortcomings of indexers or pneumatic indexing tables, such as the invariable number of workstations, rotation angle, and rotation direction.
This article introduces the control and implementation method of a four-station rotary table using a hollow rotary platform driven by a stepper motor. This device, in conjunction with a human-machine interface, can achieve arbitrary rotation direction and arbitrary station angle adjustment, and is simple to install while offering greater control flexibility.
2. System Composition
This article takes a four-station device as an example and selects the Panasonic AFPX-C30T positioning-type dedicated PLC as the controller. This PLC has 4-axis pulse drive output (2 axes 100kHz, 2 axes 20kHz), low cost, and high cost performance.
This equipment uses a Human-Machine Interface (HMI) as the display and data interaction component, specifically the GC-4401W model from Profit, which also offers high cost-effectiveness. The interface allows users to set parameters such as rotation direction, speed, and the angle of each station (i.e., processing position).
Position confirmation sensors are used to detect whether each workstation is in position. They can feed back the information of the rotated workstation to the PLC to form a closed-loop control system.
3. Torque Analysis
The hollow rotary platform selected in this paper uses a stepper motor as the main driving component, with an allowable torque of 12 Nm and a repeated positioning accuracy of ±15 seconds. The platform has an allowable inertial load of 50 Nm.
The main mechanical structural parameters of the equipment described in this article are shown in Table 1 below:
Indexing plate diameter DT=0.5m
Indexing plate thickness LT=0.015m
The diameter of the workpiece is DW = 0.15m.
The thickness of the workpiece is LW=0.09m.
The density of the workbench material is ρ = 2700 kg/m³
Number of work items n=4
The distance from the center of the indexing plate to the center of the workpiece is l = 0.22m.
Positioning angle θ=90°
Positioning time t=1s
Acceleration/deceleration time ratio A = 25%
The reduction ratio of the speed reducer is i=18
The reducer efficiency ηG = 0.7
Calculations based on the above data show that:
Acceleration and deceleration time
angular acceleration of the reducer output shaft
Maximum speed of reducer output shaft
Motor shaft angular acceleration
Motor output shaft speed
Because the frictional load is very small, it is negligible.
Inertia of the workbench
Work quality
Full load inertia
Inertia of the load referred to the motor shaft
The moment of inertia of the hollow rotary platform motor selected here is:
Motor shaft acceleration torque
The safety factor S is selected as 2 here.
Required torque
Load to motor inertia ratio
4. Software Parameter Analysis
Pulse equivalent refers to the displacement generated by a positioning control pulse output by the controller. For linear motion, it refers to the distance moved, while for circular motion, it refers to the angle of rotation.
This paper uses a two-phase hybrid stepper motor with a step angle of 1.8 degrees, a rotary platform reduction ratio of 18:1, and a repetitive positioning accuracy of ±15 seconds.
From the above parameters, it can be seen that before the platform is subdivided, the controller needs to send 3600 pulses to rotate one revolution. The pulse equivalent is 0.1 degrees. At this time, the arc length corresponding to one pulse is...
The accuracy (in meters) is approximately 0.44 mm. This accuracy is relatively low compared to both the platform's own accuracy and the machining accuracy. Therefore, the driver pulse subdivision can be set to 10. This way, the pulse equivalent converted to the platform end can reach 0.01 degrees, which is 36 seconds. The corresponding arc length is approximately 0.05 mm. This setting can meet the machining accuracy while making full use of the accuracy of the driver and motor.
5. Control Implementation
The four workstations of this equipment can be allocated as follows: loading workstation, processing workstation 1, processing workstation 2, and unloading workstation.
Figure 4 is a flowchart of the device's operation. After power-on, if it is necessary to set parameters such as position and speed, the parameters can be set on the HMI. If not, it can directly enter the working state.
To ensure operational safety, parameter settings should generally be performed only after the actual work has begun.
After power-on, the turntable rotates in reverse to trigger the home position sensor, and the origin is established. After the material is loaded at station 1, press the start button, and the turntable will start rotating. After rotating to the correct position, the loading station can perform the loading operation again. At the same time, the processing stations 1 and 2 start to perform processing operations, and the unloading station performs the unloading operation. After all four stations have completed their operations, the turntable will be rotated and started again.
6. Program Implementation
Ladder diagrams (LAD, Ladder Logic Programming Language) are the most widely used graphical programming language for PLCs. This article uses Panasonic's programming software FPWINGR for PLC programming and debugging. The ladder diagram program segment for finding the origin and rotating the workstation is shown in Figure 5 below.
This program uses the Panasonic PLC positioning instruction PLSH. When the execution condition is ON, it outputs a pulse. After the target value is determined, when the two are consistent, the pulse output stops, the turntable reaches the target position, and the rotation stops.
7. Conclusion
The rotary table based on the hollow rotary platform improves the flexibility and adaptability of the overall equipment, has a high cost performance, is simple and reliable to implement, and can be flexibly adjusted and expanded according to the actual application environment. It is an economical and practical processing equipment.
References
[1] Zhang Zhiyong. Research on high-precision rotary platform plotter [M]. Northwestern Polytechnical University, 1997
Author Bio: Contact via QQ
Guo Huifang (1982-), female, from Hohhot, Inner Mongolia, Master's degree, Tianjin Jinya Electronics Co., Ltd., No. 95, Nanhai Road, Tianjin Economic and Technological Development Area, Electrical Engineer, Email: [email protected], 022-59826188, Research direction: Control Theory and Control Engineering
Chu Zhen (1981-), male, from Tianjin, Bachelor's degree, Laboratory Engineer, Danfoss (Tianjin) Co., Ltd., No. 9 Quanhui Road, Wuqing Development Zone, Tianjin, Email: [email protected], 022-82196637, Research direction: Measurement and Control
