This paper presents a multi-axis control system of bar tacker. A bar tacker must meet the following requirements: feeding accurately, cutting automatically, needle stopping precisely and quickly, et ac. In order to achieve these functions, multi-thread synchronization control was introduced to ensure the multi-axis collaborative motion. And time-based PI method with velocity feed-forward was used to control the needle stop position. The software of this control system was programmed based on embedded Windows platform. At present this control system has been tested in the factory and the test results show that this method can accurately control the multi-axis motion and produce good sewing patterns. Besides lockstitch bar tacker, this control system can also be applied to other intelligent sewing machines by minor changes and improvement. VS Sewing Machines
Bar tacker is a special automatic sewing machine which used to reinforce the force area on clothing, bags or other apparel items. With the automation development of garment factory, these intelligent machines demand more and more. Currently, some foreign manufacturers did better in this field. Representative products have Japanese Brother KE-430D and Juki LK-1900A. In domestic there are also a number of organizations in the study of intelligent sewing machines , many of them use the bought control board which may not satisfy the special control requirement of sewing machine or have unstable performance. The common problems include feeding out of place, bad stitch, off line and so on. To resolve these problems and achieve independent property rights system, a self-designed control system is introduced. This paper only focuses on the software realization of the control system. The main difficulties are the multi-axis collaborative control and the high-precision needle stopping position control. The rest of paper is organized as follows: part II introduces the whole control flow chart of bar tacker briefly, part III and IV present the multi-thread synchronization control and time-based servo position control respectively. Part V and VI give the experiment results and conclusions.
The focuses of study are the multi-axis collaborative control in sewing procedure and needle stopping position control at the end of sewing which correspond to the two dashed parts in Fig. 1. A multi-thread programming approach is used to control multi-axis collaborative motion and a time-based PI control algorithm is presented to control needle stop position.
As an intelligent machine, bar tacker control system should automatically implement these functions: needle moving (master-axis), automatic feeding (x-axis, y-axis), thread cutting, thread winding, thread tension, foot pedal pressing, clamp lifting and so on . In this system, servo motor drives the needle moving and hooking, step motors are used to control the feeding mechanism and presser foot, and electromagnets control thread cutting and tension. Fig.1 is the control flow chart of bar tacker https://www.vssewingmachine.in/
Multi-thread programming approach reduces the complexity of the flow control. It makes the program more simple and effective. In this system, each thread has a synchronization event. The thread handling program is executed only when the event is triggered. Bar tacker system include the events of feeding, foot pedal, thread cutting, thread tension and clamp which all triggered by the location of servo motor. Reading servo encoder value continuously is an ordinary method for obtaining the servo location. But this method will bring serious time delay. In our system, the ARM interrupt signals are used to register events. It can trigger the event signals at proper position and realize multi-thread collaborative control precisely. For bar tacker system, collaborative control mainly refers to the three-axis movement of servo motor and x-y feeding motors. Feeding event affects the sewing performance greatly. To ensure the feeding accuracy, servo speed and step motor speed should be adjusted to complete feeding pulse during sewing process.The position control is achieved by adjusting the speed of servo motor. In ideal situation, the servo speed decelerates to zero and stops at the target location. PI control algorithm is the commonly used method for position control, but it should have some improvement for particular application. In this system, a velocity feed-forward factor is added in the PI algorithm to ensure the stability of control.Normally, the control of needle stop position will be more accurate if the speed is lower near the target location. But for bar tacker system, the servo motor rotates and drives mechanical cam cutting thread automatically. The thread cutting position is near the target position. If the servo speed is too small, the impact of cam is large and may cause great overshoot. To avoid this happening, a minimum cutting speed Vtrim is limited in needle stopping position control. The servo speed is expressed as follows:This paper implements the software control of bar-tacking machine and mainly focuses on the multi-axis collaborative control and needle stopping position control. The multi-thread synchronization control method is introduced to realize multi-axis motion timing control. Automatic feeding is the most important event in multi-thread control. To ensure the accuracy of feeding position, servo speed adjustment and feeding pulse compensation are used during sewing process. These can reduce the feeding error and improve the pattern performance at high sewing speed. At the last sewing stitch, a time-based control method is present to control servo speed. At each timer period, the improved feed-forward PI servo control method is adopted. It has good speed response and makes the needle stop precisely at target location. According to the sewing pattern, this control system is feasible for bar tacker and has good sewing performance at high speed. For minor changes and improvement, it may also be applied to other intelligent sewing machines.