Automated Thread Cutter
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The document describes an automatic thread cutter device designed to reduce non-value adding time in a garment production line. It attaches to the back of sewing machines and uses infrared sensors and rollers synchronized to the sewing speed to detect the cloth edge and cut threads without damaging garments. Testing showed it could cut threads within 10mm of the desired distance from the edge for different cloth types and angles. Implementing this automatic device was estimated to save over 90 hours and $495.70 per month by eliminating manual thread cutting time.
Automated Thread Cutter
- 1. AUTOMATIC THREAD CUTTER Kasun Vimukthi Jayalath, Sathananthan Harisha MAS Active Contourline, Pallekele Department of Electrical and Electronic Engineering, University of Peradeniya, Sri Lanka Abstract: The production line in MAS consists with sewing machines and other required machines which individually perform a certain operation and pass the work-in-process to the next stage. The time consumed for each operation is set beforehand and reducing this time is the objective of the automation department which benefits the organization. With that motivation we ran down to an operation of thread cutting which is frequently applied in production line where automation could be involved to reduce the operation time. Requirement was to cut the remaining thread just after the sewing operation. Our application is a small add on device that is fixed to the back of sewing machine. It is synchronized with the sewing speed of the machine and detects the pattern of the cloth edge, then cut the thread without damaging the cloth. 1. Introduction There was an inbuilt thread cutting mechanism in most of the machines. But certain sewing machines did not have this mechanism. Hence this was achieved manually where a team member had to manually cut the thread and a reasonable time was allocated to this operation which was a non-value adding activity. Therefore we designed an automatic thread cutter where we drove cloth little bit further beyond the needle point using two speed synced rollers. Simultaneously we programmed the processor to measure the angle of the incoming cloth edge which sometimes inclined and using this information, the best point to cut without damaging the cloth was calculated. Then the thread was cut at the right position and the right time using a pneumatic controlled blade. And we included an additional facility where the whole setup can be lifted up at any point of time, therefore the operator can manage the cloth if there were any problem. Minute errors may damage the cloth and it may lead to reject the garment which will cost the production big time. Therefore, building an automated system to meet that requirement was quite hard because we had to handle the cutting blade and driving rollers synchronize properly with the sewing speed of the machine which consumed more time. We had to deal with some practical problems such as vibration, different cloth materials, thread materials and space limitation. 2. Analysis on saving We did a survey to find out how much money that can be saved by the organization at the completion of the product. The relevant details were taken from the database of December 2015. Table 2.1 Operations going on progresses Module Number Number of team members involved Operation Machine Style number Quantity for November 12 2 Bottom hem- back Flat Lock 703090 13932 14 1 Bottom hem- back Flat Lock 703088 3400 17 2 Design Stitch Flat Lock 689264 7456 18 2 Design Stitch Flat Lock 689284 7456
- 2. Table 2.2 Operation and its TMV Operation TMV saving 15- TCUT 50 14- TCUT 25 31- TCUT 50 32- TCUT 25 Total 150 Table 2.3 Calculation of the saving Style No QTY TMV Saving Total 703090 13932 300 4179600 703088 3400 150 510000 689284 7456 300 2236800 689284 7456 300 2236800 Total TMV saving 958160 / TMV per min /16.67 Total minute saving per month 5496.82 mins Total hour saving per month 91.8 hr Value per hour *$ 5.4 per hr Total money saving per month $495.7 Eliminated TMV Sample 703088 Assume: Each operation has 2 cutting operations 3. Mechanical design
- 3. Figure 3.1 Mechanical design Figure 3.2 Placement of the Thread Cutter 3.1 Pneumatic cylinders and pneumatic cutters The mechanical parts of the innovation was designed to fix it at the back of the sewing machine. L shaped iron bracket (Thickness – 0.5mm) hold the Iron frame carrying rollers, stepper motor and cutter. 2 pneumatic cylinders (Single Rod, Double acting, 10mm bore, and 60mm stroke) fixed to the bracket. Those cylinders were activated and the whole iron frame was lifted when the sewing operator wants to remove the cloth from the machine. At normal operation the cylinders were released and laid down on the cloth to push the cloth towards the cutter. The cylinders were capable of holding a heavy weight and there was a spring mechanisms at both rod edge to maintain the pressure of the rollers on the cloth and to compensate the vibration while sewing. The cutter was placed in between two rollers which had a single acting pneumatic cylinder and a sharp angular blade fixed firmly at the end of the flat rod. 3.2 Infrered sensor panel Sensor panel consists with 7 industrially used infrared sensors which were very reliable. The angle of the edge of incoming cloth was calculated using some logical combinations. On the bed there was a reflective sticker which reflects the infrared beam back to the sensor. When it was covered by some non-reflective material the sensor detects it. When cloth was detected by one of the sensor the timer was started to count till it reached the other end. The time difference was calculated. This time difference fed in to the microcontroller and the time of cut was calculated. This decision was made using a logarithmic scheme. When the edge angle of the cloth was larger (e.g.: 1st cloth piece of figure 2.1), there was a need to pay extra care not to damage the cloth. So a large clearance was set. When the angle was small, the clearance was smaller.
- 4. Figure 3.3 logical combinations for different cloth 3.3 Rollers Two rollers were driven by the stepper motor placed on the top. Power was transmitted through a belt drive to two rollers. Stepper motor (rated current at 1.2A and 1.8 degree per full step) had driven by the microcontroller synchronized with sewing speed. Sewing speed was captured using encoders fixed to the main wheel. Bearings was penetrated to the iron frame to ease the rotation of the rollers by reducing the friction. The basic requirement of the machine was to synchronize the roller speed with the machine sewing speed. Unless otherwise the cloth may twists and stuck in the machine. To accomplish this task we tapped the encoder built in the machine which gave a pulse on each stitch cycle. We observed that a certain distance of cloth went inside for a single stitch cycle at a certain sewing speed. With the knowledge of that, we found out that distance travelled during a cycle. That distance should be pulled by the rollers. Then we calculated the number of steps needed to be rotate in a stitch cycle to match with the sewing speed assuming no slip between rollers and cloth. The number of steps was always changing with the change in sewing speed. Speed of the machine in terms of steps needed to be found out. Hence we multiply the speed of the machine with the ratio, . 4. Results We conducted few experiments to clarify the reliability of our method. But still more number of experiments should be conducted to bring this innovation to the production floor. Initially we tested couple of experiments to see whether the rollers were synced enough to run in high speed swing scenarios at continuouss operation. So we inserted a piece of cloth (length 10cm) in to the machine and to rollers. Time taken by those two instances were recorded for different speeds. We tested 5 different types of cloths and measured the mean cutting distance from the edge of the cloth achieved in each trail.
- 5. Table 4.1 synchronizing the rollers Table 4.2 Results of the cutting distances Type Cutting distance from edge (mm) Desired distance from the edge (mm) Error(mm) Type 1 (45 even slope) 15 10 5 Type 2(-45 even slope) 16 10 6 Type 3 (45 convex type) 9 5 4 Type 4 (0 flat) 6 1 5 Type 5 (45 concave type) 12 5 7 5. Conclusions We completed designing and implementing two rollers which rotate at the same sewing speed which varies time to time by tapping encoders come with the machine. The similar thing has achieved using a mechanical method before. We replaced that mechanical method in to an electronic feedback loop system. Applying this method, any number of rollers attached to a stepper motor can be driven by the operator sitting at any place around. We had to compromise with time to complete some important part of the project. 10 weeks of training period was not enough to complete final part of the project. We built the mechanical parts and coding completely, but could not perform enough test runs to ensure the efficiency of the system. Future work We are currently extending the coding to build up a closed loop system to the entire system which has not yet been completed. Mechanical faults were affecting to the end results badly. To get rid of those practical issues, we are trying to machine those mechanical parts using CNC. Acknowledgement We would like to express our deepest appreciation to all those who provided us the possibility to complete this project to this extent. A special gratitude to the former General Manager Mr Venura Aththanayake and Mr. Viraj Wijesinghe, Mr Chathushka Hendalage whose contribution in stimulating suggestions and encouragement helped us to coordinate our project in a successive manner. Furthermore we would also like to acknowledge with much appreciation the crucial role of the staff of MAS-Contourline, pallekele specially Mr Lasantha De Silva and Mr. Prasanna who gave the permission to use all required equipment and the necessary materials to complete our product. We would also like to appreciate the guidance given by other supervisor as well as the panels especially in our presentations by providing their comment and advices to improve our presentation skills. Through sewing machine (sec) Through rollers(sec) Difference (sec) 20 22 2 25 28 3 30 34 4 40 45 5 50 55 5 60 67 7 80 88 8