The hemstitch sewing machine was invented in 1893 by Karl Friedrich Gegauf. In 1932, his son Fritz introduced the first household sewing machine and the inventions and patents from Bernina have kept coming ever since. The company, based in Steckborn, Switzerland, stands for the highest quality and durability: BERNINA sewing machines must therefore meet very high standards. They must be fast, low vibration, quiet and wear-resistant. They should also stop with high precision, execute moves in time and repeat them predictably.
The mechanical challenges of a sewing machine are complex: First, a sewing machine is composed of a number of vibrating parts that mutually influence each other. The vibrations are often associated with high imbalances due to the nature of the construction. When vibration frequencies are high, even the smallest deviations at the micro-level can substantially affect the functionality of a sewing machine. Also, depending on the material used, the upper and lower thread may require different and often unpredictable movements, sometimes in the tightest of spaces.
Facilitating a diverse range of tests with the right camera
To analyze the problems arising from this, BERNINA AG has to apply accurate, efficient and reliable measuring instruments. These include the MotionBLITZ EoSens ® mini2 by Mikrotron. They started using the high-speed camera in the construction and development department in 2009. Mr. Durville, head of the department, and Mr. Schwyn, test engineer at BERNINA AG, were particularly impressed by their flexibility. “The camera has quickly established itself as a flexible tool for many testing purposes,“ says Mr. Schwyn. It records the movement of the thread, but also monitors components operating under spring pressure or the needle-looper movement and checks time sequences. The resolution and speed of the camera are adjustable. At a resolution of 1,696 × 1,710 pixels (3 megapixels), the camera takes 523 images per second. The images let you see every detail. Higher frame rates of up to 200,000 frames per second are possible at a lower resolution.
Recording the movement of the thread
A special challenge in the development of a sewing machine is the controlled movement of the thread: Since commercially available threads come with a variety of surfaces, thicknesses, resistances and flexural properties, it is difficult to keep the grain line under control. In addition, the operational parameters may run from a speed of 2 m/sec to being completely paused. In the latter case, there is a danger that the thread may become hooked on machine components or slip out of the thread guide.
For a regular and high-quality seam, it is extremely important that the slip motion of the thread remain under control at all times and everywhere. The MotionBLITZ EoSens ® mini2 by Mikrotron makes the movement of the thread visible to the human eye, meaning the design process can be brought to bear on it.
Monitoring the thread guide
Thanks to the high-speed imaging of the MotionBLITZ EoSens® mini2 it is possible to check whether the thread is moving in a controlled way or if the alternations of tension and release are too great. With an image size of 1,696 × 1,710 pixels and a frame rate of 512 frames/second, the camera delivers high-resolution and accurate shots.
Monitoring components under spring pressure
In a sewing machine, spring pressure enables many parts to stay in position or allows them to perform the necessary movements without hindrance. For this, one usually alternates between high and low pressure. High pressure leads to high friction and wear, while low pressure goes hand in hand with low reliability. The high-speed camera MotionBLITZ EoSens® mini2 helps manufacturers to find the right spring design faster and more effectively.
Monitoring the spring pressure
The MotionBLITZ EoSens® mini2 is used to control the spring pressure of two components. A high frame rate of 3,668 frames/second was chosen for the image. A resolution of 528 × 652 pixels was sufficient to document the interaction of the two components in Detail.
Analyzing the sensitive needle-looper movement
The central piece of a sewing machine is the so-called looper. It detects the thread, which is “offered” to it by the needle. Only a few hundredths of a millimeter determine whether the thread is detected by the looper or not, i.e., whether a stitch is created or not. The needle is guided from the top of the machine; the looper is guided from the bottom of a sewing machine.
The long mechanical lever arms, the high speed and the many moving parts cause vibrations that threaten this very important function. Here the high-speed camera MotionBLITZ EoSens® mini2 also delivers precision.
Monitoring the needle-looper movement
The MotionBLITZ EoSens® mini2 allows various high-speed recordings of the sensitive interaction between needle and looper.
Checking temporal sequences
A sewing machine can only fulfill its task if the temporal processes are executed with absolute precision and accuracy
- The fabric may move only as long as the needle is not inserted.
- The needle should only execute the ZZ movement if it is not inserted in the fabric.
- The servomotor for the fabric transport length should only move when its not transporting.
- The looper must then be exactly on the spot when the needle forms a small thread loop.
All these processes take place in the range of milli- and microseconds, and are therefore difficult to analyze in a conventional manner. Mr. Schwyn tests, checks and corrects these processes with the high-speed MotionBLITZ EoSens® mini2 camera.
His company has also greatly benefited from the technological developments in Mikrotron cameras, Mr. Schwyn remarks. The improved handling, image processing and speeds have further increased the capabilities of the current camera model, while simplifying the application. “We use the camera very frequently and consistently,” says Mr. Schwyn. Major technical problems or difficulties in handling have not arisen. If problems occur, they can quickly be solved internally.