What Is Shuttering Material?

The curtain shutter is composed of a front curtain and a rear curtain. The front curtain runs from one side to the other to open the shutter for exposure, and the rear curtain runs from one side to the other to close the shutter to end the exposure.

Chinese name: curtain shutter

Definition: It consists of two opaque curtains (one of which has a gap) on the focal surface, and the exposure time is controlled by the movement of the curtain.

Applied disciplines:

Early curtain shutters were made of opaque cloth curtains, also called cloth curtain shutters. Spring shutters drove the cloth curtain shutters to operate. The shutter curtains operated slowly from the beginning to the end, and the shutter curtains began to run until The end time of the operation is about 1/60 second, so it is difficult to achieve a shutter opening time shorter than 1/1000 second.

Assume that the running time of the camera's shutter curtain from side to side is 1/60 second. We set the camera's shutter open time to 1/125 second. When the front curtain runs halfway, the 1/125 second time comes, and the rear curtain starts to run. At this time, the gap between the front curtain and the rear curtain keeping one-half of the focal plane continues to run at the same time. When the front curtain runs in place and stops, The rear curtain has also reached a half position, the rear curtain continues to run until the shutter is completely closed, completing the exposure process of 1/125 seconds. The same reason, if we set the shutter opening time of 1/1000 second, then the front curtain only runs 1/16 of 1/1000 seconds, and the rear curtain starts to run at this time. At this time, the front curtain There is only a very small gap between the focal plane and the rear curtain with a length of 1/16 of the focal plane, which sweeps through the focal plane to complete the exposure process of 1/1000 second. For a 135 film camera, the gap across 1/16 of the focal plane is 2.1875mm.

The camera's shutter curtain is slow, and

With the development of science and technology, the combination of multiple overlapping steel shutters replaced the original cloth shutter, and the operating speed of the curtain shutter increased. As the focal plane is 35 mm in the horizontal direction and 24 mm in the vertical direction, the lateral-travel shutter was later changed to a vertical-travel shutter, which shortened the shutter running distance and further shortened the running time.

The "steel sheet shutter" mentioned above is not necessarily made of "steel sheet", as long as it is a rigid and rigid material, shutters including plastic sheets are also called "steel sheet shutters".

After that, some cameras have been applied very tough and thin

As everyone knows, because the target illumination range of aerial photography is wide,

Figure 1 Schematic diagram of single-curtain shutter structure

To take an image, you must control its exposure to ensure that it gets a uniform exposure at each point in the format. Therefore, the aerial shutter must not only have a wider exposure time adjustment range and higher efficiency, but also need to ensure higher exposure accuracy. Because the CCD device used is not equipped with an electronic shutter, it is necessary to design a focal plane mechanical shutter to complete the exposure function. According to the requirements of use, the main choices of focal surface shutters are curtain shutters and steel shutters. The exposure principle of the two is similar. Both are through the structure to create a light-passing slit in front of the photosensitive medium to expose the photosensitive medium. The difference is the difference in material and structural form. The exposure actuator of a curtain shutter is a curtain with slits, and the material for its production is usually a metal foil; while the exposure actuator of a steel shutter is composed of several metal plates that are sequentially staggered.

Figure 2 Schematic of shutter curtain

The leaves are spliced. The exposure element of the steel sheet shutter is relatively complicated, and the curtain shutter has higher stability than the exposure element. The curtain shutter is divided into single-curtain shutter and double-curtain shutter. The difference between the two shutters lies in the way of controlling the exposure time. The single-curtain shutter controls the exposure time by controlling the slit speed, while the double-curtain shutter The width of the slit controls the exposure time. The curtain shutter mainly exposes the shutter through a curtain with a rectangular opening, and the exposure method is linear exposure. During the exposure, the rollers are used to drive the curtain motion to sequentially expose each point on the web.

In comparison, the single-curtain shutter structure is simpler, but the speed stabilization accuracy of the roller is not easy to achieve. The double-curtain shutter is relatively easy to adjust the slit width, but the structure is relatively complicated. Because the shutter must meet the requirements of miniaturization and light weight under the premise of achieving exposure accuracy, this article uses a single-curtain shutter as a device to control the exposure of the area array CCD camera.

Design of curtain shutter shutter

(1) Scheme design of shutter assembly

Aiming at the structural size of the CCD device and considering the space size constraints at the focal plane, the shutter

Figure 3 Schematic diagram of shutter drive

The design space and structure adopts the form of curtain surround area array CCD, and the shutter assembly is composed of shutter mechanism and driving mechanism.

The single-curtain shutter structure is shown in Figure 1. The shutter changes the traditional two-roller shaft structure and adopts the form of a four-roller shaft. The shutter curtain has the characteristics of a continuous flexible body and a certain tensile capacity in order to During the process, the exposure area is kept flat, so the selection of the shutter material is directly related to the exposure performance of the shutter. According to its movement form and accuracy requirements, timing belts are used as curtains for shutters, and rollers are used for timing rollers. The timing belt has high motion accuracy and has sufficient tensile strength and abrasion resistance. The shutter curtain is shown in Figure 2. That is, the structure of the timing belt is used to complete the shutter.

Figure 4 Three-dimensional schematic diagram of the shutter assembly

Exposure function.

(2) Design of drive components

The shutter drive mechanism is mainly composed of a motor, a clutch, and a gear transmission pair. Figure 3 is a schematic diagram of the shutter drive mechanism. The shutter motor runs continuously. When the clutch is disconnected, there is no torque output and the shutter slits are not moving. When an exposure instruction is received, the clutch is turned on, and the motor power drives the roller shaft through the gear pair, thereby driving the curtain movement to expose the shutter. FIG. 4 shows a three-dimensional model of the shutter assembly.

The designed shutter has been greatly optimized in space, and it is well adapted to the structural dimensions of the area array CCD device and the focal plane space.

Analysis of exposure accuracy of curtain shutter

(1) Mathematical model of shutter exposure accuracy

To ensure the quality of aerial images, the exposure accuracy of the shutter needs to be higher than 0.1. It can be known from the exposure principle of the shutter that the factors that affect the shutter exposure accuracy are the speed accuracy of the shutter curtain movement and the dimensional accuracy of the slit width. For single-curtain shutters, the slit width dimension is constant, so its effect is ignored.

As can be seen from the above formula, the exposure accuracy of the shutter depends on the accuracy of the slit stabilization speed. The factors that affect the speed stabilization accuracy are mainly the transmission accuracy caused by the structure and the motor speed stabilization accuracy.

(2) Calculation of structural transmission error

Figure 5 Timing zone motion curve

In each link of the structure, the factors that affect the transmission accuracy are mainly the transmission accuracy of the gears of the drive components and the speed error introduced by the polygonal effect of the timing belt.

The calculation results show that the error of the second-stage gear meshing pair is slightly greater than that of the first-stage gear meshing pair, which is because the second-stage gear is an acceleration stage; the final result shows that the exposure accuracy error caused by the gear structure transmission error is 5.83%. Since the shutter curtain is made of a timing belt, the timing belt will produce a polygonal effect during transmission to affect the motion accuracy. When the timing belt is completely in mesh with the pulley, the pitch line of the belt is wound around the pulley in the form of arcs and fold lines alternately connected to form a polygonal pitch line. Due to the periodicity of the belt pitch P, the geometric relationship between the polygonal shape of the pitch line and the tooth profile parameters of the belt within one pitch is analyzed, and it is assumed that the belt is a flexible body, and the belt teeth are not bent. gap. Figure 5 shows that the timing band speed error caused by the polygon effect is 0.1%. Because it is an order of magnitude lower than the error caused by the mechanical structure, its effect is not considered.

Conclusion of curtain shutter research

Based on the analysis of the exposure principle of the curtain shutter, a new type of curtain shutter with a timing belt as a shutter and a timing roller as a roller are designed by utilizing the characteristics of high timing belt transmission and stable movement. According to the meshing principle of the timing belt transmission, combined with the shutter transmission system and the control system, the exposure accuracy of the shutter was analyzed and calculated. The results show that the transmission error of the timing belt is 0.1%, which is an order of magnitude lower than the structural transmission error. The system's exposure accuracy is 0.067. The photoelectric method was used to experimentally measure the exposure time of each point on the web. The results showed that the exposure accuracy of each point on the web was 0.056. The shutter can achieve a wide range of target illuminance range aerial photography exposure. ^[3]