PTZ dome cameras. The mechanism determines the cost.
The reason for this publication was the appearance on the Russian market of technical security equipment of Chinese-made PTZ dome cameras with video modules (camera plus lens) from well-known world manufacturers. The prices for such models have caused a considerable stir. The cameras offered by Chinese companies are 2 times cheaper than their counterparts from famous manufacturers. And we are not talking about typical Chinese copies. The video module is real. What is the reason for the cheapness then?
It must be acknowledged that the current global economic model, using the principles of globalization, has intensified competition between manufacturers to such an extent that it forces a number of well-known companies to either bring their own developments only to the level of technology with subsequent sale, or to supply the market with not only the product, but also various components. In particular, we are talking about video modules for PTZ dome cameras. Indeed, well-known Japanese and South Korean companies are manufacturers and suppliers of video modules for a wide range of companies in the market of security video surveillance systems.
The optical-electronic module (photo 1) consists of a video camera with a built-in zoom lens, which has a menu for setting up various functions, and a set of interfaces (video output, RS-232/485, etc.). The video module can be built into an individually designed case. Thus, we get a ready-made TV camera that does not look like a prototype. There are not so many developers and manufacturers of video modules compared to the number of camera manufacturers. The latter, as a rule, hide the origin of the components, especially since they often modify the software of video modules. But this is true only for international companies. Of course, unknown cooperatives from China, trying to prove the quality of their products, in every possible way flaunt the origin of the components of their models. However, in order to offer a competitive product, the case is not enough — the price of the camera will not be fundamentally lower than the price of a similar model from the module manufacturer. Another matter, a more complex device — a rotating camera, here there is something to save on. Of course, on the rotating mechanism.
Types of mechanisms
More than 15 years have passed since the appearance of PTZ dome cameras. During this time, the design of the PTZ mechanism has undergone significant changes. If the first models of PTZ dome cameras were no different from a conventional PTZ camera, only installed in a hemispherical housing, then with the advent of integrated video modules, which were discussed above, with a small weight and size, the drive mechanism began to change.
Photo 2 shows three types of PTZ mechanisms — a gear drive, a belt drive, a direct drive mechanism from the engine and the approximate time of their appearance on the market. It also shows the characteristic values of the speed of rotation of cameras in the horizontal plane and the positioning accuracy for each type of drive.
Television cameras using the first two types of drives are widespread. Direct drive from a stepper motor is still rare, but it provides the highest performance and positioning accuracy. Direct drive has no parts subject to wear and friction, which guarantees high accuracy and dynamic characteristics. Most models use a polymer belt as a belt drive. Due to their light weight and the use of belt drives, dome cameras have become high-speed. Of course, the performance and durability of the drive greatly depend on the quality of the belt material. As you can see, the most modest characteristic is that of a gear drive. Such a drive is often used in cheap Chinese models.
Importance of characteristics
At first glance, 240 degrees per second is more than a high speed for positioning (although this may not be enough to handle alarms when integrating the camera with a security system). Cameras with belt and direct motor drives have a horizontal rotation speed of up to 600 degrees per second. A more fundamental characteristic is the positioning accuracy, namely the accuracy of the preset. For cameras with a gear drive, the accuracy does not exceed 0.5-0.4 degrees/sec. If, for example, a Samsung video module with a 37-axis zoom lens is used with such a drive, then at a maximum zoom of 300 m, an error of half a degree is a discrepancy with the preset point of more than 2 m! For cameras using belt drives, the typical value of positioning accuracy to a preset position is 0.1 degrees. For a direct drive, this value is even lower.The minimum rotation and tilt speed is also important for dome PTZ cameras. To monitor moving objects at a great distance, the drive must provide a rotation/tilt speed of no more than 0.1 degrees per second, if we are talking about video modules with 23–30x zoom lenses. Otherwise, it is necessary to regularly change the observation scale, which reduces the efficiency of observation and requires a certain skill from the operator. For TV cameras with 35–37x zoom lenses, the minimum rotation/tilt speed should be 0.02–0.05 degrees per second. For cameras with lenses with a magnification of 40x and higher, no more than 0.01 degrees per second. Such parameters can be provided by a high-quality mechanism with a belt drive. Unfortunately, the reliability and real characteristics of the PTZ dome camera drive cannot be determined based on the data specified by the manufacturer. In reality, they may be lower. However, you can get a certain idea of the model and its capabilities. And most importantly, find the answer to the question of why this camera is cheaper.