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Как работает бесштоковый цилиндр

Введение

Rodless cylinders are a type of pneumatic component that can move a load linearly with the help of compressed air. The unique feature of a rodless cylinder is that it moves the load alongside the piston, unlike regular pneumatic cylinders that use a rod to push or pull the load from the piston. This design has several advantages, such as providing the same stroke length in less space, no rod buckling to worry about with higher loads or lengthy strokes, and delivering the same force in each direction. Rodless cylinders are commonly used in various applications, including material handling, loading, lifting, and net cutting. Figure 1 shows an example of a rodless cylinder.

Рисунок 1: Бесштоковые цилиндры

Types of Rodless Cylinders

There are three main types of rodless cylinders, each of which refers to how the piston is connected to the carrier to allow motion in the load. These types are Magnetic, Cable, and Slotted. The Slotted design is the most versatile and widely used, which is why we will be discussing it in this article. It can be seen in Figure 2.

Рисунок 2: Бесштоковый цилиндр с прорезями и красными полосами

How Does a Rodless Air Cylinder Work?

The key parts of a rodless cylinder can be seen in Figure 3. An internal piston (A) moves inside the cylinder barrel (E) and is driven by compressed air. Depending on the air pressure on each port, the piston moves in either direction along the length of the cylinder. The piston is attached to a carrier that supports the mounted load and moves along with the piston. The metal bands (D) allow the carrier to move back and forth while making a reliable seal with the cylinder slot. Under the carrier, the bands are bent away from the slot to allow a connection between the piston and carrier. There are adjustable end-cushioning on both ends (B) to prevent any hard stops after the complete travel length in the end caps (C). Figure 4 shows a slotted rodless cylinder design and how the mechanical connection is made through the bands.

Figure 3: Components of a rodless cylinder

Рисунок 4: Механическое соединение поршня бесштокового цилиндра с пазом и держателем (красный) с помощью лент (серый)

Load Consideration

Properly understanding how loads affect a rodless cylinder ensures proper function. With different weights, weight spot, and speed, a moment can be formed that needs to be accounted for. A moment is a force that causes a body to rotate around a specific point or axis. Figure 5 displays the three moments to consider (mentioned below) along with formulas on how to calculate them. We will then use this calculated moment force to the rodless cylinder's published bending moments (typically they list the maximum) to ensure our forces are under this limit.

Figure 5: An example of how a moment is created and calculated

  • Шаг (Ма): Can handle these moments effectively, and in many cases, better the longer the carrier is. The acceleration and deceleration force affect this moment.
  • Ролл (г-н): Very sensitive to these moments. An off-centered load may cause these moments.
  • Рыскание (Mv): Somewhat sensitive to these moments but are less common.

Acceleration & Deceleration

Unlike a normal with a rod, a rodless cylinder must support the resulting moments from acceleration and deceleration. Think of this like a “jerk,” which is the same force you feel when you accelerate/slow down in a car; you jerk back/forward while in the car because of the moment of force. The force in these equations is equal to the mass multiplied by the acceleration (or deceleration). If it is a deceleration force, you need to consider the adjustable cushioning at the end of the stroke length. More forces can also influence the total force in either direction, like friction and breakaway forces.

Вертикальный монтаж

Vertical applications have two additional critical concerns regarding the load. First, you have to battle against gravity (or with gravity) when moving the load and holding the load. In addition, if you are holding the load, you need to make sure the pneumatic cylinder does not leak air, and the air supply is continuous to prevent any motion once in the position due to gravity.

Дополнительные компоненты

Бесштоковый цилиндр требует наличия следующих пневматических систем / компонентов для эффективной работы:

  • Pneumatic air supply: To supply clean and compressed air that drives the rodless cylinder.
  • Pneumatic solenoid valve: To control the flow of compressed air.
  • Pneumatic hose: To supply compressed air to ports, valves, and other devices.

Advantages and Disadvantages of a Rodless Cylinder

Rodless cylinders differ from standard cylinders and provide several benefits in comparison. These benefits include:

  1. Smaller footprint for equivalent stroke length, making them perfect for applications with limited space.
  2. Ability to better support higher loads and moment forces.
  3. Without a rod, they reduce the risk of rod bending and buckling.
  4. Same force in each direction.

Rodless cylinders also have a few disadvantages:

  1. Уязвим к окружающей среде пыли и мусора.
  2. Load movement is fixed on the length of the cylinder.
  3. Inner and outer bands may wear over time as they stretch.
  4. Air leaks due to band wear can lead to the loss of air pressure.

Аксессуары

Приложения

Rodless cylinders, due to their many advantages, are used in various industries. Some common applications include:

  • Автомобильная
  • Производство
  • Робототехника
  • Еда и напитки
  • доставка
  • Коммерческое шитье
  • Подъем складов
  • Печать
  • Окраска распылением
  • Изготовление шин
  • Оптическая сортировка

Критерии выбора

The following criteria need to be considered when selecting a rodless cylinder:

  • Скорость хода: This is the speed at which the piston moves within the cylinder. This would depend on the air pressure supplied at each port and the load.
  • Carrier load: The carrier has to be able to support and move the mounted load securely and effectively.
  • Мертвая длина: It is the length of the cylinder that cannot be used due to internal parts and room required for end-of-stroke. This is required to determine the working cylinder length demanded for the application.
  • Длина цилиндра: Это фактическое рабочее расстояние хода, то есть расстояние, на которое будет перемещаться груз.
  • Давление воздуха: As the piston is driven by compressed air, there must be availability of continuous air pressure throughout the application.
  • Размер отверстия: Bore dimension may be chosen according to your capacity range expected for the application. For a cylinder to perform at maximum capacity, a larger bore size should be considered.

FAQ

  • How does a rodless cylinder work?
    A rodless cylinder includes an internal piston that moves in the cylinder driven by compressed air. The piston is connected to a carrier, which supports the load and moves it in a linear direction with the piston.
  • Как определить силу воздушного цилиндра?
    The force exerted in the cylinder is the product of air pressure applied and usable piston area.
    F = П х А
    Where, F is the air cylinder force (lbs); P is air pressure (psi); A is cylinder bore area (in2).
  • What are the advantages of a rodless cylinder?
    The advantages of a rodless cylinder include a smaller footprint for equivalent stroke length, the ability to better support higher loads and moment forces, no rod to worry about bending or buckling, and the same force in each direction.
  • What are the disadvantages of a rodless cylinder?
    The disadvantages of a rodless cylinder include being vulnerable to environmental dust and debris, load movement being fixed on the length of the cylinder, inner and outer bands wearing over time as they stretch, and air leaks due to band wear leading to the loss of air pressure.
  • What are the common applications of rodless cylinders?
    Common applications of rodless cylinders include automotive, manufacturing, robotics, food and beverage, packaging, commercial sewing, warehouse lifting, printing, spray painting, tire fabrication, and optical sorting.

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