Pneumatic systems are widely used for many reasons. They’re durable, clean, affordable, and fairly easy to install and maintain. They move loads in a variety of ways: pushing, pulling, lifting, lowering, and rotating. And they can handle widely varying payloads. While not ultra-precise in terms of positioning capabilities, they are accurate enough for countless applications.

Pneumatic cylinder然而,在选择组件时,气动系统的相对简单性可能是欺骗性的。来自现成版本的圆柱和阀门的数千种,尺寸和变化,自定义设计。选择的纯粹数量可能会压倒,特别是当在混合中添加诸如传感器的选项时。

花时间选择职位的合适组成部分有助于确保良好的性能,降低费用,提高循环率和延长设备生活。This article examines the parameters – load, force factor, speed, and sequencing, as well as the impact of other components – that engineers should take into account when selecting a cylinder for a pneumatic system.

Cylinder Types

虽然有许多类型的气缸,但它们的结构相当相似。基本上,圆筒是密封管。它含有一个杆,附接到活塞,其延伸穿过一端的开口。压缩空气通过圆筒一端的端口进入,导致活塞杆移动。在另一端,第二港口让空气逸出。了解基础知识有助于展示不同的应用如何影响气缸和活塞杆。万博官网手机登陆

选择圆筒的第一步是决定是否使用单次或双手作用样式。当名称意味着时,单作用汽缸使用压缩空气在一个方向上移动负载,例如提升物体。通过单作用圆柱体,空气仅供应到活塞的一侧,而另一侧通风口向环境。一旦移除空气压力,弹簧(或在某些情况下,重力)将活塞返回到其原始位置。

双作用滚筒使用压缩空气在两个方向上为杆供电并移动负载,例如打开和关闭栅极。这种类型的气缸使用更多能量,但它非常适合需要推动和拉动的负载。

However, force calculations can get complicated. In single-acting cylinders with a spring, the spring force opposing the push or pull increases as the stroke progresses. And in double-acting cylinders, push and pull forces are not equal, as designers must account for the rod area in making force calculations. Manufacturers’ catalogs often list push and pull values for both double-acting and single-acting cylinders, with and without springs, simplifying calculations for users.

加载and Speed

在确定气缸类型和活塞尺寸时,负载是主要考虑因素。(Figure 1)活塞区域(力因子)乘以气缸中的气压给予可用的力。

Large pneumatic cylinders to handle high pressures

一般规则是选择一个力因子,该力因子将产生比负载大的力为25%,以帮助补偿摩擦和损失。气动系统在超大方面非常宽容,但在购买价格和能源消耗方面,使用太大的组成部分增加了不必要的费用。

孔径(力因子)确定给定压力的力。在植物中的工作压力通常可以在10至150psi范围内,是选择孔径时的首次考虑。

Another important consideration is the amount of force that the application requires. Suppliers often provide charts to assist with calculating bore size. If the bore diameter is between sizes, fluid-power experts recommend rounding up to the next size.

要记住钻孔直径的推力也很重要。例如,两英寸直径的圆筒具有一英寸直径单元的功率四倍。因此,将钻孔加倍推动推力。

除了负载外,设计人员还必须考虑到负载将移动的速度。当压缩空气通过系统流动时,由于摩擦压力损耗,由于管壁摩擦,弯曲弯曲,阀门和配件中的限制(为几个问题)。随着空气必须通过阀门,管道和端口流动,更高的速度导致更大的压力损失。达到更高的速度还要求汽缸在较短的时间内提供更多的力。可能需要超过负载50%以上的力来可靠地移动高速负载。

例如,典型的空气压缩机可以在100psi下向系统提供空气。在具有缓慢移万博官网手机登陆动载荷的应用中,活塞可用的实际压力可能降低到不小于90psi。具有相同的负载以更快的速率移动,可用压力可以降低至70 psi。

压力损耗可以通过增加压力来弥补,但必须谨慎完成。压力太大在圆柱体上产生应力,可能会损坏气缸以及负载。在这些情况下,最好选择更大的圆柱体。(Figure 1)还要记住,提高系统压力意味着压缩机必须更加努力,越来越大的整体气动系统的能耗。

Heavy Loads

With heavy loads, the size of the piston rod is as important as the cylinder size and air pressure. A common problem is overloading the rod, which often happens when pairing a heavy load with a long cylinder rod. During horizontal motion the load will hang off the end of the rod, which may cause the rod to bend when fully extended. When lifting a heavy vertical load, the piston rod may even buckle if it’s too small.

气缸主要设计为推动或拉动负载,因此支撑重侧载荷需要额外的计划。将气缸支撑尽可能靠近活塞杆的中心线,应考虑到设计中。

另一个考虑因素是杆长度。大约24英寸和更长时间的笔画可能会损害长而瘦的杆。在这种情况下,最好的解决方案是选择更大的圆柱体。一些制造商还提供具有过大的活塞杆的气缸,在某些情况下可能更经济。

Also consider cylinders with guide rods in difficult loading situations. With blocks and rods mounted parallel to the piston rod, guided cylinders prevent the piston from rotating and increase load-carrying capacity, thanks to the added support of the guide rods and additional bearings. This is important when a system is subjected to large side loads or requires highly accurate controlled linear motion. (Figure 2引导气动气缸防止损坏

最后,其中负载坐在外部托架上的无杆圆柱体,其沿管滑动,也可以用于具有长冲程,重载或高力矩载荷的应用。万博官网手机登陆这些汽缸有许多不同的配置,它们的紧凑尺寸使得它们在狭小的空间中良好。

Getting the Valves Right

阀门控制气动系统中空气的开关和路由。除了控制压缩空气的流动之外,阀门还引导了耗尽空气的流动。气动系统中使用了许多类型的阀门,具体申请要求最佳选择。万博官网手机登陆

设计气动系统时的一个常见错误是正确地指定圆柱,但尺寸润滑阀门。适当匹配的阀门和圆柱体是势在必行的,因为气缸不会像阀门一样移动,如果阀门太小。具有更高的速度,必须增加气流以便更快地移动负载,并且通常表示流量较高的阀门。

Most valves come with a flow coefficient (Cv) rating. In essence, the bigger the Cv, the more air flows through the valve. The valve rating should typically be selected for a 5-psi pressure drop at the required flow rate to drive the cylinder at the desired speed.

流量控制阀在控制气缸速度下工作。这些可以是控制阀排气口或安装在气缸上或附近的特殊阀上的可调节限制器。圆柱形的流量控制具有单向旁路内置,以允许在一个方向上的自由流动和另一个方向的限制流动。为获得最佳效果,请安装这些阀门,以便将自由流入圆柱体并限制流出。

改善循环时间

位置开关和传感器可以提高整体气动性能。在具有序列操作的多个气动执行器的系统中,在每个汽缸中指示活塞位置的位置传感器将促进更短,更可靠的循环速率。

Simple switches such as reed, Hall-effect, and magneto-resistive switches are all commonly used as position sensors on pneumatic actuators. Regardless of the type, they all detect the piston position as the cylinder approaches the end of the stroke.

Without sensors, unnecessary stops (time cushions) must be built into the timing of the system. This is the result of air-supply variations and other factors. In a plant, airflow might be slightly less during the afternoon as compared to the morning. This means in the afternoon it might take a fraction of a second longer to complete the stroke, which could disrupt the timing of other steps in an operational sequence. To adjust for these and other variations, low-cost sensors should be included in the design. Adding such sensors will result in shorter cycle times, smoother operation, and higher operating efficiency.

由于其低的气动系统仍然很流行entry and maintenance costs. While they’re relatively simple, weight, force, speed, and other requirements must be considered at the design level to ensure proper operation. Given the many different types of cylinders, valves, and sensors, taking the time to determine the right components in a pneumatic system – and how they interact – will result in better performance in both the short and long term.

Considerations for Effective Cylinder Performance

在将气动气缸设计成机器,机器人和任何其他设备时,为每个因素进行账户:

加载– A force at least 25% greater than the load is typically necessary to make up for system pressure losses.

Force factor- 力因子只是气缸活塞的区域。力因子时间空气压力等于圆柱生产的力。

速度- 较高的速度需要更大的力量余量来克服增加的系统压力损失。

Sequencing- 添加传感器可以通过消除时间延迟来缩短循环时间。

其他组件– Available pressure at the cylinder can be affected by system compressor, filters, regulators, control valves, and all connecting piping. Right-sizing these components helps ensure the best performance from a cylinder.

- 由Pat Phillips

Fluid Power & Mechanical Products

产品管理器,AutomationDirect

Originally Posted: Feb. 2, 2015