关于冲击和振动环境下编码器的选择

工业环境经常使设备受到高强度冲击和振动。这会影响性能并损坏设备本身。在这里，我们讨论了为高冲击和振动环境选择编码器所涉及的权衡取舍，以及如何确保应用的适当寿命和性能。

Industrial environments frequently expose equipment to high degrees of shock and vibration. This can impact performance and damage the device itself. Here, we discuss the trade-offs involved in choosing an encoder for a high shock-and-vibration environment and how to ensure appropriate lifetime and performance for the application.

在指定编码器冲击和编码器振动水平较高的应用时，需要考虑三个关键因素：

编码器传感器引擎：光学与磁性

编码盘材质：玻璃、金属、聚酯薄膜

编码器组件：轴承、连接器等

There are three key factors to consider when specifying for an application with high levels of encoder shock and encoder vibration:

Encoder sensor engine: optical versus magnetic

Encoder disk material: glass, metal, Mylar

Encoder components: bearings, connectors, etc.

编码器传感器引擎

Encoder Sensor Engine

编码器可分为光传感引擎和磁传感引擎。最常见的光学编码器类型包括一个光源（通常是一个 LED）、一个检测器和一个在它们之间穿过的薄图案码盘。

光学编码器本身可以提供非常高的分辨率，这使得它们对于科学应用和半导体制造等专业制造至关重要。然而，它们可能容易受到冲击和振动的影响。码盘和源/探测器之间的气隙可以小至 0.020”。过度的冲击和振动会导致错位，从而使这些组件相互接触，从而导致损坏甚至灾难性故障。

Encoders can be divided into optical and magnetic sensing engines. The most common type of optical encoder consists of a source (typically an LED), a detector, and a thin patterned code disk that passes between them.

Optical encoders can be extremely high resolution, making them essential for scientific applications and for specialty manufacturing like semiconductor fabrication. They can be vulnerable to shock and vibration, however. The air gaps between the disk and the source/detector can be as small as 0.020”. Excessive shock and vibration can introduce misalignments that can bring these components into contact, causing damage or even catastrophic failure.

相控阵光学编码器提供了另一种选择。顾名思义，相控阵编码器使用探测器阵列来捕获信号。这有助于平均化由于编码器冲击或编码器振动引起的信号变化。探测器阵列的固态特性也使其不易受到损坏。相控阵光学编码器可承受 400G 冲击和 20G 振动，例如Dynapar HS35R重型光电编码器

对于最困难的环境，磁性编码器可能是最佳选择。磁性编码器操作类似于旋转光学编码器，尽管它们基于带有交替磁畴图案的金属轮。它们往往比光学编码器更坚固，不易受到编码器冲击和编码器振动的影响。这些设备是非接触式的，磁轮和检测器相距很远。设计有宽气隙的磁性编码器具有明显更大的间隙，例如NorthStar RIMTach RT8 磁性编码器

磁轮不能像光学编码器上的码轮那样密集地图案化。因此，磁性编码器无法匹配光学设计的分辨率。

Phased-array optical encoders provide an alternative. As the name suggests, phased-array encoders use an array of detectors to capture the signal. This helps average out signal variation due to encoder shock or encoder vibration. The solid-state nature of the detector array also makes it less vulnerable to damage. Phased-array optical encoders are available rated for 400G shock and 20G vibration and are used in Dynapar encoders such as the HS35R heavy duty optical encoder

For the most difficult environments, a magnetic encoder may be the best choice. Magnetic encoders operate analogously to rotating optical encoders, although they are based on a metal wheel patterned with alternating magnetic domains. They tend to be much more robust than optical encoders and less vulnerable to encoder shock and encoder vibration. The devices are noncontact and the magnetic wheel and detectors are widely separated. Magnetic encoders designed with wide air gaps have significantly greater clearance such as the NorthStar RIMTach RT8 magnetic encoder

The trade-off is that the magnetic wheel cannot be patterned as densely as the code wheel on the optical encoder. As a result, magnetic encoders cannot match the resolutions of optical designs.

编码器盘材质

Encoder Disk Material

光学编码器使用三种不同类型的磁盘材料：玻璃、金属和聚酯薄膜。磁盘的选择涉及性能和对冲击和振动以及其他环境因素的响应之间的权衡。对于直读编码器（不包括多分辨率的正交插值），Dynapar 为带玻璃盘的编码器提供高达 10,000 PPR、5000 PPR Mylar 盘和高达 2540 PPR 的带金属盘编码器的编码器。

尽管金属盘在承受高冲击载荷时非常坚固，但它们的分辨率有上限。光刻图案的玻璃盘提供更高的分辨率，但它们容易受到编码器冲击并且可能破碎。有一个普遍的误解，即玻璃外层可以使用聚酯薄膜，但这是不正确的。聚酯薄膜码盘在光学编码器中提供最高分辨率，同时保持极其坚固。

然而，聚酯薄膜代码磁盘确实带有警告。材料可能会因过热、变色甚至变形而损坏。为取得成功，编码器应针对应用的全部条件进行评级。

Optical encoders use three different types of disk materials: glass, metal, and Mylar. The choice of disk involves the trade-off between performance and response to shock and vibration as well as other environmental factors. For direct read encoders (not including quadrature interpolation to multiple resolution) Dynapar offers up to 10,000 PPR for encoders with glass disks, 5000 PPR Mylar disks and up to 2540 PPR for encoders with metal disks.

Although metal disks are very robust when exposed to high shock loads, they have an upper limit on resolution. Lithographically patterned glass disks provide higher resolution but they are vulnerable to encoder shock and can shatter. There is a common misconception that glass out performs Mylar but this is incorrect. Mylar code disks deliver the highest resolution in optical encoders while remaining extremely robust.

Mylar code disks do come with a caveat, however. The material can be damaged by excess heat, discoloring or even distorting. For success, the encoder should be rated for the full set of conditions of the application.

编码器组件

Encoder components

选择合适的传感器引擎和码盘材料仅代表编码器规格的一部分。编码器是一个系统，一个系统的有效性取决于其最薄弱的环节。要使编码器可靠运行，需要根据环境选择支持组件，如电缆和轴承。

如果电缆振动松动，编码器将无法运行。选择即使在长时间编码器振动后仍保持接触的锁定连接器。根据幅度、频率和持续时间，接线可能需要旋入式连接器或直接与端子接触。

布线并不是唯一容易受到连接问题影响的元素。长时间的振动会使固定电子设备的 PCB 上的焊点断裂。即使是连接到连接器的电缆中的电线也可能会断裂。出于这个特定原因，Dynapar 的磁性编码器具有完全封装的电子器件。

尽可能避免使用轴承。高水平的振动会改变轴承的负载。这会导致不均匀磨损，从而导致轴承过早失效，这也是无轴承磁编码器在造纸和钢铁厂等恶劣环境中首选的另一个原因。

Choosing the appropriate sensor engine and disk material represents only part of encoder specification. An encoder is a system and a system is only as effective as its weakest link. For an encoder to perform reliably, support components like cabling and bearings need to be chosen with the environment in mind.

An encoder can’t operate if the cabling has vibrated loose. Choose latching connectors that will remain in contact even after prolonged encoder vibration. Depending on the amplitude, frequencies, and durations, wiring may need screw-in connectors or direct wire contact to the terminals.

Cabling is not the only element vulnerable to connection issues. Prolonged vibration can fracture the solder joints on the PCB that holds the electronics. Even the wires within the cabling that link to the connector might fracture. For this specific reason, Dynapar’s magnetic encoders have fully encapsulated electronics.

Avoid bearings when possible. High levels of vibration can alter the loading of a bearing. This causes uneven wear, which can lead to premature bearing failure and is another reason why bearingless magnetic encodes are preferred in harsh environments such as paper and steel mills.

冲击和振动对编码器信号的影响

The Effects of Shock and Vibration on Encoder Signal

所有这些震动不仅仅是让编码器的操作处于危险之中。冲击和振动会影响性能。由于磁性编码器非常坚固，它们可能不会显示振动的物理影响。然而，问题可能会出现在信号中。

All that shaking does more than simply put the operation of an encoder at risk. Shock and vibration can compromise performance. Because magnetic encoders are so robust, they may not display physical effects of the vibration. The problems may show up in the signal, however.

振动在信号中以过量噪声的形式出现，表现为抖动。这是与通常由磁盘偏心引起的抖动不同类型的抖动。偏心抖动通常只出现在一个通道上，而另一个通道信号看起来很好。由过度系统振动引起的抖动会出现在所有通道上。看一个例子编码器抖动并将其与由失去耦合引起的编码器振动

极高的冲击可能会使轮盘或码盘错位，这也会影响信号质量。它可能导致所有通道上的过度抖动和/或两个通道之间的相位变化。

Vibration shows up in the signal as excess noise, manifesting as jitter. This is a different type of jitter from the one commonly caused by disk decentration. Decentration jitter typically shows up on only one channel while the other channel signal looks fine. Jitter caused by excess system vibration shows up on all channels. See an example of encoder jitter and compare it to encoder vibration caused by a lose coupling

Extremely high shock could misalign the wheel or code disk, which could also affect signal quality. It could result in excessive jitter on all channels and/or change in phasing between two channels.

冲击和振动的编码器测试方法

Encoder Testing Methodology for Shock and Vibration

在为高冲击和振动环境选择编码器时，数据表是不够的。设计需要经过严格的测试。Dynapar 编码器经过 MIL-STD-202 测试，需要扫描测试等技术。在此过程中，编码器在给定范围内以不同频率暴露于指定周期的正弦振动。例如，一个编码器在 5 到 2000 Hz 下可用于 20Gs，它将在所有三个轴上振动 24 个 10 分钟扫描，总持续时间为 12 小时。供应商应该有每个设计的测试协议和性能的详细结果。

与工程中的所有事物一样，为恶劣环境选择编码器需要权衡取舍。以上几点给出了一般指导方针。特殊应用，例如在恶劣环境下需要非常高分辨率的应用，将把这些技术推向极限。在某些情况下，OEM 需要更频繁地更换反馈设备。然而，在大多数情况下，与供应商密切合作并告知他们所有的专业要求将产生一个可以满足应用程序需求的解决方案。

When choosing an encoder for high shock and vibration environments, data sheets are not enough. Designs need to be rigorously tested. Dynapar encoders are tested to MIL-STD-202 which requires techniques like sweep testing. In this process, the encoder is exposed to a specified period of sinusoidal vibration at distinct frequencies across a given range. An encoder qualified for 20Gs at 5 to 2000 Hz, for example, would be vibrated for 24 ten-minute sweeps along all three axes for a total duration of 12 hours. A vendor should have detailed results on test protocol and performance for every design.

Like all things in engineering, choosing an encoder for rugged environments involves trade-offs. The points above give general guidelines. Specialized applications such as those requiring very high resolution for harsh environments will push these technologies to their limits. In some cases, OEMs need to resign themselves to more frequent replacement of their feedback device. In most cases, however, working closely with the vendor and informing them of all specialty requirements will result in a solution that can satisfy the needs of the application.

本文英文原文转载自：DYNAPAR-Specifying for Encoder Shock and Vibration

本文翻译by爱泽工业，如有偏颇，敬请指正。