關(guān)于沖擊和振動(dòng)環(huán)境下編碼器的選擇
工業(yè)環(huán)境經(jīng)常使設(shè)備受到高強(qiáng)度沖擊和振動(dòng)。這會(huì)影響性能并損壞設(shè)備本身。在這里，我們討論了為高沖擊和振動(dòng)環(huán)境選擇編碼器所涉及的權(quán)衡取舍，以及如何確保應(yīng)用的適當(dāng)壽命和性能。
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.
在指定編碼器沖擊和編碼器振動(dòng)水平較高的應(yīng)用時(shí)，需要考慮三個(gè)關(guān)鍵因素：
編碼器傳感器引擎：光學(xué)與磁性
編碼盤材質(zhì)：玻璃、金屬、聚酯薄膜
編碼器組件：軸承、連接器等
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.
編碼器傳感器引擎
Encoder Sensor Engine
編碼器可分為光傳感引擎和磁傳感引擎。最常見的光學(xué)編碼器類型包括一個(gè)光源（通常是一個(gè) LED）、一個(gè)檢測(cè)器和一個(gè)在它們之間穿過的薄圖案碼盤。
光學(xué)編碼器本身可以提供非常高的分辨率，這使得它們對(duì)于科學(xué)應(yīng)用和半導(dǎo)體制造等專業(yè)制造至關(guān)重要。然而，它們可能容易受到?jīng)_擊和振動(dòng)的影響。碼盤和源/探測(cè)器之間的氣隙可以小至 0.020”。過度的沖擊和振動(dòng)會(huì)導(dǎo)致錯(cuò)位，從而使這些組件相互接觸，從而導(dǎo)致?lián)p壞甚至災(zāi)難性故障。
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.
相控陣光學(xué)編碼器提供了另一種選擇。顧名思義，相控陣編碼器使用探測(cè)器陣列來捕獲信號(hào)。這有助于平均化由于編碼器沖擊或編碼器振動(dòng)引起的信號(hào)變化。探測(cè)器陣列的固態(tài)特性也使其不易受到損壞。相控陣光學(xué)編碼器可承受 400G 沖擊和 20G 振動(dòng)，例如Dynapar HS35R重型光電編碼器
對(duì)于最困難的環(huán)境，磁性編碼器可能是最佳選擇。磁性編碼器操作類似于旋轉(zhuǎn)光學(xué)編碼器，盡管它們基于帶有交替磁疇圖案的金屬輪。它們往往比光學(xué)編碼器更堅(jiān)固，不易受到編碼器沖擊和編碼器振動(dòng)的影響。這些設(shè)備是非接觸式的，磁輪和檢測(cè)器相距很遠(yuǎn)。設(shè)計(jì)有寬氣隙的磁性編碼器具有明顯更大的間隙，例如NorthStar RIMTach RT8 磁性編碼器
磁輪不能像光學(xué)編碼器上的碼輪那樣密集地圖案化。因此，磁性編碼器無法匹配光學(xué)設(shè)計(jì)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.
編碼器盤材質(zhì)
Encoder Disk Material
光學(xué)編碼器使用三種不同類型的磁盤材料：玻璃、金屬和聚酯薄膜。磁盤的選擇涉及性能和對(duì)沖擊和振動(dòng)以及其他環(huán)境因素的響應(yīng)之間的權(quán)衡。對(duì)于直讀編碼器（不包括多分辨率的正交插值），Dynapar 為帶玻璃盤的編碼器提供高達(dá) 10,000 PPR、5000 PPR Mylar 盤和高達(dá) 2540 PPR 的帶金屬盤編碼器的編碼器。
盡管金屬盤在承受高沖擊載荷時(shí)非常堅(jiān)固，但它們的分辨率有上限。光刻圖案的玻璃盤提供更高的分辨率，但它們?nèi)菀资艿骄幋a器沖擊并且可能破碎。有一個(gè)普遍的誤解，即玻璃外層可以使用聚酯薄膜，但這是不正確的。聚酯薄膜碼盤在光學(xué)編碼器中提供最高分辨率，同時(shí)保持極其堅(jiān)固。
然而，聚酯薄膜代碼磁盤確實(shí)帶有警告。材料可能會(huì)因過熱、變色甚至變形而損壞。為取得成功，編碼器應(yīng)針對(duì)應(yīng)用的全部條件進(jìn)行評(píng)級(jí)。
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.
編碼器組件
Encoder components
選擇合適的傳感器引擎和碼盤材料僅代表編碼器規(guī)格的一部分。編碼器是一個(gè)系統(tǒng)，一個(gè)系統(tǒng)的有效性取決于其最薄弱的環(huán)節(jié)。要使編碼器可靠運(yùn)行，需要根據(jù)環(huán)境選擇支持組件，如電纜和軸承。
如果電纜振動(dòng)松動(dòng)，編碼器將無法運(yùn)行。選擇即使在長(zhǎng)時(shí)間編碼器振動(dòng)后仍保持接觸的鎖定連接器。根據(jù)幅度、頻率和持續(xù)時(shí)間，接線可能需要旋入式連接器或直接與端子接觸。
布線并不是唯一容易受到連接問題影響的元素。長(zhǎng)時(shí)間的振動(dòng)會(huì)使固定電子設(shè)備的 PCB 上的焊點(diǎn)斷裂。即使是連接到連接器的電纜中的電線也可能會(huì)斷裂。出于這個(gè)特定原因，Dynapar 的磁性編碼器具有完全封裝的電子器件。
盡可能避免使用軸承。高水平的振動(dòng)會(huì)改變軸承的負(fù)載。這會(huì)導(dǎo)致不均勻磨損，從而導(dǎo)致軸承過早失效，這也是無軸承磁編碼器在造紙和鋼鐵廠等惡劣環(huán)境中首選的另一個(gè)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.
沖擊和振動(dòng)對(duì)編碼器信號(hào)的影響
The Effects of Shock and Vibration on Encoder Signal
所有這些震動(dòng)不僅僅是讓編碼器的操作處于危險(xiǎn)之中。沖擊和振動(dòng)會(huì)影響性能。由于磁性編碼器非常堅(jiān)固，它們可能不會(huì)顯示振動(dòng)的物理影響。然而，問題可能會(huì)出現(xiàn)在信號(hào)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.
振動(dòng)在信號(hào)中以過量噪聲的形式出現(xiàn)，表現(xiàn)為抖動(dòng)。這是與通常由磁盤偏心引起的抖動(dòng)不同類型的抖動(dòng)。偏心抖動(dòng)通常只出現(xiàn)在一個(gè)通道上，而另一個(gè)通道信號(hào)看起來很好。由過度系統(tǒng)振動(dòng)引起的抖動(dòng)會(huì)出現(xiàn)在所有通道上?？匆粋€(gè)例子編碼器抖動(dòng)并將其與由失去耦合引起的編碼器振動(dòng)
極高的沖擊可能會(huì)使輪盤或碼盤錯(cuò)位，這也會(huì)影響信號(hào)質(zhì)量。它可能導(dǎo)致所有通道上的過度抖動(dòng)和/或兩個(gè)通道之間的相位變化。
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.
沖擊和振動(dòng)的編碼器測(cè)試方法
Encoder Testing Methodology for Shock and Vibration
在為高沖擊和振動(dòng)環(huán)境選擇編碼器時(shí)，數(shù)據(jù)表是不夠的。設(shè)計(jì)需要經(jīng)過嚴(yán)格的測(cè)試。Dynapar 編碼器經(jīng)過 MIL-STD-202 測(cè)試，需要掃描測(cè)試等技術(shù)。在此過程中，編碼器在給定范圍內(nèi)以不同頻率暴露于指定周期的正弦振動(dòng)。例如，一個(gè)編碼器在 5 到 2000 Hz 下可用于 20Gs，它將在所有三個(gè)軸上振動(dòng) 24 個(gè) 10 分鐘掃描，總持續(xù)時(shí)間為 12 小時(shí)。供應(yīng)商應(yīng)該有每個(gè)設(shè)計(jì)的測(cè)試協(xié)議和性能的詳細(xì)結(jié)果。
與工程中的所有事物一樣，為惡劣環(huán)境選擇編碼器需要權(quán)衡取舍。以上幾點(diǎn)給出了一般指導(dǎo)方針。特殊應(yīng)用，例如在惡劣環(huán)境下需要非常高分辨率的應(yīng)用，將把這些技術(shù)推向極限。在某些情況下，OEM 需要更頻繁地更換反饋設(shè)備。然而，在大多數(shù)情況下，與供應(yīng)商密切合作并告知他們所有的專業(yè)要求將產(chǎn)生一個(gè)可以滿足應(yīng)用程序需求的解決方案。
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.
本文英文原文轉(zhuǎn)載自：DYNAPAR-Specifying for Encoder Shock and Vibration
本文翻譯by愛澤工業(yè)，如有偏頗，敬請(qǐng)指正。
