了解振動分析中的軸軌跡圖
A 軸軌跡 是一種圖表，顯示旋轉軸的幾何中心在一次或多次旋轉期間所繪製的路徑。它是軸在其 軸承游隙內的運動的二维視圖，就像你直視軸的末端一樣。這種強大的診斷方法是通過安裝一對非接觸式 接近感測器 相隔 90 度——通常為 X-Y 配置——並將它們的同時位移信號相互繪製，而不是對時間繪製。
1. 為什麼軌跡圖如此有用
標準的 時域波形 或 FFT 頻譜 顯示 振動 在單一方向上。軌跡圖結合了兩個垂直方向，以提供軸動態運動的完整圖景，讓分析師能夠視覺化運動的實際形狀和方向，而不是推斷它。那個額外的維度為診斷各種故障提供了無價的線索，這就是為什麼軌跡圖是 轉子動力學 分析的基石——特別是對於配備液體薄膜 滑動軸承的高速關鍵機械，如渦輪機、壓縮機和大型發電機。
由於探頭直接相對於軸承測量位移，軌跡圖還揭示了軸在其游隙中的位置，而不僅僅是它移動的距離——這是安裝在機殼上的 加速規 根本無法提供的資訊。添加 轉速計 或 鍵相 標記將每次旋轉印記在軌跡上，固定其 相位 並使進動方向無歧義。
2. 如何解讀軌跡形狀
軌跡的形狀、大小和方向是作用在轉子上的力的直接指標。熟練的分析師通常只需查看軌跡的形狀即可診斷機器的狀況。
圓形或橢圓形軌跡
一個簡單的圓形或橢圓形軌跡，位於軸承中心，通常表示一個行為良好的轉子，由單一頻率主導——最常見的是 不平衡。如果軸承支撐剛性在兩個方向上相同（各向同性），軌跡將是圓形的；如果剛性在水平和垂直方向上不同（各向異性），軌跡將是橢圓形的，這在實踐中非常常見，因為大多數機器在垂直方向上比水平方向更剛硬。
扭曲、數字 8 形或香蕉形軌跡
當軌跡從簡單的橢圓變形時，多個頻率正在影響軸的運動：
- A 「香蕉」形或新月形軌跡 通常與 不對心，其中同時存在 1× 和 2× 頻率。
- A 數字 8 形 是強 2× 組分的經典標誌，是軸不對心的教科書指標。帶有內部環的 8 字形通常表示更嚴重的狀況或存在摩擦。
帶有折角或尖角的軌跡
軌跡中方向的急劇變化、平坦區域或「折角」是 轉子與定子摩擦. They show that the shaft’s motion is being momentarily constrained as it makes contact with a stationary component such as a bearing, a 密封件或機殼）接觸時受到瞬間約束。
高度不規則的軌跡
一個不規則、不穩定或看起來充滿「雜訊」的軌跡可能表示嚴重的機械 鬆動、液體誘發的不穩定性，如 油膜渦動 或 油膜振盪，或泵或壓縮機中的湍流條件。
3. 進動方向：順向與逆向
軌跡繪製的方向，相對於軸旋轉的方向，本身就是一個關鍵的診斷因素：
- 正向進動： 軌跡沿著與軸旋轉相同的方向繪製。這是不平衡等力的正常行為。
- 逆向進動： 軌跡沿著與軸旋轉相反的方向繪製。這是一種異常狀況，可能表示 軸裂紋、嚴重摩擦或某些類型的液體誘發不穩定性。
區分這兩者需要每轉一次的相位標記；沒有它，軌跡顯示形狀但不顯示行進方向，診斷區分就會丟失。
4. 現場診斷中的軌跡
永久安裝的接近探頭連接至監控系統是在大型關鍵機器上捕獲軌跡的教科書方法，但基本原理——兩個垂直位移信號相互繪製並帶有相位參考——同樣適用於現場工程師。像 Balanset-1A 這樣的便攜式雙通道儀器可以同時在兩個平面上測量同步振幅和相位，因此一旦軌跡或頻譜確認 不平衡 是主導力，相同的設置就可以直接進行到 現場動平衡 和校正狀態的驗證。當軌跡反而揭示不對心、摩擦或不穩定性時，該發現會將工作重新導向對中或機械修復，而不是動平衡校正。
Displacement Orbit versus Velocity Orbit
The two are not the same measurement, and the difference decides what you are entitled to conclude from the picture. A pair of proximity probes reads shaft 位移 relative to the bearing, so the plot is a true map of where the journal sits inside its clearance, and the DC part of the same signal yields the 軸中心線. A portable two-channel analyser with accelerometers clamped to the bearing housings plots two 速度 channels against each other, in mm/s: what you see is the motion of the housing, not the position of the shaft.
What survives the change of transducer is the geometry. Shape, orientation and precession direction are set by the pattern of forces acting on the rotor rather than by the sensor, so the familiar families still appear — a smooth ellipse when 1× dominates, a crescent or figure-8 when a strong 2× component is present, flattened sides and kinks when something rubs. What does not survive is absolute position: a velocity orbit cannot tell you how much clearance is left, and it cannot be rescaled into micrometres of shaft motion. Use it in the field to identify the fault family; reach for proximity probes when the question is where the shaft is actually running.
Where the Orbit Lives in the Balanset Software
On a Balanset-1A the orbit is one tab of the vibration-meter window, opened with the F5 key from the main window; the window requires device firmware 5.5.0 or newer. The “X-Y Orbit” tab plots channel 1 on one axis against channel 2 on the other at a 1:1 axis scale, so a circle on screen is genuinely a circle and not an artefact of unequal axes. On the four-channel Balanset-4A a second orbit, for channels 3 and 4, is drawn beneath the first.
A switch above the chart decides what is drawn:
| 模式 | What is plotted | When it is the right view |
|---|---|---|
| Unsynced | The raw trajectory, with no revolution reference | No tachometer is available, or you want to see everything the signal contains |
| Sync (raw) | The most recent revolutions overlaid, aligned to the tachometer mark | Judging repeatability — a stable, closed figure means the motion repeats turn after turn |
| 1× | The rotational component alone: a clean ellipse that matches the V·o and F readings | Confirming the unbalance vector before balancing |
Without a tachometer mark the two synchronised modes have nothing to synchronise to, the program says so in the chart title, and “Unsynced” becomes the only honest view. This is the practical form of the point made in section 3: no once-per-revolution reference, no precession direction.
Reading the Numbers Beside the Orbit
The tiles next to the chart carry three values per measuring plane, and together they are the fastest sanity check available before you start interpreting shapes:
- V·s — broadband RMS velocity across the working band, in mm/s.
- V·o — the 1× component alone, at rotational frequency, in mm/s.
- F — 這 相位 of that 1× component, in degrees.
The rotational component is part of the total by construction, so V·o can never exceed V·s, and the ratio between them predicts the orbit before you look at it. When V·o sits close to V·s, nearly all the energy is at 1×, the orbit collapses to a clean ellipse, and 不平衡 is the dominant force. When V·o is markedly smaller, the difference is harmonics and broadband noise — and it is exactly that residue which bends the ellipse into the crescents, figure-8s and kinks described in section 2. A badly distorted orbit reported alongside V·o ≈ V·s is a contradiction, and the instrumentation is the first thing to check.
Beneath each plane sits a stability bar: grey while the reading is still drifting, green once the coefficient of variation over the last twelve stream values falls below 10 %, orange when the spread exceeds 20 %. An orbit captured while that bar is orange is not a diagnosis — it is a photograph of a machine that has not settled.
Confirming the Shape Against the Spectrum
The orbit tells you that something is distorting the ellipse; the spectrum tells you which order is responsible. The “Wave Spectrum” tab of the same window shows the waveform above and the velocity spectrum below, with dashed guides placed at exact multiples of the measured rotational speed rather than at the nearest tall bar — so a peak that misses its marker is not a harmonic of shaft speed at all and belongs to bearings, gear mesh or blade pass instead. A dominant 2× beside a crescent or figure-8 orbit points at 不對心; a peak between 0.43× and 0.48× under a drifting, unstable orbit is the signature of 油膜渦動; broadband content with flattened orbit sides points at a 摩擦.
The selector below the chart switches the spectrum between velocity and acceleration. Velocity is the axis to use when reasoning about the orbit, because the orbit itself is drawn from the velocity channels.
Watching the Orbit Through a Resonance
An orbit is a snapshot at one speed, and the shape can change completely a few hundred RPM away. The “Run-down” tab records the whole coast-down instead: 1× amplitude and phase are logged against falling speed, one raw value per revolution with no smoothing, down to a stop threshold that can be set anywhere between 100 and 2000 RPM and defaults to 300. A resonance announces itself as an amplitude peak accompanied by a phase rotation of roughly 180° — the same critical speed that a 坎貝爾圖 predicts where an excitation line crosses a natural-frequency curve. The full run-down report keeps the X-Y orbit captured at working speed alongside those curves, so the shape and the resonance map end up in one document.
5. 軌跡圖顯示的內容
總之，單個軌跡圖一瞥即可提供大量資訊：
- 軸振動的總體振幅。
- 軸運動的形狀，有助於識別故障類型。
- 進動方向，順向或逆向。
- 軸在軸承游隙中的平均位置——其 軸中心線.
與 FFT 頻譜和時間波形結合分析，軌跡讓分析師能夠對機器的動態行為做出高度自信且詳細的 診斷 ——將「多少」、「什麼形狀」和「哪個方向」結合到一個決定性的圖景中。
