The Sensor That Read 0.05 mm Vibration
We mounted a laser sensor (article 134) on a machine. The sensor measured part height. On the bench, the reading was stable. On the floor (next to a stamping press), the reading vibrated — 0.05 mm jitter. The press cycled every 2 seconds. Its vibration traveled through the floor to the sensor. The measurement was noisy. The problem: the sensor wasn’t isolated from the floor vibration. We added vibration isolators (rubber pads) under the sensor’s mount. The isolators dampened the vibration. The reading stabilized. The mistake was bolting the sensor directly to the floor (which transmitted the press’s vibration).
Vibration isolator selection decouples the machine from the floor vibration. This article covers the choices.
Sources of Vibration
Vibration comes from:
- The machine itself: A fast axis (article 130), a press, a vibrating feeder.
- Neighboring machines: A stamping press, a punch, a HVAC system.
- The floor: The building floor transmits vibration.
A precision sensor (article 134) or a machine tool needs a stable platform. Vibration ruins the measurement (or the machining).
Isolator Types
Rubber Pads
A simple rubber pad (neoprene) under the machine’s feet. Cheap. Dams high-frequency vibration (over 20 Hz). But it can’t be adjusted (the machine sits on the pads). For light machines, general damping.
Leveling Mounts (Article 118)
A leveling mount (article 118) with a rubber pad (or a spring). It both levels (article 118) and isolates (dampens vibration). The rubber (or spring) decouples. Standard for most machines.
Spring Isolators
A steel spring (coil) under the machine. Isolates low-frequency vibration (under 20 Hz). For a heavy machine (a press, a grinder). The spring has a natural frequency (very low) that isolates the vibration.
| Isolator | Frequency | Best For |
|---|---|---|
| Rubber pad | High (>20 Hz) | Light, general damping |
| Leveling mount (rubber) | Medium | Most machines (default) |
| Spring isolator | Low (<20 Hz) | Heavy, presses, grinders |
Step 1: Identify the Vibration Source
Find the vibration source (a press, a grinder, a fast axis). The vibration frequency (Hz) determines the isolator. A high-frequency vibration (a fast axis, 50 Hz) needs a rubber pad. A low-frequency vibration (a press, 2 Hz) needs a spring isolator. If the isolator’s natural frequency is near the vibration frequency, it resonates (worse). Pick an isolator with a natural frequency well below the vibration frequency.
The isolator rule: The sensor that vibrated had no isolator (bolted to the floor). Use a leveling mount with a rubber pad (article 118) for general. For a heavy press, use a spring isolator. The isolator’s natural frequency must be well below the vibration frequency (otherwise it resonates).
Step 2: Don’t Over-Insulate (Drift)
A machine on soft isolators can drift (it moves slightly with temperature or load). For a precision machine (a CMM, a vision system), the drift is unacceptable. Use stiff isolators (or a rigid mount, anchored to the floor). The isolator must damp vibration but not let the machine drift.
Step 3: Anchor (For a Precision Axis)
For a precision axis (a rail, a screw), anchor the machine to the floor (bolts in concrete). The anchor holds the machine (no drift). The vibration comes through the anchor (but the machine’s own stiffness handles it). For a precision axis, anchor it (don’t isolate — anchor).
Step 4: Isolate the Sensor, Not the Machine
For a sensor (article 134), isolate the sensor (mount it on a separate, damped bracket). Don’t isolate the whole machine (it might drift). A small, dedicated isolator under the sensor decouples it from the machine’s vibration. The sensor that vibrated (next to a press) needed a small isolator (not a machine-wide one).
An Isolator Checklist
- What is the vibration source? (Press? Fast axis?)
- What is the vibration frequency? (Hz?)
- Is the machine light or heavy?
- Use a leveling mount (rubber)? (Article 118?)
- For heavy/low-frequency: spring isolator?
- Does the isolator resonate? (Natural frequency?)
- Does the machine drift? (Over-isolated?)
- For precision: anchor to the floor?
- For a sensor: isolate the sensor? (Small isolator?)
- Is the reading stable? (Test?)
The Bottom Line
Vibration isolator selection decouples from the vibration. The sensor that vibrated was bolted to the floor. Use a leveling mount with a rubber pad (general). For heavy/low-frequency, use a spring. For precision, anchor to the floor. The sensor that measured steadily wasn’t on the heaviest mount — it was isolated from the source.
