Sensor integration
Mount, protect, reference, and validate sensors so their measurements describe the intended physical quantity.
A reading needs a known relationship to what the is measuring. Mounting, reference position, field of view, electrical compatibility, and all affect that relationship.
Sensor requirements
Distinguish a 's rotation from a slide's extension, a switch contact from successful , and a camera detection from confirmed capture. Each requires a physical relationship between sensor and .
| Sensor | question |
|---|---|
| Motor encoder | Which is measured, and what ratio relates it to the output? |
| Limit switch | What touches it, at what repeatable position, and can it be overdriven? |
| Distance or color sensor | What surfaces, angles, and lighting are inside its useful range? |
| Tracking wheel | Does it maintain contact through the intended robot motion? |
| Camera | Is the mount rigid and is the target visible in all necessary positions? |
Use the exact manufacturer datasheet to define operating range, electrical connections, device compatibility, and any need for level conversion.
Measurement quality
| Term | What to check |
|---|---|
| Bias | An estimated systematic offset from a suitable reference. Repetition alone does not remove it. |
| Precision | Agreement between repeated measurements under specified conditions. Record the spread, not just one reading. |
| Resolution | The smallest change in the physical quantity that produces a discernible change in indication. Extra decimal places do not establish it. |
For an illustrative 100 mm reference, readings of 102, 102, 103, 102, and 102 mm average 102.2 mm. Their small spread does not remove the estimated +2.2 mm offset. Test across the useful range before choosing a calibration correction; one offset cannot fix every scale, mounting, or geometry error.
Sensor mounting
Mount the sensor to a stable and keep adjustment deliberate. A camera calibrated in one pose cannot be treated as unchanged after its bracket bends. A limit switch that moves whenever its cable is pulled cannot provide a repeatable zero.
Leave for the connector and . Keep cables out of the object's path and the mechanism's moving envelope. Make replacement possible without silently changing the reference position.
For passive , mounting height, contact force, and wheel alignment affect what is measured. The odometry article connects the physical arrangement to localization.
Calibration
For an encoder-based extension, command several positions across travel and compare encoder readings with a ruler or other suitable reference. Record units, exact ratio, spool geometry, and the direction convention. Check both approach directions to expose or slack.
If the encoder measures the motor, check what happens when a belt skips or a hub slips. The motor can turn normally while the mechanism fails to move as expected.
For a mechanism that needs to recover its full turn count after power loss, multi-turn position covers a two-encoder arrangement using the Chinese Remainder Theorem.
Measurement timing
A fast control loop does not make a slow sensor produce fresh readings. Record the sensor's update timing separately from the loop period. Camera exposure, communication, filtering, and scheduling can all add delay before a measurement affects motor output.
For an illustrative target moving at 0.8 m/s, a total delay of 50 ms corresponds to 40 mm of travel. A stable but delayed detection can therefore miss a small acquisition window. Measure the whole sensing-to-action delay under representative load rather than relying only on the advertised sensor rate.
Keep acquisition timestamps or sequence numbers where available. Repeatedly reading one cached result does not supply independent measurements to a filter. Use measured loop intervals in controller calculations and test variable timing as well as the average period.
Sensor failures
Verify what happens when a switch is disconnected, an object is absent, a camera is obscured, or a target leaves the useful range. Choose a and recovery behavior suited to the task. A failed home reference should stop motion safely instead of letting the drive indefinitely.
Test the exact sensor and processor on the robot under expected lighting, vibration, and simultaneous electrical load. Vision overview contains programming guidance; use the official wiring guide for electrical integration.
Version the mounting transform, calibration values, and hardware revision together. Repeat the affected calibration after replacement, bracket adjustment, or a change to transmission geometry.