“We need ±0.05 mm” is a starting point for a discussion, but it leaves important questions unanswered. Where is the position measured? Does the value apply while moving, after a normal stop or after a separate station mechanism locates the fixture? What load and process force are present?
Separate three different requirements
| Requirement | What to define |
|---|---|
| Travel accuracy | How the moving fixture follows the required path and datum |
| Stop repeatability | How closely the fixture returns to the same point after repeated moves |
| Secondary station location | Position after a locating or positioning mechanism engages |
A drive can bring a carriage to a station while a separate mechanism establishes the process datum. The final station result depends on that arrangement, not just the rail profile.
Read the brochure statement in context
The supplied company brochure reports overall secondary positioning accuracy of ±0.05 mm and slider flatness of ±0.01–0.03 mm. These statements describe different properties. They are not interchangeable, and they do not establish a tested rating for every proposed rail, carriage or conveyor configuration.
The website therefore keeps the rail dimensional catalogue separate from project accuracy targets. For a quotation, identify the mechanism and measurement conditions that would make a proposed number meaningful.
Define the datum, load and measuring point
A fixture can extend beyond its carriage, and a small angular change can affect a remote measuring point. Describe the actual workpiece reference instead of requesting a value only at an unspecified point on the carriage plate. Include fixture mass, centre of gravity and process forces during the check.
Specify whether the target is needed at one station or every station, in one direction or several, and after how much settling time. Note any temperature or cleaning conditions important to the process. Agree the test method rather than assuming a brochure number includes all these conditions.
Consider station positioning in the layout
The catalogue includes lifting and swing-arm positioning mechanisms. Their selection requires engagement space, the intended datum, actuator interfaces and process loads. Include the timing of engagement and release in the overall machine sequence.
Access for adjustment and maintenance also matters. A station mechanism that cannot be reached after guarding and tooling are installed can complicate commissioning and service.
Agree measurable acceptance criteria
- Identify the drawing revision, fixture reference and station.
- State the payload, process force and operating condition.
- Define the approach direction, motion cycle and settling time.
- Agree the measuring method, repetition count and allowable result.
- Record whether the criterion applies before or after secondary location.
This gives both supplier and customer a common basis for inspection. It also prevents a rail dimension, carriage flatness value and process-position requirement from being treated as the same specification.
Common questions
Does a precise rail guarantee the final workpiece position?
No. The fixture, drive, joints, supporting structure, station mechanism and operating conditions all belong in the system review.
What should an accuracy enquiry include?
A drawing of the measuring point, target value, load condition, station process and proposed acceptance method. Use the project enquiry form to start the review.