Introduction: Deciding between linear and non-linear error compensation and deciding whether a single-axis digital readout needs 0.1 micron resolution are two separate engineering choices that often get collapsed into one specification conversation.
On a precision stage, form grinder, or inspection axis, the encoder may repeat perfectly at one point yet drift from the true distance as the carriage moves away from the datum. That pattern raises two practical questions: which compensation setting fits the axis, and does the job need 0.1 micron resolution? The answer depends on what resolution actually reports, which error pattern each compensation type corrects, and whether the mechanics and encoder can hold that step in daily production.
Why resolution alone does not define a precise single-axis measurement
Resolution is the smallest increment a readout can display. On a single-axis unit it might be 5 μm, 1 μm, or 0.1 μm, and it describes how finely the counter resolves position. It says nothing about how close that number sits to the real distance. Three other properties decide that. Repeatability is how reliably the axis returns to the same reading at the same position. Systematic scale error is a consistent deviation across the whole travel, like a slight slope. Position-dependent error changes shape along the axis. Metrology practice keeps these quantities separate, and teams that treat the display step as an accuracy number end up comparing the wrong figures. Mechanical geometry adds a factor that no display step can remove. When the scale sits away from the line where the measurement actually happens, a small angular tilt of the carriage turns into a linear error — the classic Abbe offset problem covered in machine design teaching. The further the scale is mounted from the measurement line, the more that tilt is amplified, and the resulting error is often larger than compensation can absorb. Thermal growth, guideway straightness, and bearing play add their own contributions. The real question is whether the axis produces a repeatable, mappable deviation that the readout can correct, and whether the remaining error fits the tolerance the job demands.
How linear and non-linear error compensation work in a DRO
Both compensation types run inside the readout. The DP-20 processor in the Easson ES-19 supports both linear and non-linear error compensation, along with vibration filtering. It takes the count coming from the encoder, applies a correction, and displays the corrected value, so the operator sees a position that better matches the real distance. What separates the two compensation types is the shape of the error each one can follow. Linear compensation handles deviation that grows at a steady rate; non-linear compensation handles deviation that curves, reverses, or peaks somewhere along the travel. Choosing between them starts with measuring the axis, not with reading a specification sheet.
1. Linear Compensation Corrects Consistent Scale Deviation Across Travel
Linear compensation assumes the error on an axis grows proportionally with distance. If the carriage reads 0.02 mm long over 300 mm of travel, that same ratio applies at 100 mm and at 250 mm, so the readout can correct it with a single factor, usually entered in parts per million or as measured-versus-true values taken at two points. It covers scale grating error, uniform thermal expansion, and small assembly offsets that behave the same way at every position. What it cannot do is follow an error that changes direction or varies in the middle of the stroke, which is why a two-point check that looks excellent at both ends can still hide a large deviation at the center of a long axis.
2. Non-Linear Compensation Addresses Position-Dependent Error Patterns in Single-Axis Travel
Non-linear compensation works from a map instead of a slope. Travel is divided into segments, each carrying its own correction value, so the readout follows a curve that rises, flattens, or reverses along the axis. That is the shape produced by ballscrew pitch error, guideway straightness variation, local wear near a frequently used zone, and frame distortion under load. The map usually comes from a laser interferometer run or a step-gauge measurement, and its quality depends on the points captured. On the ES-19, this correction runs alongside vibration filtering, a useful pairing: a stable count keeps the correction accurate during fast traverse, and the 250 kHz bandwidth holds onto fine-pitch encoder edges. Compensation corrects known patterns, so mounting, encoder quality, and shop environment still determine the final number the axis can hold.
When 0.1 micron resolution makes sense for a single-axis task
0.1 μm resolution earns its place when the axis itself is the measurement reference rather than a positioning convenience. Metrology lab stages, lapped and seated surfaces, form grinding with sub-micron infeed, and alignment fixtures verified against a laser interferometer all live in that territory. Many engineers work to a simple rule: the readout step should be roughly one tenth of the tolerance band, so a job held to ±1 μm needs a display that resolves 0.1 μm to give the operator usable judgment. At that level the resolution is not decoration — it is the difference between seeing a slow trend and guessing at it, and it also makes a correction map smoother because the data points are finer. For most single-axis positioning work, though, the finer step costs more than it returns. General milling and drilling, long travels, and jobs with 0.02–0.05 mm tolerances are served better by 1 μm or 5 μm, where the last digit stays steady instead of reacting to every vibration on the shop floor. A long axis at 0.1 μm resolution often shows a restless final digit unless the machine, the scale, and the environment are all prepared for it. When you evaluate a digital readout system supplier, ask which resolution steps are selectable, what encoder signal period each step expects, and whether the axis mechanics can hold that step in production. A single hardware platform can cover both cases. As a digital readout manufacturer, Easson offers the ES-19 with 5 μm, 1 μm, and 0.1 μm length resolution, angle options from 0.0001° to 1°, TTL/RS-422 input, USB 2.0 and UART 3.3V as standard, and optional RS232C. The same embedded unit can serve a fine metrology axis or an everyday positioning axis. Orders start at one set for evaluation, with capacity of 1000 sets per month for production programs.
Conclusion
Resolution, compensation, and mechanics form one system, and the decision follows from that. Read the error pattern on the axis first: a steady slope points to linear compensation, while a curve that shifts along the travel calls for the non-linear map. Then match the display step to the tolerance, choosing 0.1 μm when the axis is a measurement reference and 1 μm or 5 μm when it is a positioning aid. If a single-axis embedded readout fits your project, request a quote for the ES-19 and confirm the resolution option, interface choice, sample set, and scheduling for your build.
FAQ
Q：What is non-linear error compensation in a digital readout?
A：It is a correction method that divides axis travel into segments, each with its own correction value, so the readout follows an error curve instead of a straight line. It suits position-dependent patterns such as ballscrew pitch error, guideway straightness variation, and local wear. On the ES-19, the DP-20 processor applies this correction alongside vibration filtering to keep fine-pitch encoder signals stable during fast traverse.
Q：Does 0.1 micron resolution guarantee 0.1 micron measurement accuracy?
A：No. Resolution is the smallest increment the display can show, while accuracy depends on the encoder, scale mounting, Abbe offset, guideway condition, and calibration of the whole axis. You can have a 0.1 μm display on an axis that holds only a few microns of real accuracy. The practical way to plan is to measure the axis, apply compensation for the repeatable error, and treat the display step as one input; final accuracy comes from the whole axis.
Q：Which single-axis tasks benefit from DP-20 error compensation?
A：Tasks where the deviation repeats across travel benefit most: form grinders, single-axis precision stages, inspection and calibration axes, and any slide whose position is checked against a laser interferometer or step gauge. Linear compensation handles a steady slope; non-linear compensation handles the curved portion. Together with vibration filtering, that keeps readings clean during fast moves, which matters when the axis is used for measurement rather than simple positioning.
Sources / References
Elements of Mechanical Design – MIT OpenCourseWare
No comments:
Post a Comment