Poor Positioning Accuracy? Stop Blaming Encoders! The Real Errors Come From Transmission Chains

Engineers engaged in equipment commissioning, after-sales maintenance and automation retrofits have almost all encountered this frustrating problem:

Abnormal positioning deviation, reversing drift and over-travel error frequently occur even with correct parameter settings and no electrical alarms. Most technicians immediately attribute the fault to encoders and rush to replace or upgrade them, only to find the problem remains unsolved with unnecessary time and material costs wasted.

Over 90% of positioning inaccuracies on industrial equipment have nothing to do with encoders themselves.

An encoder is merely a signal acquisition component that faithfully feeds back the actual rotation angle and pulse signals of the shaft. As long as the encoder hardware is intact and signals are stable, its output data stays accurate.

The final positioning deviation, backlash error and cumulative travel error of equipment all stem from error transmission and superposition across the mechanical transmission chain: misalignment during encoder installation, coupling clearance, reducer backlash, lead screw pitch tolerance, gear transmission clearance and more.

Today’s article breaks down common misconceptions in industrial commissioning, teaching you to distinguish encoder faults from mechanical transmission errors and troubleshoot positioning issues efficiently.

01 Core Principle: Encoders Reflect Errors Instead of Generating Them

A fatal misunderstanding shared by many engineers: equating end-effector positioning accuracy with encoder detection precision.

Clarify the underlying logic:

✅ Encoder = Detection Unit

It only reads shaft angles and outputs ABZ pulse signals, responsible for 'accurate measurement'.

✅ Transmission Mechanism = Execution Unit

The full assembly including motor, coupling, reducer, gears, lead screws and guide rails takes charge of 'accurate movement'.

Core conclusion: Accurate measurement ≠ Accurate movement.

Even with ultra-high-precision encoders, end positioning will go out of tolerance if gaps, misalignment or wear exist in the transmission chain. Encoders cannot compensate for physical mechanical errors.

02 Five Major Sources of Transmission Errors — The Real Culprits Behind Poor Accuracy

Most on-site precision failures originate from the following five mechanical links, which shall be prioritized during troubleshooting.

1. Encoder Installation Errors (Most Common & Easily Overlooked)

Perfect encoder performance is wasted by improper mounting.

Shaft misalignment

Eccentricity or tilt between motor shaft and encoder shaft triggers radial runout and axial float during operation, resulting in periodic positioning fluctuation, low-speed jitter and fixed point offset.

Improper coupling selection & assembly

Aged elastic pads, excessive clearance, loose set screws or incomplete locking create idle travel during forward/reverse switching. In severe cases, shaft slippage and abnormal pulse acquisition lead to positioning drift and poor repeatability.

Insufficient bracket rigidity

Thin or loosely fixed brackets shift slightly under vibration, causing periodic signal fluctuation and severely reduced stability.

2. Reducer Backlash Errors (Root Cause of Reversing Deviation)

Gear meshing creates inherent backlash — an uncorrectable mechanical hard error for encoders.

During forward/reverse switching, gear clearance converts directly into positioning offset, presenting inconsistent positioning readings between forward and reverse strokes.

Meanwhile, gear machining tolerances and wear generate single-cycle periodic errors; the longer the equipment runs, the worse the accuracy.

3. Lead Screw Transmission Errors (Common Defect on Long-Travel Linear Equipment)

Deviation accumulates with travel length for linear motion machines.

Cumulative lead error

Inherent pitch manufacturing tolerances on lead screws build up linearly as travel extends. Tiny deviations are negligible over short distances but exceed tolerance for long strokes.

Failed nut preload

Loosened preload structures enlarge clearance and create reverse idle travel, causing inconsistent bidirectional positioning.

Screw deformation & misaligned support seats

Jitter and eccentricity occur under load, drastically amplifying dynamic errors.

4. Multi-Stage Gear Transmission Errors (Layered Error Amplification)

Accuracy degrades exponentially with stacked gear stages.

Gear side clearance, tooth profile errors and mounting center distance deviations produce minor gaps at each stage, which superpose into obvious positioning errors at the equipment end. More transmission stages mean worse overall precision.

5. Overall Mechanical Rigidity & Fit Errors

Guide slider clearance, stretched timing belts, frame deformation and flexible load deflection, though trivial individually, stack with primary transmission errors and drag down overall equipment precision.

03 On-Site Quick Identification: Encoder Fault or Mechanical Defect?

No oscilloscope or disassembly required — simple tests tell the difference instantly.

Scenario 1: Mechanical Transmission Error (90% of Cases)

Regular error pattern: periodic fluctuation, fixed reversing offset, larger deviation with longer travel

Stable readings with shaft locked statically, no drifting

Slight or negligible improvement after switching to higher-resolution encoders

Smooth equipment operation without alarms or lost pulses

Scenario 2: Encoder Hardware Fault (Rare Cases)

Random irregular errors, erratic jumping position readings

Continuous value drift even when the machine stands still with locked shaft

Distorted waveforms, missing phases or lost pulses during signal inspection

Full accuracy recovery immediately after encoder replacement

04 High-Precision Optimization Solutions: Resolve Positioning Errors From The Source

To boost equipment precision fundamentally, optimize transmission chains instead of blindly replacing encoders.

Standardize encoder installation

Adopt high-precision bellows couplings, strictly calibrate coaxiality and control radial runout ≤0.02 mm; reinforce mounting brackets to eliminate vibration-induced displacement.

Eliminate transmission backlash

Specify zero-backlash reducers for high-precision applications; use double-nut preloaded lead screws; inspect gear wear regularly and replace aged transmission parts timely.

Correct errors via system parameter compensation

Activate backlash compensation and lead screw pitch compensation in motion controllers to offset fixed inherent mechanical errors and greatly improve positioning & repeat positioning accuracy.

Calibrate full coaxiality for the whole machine

Align motor, reducer and lead screw integrally to reduce eccentric stress and dynamic runout, cutting error transmission at the source.

Closing Remarks

A classic consensus in automation industry:

Encoders determine the upper limit of equipment precision; mechanical transmission determines the lower limit.

Most positioning failures stem from accumulated transmission clearance, poor assembly precision and mechanical wear, rather than low-end component selection.

Next time you encounter tolerance excess, reversing drift or poor repeat positioning: troubleshoot the transmission chain first, then consider encoder replacement. Avoid detours and unnecessary costs.

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???? Technical Takeaway

This article systematically sorts out core error causes, identification methods and implementable rectification plans for positioning faults, serving as a practical reference for on-site commissioning, after-sales troubleshooting and equipment performance optimization.

We will keep releasing in-depth guides on automation fault diagnosis, precision optimization and assembly processes to help you solve complex equipment issues faster with fewer debugging setbacks. Follow us for more industrial control hardcore technical content!