Dual-Encoder Spindle Control

Eliminating Mode Boundaries in Dual-Encoder Spindle Control

In advanced micro and nano-scale machining and high-performance motion platforms — the kind we build at Polaris Motion — spindle behavior is not a peripheral detail. It defines surface quality, feature accuracy, and overall machine credence.

Across our 5-axis and multi-axis CNC systems, we frequently push spindles into two very different operating regimes. On one end, ultra-fine positioning is required for precision indexing, interpolation, and nano-level feature control. On the other, we demand extreme rotational speed and aggressive acceleration to maintain throughput and dynamic response.

To support this range, the spindle architecture includes two feedback encoders:

• A high-resolution position encoder, delivering ultra-fine angular accuracy but with limited bandwidth.
• A velocity encoder, lower in resolution but capable of handling ultra-fast rotation and high-bandwidth control loops.

Individually, each encoder performs well. Together, however, they exposed a systems-level problem.

The Problem: A Boundary Inside the Control System

Historically, switching between position and velocity feedback required explicit mode changes. Moving from precision positioning to high-speed rotation involved controller resets, firmware state transitions, and multiple low-level adjustments.

In theory, this was manageable. In practice, it introduced inefficiency:

• Interruptions during process transitions
• Added commissioning complexity
• Increased firmware maintenance burden
• Reduced adaptability during dynamic operation

In high-speed, ultra-precision material processing — particularly when synchronizing with stage axes and fast-tool single-point diamond cutting — those interruptions are not just inconvenient; they constrain performance.

The spindle became artificially divided into “precision mode” and “speed mode.” Yet the machine itself does not operate in discrete boxes. Acceleration profiles, contouring moves, and tool and material interaction continuously shift operating demands.

The control architecture needed to reflect that reality.

The Solution: Hybrid Feedback Inside the Control Layer

We developed a hybrid feedback algorithm within our UniverseOne™ control framework that eliminates hard switching boundaries between encoders.

Instead of requiring manual mode selection, the new algorithm dynamically manages both feedback sources in real time. It automatically transitions between position-dominant and velocity-dominant feedback — even during high-speed rotation and acceleration.

Key characteristics of the approach:

• No controller reset required
• No interruption of spindle motion
• No firmware reconfiguration during operation
• Continuous adaptation based on operating conditions

When precision positioning dominates, the control loop leverages the ultra-fine resolution of the position encoder. As rotational speed and dynamic demands increase, the algorithm shifts emphasis toward the high-bandwidth velocity encoder.

The transition is seamless. There is no discrete event visible to the operator or upstream motion planner.

The spindle behaves as a unified, adaptive system.

Why This Matters in Our Machines

In Polaris multi-axis ultra-precision systems — where linear coordinated axes, and rotary motion must operate in tightly synchronized time domains — control continuity is critical.

A forced reset or abrupt feedback transition does more than pause motion. It disrupts synchronization across the machine, affects trajectory planning, and adds unnecessary complexity to the firmware layer.

By embedding hybrid feedback logic directly into the control architecture:

• Dynamic performance improves across the entire speed range
• Commissioning becomes simpler
• Firmware architecture becomes cleaner
• Operational downtime is reduced
• System reliability increases

Equally important, the control system becomes more scalable. As we continue expanding toward higher axis counts and higher bandwidth applications, the Mercury™ network and distributed control nodes benefit from reduced switching logic and more predictable feedback behavior.

The Outcome: Precision and Bandwidth Without Compromise

The spindle is no longer partitioned by artificial control modes. It continuously adapts to the machine’s operating state.

• Precision when nano-level accuracy is required
• Bandwidth when speed and acceleration dominate
• Seamless behavior during transitions

This hybrid feedback approach reflects how we design systems at Polaris Motion: not as collections of components, but as integrated, adaptive control architectures.

The result is measurable improvement in spindle responsiveness, stability, and high-speed performance — while simultaneously reducing firmware complexity and operational risk.

In high-performance laser machining, the difference between theoretical capability and practical performance is often found inside the control system. By removing the boundary between position and velocity feedback, we closed that gap.

Polaris Motion
512 Frances Avenue
Victoria, BC, V8Z 1A
Canada