Why Constant Velocity and Synchronized Motion Performance across Multiple Axes Matters for Ultrafast Laser Machining, Imaging, and Metrology

Why Constant Velocity and Synchronized Motion Performance across Multiple Axes Matters for Ultrafast Laser Machining, Imaging, and Metrology

Children learn from an early age that focused light through a magnifying glass will create heat if left in the same position for too long or that pictures taken with an unsteady camera result in blurry images.  In a modern context, these same principles apply to ultrafast lasers or line scan cameras where uniform motion is important to process optimization without defects or image distortion. 

Modern laser processing, machine vision, and metrology systems rely on precision motion and automation mechanisms – and the ability to provide synchronized multi-axis dynamic motion performance with tight velocity regulation on complex trajectories has a big impact on the results.   

If the path velocity is unstable, or during acceleration / deceleration phases the correlation of position and laser power is unknown or cannot be controlled tightly, the amount of material ablated, the quality of a cut or weld would vary, along with the velocity of the motion system.

Video: Constant Velocity Control for Additive Manufacturing – Spiral Motion
Applications in laser direct write and direct material dispense rely on constant motion for uniform dose, features, and linewidths.

Solid Mechanics

PI’s multi-axis systems as shown above are used in applications for high-performance coordinated multi-axis scanning performance. Left to right: V-551 linear motor stage XYZ stack, A-311 planar air bearing stage with counterbalanced Z-stage on granite bridge, and V-508 series compact and linear motor stages for photonics alignment

In order to avoid the above variations, a solid mechanical base with excellent dynamic properties, guiding, and position measuring systems is required. Here, proprietary technology extends from the core outward to the controls. It starts with stiff construction and an engineering design with low friction/quiet bearings (both mechanical and air) built on advanced grinding and machining processes. A prerequisite for high dynamics and excellent speed regulation, large ironless linear or torque motors are at the core of all positioning and automation systems for high precision industrial motion applications. Position feedback information is provided by proprietary nanometer- or sub-nanometer resolution linear encoders, preferably based on absolute measuring technology.

Air bearing systems with PI’s state-of-the-art motion controllers provide the speed, coordinated precision motion, reliability, and clean room compatibility required in advanced manufacturing applications, such as wafer dicing.

Advanced Controllers

A-824, 8-axis controller, EtherCat compatible Learn more

A-81x Series PIGlide Controllers based on ACS EtherCat connectivity with integrated low-noise amplifiers are optimized for dynamic range on the system and offer advanced multi-axis motion profiling algorithms to build complex optimized trajectory paths. These trajectory paths are followed with tight servo loops using real time disturbance attenuation resulting in best regulated dynamics to achieve world leading process goals.

Raster Scan Motion Performance (XY)-Line Scans

The above plot shows dynamic performance of a V-551 in an XY raster scan application with critical velocity stability requirements on the scan axis. Scan axis velocity is shown here as measured (purple) with motion in blue. The scale is in mm and mm/sec. 
On close inspection, the motion characteristics and velocity variation can be appreciated more fully. Here, the velocity was commanded at 50 mm/sec and regulated within 50.00 ±0.0305 mm/sec (PTP).
High performance motion control yields uniform, high quality laser processing results.
Video: Processing of high-density structures such as laser drilling or laser marking of PCBs requires highly coordinated motion and synchronization with lasers and other equipment. 

Vector Scan Performance with Coordinated Multi-axis Constant Velocity

Here, we perform a multi-axis synchronized curvilinear motion at constant velocity of 100 mm/sec in an ultrafast laser application. The XY positions can be observed in green and blue and the velocity in yellow. Observe how the synchronized motion transitions from unconstrained velocity to commanded combined constant velocity. 
A parametric plot is shown with the P-shaped path programmed for constant velocity and the velocity shown during that portion of the path (in yellow).
Upon closer inspection, the combined vector velocity performance can be fully appreciated, offering a consistent laser dose at a constant rep rate in the ultrafast process (100 mm/s ±0.1195).
SPC Laser Materials Process and 3D Print Software taps into this advanced controls capability and stage performance. Shown here is a rectangular motion path created in the software with automatic corner rounding and constant velocity enabled. The timewise dots show the constant rate in effect.
In applications where there is advanced triggering capability (often called PEG, position event generator) with an external device (Laser, Line Scan Camera, etc.) on single or multi-axis motion, PI offers the LCM Laser Control Module. This can provide fixed distance triggering as shown above during non-uniform acceleration and deceleration phases.

Product Overview

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