Application Note AN00230

CRS Frequently Asked Questions
1 Introduction
Our CRS Series of novel resonant scanners are ideally suited for high-speed imaging in real time. TheCRS oscillates at a fixed, resonant frequency with a sinusoidal waveform; this unique scanner design
enables a rapid scanning rate. The mirror is engineered out of lightweight beryllium, and broadband
coatings which reflect a wide range of laser wavelengths. When paired with a galvanometer, the CRS
enables high-speed raster scanning over a two-dimensional field and is well-suited for microscopyand scanning laser ophthalmology applications.

2 Frequently Asked Questions
2.1 General
2.1.1 Typical CRS Mounted Sets
Table 1 - Typical CRS Mounted Sets
Part #Galvo

Servo

Clear Aperture

Coating

6SD11015

CRS8K

671-1-FS26

5 mm

Silver671-1HP-FS26

5 mm

Silver671-0HP-FS26

5 mm

Silver671-2HP-FS26

5 mm

Silver6215H
6SD11798

CRS8K
8315K

6SD11502

CRS8K
6215H

6SD11328

CRS8K
8315K

*Note: Silver coating provides reflectivity ≥90% for wavelengths ≥450 nm
2.1.2 CRS Generations
2.1.2.1 Differences
1.
Part number, the Gen 1 CRS begins with “1-003” and the Gen 2 CRS begins with “CRSxxK”, where xx
is either 04, 08 or 12. For example, 1-003-3002009 is a Gen 1 CRS, and 6SC04KA040-01Y is a Gen 2 CRS.

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Application Note AN00230

Figure 1 - Visual comparison of the two versions.
2.
Visually, the Gen 2 CRS has a miniaturized cable connector and a 0.14 inch hole. Most models of theGen 2 CRSs have an integrated cable, but some have cables separate from the scanner.
2.1.2.2 Benefits of the Gen 2 CRS compared with Gen 1 CRS
1. Improved production process that provides higher peak toque
2. Single power supply of 12V, instead of needing both ±15 V and 5 V power supplies.
3. Smaller servo board.

2.2. Datasheet
2.2.1 Frequency Tolerances
Due to the mechanical design of the CRS, it is unlikely to get two units with the exact same frequency.
However, it can be expected that a CRS’ frequency will fall within the frequency tolerance range that is
specified in the datasheet.
1. The actual frequency of a CRS is based on the production process.
2. It is not possible to frequency/phase lock two CRS units.
2.2.2 Trace to Retrace Wobble RepeatableThink of trace and retrace each as one direction in a bi-directional scan motion. The scanmotion is in reality
a very compressed ellipse with the major axis measured as the scan angle and minor axis the trace-toretrace wobble. These motions are repeatable and are especially important when the scanner is used bidirectionally.

Scan AngleTrace
Max Wobble
Retrace
Figure 2 – Trace to retrace wobble.

Wobble is due to cross-axis motion from off-balance mass. For a CRS, it is due to tolerance stack-ups toexactly centering mirror mass and magnet mass.
As shown in Fig.2, wobble amplitude is defined as the minor axis of the ellipse. The maximum wobble
occurs at the center of the scan field and should be within the rangeof the specified value in the datasheet.
Please check the “Certificate of Conformance” of each CRS for its specific wobble value.The maximum
amplitude of the wobble will be provided.
For bi-directional scanning, the anticipated line spacing should take consideration of the wobble.

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Application Note AN00230

It has been observed that this wobble changes linearly with scanner amplitude. In otherwords, wobble
increases when scanning at larger angles.

2.3 Hardware/Components
2.3.1 Power Supply
For just a single CRS set, Cambridge Technology recommends a power supply with 12 V and 1 A. The
CRS operates at only one frequency, it is very efficient and doesn’t require alot of power.
2.3.2 Mating Connectors to the CRS PCB
Table 2 - Mating Connectors
Manufacturer

Manufacturer Part #JST

SSHL-002T-P0.2

JSTGHR-09V-S*Note: Mating cables are included in the CRS sets

2.4 Set Up and Features
2.4.1 Temperature Control
Both warm up and heat-sinking are required to achieve the maximum stability.
1. Scanner:a. 10-40 °C operating environment temperatureb. -20-60 °C storage environment temperaturec. The scanning frequency of the scanner decreases 0.5 Hz as the temperature risesevery 1 °C at
the rotor
d. The scanning frequency spec in its “Certificate of Conformance” is tested at roomtemperature.
2. Servo:a. Adequate thermal dissipation with the thermal pad and heat sink provided byCambridge
Technology.
2.4.2 Dust Control
1. Precautions should be taken to protect the CRS scanners from dust. The mirror coatingcan become
damaged due to dust.
2. Cleaning the mirror regularly, will not necessarily extend its life.
2.4.3 Considerations for Synchronization
1. Frequency of the slow axis

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Application Note AN00230

a. Value: CRS’ frequency divided by an integer
For example: For a 8 KHz CRS, the frequency of the CRS should be in the range of7910 +/- 15Hz, so let’s assume a frequency of 7900 Hz. In this case, with a 395 Hz frequency for the slow
axis, there are 20 periods of the CRS in each period of the slow axis.
b. The frequency of the slow axis should also consider the capabilities of the slow axis’galvo. With
these considered, the proper additional frequency divider circuit could be set.
*Note: The customer is responsible for building the frequency divider circuit and implementing theappropriate trigger.
2.4.4 Can a CRS Pair Draw Circles?
Due to the CRS’ design, as mentioned in Sec. 2.2.1, it is not possible to frequency lock orphase lock twoCRS units. Additionally, the CRS scanner is an open-loop scanner, so it is not possible to compensate forthe variation. Other than that, the magnet end will heat up which causes drift of frequency, too. In
conclusion, you might be able to mark a circle fora small period of time, but it will be extremely hard tomaintain.
2.4.5 Can the Backside of the Mirror Be Exposed with a Laser Diode forSynchronization
Purposes?
Yes. The 8K and 12K CRSs have a dual-side mirror coating option for silver coating. For the 4K CRSs, thebackside of the mirror is slightly shaped and isn’t polished, so it isn’t ashighly reflective as the frontsideof the mirror.
2.4.6 Pixel Clock (For Gen 1 CRSs)
Pixel Clocks are no longer available for future orders of both Gen 1 and Gen 2 CRSs.
The pixel clock phase locks with the CRS sync signal and enables synchronization with other devices.
Notice that when the red light is illuminated, phase lock is not being achieved, indicating a problem.
2.4.7 Position Feedback
Since it is an open-loop system, there is no position signal. However, it is possible toobserve the“Velocity (Coil)” and “(CRS) Sync”.
1. Velocity (Coil): Expected to be a sine waveform.
2. (CRS) Sync: A square wave in sync with the velocity signal. The rising edge and fallingedge eachindicate the trace and retrace of the CRS.

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Application Note AN00230

Although this doesn’t provide the live position signal, but it can be an indication of errors.For example,at rare occasions, the frequency of the CRS Sync signal can be incorrect or asymmetrical.
1. Pins for the Gen 2 CRS
Velocity: Pin2
Sync: Pin3

Figure 3 – Pin information for Gen 2 CRS

2. Test points/pins for the Gen 1 CRS
Velocity coil: TP3 & TP4
CRS Sync: Pin8

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Application Note AN00230

Figure 4 – Pin and test point information for Gen 1 CRS

3 Additional Resources
Document location: SharePoint > Applications Engineering > Product Library > CRS
1. Datasheet Resonant Scanner.
2. Pixel Clock Time Diagram.
3. CRS Temp and Jitter.
4. Scanner Component and Head Development for Confocal Microscopy Using MovingMirror
Technology
5. Vidreo – Resonant Scanning Concept:
http://scanimage.vidriotechnologies.com/display/SI2016/Resonant+Scanning+Conce pt© Novanta Corporation. All rights reserved.

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