The METIRIO Encoder is a reflective optical encoder designed for precise measurements of linear and rotary displacement. It outputs analog sine and cosine displacement signals, making it suitable for integration as an OEM component into positioning systems that utilize scales for closed-loop motion control. The compact METIRIO readhead is a small flip-chip package, similar to the SON standard, with soldering pads on the bottom side.
Function Description:
The METIRIO encoder system's basic component is the readhead, available in various housing variants. The core is the OEM METIRIO Readhead, a flip-chip sensor package with fully integrated optical and electrical functionality. All housing variants are based on this core component, ensuring identical technical specifications except for external dimensions and connection pinout.
The encoder operates by illuminating a reflective scale with a light source. The reflected light, combined with the readhead's grating optics, generates a specific light pattern. This pattern's distribution changes with the relative displacement between the scale and the readhead. Photodiode arrays within the readhead detect this light pattern, converting it into amplified output voltages with a 1 V peak-to-peak amplitude.
In addition to the periodic incremental track, the scale can include a second track with reference marks. These marks also reflect light to a separate light-detecting array within the readhead, generating a TTL-shaped reference signal for each detected mark. The readhead outputs two incremental signals phase-shifted by π/2, which, when plotted against displacement, exhibit a sinusoidal shape. These signals, along with the reference signal, allow for the calculation of absolute position.
The METIRIO A1 variant includes an aluminum housing with mounting threads, the integrated METIRIO Readhead, a cable with strain-relief, and a connection plug. It can be further integrated into tailored external housings. The encoder is designed to connect to a motion controller that provides power, interprets, and processes the output signals for closed-loop movement.
Important Technical Specifications:
Absolute Maximum Ratings:
- Operating temperature: 0 to +80 °C (no dew condensation)
- Storage temperature: -20 to +80 °C (no dew condensation)
- Maximum baking temperature: 150 °C (repeated > 1 h)
- Supply voltage (VDD): 3.0 to 5.5 V
- Max. power consumption (Pel): 310 mW (all outputs terminated)
- ESD susceptibility: 4 kV (HBM, AEC-Q101)
- Max. radiant output power (Фmax): <360 mW (short circuit current IF = 1000 mA)
- Ambient pressure (p): > 10-11 mbar
General Electro-optical Characteristics:
- Current consumption (IDD): 20 mA (typical)
- Differential analog output voltage (Usin,cos): 1 Vpp (appropriate gain settings)
- Reference output (Uref): RS485 Square wave
- Integrated channel noise (URMS): 450 µVRMS (500 kHz bandwidth)
- Max. bandwidth (f3dB): 500 kHz (3 dB cutoff)
- Central emission wavelength (λpk): 850 nm
- Radiant output power (Фе): < 45 mW (typical)
Digital Specification (I²C Timing):
- SCL Frequency (fCLK): 400 kHz
- Minimum pulse width High (THIGH): 0.6 µs
- Minimum pulse width Low (TLOW): 1.3 µs
- Start condition Hold time (tHD-Start): 0.6 µs
- Start condition Setup time (tSU-Start): 0.6 µs
- SDA setup Hold time (tHD-Data): 0 ns
- SDA setup Setup time (tSU-Data): 100 ns
- Rise time (tr): 300 ns
- Fall time (tf): 300 ns
- Stop condition Setup time (tSU-Stop): 0.6 µs
- Data valid time (tvD-Data): 0.9 µs
- Acknowledge time (tvD-Ack): 0.9 µs
Environmental Conditions:
- Operating temperature range: 0 °C to 80 °C
- Maximum baking temperature: 150 °C (repeated short term < 1h)
- Ambient pressure: 10-11 mbar to 2 bar
- Humidity: 80% non-condensing at 40 °C for 96 h (EN 60068-2-78)
- Shock: 1000 m/s², 11 ms half sine (EN 60068-2-27)
- Vibration: 500 m/s², 10 - 2000 Hz sinusoidal (EN 60068-2-6)
- UHV compatible (low outgassing according to NASA ASTM E595)
- RoHS compliant
- Non-magnetic
Mechanical Data (METIRIO Readhead):
- Package: flat-no-leads
- Dimensions: 6.6 x 5.1 x 1.7 mm²
- Weight: 0.12 g
- Soldering pads: gold
- Pad size: 0.9 × 0.25 mm²
- Pad pitch: 0.75 mm
Scale Specifications:
- Incremental pitch: 20 µm
- Minimum track width: 1.4 mm
- Ideal aperture ratio: 50/50
- Reference mark extension: 0.5 mm (25 periods)
- Separation between neighboring reference marks: > 1.5 mm
- Rotary scale optical diameter (doc): discrete values (e.g., 13.04 mm for 2048 CPR, 191.00 mm for 30000 CPR)
- Smallest bending radius for convex scales: R > 60 mm
Usage Features:
- Sub-nanometer resolution: Enables highly precise displacement measurements.
- Compact design: Most compact encoder in its class, suitable for integration into small spaces.
- UHV compatibility: Can operate in ultra-high vacuum environments due to its non-encapsulated package and low outgassing materials.
- Multiple scale options: Compatible with linear, convex, and rotary scales, offering flexibility for various applications.
- Adjustable settings: Output incremental and reference signals can be adjusted via an I²C interface to optimize encoder signals. This includes LED current, gain factors, and offset correction.
- Power-down mode: Features an energy-saving mode with very low current consumption (< 1 mA) when a HIGH voltage is applied to the power-down pin.
- Reference pulse adjustment: Adjustable comparators allow conversion of diode signals to an RS485 pulse signal, with adjustable width and position to match one period.
- OEM integration: Designed as an OEM component, allowing users to integrate it into custom machinery and positioning systems.
- Monitoring and alignment tools: SmarAct Metrology provides accessories like the ENCODER INTERFACE MODULE (IM), ENCODER EVALUATION MODULE (EEM), and ENCODER EVALUATION PROGRAM (EEP) to facilitate setup, signal monitoring, and alignment. The EEM and EEP offer a graphical user interface for easy communication and visualization of analog signals.
- Mounting flexibility: Can be glued or soldered directly onto a PCB or solder-wired. The cover glass or side frame provide accurate reference surfaces for mechanical mounting.
Maintenance Features:
- No required maintenance: METIRIO encoder devices generally do not require maintenance.
- Cleaning advice: Cleaning of the glass surface of the readhead or the scale is advised in case of contamination to achieve optimal signal quality. Use proper tissues to avoid scratching.
- UHV cleaning: To maintain UHV capability, avoid Acetone or other chemicals in the final cleaning step, except for N-heptane (CH3(CH2)5CH3) and Propan-2-ol (CH3CHOHCH3).
- Contamination awareness: Any contamination on the scale can lead to signal distortions, loss of signal quality, and measuring errors, necessitating periodic cleaning or cleaning upon visible contamination.
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