absolute encoders and motors for -80°C

Absolute encoders and motors for -80°C

27/03/2007 IRAIT Team [email protected]

absolute encoders and motors for -80°C



motors

Choosing a drive system for our application.To be taken into account:

speed mechanical load characteristics smoothness of motion resolution temperature other environmental conditions

our choose for IRAIT telescope: stepper motors

a stepper motor is an electromagnetic driving system that moves around a particular reproduceable step angle due to defined wiring and triggering of windings (phases). With a motor control that triggers the phases, a quasi-continuous rotation is achieved. The smallest possible resolution of positioning depends on the motor as well as on the type of drive. An usual value for the resolution of commercial stepper motors is 200 steps per revolution; however, resolution can be considerably increased by electronic micro-stepping.With the right design of bearings and windings, a stepper motor is able to work in extreme environmental conditions.



motors

our choose:

PHYTRON stepper motors, model ZSH87/3.200.5 PLE80/1 3:1

stepper motors advantages for our application:

high torque at low speeds, e.g. during tracking smoothness of motion, at least using good driving electronics low temperatures tolerant, choosing the right commercial product no need for an encoder to get reproduceable positioning (*)

(*) but a loss of steps must be avoided! Typically a bad design and/or a bad tuning of the driving system, in presence of irregular loads, can produce a loss of steps.Anyway, as you will see, we have ALSO absolute encoders on telescope axes...



motors

PHYTRON ZSH87/3.200.5 PLE80/1 3:1

2 Phase Stepper Motor integral gearbox (3:1 ratio) for -30°C/+8 0°C 5A per phase5.4 Nm holding torque (before the gearbox)



motors

PHYTRON ZSH87/3.200.5 PLE80/1 3:1

2 Phase Stepper Motorsintegral planetary gearbox (3:1 ratio) for -30°C/+8 0°C bipolar current per phase: 5Aholding torque: 5.4 Nm max. permissible output torque: 40 Nmtorsional backlash: <15‘number of magnets: 3permissible bearing axial load: 180N permissible bearing radial load: 280N200 steps, 1.8° step angle insulation class: F

Phytron is well known for its catalogue of in-vacuum and cryo stepper motors

frequency behaviour (control pulses) for two supply voltage values



motors

our choose for driver electronics:

PHYTRON SLS-4xPAB93-70

4 axis Rack Mount Power Driveincluding 4 power stages PAB93-70230VAC power supply

power stage PAB 93-70 micro 256supplier in Italy: MICOS Italia Gmbhhttp://www.micos.it



motors

Climatic chamber tests (from 0°C to -80°C) in Germany (Phytron)

Tested system behaviour in working conditions at various temperature values. Tested speed constance and motion smoothness and resolution at low temperatures, especially for low speeds (tracking).The system has been calibrated at -30°C. It works without problem at this temperature; with lower temperatures, there will be no damage. Giving power supply to the motors leads their temperature over -30°C; at that point we can move the telescope.A derating has been applied, to take into account the effect of low pressure values.

We are using commercial off-the-shelf products; the cost-benefits ratio is very good.



motors

IRAIT drive groups mechanical configuration 2x motors (primary and bk)2x 90° 1:1 gearboxes2x 1:20 gearboxes2x pinionsredundancy and backlash reduction



motors

IRAIT azimut drive group

2x motors2x 90° 1:1 gearboxes2x 1:20 gearboxes2x pinions1x slewing bearing



motors

IRAIT azimut drive group



motors

IRAIT elevation drive group

2x motors2x 90° 1:1 gearboxes2x 1:20 gearboxes2x pinions1x gear sector



motors

IRAIT elevation drive group



motors

mounting/dismounting operations...



motors

High degree of STABILITY; unmatched chemical and solvent resistance; thermal and oxidative stability; excellent radiation stability. COMPATIBILITY with a broad selection of materials inert to most plastics, metals, and elastomers, liquid and gaseous oxygen. SAFE; non-flammable, non-toxic, no volatile organic compounds, NSF certified, BAM approved. Broadest operating TEMPERATURE range of all classes of lubricants (- 90°C to 290°C).www.solvaysolexis.com

special grease...



absolute encoders

Choosing a position feedback system for our application.We don’t have encoders on motor axes; we use an angular position readout directly on telescope axes, at the end of kinematic chain (1:1440 total ratio).

To be taken into account:

resolution and repeatability of angular measureproblems with heating (below primary mirror and around optical path -Nasmyth-)operating temperatureother environmental conditions

our choose for IRAIT telescope:

Heidenhain RCN 700 series absolute encoders



absolute encoders




absolute encoders

29 bits = 536.870.912 positions per revolution

1 arcsec on sky → 414 counts

hollow through shaft Ø100mm



absolute encoders

HEIDENHAIN encoders with optical scanning incorporate measuring standards of periodic structures known as graduations. These graduations are applied to a carrier substrate of glass or steel. These precision graduations are manufactured in various photolithographic processes. Graduations are fabricated from:

extremely hard chromium lines on glass or gold-plated steel drums, matte-etched lines on gold-plated steel tape, three-dimensional structures etched into quartz glass,

Manufacturing processes and typical grating periods: 40 µm with AURODUR 20 µm with METALLUR 10 µm with DIADUR 4 µm with etched quartz glass

Circular graduations of absolute angle encoders



absolute encoders

Photoelectric scanning

HEIDENHAIN uses the imagingscanning principle for absolute angle encoders:

Parallel light hits the grating structure (scanning reticle) and light passes through the gaps.

When the measuring standard moves in relation to the scanning reticle, the incidentlight is modulated (light / no light).

Photovoltaic cells convertthese variations in light intensity into electrical signals.



absolute encoders



absolute encoders




absolute encoders


interface card IK200



absolute encoders

Heidenhain RCN 700 series absolute encoders (over LAN)



absolute encoders

Climatic chamber tests (from 0°C to -45°C) in Italy (Perugia University)

Tested system behaviour in working conditions (encoder rotated by a motor at different speeds) at various temperature values. A specialist from Heidenhain supervised the tests. Heidenhain suggested a series of tests over the electrical signals coming from the encoder, with a particular attention to the incremental signal, to check for a signal level degradation with low temperatures. The behaviour of the system has been perfect.The tests doesn’t cover the full range of expected temperatures at DomeC, but the self-heating of the device will keep it over the minimum value tested.



absolute encoders

Chamber RH% sensor

Chamber T sensor (pt100)

Encoder T sensor (pt100)

Motor T sensor (pt100)Motor HeaterRCN 727 Encoder

PLC

Control Box

Climatic ChamberSupervisor PC

RS-232

Power Supply

Power Supply

EnDat

IK 220 Pci Card

Main PC

tests setup



good luck IRAIT!

Documents

absolute encoders and motors for -80°C