Extreme-ultraviolet Imaging Spectrometer
EIS
Solar-B NRL Provided Mechanisms
Preliminary Electrical Interface
Control Document
put provided by the system central processing unit
into analog shaft rotation required to actuate the
optics mechanism. The proposed actuator is a
four-phase size 16 permanent magnet stepper motor. This type of actuator provides for easy interface, quick starting and stopping, as well as directional reversal. The motor has a small amount of
detent torque when coupled with a gearhead that
will allow for the removal of motor power without
the loss of position. The schematic diagram is
shown in Figure 1.
1.0 Introduction
1.1 Scope. This Interface Control Document
defines and controls the interfaces between the
electromechanical hardware associated with the
EIS flight instrument optics package and the driving electronics package.
1.2 Purpose. The actuator specification will be
described to a level satisfactory to begin design of
the electrical support hardware for flight and
ground support operations.
1.3 Actuator Overview. See Table 1.
YEL
YEL/WHT
WHT
2.0 Mirror Subassembly
The primary mirror subassembly consists of the
optic (3.5 kg), the optic housing, and actuators (2.5
kg). Coarse motion (±8 mm) of the optic along the
raster direction is obtained with a geared stepper
motor. The motor/gearhead/resolver assembly will
be provided by CDA Astro Intercorp. This is an
Astro size 16 four phase stepper motor coupled to
a gearhead and a linear ball screw actuator. Attached to the optic translation stage is a brushless
resolver capable of ±10 arc-min accuracy.
Further precision to mirror pointing is provided
by a PieZoelectric Translator (PZT). Rotation adjustment of up to ±2 arc-min is possible. Precise
and repeatable movement of the mirror is possible
with a closed loop servo amplifier utilizing a strain
gauge sensor and a step programmable power supply.
2.1 Stepper Motor. Stepper motors have been
chosen to provide conversion of digital control in-
M
BLK
RED/WHT
RED
Figure 1. Stepper Motor Schematic
2.1.1 Drive Logic Requirement. T h e o p e r a tional requirements of the motor driver circuit are
as follows. The four phases of the motor are driven
single phase (one phase energized at a time). The
stepper commutation logic provides a pulse sequence shown in Table 2 to the current drivers.
The phase and number of input pulses feed to the
drive circuit control rotation. Speed is controlled
by the frequency of the pulses applied. Optionally,
the duty cycle of the pulses may be controlled to
provide a balance between torque delivered to the
load and power savings. The drive circuitry controls the motor speed, direction, position, torque,
and power applied to the motor.
Table 1. Mechanism Characteristics
Mechanism
Subassembly
MIR
Primary Mirror
Subassembly
SLA
Slit/Slot Subassembly
GRA
Grating Subassembly
Translation
Actuator
Encoder
Average Duty Cycle
Peak Internal
Power
Average
Power
10 W
0.0046 W
Coarse Position
Size 16, 4 phase step- Resolver
per motors
2 (20 sec) operations per
day
Fine Position
Piezoelectric Transducer
0.5V step per five seconds
0.29 W
<0.05 W
12, 4 phase step- Resolver
Slit/Slot Exchange Size
per motors
2 operations per hour
3W
0.0042 W
Shutter
1 operation every 5 seconds
2.6 5 W
0.0122 W
2 (20 sec) operations per
month
10 W
0.0046 W
Brushless DC motor
Strain gauge
Optical encoder
16, 4 phase step- Optical encoder
Focus Mechanism Size
per motors
NOTE: Duty cycle, peak internal power, and average dissipated power values are preliminary estimates.
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1
Phase A Study
Extreme-ultraviolet Imaging Spectrometer
EIS
Table 2. Coil Energizing Sequence for Stepper Motor
Step #
Black
φ1
1
—
Yellow
φ3
Red φ2
2
White
φ4
—
3
—
4
5
Yellow /
White
—
—
voltage and frequency signal. The stator output
voltage than varies sinusoidally with the rotor position. The sine and cosine outputs of the stators
are coupled directly to the resolver to digital converter and are converted to a binary output through
a ratiometric tracking algorithm.
2.2.2 Logic Requirements. The driving hardware for this circuit consists of a sinewave generator. This circuit may be a sine wave oscillator or a
Digital to Analog Converter with a simple quantizing filter. The stator outputs run directly to the resolver chip whose digital output is placed on the
CPU data bus. A suggested resolver to digital converter would be the Analog Devices AD2S80 set to
resolve to 12 bits digital.
2.3 Piezoelectric Translator.
2.3.1 Description. The Physik Instrumente P845.40 is a high resolution actuator that can provide fast submillisecond response with subnanometer resolution. An internally integrated strain
gauge allows for ultra high resolution position
sensing when operated within a closed loop servo
amplifier topology. These devices are stacked element with a maximum displacement of 60 microns
with 0.1% linearity and repeatability under servo
control. Electrical and power supply specifications
are given in Tables 4 and 5.
Red /
Black
+
+
+
+
+
+
+
+
+
+
2.1.2 Electrical Specification. For proper operation the motor requires +28 VDC (±2 V) to the
center taps. Each winding has a resistance of ≅78
ohms. The power required will be 10 W at 28
VDC. The motor step rate is TBD.
2.2 Resolver Interface. Position sensing for
the mirror subassembly is achieved via a brushless
resolver transducer. This device is used to translate
angular rotor position into orthogonal components
consisting of sine and cosine signals. The schematic diagram of the resolver is shown in Figure 2. Table 3 gives the resolver electrical characteristics.
RED/WHT
1
6
R
BLK/WHT
BLK
4
5
3
2
RED
YEL
BLU
Table 4. PZT Electrical Specification
Figure 2. Resolver Schematic
Table 3. Resolver Electrical Specification
Operating Voltage
-20 to 120 VDC
Capacitance
29 µF ±20%
Resonant Frequency
7.5 kHz
Strain Gauge
TBD
Bridge Excitation
5 –10 V DC
Excitation
4.0 Vrms
Frequency
2500 Hz
Output
2 Vrms ±5%
Ripple
≤10 mV p-p
Total Fundamental Null
25 mVrms
Step Programmable Input
0 to 4.095 V (1bit = 30 mV output)
Phase Shift
0° ±10°
Input Current
6 mA rms max.
Table 5. PZT Power Supply Specification
Output
2.3.2 Servo Loop Amplifier. The PZT device
is designed to operate within a closed loop environment controlled by a Proportional/Integral tunable Instrumentation amplifier. A simple block diagram is shown in Figure 3.
The servo amplifier will require several control
registers within the digital controller in order to
maintain the close tolerance operation of the loop.
These registers will give the experiment the ability
to fine tune the operation of the actuators for the
20 arc-min spread ±10 (repeatable to
Absolute Angular Accuracy within
several arc-min)
Direction of Rotation
CW and CCW
Dielectric
500 Vrms, 60 Hz
Op. Temp
-80˚C to +225˚C
2.2.1 Position Sensing. Rotor position is determined by a resolver to digital converter. The resolver rotor is excited by application of a fixed
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-20 to +120 VDC
2
Phase A Study
Extreme-ultraviolet Imaging Spectrometer
Reference In
Control and Status
Registers
Servo
On/Off
Power
Supply
PZT
Amp.
Displacement / µm
Digital
Controller
EIS
PZT
P Term
Notch
Filter
I Term
Strain
Gauge
100
Closed Loop
90
80
70
60
Open Loop
50
Proportional / Integral Amplifier
Instrumentation Amplifier
Gain
40
30
Range
Adj.
Filter
20
Figure 3. Servo Control Loop Block Diagram
10
finest resolution possible. Direct access to the servo loop to gain digital and analog feedback to the
controller as well as receiving operating parameters from the controller is necessary. Table 6 lists
several examples of the registers that will be necessary to properly maintain a stable loop.
0
0
Parametric
Registers
Proportional Term
Servo On/Off
HVPS Voltage
Integral Term
Strain Gauge Output
Reference In Voltage Bias Offset
HVPS Voltage Output
Typically, the resistive film strain gauge would
be conditioned for range, bandwidth and gain before reaching the PI controller which generates a
error voltage proportional to actual PZT position
(strain gauge output) vs. the desired position set by
the reference voltage. The actual performance of
this hardware is controlled by the hardware and bias settings of the associated circuits and component tolerances. The amplifier output would be
used to control the programmable power supply
closing the loop. The performance of the PZT servo amplifier is shown graphically in Figure 4.
4
5
6
7
8
9
10
Ctrl Input/V
Table 7. Coil Energizing Sequence for Stepper Motor
Step
#
Black
φ1
1
—
2
3.0 Grating Focus Subassembly
3
The grating subassembly consists of the optic
held captive in a linear translation carriage capable
of ±1 cm of movement from the center or Focus
position. Optical encoders are used for position
feedback to the drive electronics. Three encoders
provide for +z limit, -z limit, and Focus indicators.
The stepper motor is a Astro size 16 with integral
gearhead and a linear ball screw that couples to the
translation mechanism.
5
Red φ2
Yellow
φ3
White
φ4
—
—
4
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3.1 Stepper Motor.
3.1.1 Stepper Motor Logic Requirement.
The operational requirements of the motor driver circuit are as follows. The four phases of the
motor are driven single phase (one phase energized at a time). The stepper commutation logic
provides a pulse sequence shown in Table 7 to the
current drivers. The phase and number of input
pulses feed to the drive circuit control rotation.
Speed is controlled by the frequency of the pulses
applied. Optionally, the duty cycle of the pulses
may be controlled to provide a balance between
torque delivered to the load and power savings.
The CPU software shall control the motor speed,
direction, position, torque, and power applied to
the motor.
Status Registers
Actual Position
2
Figure 4. Servo Loop Performance
Table 6. Control Registers
Set Point Registers
1
—
—
Yellow /
White
Red /
Black
+
+
+
+
+
+
+
+
+
+
3.1.2 Electrical Specification. For proper operation the motor requires +28 VDC (±2 V) to the
center taps. Each winding has a resistance of ≅78
ohms. The power required will be ~10 W at 28
VDC. The motor step rate is TBD.
3.2 Optical Encoders. The optical encoders
are used in an opto-interrupter mode to provide a
3
Phase A Study
Extreme-ultraviolet Imaging Spectrometer
EIS
TTL level indication that the translation stage has
reached a limit or mid-point in its travel.
YEL
YEL/WHT
WHT
3.2.1 Electrical Specification. A representative circuit is shown in Figure 5 for the nominal
optical encoder design. Shown, are the Texas Instruments TIL24 and TIL601 devices. These are
available with high reliability screening and small
package size.
M
BLK
RED/WHT
RED
+5V
Figure 6. Stepper Motor Schematic
+5V
single phase (one phase energized at a time). The
stepper commutation logic provides a pulse sequence shown in Table 8 to the current drivers.
The phase and number of input pulses feed to the
drive circuit control rotation. Speed is controlled
by the frequency of the pulses applied. Optionally,
the duty cycle of the pulses may be controlled to
provide a balance between torque delivered to the
load and power savings. The CPU software controls the motor speed, direction, position, torque,
and power applied to the motor.
Output
TIL24HR2
TIL601HR2
Optical Encoder
Figure 5. Optical Encoder Schematic
3.2.2 Drive Logic Requirements. Typically,
the output of the encoder is run into a schmitt triggered buffer to square up the edges and the high or
low read directly into a digital I/O port for poling
by the CPU software. The encoder hardware
should have the ability to be powered down when
not in use to prolong the lifetime of the optoelectronic devices.
Table 8. Coil Energizing Sequence for Stepper Motor
Black
φ1
1
—
2
Yellow
φ3
White
φ4
—
4
5
Red φ2
—
3
4.0 Slit/Slot Subassembly
—
—
Yellow /
White
Red /
Black
+
+
+
+
+
+
+
+
+
+
4.3 Stepper Motor Electrical Specification. For proper operation the motor requires +28
VDC (±2 V) to the center taps. Each winding has a
resistance of ≅250 ohms. The power required will
be ~3 W at 28 VDC. The motor step rate is TBD.
4.4 Resolver Interface. Position sensing for
the slit/slot subassembly is achieved via a brushless resolver transducer. This device is used to
translate angular rotor position into orthogonal
components consisting of sine and cosine signals.
The schematic diagram of the resolver is shown in
Figure 7. The electrical characteristics are given in
Table 9.
4.4.1 Position Sensing. Rotor position is determined by a resolver to digital converter. The resolver rotor is excited by application of a fixed
voltage and frequency signal. The stator output
voltage varies sinusoidally with the rotor position.
4.1 Stepper Motor. The EIS Slit/Slot Subassembly requires a coarse (stepper motor) with a rotary resolver for position indication. Stepper motors have been chosen to provide conversion of
digital control input provided by the system central processing unit into analog shaft rotation required to actuate the optics mechanism. The proposed actuator is a four-phase size 12 permanent
magnet stepper motor. This type of actuator provides for easy interface, quick starting and stopping, and directional reversal. The motor has a
small amount of detent torque when coupled with
a gearhead that allows for the removal of motor
power without the loss of position. The schematic
diagram is shown in Figure 6.
4.2 Drive Logic Requirement. T h e o p e r a tional requirements of the motor driver circuit are
as follows. The four phases of the motor are driven
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Step
#
4
Phase A Study
Extreme-ultraviolet Imaging Spectrometer
RED/WHT
1
6
R
BLK/WHT
BLK
YEL
BLU
4.4.2 Logic Requirements. The driving hardware for this circuit consists of a sine wave generator. This circuit may be a sine wave oscillator or a
digital to analog converter with a simple quantizing filter. The stator outputs run directly to the resolver chip whose digital output is placed on the
CPU data bus. A suggested resolver to digital converter would be the Analog Devices AD2S80 set to
resolve to 12 bits digital.
RED
4
5
3
2
EIS
4.5 Shutter. The shutter is used to precisely
control the exposure time of the CCD camera. This
high usage, high reliability design uses a brushless
DC motor with optical encoding for position indication feedback. This unit is borrowed from an existing design from SOHO/MDI. The power requirements are given in Table 10.
Figure 7. Resolver Schematic
Table 9. Resolver Electrical Specification
Excitation
4.0 Vrms
Frequency
2500 Hz
Output
2 Vrms ±5%
Total Fundamental Null
25 mVrms
Phase Shift
0° ±10°
Input Current
6mA rms max.
Absolute Angular Accuracy
14 arc-min spread ±7 (repeatable to
several arc-min)
Direction of Rotation
CW and CCW
Dielectric
500 Vrms, 60 Hz
Op. Temp
-80˚C to +225˚C
4.5.1 Drive logic Requirement. The electronics package must be capable of driving the shutter
mechanism through 360 degrees of rotation. In addition, the integration time or time the shutter is
held open must be variable. Power to the motor
and optical encoders is removed after each operation to conserve power dissipation.
The sine and cosine outputs of the stators are coupled directly to the resolver to digital converter
and are converted to a binary output through a ratiometric tracking algorithm.
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Table 10. Shutter Electrical Specification
Power
5
+15 VDC
0.150 A peak (motor)
+5 VDC
0.080 A peak (optical encoder)
Phase A Study