Left Hand Design

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Left Hand Design
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Modeling Actuators
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1 Introduction to Left Hand Design

Left Hand Design Corporation is company in Boulder, CO that provides precision pointing systems and components. They advertise tailored performance available on short notice.

1.1 Left Hand Design Actuator Modeling

The Left Hand Design actuators are linear actuators that produce force in 1 direction. The force is advertised to be proportional to the current applied through single phase coils (eliminating the need for commutation). These were the only items on the Left Hand Design website that I could not find a bandwidth for so I emailed them. An engineer at Left Hand Design was gracious enough to supply the following information.

 You can most accurately model Left Hand Design Corporation's actuators as k/(s+a) where k is the 
 gain in force (or torque) per amp and (s+a) is a first-order pole at about 2,000 Hz.  
 The pole represents the actuator coil's resistance/inductance (R/L) term.  
 These are Lorentz-Force-based linear electro-magnetic actuators.
 
 Larry Germann

1.2 Transmissive Fine Steering Optics

Left Hand Design offers fine steering capability through the use of transmissive optics. Transmissive optics work by bending light through refractive optics. Through that refraction the beam is steered laterally. Left Hand Design states that the optics are capable of 1000 Hz closed-loop bandwidth. The transmissive optics provide

  • 2-axis steering motion
  • closed-loop servo for accuracy
  • flexure suspension
  • electro-magnetic actuators

The transmissive optics can be used for

  • Pointing
  • Jitter Correction
  • Alignment
  • Line-of-Sight Stabilization
  • Scanning
  • Chopping
  • Tracking

1.3 Left Hand Design Fine Steering Mirror Modeling

The Left Hand Design Fine-Steering Mirror (FSM) is a 2-axis mirror with a range of travel from 2 to 10 degrees (half angle). The FSM is suspended on flexures (probably providing a 2nd order transfer function for the mechanical, dynamic, portion of the plant model). The FSM is rotated (tip/tilt) using electro-magnetic actuators. The FSMs are available with servo control electronics and reaction and momentum compensation.

The FSMs can be used for

  • Pointing
  • Jitter Correction
  • Alignment
  • Line-of-Sight Stabilization
  • Scanning
  • Chopping
  • Tracking

Possible Left Hand Design FSM applications are

  • Image Motion Compensation
  • Earth observation from orbit
  • Instrumentation equipment
  • Infra-red inspection
  • Laser sugery
  • Interceptor seeker optical heads
  • Ground and Space based astronomy
  • Video cameras
  • Laser communications
  • Photolithography
Table 1: Left Hand Design Fine Steering Mirror Model Parameters
Product # Nominal Bandwidth (Hz) High Bandwidth (Hz)

FO15

500

3000

FO20

400

2000

FO25

350

1700

FO35

300

1500

FO50

250

1200

FO75

200

1000

FO100

150

750

FO150

80

400

FO250

40

200

FO400

20

100

FO625

15

65

FR100

200

1000

FR150

120

600

FR250

60

300

FR1000

12

60

2 Notes

The Left Hand Design site provided a lot of good information on bandwidths. Some key information not provided is damping (assuming a 2nd) order system) and noise. A convenient assumption would be a damping of LaTeX: \frac{1}{\sqrt{2}}. However, a more conservative assumption would produce something some peaking (I'd start with 6 to 10 dB of closed-loop peaking).

3 External Sites