Real Time Enhanced Accuracy Options

Enhanced Accuracy Options

  • Provides industry leading positioning accuracy with little or no sacrifice in
  • positioner / measurement speed
  • Based on proprietary MI Technologies algorithms, techniques and processes
  • Different options are available to meet a variety of needs
  • Based on capabilities built into the MI-710C Integrated Position Controller
  • Can be used to improve the accuracy of non-MI positioners
  • (MI-710C Integrated Position Controller required)

Introduction

Many of today’s antenna measurement applications require extreme positioning accuracy. Sometimes these accuracy requirements are beyond the existing state-of-the-art in mechanical positioning systems. Because of this, MI Technologies developed techniques that are used to enhance the accuracy of the mechanical systems to meet today’s most demanding positioning requirements.

Excellent positioning accuracy must always be based on a sound mechanical design and control system implementation. MI Technologies is an industry leader in advanced mechanical design, including heavy positioning systems, scanners, arches, gimbals and RCS rotators. To achieve accuracy beyond the native accuracy of the positioner, MI developed the following systems to enhance positioning accuracy:

SINGLE

Options Overview

Single Axis Error Correction:

  • Corrects repeatable errors inside the positon control loop for one axis

Multi Variable Path Correction:

  • Corrects repeatable errors when the motion of interest is the resultant of multiple mechanical axes

Z-Axis Laser Correction

  • Corrects probe Z axis position on scanners.
  • Combines Error Map correction and Real Time Laser Correction techniques
  • Results in high speed scanning with high fidelity
  • Repeatable and non-repeatable errors are corrected

Multi Axis Laser Correction

  • Excellent for providing high fidelity in the largest scanner systems
  • Compensates for Thermal Drift and structural deformation
  • References stable monuments in the range in real time
  • Corrects probe X, Y, and Z
  • Combines Error Map correction and Real Time Laser Correction techniques
  • Results in high speed scanning with high fidelity
  • Repeatable and non-repeatable errors are corrected

Advanced Error Correction Techniques

The MI-710C facilitates two methods of Advanced Error Correction intended to enhance overall system accuracy by removing repeatable errors.  The two methods utilized include Single Axis Error Correction and Multi-Variable Path Correction. Both techniques utilize MI services to precisely measure the repeatable errors in the candidate axis and determine which method would provide the best accuracy.

Single Axis Error Correction

As the name implies, this error correction technique is applied in real time to a single axis of a positioning system. That axis can be a rotary or linear axis. This Enhanced Accuracy Option consists of the following:

  • Measurement Services to characterize the positioning errors that are repeatable and a function of axis position. These errors are commonly due to native encoder accuracy or bearing runout and many times represent the dominant error contributor for a single axis of motion.
  • MI-710C Integrated Position Controller: This error data is then loaded into the MI-710C.
  • Does not use a laser during data acquisition- only for a one-time offline characterization of positioning errors.

The MI-710C will then apply our proprietary algorithm to correct the reported position data inside of the control loop. This means that the error correction goes beyond correcting the reported position: it actually causes the axis to ‘go to’ the commanded position more accurately. This is done in real time without a speed penalty.

Multi-Variable Path Correction

Many times the position of interest can be a function of multiple physical axes. At the system level, position errors on one axis can be influenced by the position of other axes. To solve this problem, the MI-710C features coordinated motion with multi-axis error correction. Using a tracking laser, position error for an axis is measured as other axes are varied. A multi-dimensional error correction table is generated. The system is capable of including up to 4 inputs (e.g. position of other axes, temperature, etc.) in the correction algorithm. Acquisition of error correction data using a tracking laser is now highly automated and therefore more economical to implement. As a result, the entire multi-axes positioning system can be characterized in a matter of hours rather than days. This is particularly beneficial when characterizing/correcting system errors during final installation and periodic calibration. This technique does not use a laser during data acquisition- only for a one-time offline characterization of positioning errors.

Z-Axis Laser Correction

  • Uses a combination of previously measured error data and real-time laser tracking to achieve unparalleled planarity (0.001” RMS typical)
  • Can be applied to spherical scanning as well as planar
  • Corrects for repeatable and non-repeatable error sources
  • Consists of:
    • Spinning Laser Kit
    • Services to pre-measure planarity errors
    • Optional MI-3066 and software that provides improved accuracy and capability through the following features:
      • Provides ‘look ahead’ capability for Z-axis correction to make the correction faster and more accurate.
      • Reduces effects of Z-axis dynamics
      •  Optimizes the Z-axis control loop
      •  Aligns scan and laser planes
      •  Verification of planarity during MI-3000 Acquisition
      •  Utilities for tuning and Configuration
      •  Builds map of error data

Application

ZACIS webZ-Axis Laser Correction is intended for all but the largest planar near-field scanners when a very high degree of fidelity is required. 

Description

Z-axis Laser Correction implements a fully automated three-stage real-time compensation for Z using a spinning laser. The first two compensation stages take offline measurements to form a map of Z corrections to be followed as a function of other axes. The third compensation stage uses laser target readings to drive the laser target to the laser plane. Because all the repeatable error is compensated with the first two stage corrections, the real-time laser corrections are typically very small and account for low frequency effects such as tilt and translation. This permits extremely high-fidelity performance even at high scan speeds.

 

Multi-Axis Laser Correction

  • Tracking Laser and several laser targets
  • Z-axis error compensation to a plane or sphere a specified distance from the AUT
  • Multi-Axis error compensation relative to a fixed point in the range
  • Laser updates performed between scans at user-specified interval
  • Laser updates always performed just before thermal drift measurements
  • Achieves planarity of 0.05 mm (0.002”) RMS (typical)
  • Combines Error Map correction and Real Time Laser Correction techniques

Application

Multi-Axis Laser Correction is intended for large near-field scanners (such as the MI-815-66X66 Horizontal PNF Scanner) when a very high degree of fidelity is required. One of its primary capabilities is to monitor and compensate changes in scanner size and shape with changes in temperature. For most antenna-measurement facilities, the combination of temperature regulation, structural dimensions, and required position accuracy permit these thermal effects to be ignored. However, as structural dimensions become longer, wavelengths become shorter, and/or temperature regulation becomes less feasible, there will be a threshold where thermal (and/or other) effects on physical structures must be compensated in order to meet measurement-fidelity requirements.

PICTURECORRECTION web

Description

Multi-Axis Laser Correction implements a fully automated two-stage real-time compensation for multi-axis of motion using a tracking laser. The first compensation stage takes off-line measurements to form a multi-axis error map to develop multi-variable path correction. The second compensation stage is performed periodically during each acquisition, updating as necessary the multi-variable path corrections and constraining the probe distance from the AUT. The first compensation stage represents open-loop real-time correction of repeatable errors. The second compensation stage represents low-rate closed-loop real-time correction of dynamic errors with low spatial frequency.