Using Customized Rotation Systems with Voyantic Tagformance

Application Note

Published 9/2014 - Revised 3/2017
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1 Introduction

This application note describes the available interfaces in the Voyantic Tagformance system for using customized rotation systems.

2 Voyantic Rotation Systems

Voyantic offers three types of rotation systems:

Rotation System for RFID Measurement Cabinet, code CA-HW-ROT
Type: Stepper motor outside the cabinet
Platform diameter: 33 cm (13”)
Max object size: ~30 cm x 30 cm x 30 cm
Max object weight: ~10 kg (11 lbs)

Rotation System for Large RFID Measurement Cabinet, code LC-HW-ROT
Type: Stepper motor outside the cabinet
Platform diameter: ~50 cm (19.7”)
Max. object size: ~50 cm x 50 cm x 50 cm
Max. object weight: ~20 kg (44 lbs)

Tag Rotation System, stand alone, code TF-AC-ROT
Type: Stand-alone
Platform diameter: ~50 cm (19.7”)
Max. object size: ~50 cm x 50 cm x 50 cm
Max. object weight: ~20 kg (44 lbs)

In addition, it is possible to build and use an own customized rotation system.

3 Interface for Customized Rotation Systems

There are three alternative ways to interface a Rotation System to Voyantic Tagformance:

  1. Stepper motor drive
  2. File based system
  3. GPIB based system.

3.1 Stepper Motor Drive

In the Tagformance user interface, the rotation angle is controlled from one of the three instances:

  1. orientation control window
  2. scripter
  3. orientation measurement.

To control the orientation angle, the Tagformance outputs two signals: ‘step’ and ‘direction’. When an amount of incremental rotation is desired, the corresponding number of pulses is sent in the ‘step’ signal. The amount of pulses needed for a full revolution is specified in the Tagformance software options.

If an USB-6008 data acquisition device (DAQ) is connected to the same computer running the Tagformance GUI, and analog input conditions in AI0 and AI1 are met, then the device starts to transmit these signals to a stepper motor driver.

Figure 1. Voyantic Rotation system

A wiring diagram used in Voyantic Rotation Systems is described in figure 2.

Figure 2. Wiring diagram of Voyantic Rotation System

Voyantic uses as standard the National Instruments’ USB-6008 USB DAQ and the Geckodrive G203V digital stepper motor driver in its rotation control systems. In figure 3 the components are shown installed on a Voyantic large RFID measurement cabinet.

Figure 3. USB DAQ, Stepper motor drive and Stepper motor on a Large RFID Measurement Cabinet

3.2 File Based System

Tagformance software writes the current desired absolute rotation angle value in degrees with three digits (e.g. 0 degrees = 000, 30 degrees = 030, 270 degrees = 270) to a file: /Tagformance/Data/angle_position.txt.

The measurement delay value in the Tagformance GUI options should be set to a non-zero value indicating how much time is given between updating the angle_position.txt file and proceeding with the measurement.

Any rotation system can be controlled with a simple script that polls the value in the file and transmits the information further to the rotation system driver.

3.3 GPIB Based System

Voyantic has a generic application for GPIB based rotation systems. GPIB based system has two components; RotationController application and GPIB_config text file. GPIB_config file is used for setting GPIB address of the rotation table and defining needed commands for the rotation table. Requirement for the PC is either a GPIB card or an USB–GPIB adapter cable.

Like file based systems, RotationController monitors \Tagformance\Data\angle_position.txt file. When an angle change is detected in the angle_position.txt file, it commands the rotation table to turn accordingly. GPIB based system requires a delay before measurement setting on the Tagformance options. The delay must be set long enough for the rotation table to reach any expected angle change before starting a new measurement.

4 Notes and Tips

Interference from the rotation system to tag measurement can be minimized by using one or both of the following methods:

  1. The stepper motor and the motor drive are placed to a distance from the measurement area, for example outside of the measurement cabinet. This method is used in Voyantic RFID Measurement Cabinets.
  2. Rotating table, and related gear system, may have metallic parts reflecting RF signal and disturbing the measurement. Effect of the reflected signal to tag performance can be minimized by placing a layer of RF absorbing material in between the tag and the metallic parts. In the Voyantic Rotation systems an absorber layer of about 1 cm is used in between the gear and the tag to be measured.