Overview of the FlexMotion architecture

Publish Date: Sep 06, 2016 | 20 Ratings | 3.95 out of 5 | Print

Overview

This document contains a brief overview of FlexMotion, and describes its different components.

Table of Contents

  1. Overview of communication between the FlexMotion application and board
  2. Overview of communication between RTOS and motors
  3. The four FlexMotion components
  4. Details on the FlexMotion components

1. Overview of communication between the FlexMotion application and board

The following image shows how FlexMotion programs communicate with the FlexMotion board:

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2. Overview of communication between RTOS and motors

The basic components of a motion controller fall into three categories:

  1. Supervisory control -- Does all the command sequencing and coordination
  2. Trajectory generator -- Generates the motion profile on the fly (multi-axes)
  3. Control loop -- Does the fast, closed-loop control with position, velocity, and trajectory maintenance on multiple axes simultaneously


The following image shows the motion controller components and how they interact:

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3. The four FlexMotion components

The FlexMotion board includes the following four components:

  1. The 68331 microprocessor -- A 32-bit microprocessor
  2. The DSP -- The 2111 fixed-point DSP (2185 on the 7344 boards) from Analog Devices
  3. The FPGAs -- The FPGAs implement the quadrature encoder and stepper pulse generator (in the case of FlexMotion-6C, a zilog is used for the stepper pulse generator)
  4. Motion I/O -- I/O dedicated for motion such as limits, home switches, breakpoints, and high-speed capture


The following image shows the interaction of the different FlexMotion components:

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4. Details on the FlexMotion components

The following sections describe the FlexMotion components in more detail.

The 68331 Microprocessor 
The 68331 microprocessor has the following functions:

  • Runs the RTXC real-time OS
  • Handles all bus communication (from the host)
  • Executes user-defined threads
  • Does the “Find Home” and “Find Index” for initialization of motion systems
  • Handles all vector space calculations
  • Generates spherical and helical trajectory


The Task or Thread priority is as follows:

  1. Spherical and helical trajectory generator task
  2. Event Handler task
  3. Host communication task
  4. Acquire Samples task
  5. Find home, Find Index, Programs 1-10, and watchdog task -- all time-sliced every 2 ms


The interrupt priority is as follows:

  1. E-stop or shut down
  2. Host interrupt -- when a new command is sent to the board
  3. DSP interrupt -- when the DSP has a message for the 68331
  4. Timer interrupt


The onboard programs, which you download to the processor, have the following characteristics:

  • Memory -- for the 7344 boards, 64 Kbytes of RAM and 128 Kbytes of FLASH; for FlexMotion-6C, 32 Kbytes of RAM and 32 Kbytes of FLASH
  • Multithreading -- 10 programs (threads) can execute at a given time, in addition to host communication
  • Easy ways to create loops and waits
  • 120 onboard variables


The DSP
The DSP has the following functions:

  • All point-point trajectory generation
  • The control loop (PID)
  • Stepper pulse generation
  • Electronic gearing
  • Move blending
  • Cubic splining -- for smoother and more accurate curves


FPGAs
The FPGAs have the following functions:

  • Quadrature decoder counters
  • High-speed capture
  • Position breakpoints
  • Limit switch detection (7344 only)
  • Stepper pulse generation (7344 only)
  • RTSI (7344 only)


Motion I/O
In addition to the I/O dedicated for motion, FlexMotion includes the following I/O components:

  • 12-bit ADCs -- for analog feedback and analog gearing. The FlexMotion-6C has 8 ADC channels, while the 7344 has 4 ADC channels.
  • Digital I/O -- general purpose I/O for ancillary use. The FlexMotion-6C has 24 bits of DIO, while the 7344 has 32 bits of DIO.

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