Archived: Overview of the FlexMotion architecture

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

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:

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:

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.