September 1997, Issue 86

PC/104 Quarter:
Motion Control with PC/104

TIMING DIAGRAMS

The secret to coordinating multiple axes of motion control with hundreds of possible discrete I/O signals on a multimillion-dollar machine is to design with the aid of system or machine timing diagrams.

The timing diagram is to a system what a flowchart is to software. The timing map specifically details the actions of the machine parts and product at any point in the process, both mechanically and electrically.

Once the system is ready for startup, the timing diagram becomes your best debugging tool. Since it serves as a function map of the system, real-time machine operations that require multitasking become immediately evident.

Figure 3 shows a timing diagram for developing the operating requirements of a rotary brush machine (used in floor buffing and scrubbing machines). The graph shows the required machine function operation during a 360º head cycle.

A 360º rotary head motion is converted into linear motion and drills holes in round wooden discs. After each hole is drilled, the disc is indexed (without stopping the drill head), which results in a circular pattern of holes around the disc. At assembly, bristles are inserted into the holes to form the brush.

The actual machine uses five axes of motion--two rotary and three in-line--operating speeds up to 250 holes per minute. An algorithm triangulates the positions of the inline axes for disc tilting and radius placement, while the rotary axes rotate the wooden discs for drilling and bristle insertion.

All this must keep up with a hydraulic head that cycles at 250 rpm or one revolution in 0.24 s. Also, operators can load new brush data from a master/host where new brush patterns are produced, or it may be producing daily work logs and set-up information for building other brushes.