DESCRIPTION

The Microcontrole IP28 is a 4-axis motor indexer for use with stepping motors or with direct current motors with encoders. It is interfaced either via RS-232C or by GPIB (IEEE 488). Being programmable, an entire motion sequence, including backlash, may be down loaded, thus retaining the asynchronous nature of moves.

Normally, power is supplied by TL78A power units which can be very simply multiplexed using the 4-bits of the programmable outputs of the IP28. Thus, up to 32 motors can be controlled by one IP28. Unfortunately, this usage presents the two following difficulties:

1. only four motors (of the same bank) may be moved simultaneously, and
2. the internal registers can only keep track of the positions of four axes.

One solution is to keep track of all motor positions using separate readable up/down counters (such as the Microcontrole HC 88). Another solution is to always work with relative displacements and to keep track of the positions by the software. This is technique is currently employed by spec. Consistency is insured by searching for a mechanical origin (switch or optical encoder). Note that the TL78 power modules display a position (usually set to the user angle) so that angles are not really lost when switching banks. Generally, the hardware is homogeneous so there is little or no problem about loosing steps (which results in a "controle d'ecart", anyways). One must beware when restarting from a power failure, and search for the origin for each axe (see below).

One cannot set the internal registers - only define zeros. Thus, we ignore the IP28's floating zero and only use its mechanical zero. This is set by the command "O[WXYZ];\r" which is incorporated in sync() and in the spec command chg_dial(motor, 0). Changing a dial setting to a non-zero value disables hardware angle tracking, re-enabled by searching for the mechanical origin. IP28 users will probably want to undefine the macro set_dial and define a new macro zero - this macro SHOULD NOT MODIFY THE USER OFFSETS! (see macros/surf.cea).

spec tries to make best use of the IP28. Most of the above problems can be avoided if one puts the four, most often used motors (4-axes) on one TL 78A bank. Note that a bank may consist of several TL78A chassis which may be not fully occupied when using large motors due to a limitation in power.

BUGS AND CAVEATS

Besides being able to only track 4 motors at a time, positions may be read only after motion has terminated. Thus, spec updated move macros cannot be used with the IP28.