The Single Axis State Diagram

The following diagram normatively defines the behavior of the axis at a high level when multiple motion control Function Blocks is simultaneously activated. This combination of motion profiles is useful in building a more complicated profile or to handle exceptions within a program. (In real implementations there may be additional states at a lower level defined). The basic rule is that motion commands are always taken sequentially, even if the PLC had the capability of real parallel processing. These commands act on the axis’ state diagram.

The axis is always in one of the defined states (see diagram below). Any motion command that causes a transition changes the state of the axis and, as a consequence, modifies the way the current motion is computed. The single axis state diagram is an abstraction layer of what the real state of the axis is, comparable to the image of the I/O points within a cyclic (PLC) program. A change of state is reflected immediately when issuing the corresponding motion command.

Note

The response time of immediately is system dependent, coupled to the state of the axis, or an abstraction layer in the software.

The diagram is focused on a single axis. The multiple axis Function Blocks, MC_CamIn, MC_GearIn and MC_Phasing, can be looked at, from a single axis state diagram point of view, as multiple single-axes all in specific states. For instance, the CAM-master can be in the state Continuous Motion. The corresponding slave is in the state Synchronized Motion. Connecting a slave axis to a master axis has no influence on the master axis.

The state Disabled describes the initial state of the axis. In this state the movement of the axis is not influenced by the Function Blocks. The axis feedback is operational. If the MC_Power Function Block is called with Enable=TRUE while being in state Disabled, this either leads to Standstill if there is no error inside the axis, or to ErrorStop if an error exists.

Calling MC_Power with Enable=FALSE in any state, the axis goes to the state Disabled, either directly or via any other state. If a motion generating Function Block controls an axis, while the MC_Power Function Block with Enable=FALSE is called, the motion generating Function Block is aborted (CommandAborted).

The intention of the state ErrorStop is that the axis goes to a stop, if possible. There are no further Function Blocks accepted until a reset has been done from the ErrorStop state.

The transition Error refers to errors from the axis and axis control, and not from the Function Block instances. These axis errors may also be reflected in the output of the Function Blocks instances errors.

Issuing MC_Home in any other state than StandStill will go to ErrorStop, even if MC_Home is issued from the state Homing itself.

Function Blocks which are not listed in the single axis state diagram do not affect the state of the axis, meaning that whenever they are called the state does not change. They are:

MC_ReadStatus; MC_ReadAxisError; MC_ReadParameter; MC_ReadBoolParameter; MC_WriteParameter; MC_WriteBoolParameter; MC_ReadActualPosition and MC_CamTableSelect.

Calling the Function Block MC_Stop in state StandStill changes the state to Stopping and back to Standstill when Execute = FALSE. The state Stopping is kept as long as the input Execute is true. The output Done is set when the stop ramp is finished.

Function Block state behavior

Note

1. In this state ErrorStop or Stopping, all Function Blocks can be called, although they will not be executed, except MC_Reset and Error – they will generate the transition to StandStill or ErrorStop respectively.

2. Power.Enable=TRUE and there is an error in the Axis.

3. Power.Enable=TRUE and there is no error in the Axis.

4. MC_Stop.Done AND NOT MC_Stop.Execute.