The IAxisSupervisor interface is defined within the Axis Module in order to allow Axis modules to be deployed in standalone Axis operation under manual control. For autonomous control, the axis is expected to have an Axis Group module managing it and providing it trajectory-based setpoints. The reason this interpolator functionality was not just assimilated as part of the Axis Group was that it was not considered practical to expect vendors of Axis modules to include a complete realization of Axis Group module interfaces in deployment of "One-Axis" Axis Group - even if these interfaces were "stubbed" out. It was felt that if an Axis and Supervisor were bundled together, it would be a more practical commercial packaging. Axis bundled as part of a larger control system could assume that his functionality has been subsumed as part of the Axis Group module responsibility. (This is the current thinking.)
Realizations of Axis Supervisor handle single-axis trajectory responsibilities by managing a collection of interpolation "plugs", including homing, continuous jogging, incremental positioning and absolute positioning. Interpolation is achieved by coordinating the servoing activity of an Axis via an IAxis reference. The IAxisSupervisor interface defines a container mechanism to provide a means of storing interpolated-motion component references and then providing access to the interpolated-motion component references.
An IAxisSupervisor realization uses a FSM to coordinate among the different interpolated-motion control strategies, and then manages a selected interpolation strategy to achieve axis motion based on the FSM. Each control strategy has an associated "pluggable" Axis motion control component that implements the control strategy. See also the associated interpolated-motion control component interfaces:
IAxisSupervisor coordinates between the different servoing motion control strategies by means of a FSM. Based on the selected motion control strategy, a different plug is used to control the motion. (See the OmacModule for details on component realization and how the AxisSupervisor and each plug are connected.) These interpolated-motion plugs could provide their own interpolation service or could be share an underlying profile generator as illustrated in the following Figure Axis .
Behavior
An IAxisSupervisor component manages a set of interpolated-motion control components that implement basic single-axis motion trajectory strategies. Trajectory motion consists of a sequence of desired positions, velocities, and accelerations of an axis over time. An Axis Supervisor generates a time sequence of intermediate desired configurations for an axis that matches the given rates to attain the desired position, velocity or acceleration goal. For example, to achieve continuous jogging, the IAxisJogging component would place the axis in followingAbsPosition seroving and then update new positions for the axis to follow based on attaining the jogging velocity. All interpolated-motion control components must comply with underlying Axis state. Thus, for example, moving an axis to an absolute position could not be done until the Axis positioning has been calibrated by a homing sequence.
IAxisSupervisor coordinates between the different servoing motion control strategies by means of a FSM, including events, states, and state transitions, defined by the following diagram:
Switching between interpolated motion control strategies is achieved by sending events to the Axis FSM. The FSM itself is hidden, but the Axis interface provides methods for event propagation and state query. The event propagating methods that cause FSM state transitions, which may result in changing control strategies, are: disableAxis, enableAxis, estopAxis, home, jog, resetAxis, and stopAxis. The relationship between state, events, next state and action associated with the state transition in the FSM is given in the following table, where XXX is a member of {AbsPositioning, Homing, Jogging, Incrementing}.
First State = Disabled
| Beginning State | Event | Ending State | Action |
| Disabled | enable() | Enabling | IAxisEnabling::enablingAction |
| Disabled | hardStop() | HardStopping | IAxisDisabling::hardStoppingAction |
| Enabled | hardStop() | HardStopped | IAxisErrorAndEnable::hardStopAction |
| HardStopped | reset() | Disabled | IAxisResetting::resetHardStopAction |
| Enabling | completed | Enabled | IAxisEnabling::enabledAction |
| Enabled | startXXX() | XXX | IAxisXXX::startXXXAction |
| XXX | stop() | XXXStopping | IAxisXXX::stopXXXAction |
| XXX | hardStop() | XXXHardStopping | IAxisXXX::hardStoppingXXXAction |
| XXX | completed | Enabled | IAxisXXX::finishedXXXAction except Jogging which can only be stopped |
| XXXStopping | completed | Enabled | n/a |
| XXXHardStopping | completed | HardStopped | n/a |
| XXX | (state update) | XXX | IAxisXXX::updateXXXAction |
| XXXStopping | (state update) | XXXStopping | IAxisXXX::updateXXXStoppingAction |
| XXXAbnormalStopping | (state update) | XXXAbnormalStopping | IAxisXXX::updateXXXAbnormalStoppingAction |
| XXXHardStopping | (state update) | XXXHardStopping | IAxisXXX::updateXXXHardStoppingAction |
The State Definitions and Query Table supplements the behavior model described above by the state table. This table provides a detailed description of each state and identifies the query mechanism for determining if the Axis Interpolation component is in that state. The Axis Interpolation FSM states, state description, and query methods is described in the following table where XXX is a member of {AbsPositioning, Homing, Jogging, Incrementing}.
| State | Definition | Query for State |
| AbsolutePositioning | Module is moving to an absolute position. | isAbsolutePositioning() |
| Disabled | Module is Disabled. Connections and IO points are not enabled. | isDisabled() |
| Enabled | Module is enabled. Power on to amplifiers. | isEnabled() |
| HardStopped | Module is HardStopped. Power to equipment is off. | isHardStopped() |
| Homing | Module is Homing. | isHoming() |
| IncrementingPosition | Module is incrementally Jogging. | isIncrementing() |
| Jogging | Module is under Jogging control. | isJogging() |
| Ready | Module is ready. Part of outer OMAC API state definition. | isReady() |
| Resetting | Module is resetting hard or abnormal stop or resolving fault. | isResetting() |
| StoppingXXX | Module is stopping XXX. | isStoppingXXX() |
| AbnormalStoppingXXX | Module is abnormal stopping XXX. | isAbnormalStoppingXXX() |
| HardStoppingXXX | Module is hard stopping XXX. | isHardStoppingXXX() |
The Axis interpolator plugs provide a packaging mechanism for encapsulating the FSM functionality for a specific service: homing, jogging, incremental jogging, or absolute positioning. These plugs derive from IOmac so that they are connectable and could provide event service if necessary. To simplify develop and integration these plugs are simple. Each plug provides event and activity methods for transitioning and updating the varying states motion control in a generic FSM: start, stop, update, hardstop, abnormalstop, fail and completion. The Axis Supervisor controls the life of the plug by invoking the appropriate method given the current state of the FSM. For example, to start a homing sequence, the method startHomingAction is invoked on the AxisHoming plug. Subsequently, for each cycle the AxisSupervisor is in the Jogging state, the method updateAxisHomingAction is invoked until the isCompleted method returns true. Several modes of stopping are defined for each plug to accommodate different circumstances for velocity servoing to zero. The stopping modes that have been defined are:
- normal stop - stop under current commanded deceleration limits.
- hard stop - hard or panic stop means exceed any limits, break any rules, stop as soon as possible.
- abnormal stop - safe stop as quickly as possible, save the hardware. This case typically involves some detection of an internal failure or safety violation that can be resolved. As examples of this stopping mode, suppose it has been detected that someone has entered the safety area or that someone has opened the coolant door in a CNC. These cases would cause an abnormal stop. Motion can resume by invoking a resettingAction.
Appropriate states, events and actions are associated with each state. The event stopping methods are: hardStopXXXAction, abnormalXXXStopAction, or stopXXX where XXX indicates the functionality provided by the plug. The stopping states are: hardStopping, hardStopped abornmalStopping, abornmalStopped, normalStopping and normalStopped. The stopping state queries are: isHardStopping, isHardStopped, isAbornmalStopping, isAbornmalStopped, isNormalStopping and isNormalStopped. as well as isStopping and isStopped to detect any stopping state. The updating actions are: updateHardStopping, updateAbornmalStopping, and updateStopping .
Estop is not a separate stopping mode, instead it is Resident Task that maps an Estop event into several events that can be tailored to accommodate domain-specific safety codes. For example, estop could be mapped into "stop as fast on each limit using the software limits as configured by OEM, put brakes on, cut power", or "cut power after certain time limit" depending on pertinent safety codes. To allow for the different domain-specific forms of estop, this functionality has been abstracted into a Resident Task and would use either a hard or abnormal stop to a achieve safe emergency stop as predicated by the domain-specific safety code.
As a final note, it is not encumbant on the system integrator or end-user to develop the Axis interpolator plugs. It would be expected that preconfigured Axis interpolator plugs would be provided by the axis vendor so that default functionality is available. End-users would only be expected to develop a new plug in response to satisfying some special need.