CANopen over EtherCAT for electrical drives

CANopen also defines several device profiles by establishing standard behavior and communication objects for similar devices. In the case of electrical drives, the profile is given by the CiA402 (“CANopen device profile for drives and motion control”) norm compliant with the IEC standard that defines programming languages for programmable control systems. The CiA402 norm specifies specific objects in OD in range 0x6000 to 0x67fe, what guarantees, that for a drive compatible with CiA402, typical process values such as position, velocity, or torque set-points and actual values will always be defined in the same objects with the same address regardless of the manufacturer and by such simplifies the commissioning of different drives. CIA402 also defines a state machine that corresponds to the drive’s actual operating state (Disabled, Fault, Switch ON, etc.). This state machine is controlled and monitored by two mandatory PDO entries: Control Word and Status Word. The drive cannot be started until the state machine has been put into the appropriate state.

The device states and possible control sequences of the drive are described by the CANopen state machine as follows:

The possible drive states are :

CiA402 Drive States

State	Description
NOT_READY_TO_SWITCH_ON	The drive is not ready to switch on. The drive is in boot phase. Drive motion functions are disabled. No communication established.
SWITCH_ON_DISABLED	The drive cannot be enabled via the EtherCAT interface. Drive motion functions are disabled.
READY_TO_SWITCH_ON	The drive can be enabled. Parameters can be transferred. Power may be applied. Drive motion functions are disabled.
SWITCHED_ON	The drive is enabled but idle No fault detected. Power is enabled Drive motion functions are disabled. Parameters can be transferred. No set-points are transferred from the EtherCAT interface.
OPERATION_ENABLED	Normal operation mode No fault detected. Drive motion functions and power are enabled. Power enabled. Set-points are transferred from the EtherCAT interface.
QUICK_STOP_ACTIVE	The quick stop process is executed. Drive motion functions are disabled. Power is enabled.
FAULT_REACTION_ACTIVE	A fault has occurred, fault reaction processes are executed.
FAULT	A fault is active, Drive is stopped and its functions are disabled.

State transitions are the result of events that can be either internal or triggers through the Control Word. When a command trigger for state change is received, the transition is performed before any other command is processed.

The possible transition states, their trigger events and performed actions are :

CiA402 Drive State Transitions

State Transition	Event	Action
0	Automatic transition after power-on or reset application	Drive device self-test and/or self initialization has to be performed
1	Automatic transition	Communication has to be activated
2	Shutdown command from control device or local signal	None
3	Switch on command received from control device or local signal	The high-level power has to be switched ON, if possible
4	Enable operation command received from control device or local signal	The drive function has to be enabled. All internal set-points cleared.
5	Disable operation command received from control device or local signal	The drive function has to be disabled.
6	Shutdown command received from control device or local signal	The high-level power has to be switched OFF, if possible.
7	Quick stop or disable voltage command from control device or local signal	None
8	Shutdown command from control device or local signal	The drive function has to be disabled. The high-level power has to be switched OFF, if possible.
9	Disable voltage command from control device or local signal	The drive function has to be disabled. The high-level power has to be switched OFF, if possible.
10	Disable voltage or quick stop command from control device or local signal	The high-level power has to be switched OFF, if possible.
11	Quick stop command from control device or local signal	The quick stop function has to be started.
12	Either: - Automatic transition when the quick stop function is completed and quick stop option code is 1, 2, 3 or 4. - Disable voltage command received from control device (depends on the quick stop option code)	The drive function has to be disabled. The high-level power has to be switched OFF, if possible.
13	Fault signal	The configured fault reaction function has to be executed.
14	Automatic transition	The drive function has to be disabled. The high-level power has to be switched OFF, if possible.
15	Fault reset command from control device or local signal.	A reset of the fault condition is performed if no fault exists currently on the drive device. After leaving the Fault state, the Fault reset bit in the control word has to be cleared by the control device.
16	If the quick stop option code is 5, 6, 7, or 8, enable operation command from control device	The drive function has to be enabled

CANopen uses 16-bits Status Word and Control Word to monitor and control the state machine. These PDO entries have the following bit assignment :

CiA402 Drive Words

Bit	Status Word Name	Control Word Name
0	Ready to switch on	Switch On
1	Switched on	Disable Voltage
2	Operation Enabled	Quick Stop
3	Fault	Enable Operation
4	Voltage Enabled	Operation-mode Specific
5	Quick Stop	Operation-mode Specific
6	Switch On Disabled	Operation-mode Specific
7	Warning	Reset Fault (only effective for faults)
8	Manufacturer-specific (reserved)	Pause/halt
9	Remote (always 1)	Reserved
10	Target Reached	Reserved
11	Internal Limit Active	Reserved
12	Operation-mode Specific (reserved)	Reserved
13	Operation-mode Specific (reserved)	Manufacturer-specific
14	Manufacturer-specific (reserved)	Manufacturer-specific
15	Manufacturer-specific (reserved)	Manufacturer-specific

The Status Word is only updated and written by the drive in Safe-Op and Operational states. The current drive state can be decoded from the logical combination of the bits in the Status Word:

CiA402 Drive State form Status Word

Status Word	State
xxxx xxxx x0xx 0000	Not ready to switch on
xxxx xxxx x1xx 0000	Switch on disabled
xxxx xxxx x01x 0001	Ready to switch on
xxxx xxxx x01x 0011	Switched on
xxxx xxxx x01x 0111	Operation enabled
xxxx xxxx x00x 0111	Quick stop active
xxxx xxxx x0xx 1111	Fault reaction active
xxxx xxxx x0xx 1000	Fault

The control commands allow the manipulation of the state of a drive by setting its control word. Commands are built up from the logical combination of the bits in the Control Word:

CiA402 Drive Commands to Control Word

Control Word	Command	State Transitions
xxxx 0xxx x110	Shutdown	2, 6, 8
xxxx 0xxx 0111	Switch On	3
xxxx 0xxx 1111	Switch On + Enable Operation	3 + 4
xxxx 0xxx xx0x	Disable	7, 9, 10, 12
xxxx 0xxx x01x	Quick Stop	7, 10, 11
xxxx 0xxx 0111	Disable Operation	5
xxxx 0xxx 1111	Enable Operation	4, 16
xxxx 1xxx xxxx	Fault Reset	15