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EtherCAT Operation


Overview

CORE module is compliant with CiA402 CANopen profile for motion, implemented over EtherCAT so called CoE (CANopen over EtherCAT). In current FW revision (R1.10), only ‘Cyclic Synchronization Torque’ (CST) mode is supported. Other operation modes like velocity, velocity control should be obtained on application level In CST mode, CORE supports maximum update rate from master up to 12 kHz.
Internal torque controller’s gain set has been tuned for each type of module. Advanced user can update these gains via EtherCAT SDO CORE supports firmware update via EtherCAT FoE (File over EtherCAT).


General EtherCAT device information

Device identity:

  • Vendor ID - 0x0000089a: Neuromeka EtherCAT vender ID
  • Product code - 0x30000000: Neuromeka motion device

Supported protocols:

  • CoE: standard CANopen over EtherCAT protocol
  • FoE: standard File over EtherCAT, used for driver’s firmware updating

CoE details:

  • SDO enabled and complete access: user can completely access available objects via SDO
  • Do not support PDO assign and configuration: PDO mapping is fixed, can’t be changed by user
  • Enable LWR: master can read/write PDO data in same EtherCAT datagram

Distributed clock (DC):

  • DC is a feature of EtherCAT that synchronize all EtherCAT slave devices and EtherCAT master within a small tolerant (~100ns)
  • Neuromeka CORE support 64-bit DC clock
  • In CST mode, module will operate regardless DC is enabled or disabled

SDO access

User can completely access drive variables defined by CiA402 via SDO.
SDO objects are classified into two groups:

  • Original function list: this group includes CiA402 standard objects which are used as their defined functions. It is noted that not all objects in this list are updated (some objects are always zero).
  • Alternative function list: several objects are utilized for other functions like driver temperature data, module setting, module calibration, debug…

The completed list of objects are summarized in 2 tables in: Neuromeka_CompleteSDO_List.pdf

Original function object list:


Figure 1. Original function object list

Alternative function object list:


Figure 2. Alternative function object list

Index: standard index of object, in hexadecimal
Sub-index: each object may have several sub-objects, this is index of each sub-object exist in this object
Name: standard object name, it tells object function
Type: data type of an object
Attribute: access right in OP mode
Description: more explanation for object


Slave process data (PDO)

PDO data is cyclically sent/received between master and slave devices. This is realtime communication data. Neuromeka CORE provides maximum PDO transmission speed is up to 20 kHz (50 us). CORE doesn’t support PDO assign and configuration, user must use default configuration assigned by manufacturer. Default PDO mapping is oriented for motion control, therefore pre-configured objects only serve motion control purpose (position, velocity, torque). For other driver information, like temperature, user should access via SDO.

Default PDO mapping

RxPDO
Default RxPDO object ‘Drive RxPDO’ with index of 0x1600 is mapped at sync-manager 2 (SM2). There are 5 pdo entries located on RxPDO.

PDO Name Entry
Drive RxPDO Index Sub-index Bit len Name Data type
0x6040 0 16 controlword UINT
0x607a 0 32 target_velocity DINT
0x60ff 0 32 target_velocity DINT
0x6071 0 16 target_torque INT
0x6060 0 8 modes_of_operation SINT

Table 1. Default RxPDO mapping

TxPDO
Default TxPDO object ‘Drive TxPDO’ with index of 0x1A00 is mapped at sync-manager 3 (SM3). There are 5 pdo entries located on TxPDO.

PDO Name Entry
Drive TxPDO Index Sub-index Bit len Name Data type
0x6041 0 16 statusword UINT
0x6064 0 32 position_actual_value DINT
0x606c 0 32 velocity_actual_value DINT
0x6077 0 16 torque_actual_value INT
0x6061 0 8 modes_of_operation_display SINT
Table 2. Default TxPDO mapping


CiA402 state machine

  • CORE implemented CoE CiA402 motion profile, SERVO-ON, SERVO-OFF are controlled according to CiA402 state machine.
  • Three state groups:
    • Power disabled: driver voltage was not enabled yet
    • Power enabled: high voltage is available
    • Fault: any alarm signal will cause driver to fault states
  • Rectangle blocks are driver states.
  • Yellow highlighted numbers are state transition paths.


Figure 3. CiA402 state machine diagram


Driver states

Driver states Description
Not Ready to Switch On Initial state, very quickly pass after power on
Switch On Disabled Initiation has been completed, servo is in off state
Ready to Switch On From off state, servo is commanded by control word
Switched On Main voltage has come, ready for enabling
Operation Enable Fully enabled, servo is in operation
Quick Stop Active Servo drive stops in pre-defined method
Fault Reaction Active Servo is on but an alarm is detected, soon servo will go to off state
Fault Servo off
Table 3. Driver states summary

Driver state is indicated by Statusword object. In order to change from one to another state master should send a corresponded Controlword value.


Figure 4. CiA402 state machine diagram


Control word (object 0x6040)

Set by user, change the drive states.

Index 0x6040
Name controlword
Object code VAR
Data type UINT
Access RW
PDO mapping (pre-mapped) Yes
Units -
Range -
Default value 0
Table 4. Description of controlword


Controlword is bitwise object, each bit has its own control meaning. Several bits are mandatory (M) while others are optional (O)


Figure 5. Detail information of Controlword


Status word (object 0x6041)

Set by drive internally, indicate current state of drive.

Index 0x6041
Name statusword
Object code VAR
Data type UINT
Access RO
PDO mapping (pre-mapped) Yes
Units -
Range -
Default value -
Table 5. Description of statusword


Statusword is bitwise defined, each bit indicates a specific state.


Figure 6. Detail information of Statusword

Turn on/off servo via SDO

Since all objects can be accessed via SDO, including controlword and statusword. User may turn CORE module on/off by writing suitable value for controlword via SDO. According to CiA402 state machine, a proper SERVO-ON path will be:


Figure 7. Servo ON path


A simplest way to turn off servo (SERVO-OFF) is to set controlword value of 0 (transition#9). It is recommended that before turn module on, mode_of_operation should be set first.

error_code (object 0x603F)

  • Error_code: indicates actual error inside drive.
  • Error code should be checked before starting operation and when Fault bit statusword appear.

Index 0x603F
Name error_code
Object code VAR
Data type UINT
Access RO
PDO mapping (pre-mapped) No
Units -
Range -
Default value 0
Table 6. Description of error_code


Available standard error codes in CORE (up to FW revision 1.10):

Code Name Description
0x2310 ERROR_CONTINUOUS_OVER_CURRENT Hardware over-current, need reset before re-run
0x3110 ERROR_MAINS_OVER_VOLTAGE Supplied 48V is too HIGH (> 63V)
0x3120 ERROR_MAINS_UNDER_VOLTAGE Supplied 48V is too LOW (< 41V)
0x3210 ERROR_DC_LINK_OVER_VOLTAGE Driver voltage (after enable) is too HIGH (> 62V)
0x3220 ERROR_DC_LINK_UNDER_VOLTAGE Driver voltage (after enable) is too LOW (< 40V)
0x7310 ERROR_SPEED Driver over speed, it is automatically recovery error
0xFF10 ERROR_ENCODER_BAT_LOW Low battery of encoder -> replace battery
0xFF11 ERROR_ENCODER_ERR_BIT There is error bit in encoder -> check bit count
0xFF20 ERROR_5V_SOURCE_OVER Internal 5V is too HIGH (> 5.5V)
0xFF21 ERROR_5V_SOURCE_UNDER Internal 5V is too LOW (< 4V)
0xFF22 ERROR_3_3V_SOURCE_OVER Internal 3.3V is too HIGH (> 3.6V)
0xFF23 ERROR_3_3V_SOURCE_UNDER Internal 3.3V is too LOW (< 3.0V)
0xFF24 ERROR_GATE_DRV_VOLTAGE_OVER Internal Gate driver voltage is too HIGH (> 13V)
0xFF25 ERROR_GATE_DRV_VOLTAGE_UNDER Internal Gate driver voltage is too LOW (< 9V)
0xFF31 ERROR_MOSFET_UL_THRU Low side MOSFET, channel U is damaged
0xFF32 ERROR_MOSFET_VL_THRU Low side MOSFET, channel V is damaged
0xFF34 ERROR_MOSFET_WL_THRU Low side MOSFET, channel W is damaged
0xFF39 ERROR_MOSFET_UH_THRU High side MOSFET, channel U is damaged
0xFF3A ERROR_MOSFET_VH_THRU High side MOSFET, channel V is damaged
0xFF3C ERROR_MOSFET_WH_THRU High side MOSFET, channel W is damaged
0xFF3F ERROR_MOSFET_UNKNOWN_THRU Some MOSFET is damaged -> Over current
Table 7. CORE module error code

Cyclic synchronization torque mode (CST)

After SERVO-ON and operation mode is set to CST (10), target torque will be updated by drive.
Process data timeout is 50ms: after EtherCAT state is changed to OP mode, process data must be cyclically sent to drive with period lower than 50ms.
Target torque is compared to maximum torque (max_torque) value (object 0x6072) before proceed. Default value of max_torque is 2048 which is equivalent to 42.5A on CORE500.
Actual motor speed is observed and compared to maximum motor speed (max_motor_speed, object 0x6080). Default value of max_motor_speed is 4600 rpm.
Both max_torque and max_motor_speed can be changed by users via SDO access.


Figure 8. Torque control loop

Miscellaneous

Data conversion

Torque (current): as mentioned in previous sections, all target_torque, actual_torque and max_torque values (called ecat_data) are measured in driver ADC ‘count’ unit.
They need to be converted to meaningful physical unit (Amps, Nm) using torque constant and gear ratio.

Summary of basic information for data conversion

CORE module Gear ratio Torque constant (Nm/A) Single-turn encoder resolution (counts)
CORE100 101 0.058 65536
CORE200 121 0.087 65536
CORE500 121 0.0884 65536
Table 8. CORE module - Basic information for data conversion

Torque (current) data conversion

CORE100 ecat data Motor current (A) Motor torque (Nm) CORE output torque (Nm)
Formula a I = a/96 t = 0.058I = 0.00060417a T = 101t = 0.061004a
Example 96 1.0 0.058 5.858
Table 9. Torque (current) data conversion for CORE100
CORE200 ecat data Motor current (A) Motor torque (Nm) CORE output torque (Nm)
Formula a I = a/96 t = 0.087I = 0.00090625a T = 121t = 0.10965625a
Example 96 1.0 0.087 10.527
Table 10. Torque (current) data conversion for CORE200
CORE500 ecat data Motor current (A) Motor torque (Nm) CORE output torque (Nm)
Formula a I = a/48 t = 0.0884I = 0.0018417a T = 121t = 0.2228457a
Example 96 2.0 0.1768 21.393
Table 11. Torque (current) data conversion for CORE500

Position data conversion

CORE100 ecat data Motor turns CORE turns CORE shaft angle (deg)
Formula p n = p/65536 N = n/101= p/6619136 A = 360N = 360p/6619136
Example 1241088 18.9375 0.1875 67.5
Table 12. Position data conversion for CORE100

CORE200
CORE500
ecat data Motor turns CORE turns CORE shaft angle (deg)
Formula p n = p/65536 N = n/121= p/7929856 A = 360N = 360p/7929856
Example 1982464 30.25 0.25 90
Table 13. Position data conversion for CORE200/CORE500

Velocity data conversion

CORE100 ecat data Motor velocity (deg/s) Motor speed (rpm) CORE shaft velocity (deg/s)
Formula y v = 360y/65536 r = 60y/65536=v/6 V = v/101=360y/6619136
Example 1311000 7201.538 1200.256 71.302
Table 14. Velocity data conversion for CORE100
CORE200
CORE500
ecat data Motor velocity (deg/s) Motor speed (rpm) CORE shaft velocity (deg/s)
Formula y v = 360y/65536 r = 60y/65536=v/6 V = v/121=360y/7929856
Example 1311000 7201.538 1200.256 59.517
Table 15. Velocity data conversion for CORE200/CORE500

Brake control

By default, brake control circuit is not active, brake stop CORE from motion.
There are 3 method to release brake of a CORE module

  • Servo on: when CORE is in servo-on (by SDO or PDO), brake will be automatically released
  • Using digital_output object: this object has 2 sub-indices (digital_output:0 and digital_output:1) in which the 2nd sub-object can be used to control brake, it is noted that this method only work when module is in servo-off state
           digital_output:1 = 0xAAAA : release brake
           digital_output:1 = other values: braked
  • Using brake release line: each ‘Brake lines’ connector (J2) on each driver has an ‘Brake release’ line, when this line is connected to GND, brake will be release regardless motor status