CAN Protocol

CAN Communication

Baud-Rate

The CAN communication baud-rate is 1Mbps.

Non-Periodic Communication

Messages can be sent to initialize or stop CAN communication.

Periodic Communication

The Allegro Hand control software attempts to communicate with the real or simulated hand at a regular control interval. Every 3 milliseconds, the joint torques are calculated and the joint angles are updated.

CAN Frames

Standard CAN Packet

The standard CAN packet used for communication is 14 bytes including 8 bytes of data.

typedef struct{ 
	unsigned char STD_EXT;            //type of message (Standard or Extended)
	unsigned long msg_id;		//message identifier 
	unsigned char data_length;	// 
	char           data[8];		// data array 
} can_msg;

ID (Message Identifier)

The 4 byte integer CAN message identifier (msg_id) is split into the command ID (26 bits), destination ID (3 bits) and source ID (3 bits).

1	8	16	24	26	27	29	30	32
Command ID					Dest. ID		Source ID

Command Identifiers

Variable Name	Value	Description	Destination	Source
ID_CMD_SET_SYSTEM_ON	0x01	Start periodic communication	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_SYSTEM_OFF	0x02	Stop periodic communication	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_PERIOD	0x03	Set communication frequency	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_MODE_JOINT	0x04	Command Transmission Mode	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_MODE_TASK	0x05	Command Transmission Mode	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_TORQUE_1	0x06	Index finger (1) torque command	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_TORQUE_2	0x07	Middle finger (2) torque command	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_TORQUE_3	0x08	Pinky finger (3) torque command	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_TORQUE_4	0x09	Thumb torque command	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_POSITION_1	0x0a	(unused)	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_POSITION_2	0x0b	(unused)	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_POSITION_3	0x0c	(unused)	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_SET_POSITION_4	0x0d	(unused)	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_QUERY_STATE_DATA	0x0e	Request joint state	ID_COMMON	ID_DEVICE_MAIN
ID_CMD_QUERY_STATE_DATA	0x0e	Joint state response	ID_DEVICE_MAIN	ID_DEVICE_SUB_01 ID_DEVICE_SUB_02 ID_DEVICE_SUB_03 ID_DEVICE_SUB_04
ID_CMD_QUERY_CONTROL_DATA	0x0f	Joint state response	ID_DEVICE_MAIN	ID_DEVICE_SUB_01 ID_DEVICE_SUB_02 ID_DEVICE_SUB_03 ID_DEVICE_SUB_04

Source and Destination Identifiers

Variable Name	Value	Description
ID_COMMON	0x01	Allegro Hand
ID_DEVICE_MAIN	0x02	Control PC
ID_DEVICE_SUB_01	0x03	Index Finger
ID_DEVICE_SUB_02	0x04	Middle Finger
ID_DEVICE_SUB_03	0x05	Little Finger
ID_DEVICE_SUB_04	0x06	Thumb

Case-study: Softing CAN

In this chapter, sample code demonstrating the implementation of the CAN communication interface is provide. This is the foundation for Softing PCI CAN.

Opening the CAN Communication Channel

char ch_name[256]; 
sprintf_s(ch_name, 256, "CAN-ACx-PCI_%d", ch); 
INIL2_initialize_channel(&hCAN[ch-1], ch_name); 
 
L2CONFIG L2Config; 
L2Config.fBaudrate = 1000.0; 
L2Config.bEnableAck = 0; 
L2Config.bEnableErrorframe = 0; 
L2Config.s32AccCodeStd = 0; 
L2Config.s32AccMaskStd = 0; 
L2Config.s32AccCodeXtd = 0; 
L2Config.s32AccMaskXtd = 0; 
L2Config.s32OutputCtrl = GET_FROM_SCIM; 
L2Config.s32Prescaler = 1; 
L2Config.s32Sam = 0; 
L2Config.s32Sjw = 1; 
L2Config.s32Tseg1 = 4; 
L2Config.s32Tseg2 = 3; 
L2Config.hEvent = (void*)-1; 
 
CANL2_initialize_fifo_mode(hCAN[ch-1], &L2Config);

CAN Initialization

long Txid; 
unsigned char data[8]; 
 
Txid = ((unsigned long)ID_CMD_SET_PERIOD<<6) | ((unsigned long)ID_COMMON <<3) | ((unsigned long)ID_DEVICE_MAIN); 
data[0] = (unsigned char)period_msec; 
canWrite(hCAN, Txid, data, 1, STD); 
 
Sleep(10); 
 
Txid = ((unsigned long)ID_CMD_SET_MODE_TASK<<6) | ((unsigned long)ID_COMMON <<3) | ((unsigned long)ID_DEVICE_MAIN); 
canWrite(hCAN, Txid, data, 0, STD); 
 
Sleep(10); 
 
Txid = ((unsigned long)ID_CMD_QUERY_STATE_DATA<<6) | ((unsigned long)ID_COMMON <<3) | ((unsigned long)ID_DEVICE_MAIN); 
canWrite(hCAN, Txid, data, 0, STD);

Starting Periodic CAN Communication

When you start periodic CAN communication, joint angles are automatically updated according to the torque control input.

long Txid; 
unsigned char data[8]; 
 
Txid = ((unsigned long)ID_CMD_QUERY_STATE_DATA<<6) | ((unsigned long)ID_COMMON <<3) | ((unsigned long)ID_DEVICE_MAIN); 
canWrite(hCAN[ch-1], Txid, data, 0, STD); 
 
Sleep(10); 
 
Txid = ((unsigned long)ID_CMD_SET_SYSTEM_ON<<6) | ((unsigned long)ID_COMMON <<3) | ((unsigned long)ID_DEVICE_MAIN); 
canWrite(hCAN[ch-1], Txid, data, 0, STD);

Stopping Periodic CAN Communication

long Txid; 
unsigned char data[8]; 
 
Txid = ((unsigned long)ID_CMD_SET_SYSTEM_OFF<<6) | ((unsigned long)ID_COMMON <<3) | ((unsigned long)ID_DEVICE_MAIN); 
canWrite(hCAN[ch-1], Txid, data, 0, STD);

Transmitting Control Torques

Control inputs for the four joints in each finger should be packed in a single CAN frame. The sample code below demontrates how to encode four PWM inputs into an 8 byte data buffer and how to set the CAN frame ID properly.

Note: PWM = Desired_Torque (N-m) * 800.0.
800.0 is an empirical constant that will convert torque to PWM.
As seen below, torque2pwm = 800.0

Note: The joint index order used in the following code is for Allegro Hand versions 2.0 and up. For Allegro hand 1.0 or earlier, see the code snippet after this one.

long Txid; 
unsigned char data[8]; 
float torque2pwm = 800.0f 
short pwm[4] = { 
	0.1*torque2pwm, 
	0.1*torque2pwm, 
	0.1*torque2pwm, 
	0.1*torque2pwm 
}; 
 
// This joint index order is used Allegro Hand versions 2.0 and up.
if (findex >= 0 && findex < 4) 
{ 
	data[0] = (unsigned char)( (pwm[3] >> 8) & 0x00ff); 
	data[1] = (unsigned char)(pwm[3] & 0x00ff); 
 
	data[2] = (unsigned char)( (pwm[2] >> 8) & 0x00ff); 
	data[3] = (unsigned char)(pwm[2] & 0x00ff); 
 
	data[4] = (unsigned char)( (pwm[1] >> 8) & 0x00ff); 
	data[5] = (unsigned char)(pwm[1] & 0x00ff); 
 
	data[6] = (unsigned char)( (pwm[0] >> 8) & 0x00ff); 
	data[7] = (unsigned char)(pwm[0] & 0x00ff); 
 
	Txid = ((unsigned long)(ID_CMD_SET_TORQUE_1 + findex)<<6) | ((unsigned long)ID_COMMON <<3) | ((unsigned long)ID_DEVICE_MAIN); 
	canWrite(hCAN, Txid, data, 8, STD); 
}

Note: The joint index order used in the following code is for Allegro Hand versions 1.0 and down. For Allegro hand 2.0 or later, see the code snippet before this one.

// This joint index order is used Allegro Hand versions 1.0 and down.
if (findex >= 0 && findex < 4) 
{ 
	data[0] = (unsigned char)( (pwm[0] >> 8) & 0x00ff); 
	data[1] = (unsigned char)(pwm[0] & 0x00ff); 
 
	data[2] = (unsigned char)( (pwm[1] >> 8) & 0x00ff); 
	data[3] = (unsigned char)(pwm[1] & 0x00ff); 
 
	data[4] = (unsigned char)( (pwm[2] >> 8) & 0x00ff); 
	data[5] = (unsigned char)(pwm[2] & 0x00ff); 
 
	data[6] = (unsigned char)( (pwm[3] >> 8) & 0x00ff); 
	data[7] = (unsigned char)(pwm[3] & 0x00ff); 
 
	Txid = ((unsigned long)(ID_CMD_SET_TORQUE_1 + findex)<<6) | ((unsigned long)ID_COMMON <<3) | ((unsigned long)ID_DEVICE_MAIN); 
	canWrite(hCAN, Txid, data, 8, STD); 
}

Receiving Joint Angles

Each finger consists of four joints. The joint angles for those four joints can be received via one CAN packet. The sample code below demonstrates the method for decoding the data buffer and reading the joint angles.

The sample code assumes that when fingers are in their zero positions, the joint angles from the can packet are 32768. In practice, users should perform experiments and introduce offsets to obtain the zero position.

char cmd; 
char src; 
char des; 
int len; 
unsigned char data[8]; 
int ret; 
can_msg msg; 
PARAM_STRUCT param; 
 
ret = CANL2_read_ac(hCAN, &param); 
 
switch (ret) 
{ 
case CANL2_RA_DATAFRAME: 
	msg.msg_id = param.Ident; 
	msg.STD_EXT = STD; 
	msg.data_length = param.DataLength; 
 
	msg.data[0] = param.RCV_data[0]; 
	msg.data[1] = param.RCV_data[1]; 
	msg.data[2] = param.RCV_data[2]; 
	msg.data[3] = param.RCV_data[3]; 
	msg.data[4] = param.RCV_data[4]; 
	msg.data[5] = param.RCV_data[5]; 
	msg.data[6] = param.RCV_data[6]; 
	msg.data[7] = param.RCV_data[7]; 
 
	break; 
} 
 
cmd = (char)( (msg.msg_id >> 6) & 0x1f ); 
des = (char)( (msg.msg_id >> 3) & 0x07 ); 
src = (char)( msg.msg_id & 0x07 ); 
len = (int)( msg.data_length ); 
for(int nd=0; nd<len; nd++) 
	data[nd] = msg.data[nd]; 
 
switch (cmd) 
{ 
case ID_CMD_QUERY_CONTROL_DATA: 
	{
		if (id_src >= ID_DEVICE_SUB_01 && id_src <= ID_DEVICE_SUB_04) 
		{ 
			int temp_pos[4]; // raw angle data 
			float ang[4]; // degree 
			float q[4]; // radian 
 
			temp_pos[0] = (int)(data[0] | (data[1] << 8)); 
			temp_pos[1] = (int)(data[2] | (data[3] << 8)); 
			temp_pos[2] = (int)(data[4] | (data[5] << 8)); 
			temp_pos[3] = (int)(data[6] | (data[7] << 8)); 
 
			ang[0] = ((float)(temp_pos[0]-32768)*(333.3f/65536.0f))*(1); 
			ang[1] = ((float)(temp_pos[1]-32768)*(333.3f/65536.0f))*(1); 
			ang[2] = ((float)(temp_pos[2]-32768)*(333.3f/65536.0f))*(1); 
			ang[3] = ((float)(temp_pos[3]-32768)*(333.3f/65536.0f))*(1); 
 
			q[0] = (3.141592f/180.0f) * ang[0]; 
			q[1] = (3.141592f/180.0f) * ang[1]; 
			q[2] = (3.141592f/180.0f) * ang[2]; 
			q[3] = (3.141592f/180.0f) * ang[3]; 
		} 
	} 
 
}

Download

Allegro Hand CAN Protocol (English) ----------- This page.
Allegro Hand CAN Protocol (Korean)

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Allegro, the Allegro logo, RoboticsLab, the RoboticsLab logo, and all related files and documentation are Copyright ⓒ 2008-2020 Wonik Robotics Co., Ltd. All rights reserved. RoboticsLab and Allegro are trademarks of Wonik Robotics. All other trademarks or registered trademarks mentioned are the properties of their respective owners.

Wonik Robotics's Allegro Hand is based on licensed technology developed by the Humanoid Robot Hand research group at the Korea Institute of Industrial Technology (KITECH).

Any references to the BHand Library or the Allegro Hand Motion and/or Grasping Library refer to a library of humanoid robotic hand grasping algorithms and motions developed and published by KITECH researchers.
J.-H. Bae, S.-W. Park, D. Kim, M.-H. Baeg, and S.-R. Oh, "A Grasp Strategy with the Geometric Centroid of a Groped Object Shape Derived from Contact Spots," Proc. of the 2012 IEEE Int. Conf. on Robotics and Automation (ICRA2012), pp. 3798-3804

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