2. Allegro Hand Joint Position Control

Allegro Hand Controller Basis

In the last tutorial, we created a Visual Studio (VS) project with three files:

myAHController.cpp
myAHController.h
myAHControllerCmd.h

Goals:

Create sinusoidal fashion hand motion to run at the start of AHAS.

Hand and Joint Initialization

myAHController.cpp

In developing out controller for the Allegro Hand, lets start by initializing our hand and all of its devices. For now, we will focus on the function init(). The code below will first initialize the hand, then call a secondary function, _arrangeJointDevices(), to initialize all 16 of the motors and encoders for the hand. The initialize function will also make sure all arrays to store joint positions, velocities and torques are the length of the number of degrees of freedom (DOF) and set to zero (0) to start. The locations of the four (4) fingertips (x,y,z) are also set to zero when initialized.

Please, be careful when you copy and paste the following code.
There are skipped parts in the code.
You cannot copy and paste all at once.

...
 
myAHController::myAHController(rDC rdc) 
:rControlAlgorithmEx(rdc)
, _jdof(0)                              // everything is NULL to start
, _hand(NULL)
, _is_left_hand(false)
, _demo_mode(true)		  // will be used when
, _demo_start_time(0)	          // we make our own motion
{
}
 
...
 
void myAHController::init(int mode)
{
 
	// this property is read from the myAHController XDL file
	// to determine if the hand we are using will be the right or the left
	const TCHAR* prop = NULL;
	prop = getProperty(_T("whichHand"));
	// if using a right hand
	if (prop && _tcsicmp(prop, _T("right")) == 0)
	{
		_is_left_hand = false;		        // used to tell left from right
		_hand = bhCreateRightHand();	// create the right hand
	}
	// if using a left hand
	else
	{
		_is_left_hand = true;
		_hand = bhCreateLeftHand();	// create the left hand
	}
	assert(_hand);				// if hand was not created, abort
	_hand->SetTimeInterval(0.003);	// control period is set (333Hz)
 
	_jdof = JDOF;				// 16 DOF
 
	_arrangeJointDevices();		// finds all hand motors and encoders
 
	_q.resize(_jdof);			        // array (16) holds current joint positions
	_qdot.resize(_jdof);			// array (16) holds current joint velocities	
	_torque.resize(_jdof);			// array (16) holds current joint torques
 
	_q.zero();				        // all positions, vel and torque set to zero
	_qdot.zero();
	_torque.zero();
 
	_demo_q_des.resize(_jdof);		// desired joint positions
	_demo_q_des.zero();			// used to create motion sequences
 
	memset(_x, 0, sizeof(_x[0])*4);	// sets x, y and z position to (0,0,0)
	memset(_y, 0, sizeof(_y[0])*4);	// for all four fingers
	memset(_z, 0, sizeof(_z[0])*4);
 
}
 
...

As the function _arrangeJointDevices() is called during initialization, we must also fill in this function to find all of the motor and encoder devices on the hand. The names used to find these devices can be found in the Allegro Hand AML model file. The motors are stored and accessed via the _motor[] array and the encoders are stored and accessed via the _enc[] array.

...
 
void myAHController::_arrangeJointDevices()
{
	// _jdof is 16.
	for (int i=0; i<_jdof; i++)
	{
		// oversited array intialized for storing the device name string
		TCHAR devname[32];
 
		// find all 16 motors on hand (motor1, motor2, ..., motor16)
		_stprintf(devname, _T("motor%d"), i + 1);	// device name built and stored
		_motor[i] = findDevice(devname);		// device located
 
		// find all 16 encoders on hand (enc1, enc2, ..., enc16)
		_stprintf(devname, _T("enc%d"), i + 1);
		_enc[i] = findDevice(devname);
	}
 
}
 
...

Lastly, just in case a hand already exist when we try to make a controller, lets add a piece of code that will delete any hand that already exists before creating a new one.

...
 
myAHController::~myAHController()
{
	if (_hand)		// if there is already a hand,
		delete _hand;	// delete it before creating a new one
}
 
...

myAHController.h

We must now add all of the member variables and functions accessed to the class defined in the header file myAHController.h.

#ifndef __MY_AH_CONTROLLER_H__
#define __MY_AH_CONTROLLER_H__
 
#include <list>
#include "rControlAlgorithm/rControlAlgorithm.h"
#include "BHand/BHand.h"
 
#define JDOF	16
 
// myAHController inherited from algorithm interface class
class REXPORT myAHController : public rControlAlgorithmEx
{
public:
	myAHController(rDC rdc);
	~myAHController();
 
	virtual void init(int mode = 0);
	virtual void update(const rTime& t);
	virtual int  command(const short& cmd, const int& arg = 0);
 
private:
	virtual void _readDevices();
	virtual void _writeDevices();
 
	virtual void _compute(const rTime& t);
 
	void _arrangeJointDevices();
 
 
private:
 
	// algorithm variables go here
	rTime		_cur_time;	   // current time in controller
 
	BHand*		_hand;		   // Allegro Hand
	bool		_is_left_hand;	   // bool, left?
 
	rID		_motor[16];	   // motor array
	rID		_enc[16];	   // encoder array
 
	dVector		_q;		   // joint current position
	dVector		_qdot;		   // joint current velocity
	dVector		_torque;	   // joint torque
 
	int		_jdof;		   // degrees of freedom
 
	double		_x[4];		   // location of each (4) fingertips
	double		_y[4];		   // in x, y, and z
	double		_z[4];
 
	int		_demo_mode;	   // bool, used later as flag to envoke user control
	rTime		_demo_start_time;  // time at which the demo mode starts
	dVector		_demo_q_des;	   // desired position for position controller
 
};
 
#endif

Updating the Controller

Now that we have initialized all the joint devices, we can employ a simple joint controller. This joint controller employs PID control and is part of the BHand library.

myAHController.cpp

Before actually writing the joint commands, we must first set up the controller to read the joint positions for the encoder devices and write joint torque to the motor devices.

...
 
void myAHController::_readDevices()
{
	// all 16 encoder pos. values are read and stored in _q[]
	float val;
	for (int i=0; i<JDOF; i++)
	{
		if (_enc[i] != INVALID_RID)
		{
			readDeviceValue(_enc[i], &val, 4);
			_q[i] = (float)val;
		}
	}
}
 
void myAHController::_writeDevices()
{
	// all 16 motor _torque[] values are written to the motor device
	float val;
	for (int i=0; i<JDOF; i++)
	{
		val = (float)_torque[i];
		if (_motor[i] != INVALID_RID)
		{
			writeDeviceValue(_motor[i], &val, 4);
		}
	}
}
 
...

To cause these updates to happen periodically, we must update the controller each iteration to step through time.

Each time the controller is updated, it automatically calls the following functions in order:

_readDevices()
_estimate()
_reflect()
_compute()
_writeDevices()

...
 
void myAHController::update(const rTime& t)
{
	_cur_time = t;			// controller is updated every control period
	rControlAlgorithm::update(t);
}
 
...

Now compile and run the code.

Joint Position Control

We will now employ a simple algorithm to change the joint position with time in a sinusoidal fashion. This will be done using the BHand function SetJointDesiredPosition(double* q).

...
 
void myAHController::_compute(const double& t)
{
	if (_hand)
	{
		_hand->SetJointPosition(_q.array);			// joint positions send to Bhand
 
		if (true)
		{
			_hand->SetMotionType(eMotionType_JOINT_PD);     // PID gains and motion control set
 
			static float sin_speed = 0.3;
			static float sin_amp = 10;
 
			// this is the home position for the right hand
			static double q_home_left[NOF][NOJ] = {
				{  0*DEG2RAD,	-10*DEG2RAD,	45*DEG2RAD,	45*DEG2RAD},
				{  0*DEG2RAD,	-10*DEG2RAD,	45*DEG2RAD,	45*DEG2RAD},
				{ -5*DEG2RAD,	 -5*DEG2RAD,	50*DEG2RAD,	45*DEG2RAD},
				{ 50*DEG2RAD,	 25*DEG2RAD,	15*DEG2RAD,	45*DEG2RAD}
			};
 
			// this is the home position for the left hand
			static double q_home_right[NOF][NOJ] = {
				{  0*DEG2RAD,	-10*DEG2RAD,	45*DEG2RAD,	45*DEG2RAD},
				{  0*DEG2RAD,	-10*DEG2RAD,	45*DEG2RAD,	45*DEG2RAD},
				{  5*DEG2RAD,	 -5*DEG2RAD,	50*DEG2RAD,	45*DEG2RAD},
				{ 50*DEG2RAD,	 25*DEG2RAD,	15*DEG2RAD,	45*DEG2RAD}
			};
 
 
			_demo_q_des.zero();
 
			if (_is_left_hand)
			{
				double delQ = sin_amp*DEGREE*sin(2.0*M_PI*sin_speed*(_cur_time-_demo_start_time));
				for (int i=0; i<NOF; i++)		// for fingers 1 to 4
					for (int j=0; j<NOJ; j++)	// for joints 1 to 4
					{
						_demo_q_des[i*NOF+j] = q_home_left[i][j] + delQ;
					}
			}
			else
			{
				double delQ = sin_amp*DEGREE*sin(2.0*M_PI*sin_speed*(_cur_time-_demo_start_time));
				for (int i=0; i<NOF; i++) // 
					for (int j=0; j<NOJ; j++)
					{
						_demo_q_des[i*NOJ+j] = q_home_right[i][j] + delQ;
					}
			}
 
			// joint position is set using torque PID control
			_hand->SetJointDesiredPosition(_demo_q_des.array);
 
		}
 
		// controller is updated in BHand
		// current finger tip position, and torque are updated from BHand
		_hand->UpdateControl(t);
		_hand->GetFKResult(_x, _y, _z);
		_hand->GetJointTorque(_torque.array);
	}
}
 
...

Compile once again and run AHAS from the shortcut on your Desktop. You should now see every joint moving in a sinusoidal fashion.
You can see the result in this File:Allegro tutorial 2 result.zip.
If you can't see the same result as above, download this File:AllegroHandAppStudio bhand patch.zip, unzip and paste bin, lib and include folders into
C:\Program Files (x86)\SimLab\Allegro Hand Application Studio folder.

In the next tutorial, we will demonstrate how easy it is to try out this controller on your actual Allegro Hand.

3. Interfacing with the Actual Allegro Hand

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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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2. Allegro Hand Joint Position Control

Contents

Allegro Hand Controller Basis

Hand and Joint Initialization

myAHController.cpp

myAHController.h

Updating the Controller

myAHController.cpp

Joint Position Control