Monthly Archives: August 2013

Moving beyond PoC

Switched out the old, glued together stack of sensors for a set of c-section parts that allow pressure on the sensor to be independent of the speaker. They keep falling off though.

Trying now with more glue and cure time. I also need to get some double-stick tape.

More glue worked!

Modified the code so that multiple targets can exist and experimented with turning forces off.

Proof of concept!

For the first time, all the important pieces are working together.

I added force interaction between gripper and target sphere, then determined how to make the ratio calculation work. If the sum of all of the magnitudes on the target is greater than zero, then the ratio equals the magnitude of the sum of the force vectors divided by the sum of each magnitude. A value of 1.0 means that there is no contact. A value of 0.0 is a perfectly opposing contact. As currently implemented, if the ratio is less than 0.5, then the position of the target sphere is set to the point that lies between the two grippers, otherwise the (summed) contact force vector is applied to the target.

After firing up the sim and trying it, the sense of “capture” works well and is intuitive. 

  • Need to add walls around the work environment so that the targets can’t get out of reach.
  • Need to add the metal standoffs for the speakers. I was thinking about ordering some box tubing, but the sizes weren’t optimal. I’ll bend up some metal tonight.
  • Need to start adding in the code that will support the experiments
    • Task code
    • Feedback options
      • Position and pressure only
      • Position, force feedback and pressure
      • Position, pressure and vibration
      • Position, force feedback, pressure and vibration.
  • I also need to extend the audio feedback so that arbitrary speakers can be used and positioned without adhering to Dolby positioning rules. I’ll get back to that after getting the metal speaker supports attached to the interface.

Here’s the code that matters. First, the haptic code, then the sim code. In both cases, simToPhantom and phantomToSim are the structs that are used by the shared memory system:

HDCallbackCode BaseGeometryPatch::patchCalc(){
	HDErrorInfo error;
	hduVector3Dd forceVec;
	hduVector3Dd targForceVec;
	hduVector3Dd loopForceVec;
	hduVector3Dd patchMinusDeviceVec;
	hduVector3Dd sensorVec;
	double sensorRadius = 1.0;

	if(simToPhantom == NULL){

	HHD hHD = hdGetCurrentDevice();

	/* Begin haptics frame.  ( In general, all state-related haptics calls
		should be made within a frame. ) */

	/* Get the current devicePos of the device. */
	hdGetDoublev(HD_CURRENT_POSITION, devicePos);
	hdGetDoublev(HD_CURRENT_GIMBAL_ANGLES, deviceAngle);
	hdGetDoublev(HD_CURRENT_TRANSFORM, transformMat);

	forceVec[0] = 0;
	forceVec[1] = 0;
	forceVec[2] = 0;

	for(int targi = 0; targi < SimToPhantom::NUM_TARGETS; ++targi){
		patchPos[0] = simToPhantom->targetX[targi];
		patchPos[1] = simToPhantom->targetY[targi];
		patchPos[2] = simToPhantom->targetZ[targi];
		patchRadius = simToPhantom->targetRadius[targi];

		targForceVec[0] = 0;
		targForceVec[1] = 0;
		targForceVec[2] = 0;
		for(int sensi = 0; sensi < SimToPhantom::NUM_SENSORS; ++sensi){
			loopForceVec[0] = 0;
			loopForceVec[1] = 0;
			loopForceVec[2] = 0;

			sensorRadius = simToPhantom->sensorRadius[sensi];
			sensorVec[0] = simToPhantom->sensorX[sensi] + devicePos[0];
			sensorVec[1] = simToPhantom->sensorY[sensi] + devicePos[1];
			sensorVec[2] = simToPhantom->sensorZ[sensi] + devicePos[2];
			sensorRadius = simToPhantom->sensorRadius[sensi];

			if(sensorVec[0] == 0.0){

			/* >  patchMinusDeviceVec = patchPos-devicePos  < 
				Create a vector from the device devicePos towards the sphere's center. */
			//hduVecSubtract(patchMinusDeviceVec, patchPos, devicePos);
			hduVecSubtract(patchMinusDeviceVec, patchPos, sensorVec);
			hduVector3Dd dirVec;
			hduVecNormalize(dirVec, patchMinusDeviceVec);

			/* If the device position is within the sphere's surface
				center, apply a spring forceVec towards the surface.  The forceVec
				calculation differs from a traditional gravitational body in that the
				closer the device is to the center, the less forceVec the well exerts;
				the device behaves as if a spring were connected between itself and
				the well's center. */
			double penetrationDist = patchMinusDeviceVec.magnitude() - (patchRadius+sensorRadius);
			if(penetrationDist < 0)
				/* >  F = k * x  < 
					F: forceVec in Newtons (N)
					k: Stiffness of the well (N/mm)
					x: Vector from the device endpoint devicePos to the center 
					of the well. */
				hduVecScale(dirVec, dirVec, penetrationDist);
				hduVecScale(loopForceVec, dirVec, stiffnessK);

			if(phantomToSim != NULL){
				phantomToSim->forceMagnitude[sensi] = hduVecMagnitude(loopForceVec);
				phantomToSim->forceVec[sensi][0] = loopForceVec[0];
				phantomToSim->forceVec[sensi][1] = loopForceVec[1];
				phantomToSim->forceVec[sensi][2] = loopForceVec[2];

				phantomToSim->targForceMagnitude[targi][sensi] = hduVecMagnitude(loopForceVec);
				phantomToSim->targForceVec[targi][sensi][0] = loopForceVec[0];
				phantomToSim->targForceVec[targi][sensi][1] = loopForceVec[1];
				phantomToSim->targForceVec[targi][sensi][2] = loopForceVec[2];
			hduVecAdd(forceVec, forceVec, loopForceVec);
			hduVecAdd(targForceVec, targForceVec, loopForceVec);
		if(phantomToSim != NULL){
			phantomToSim->targForcesMagnitude[targi] = hduVecMagnitude(targForceVec);

	// divide the forceVec the number of times that a force was added?

	/* Send the forceVec to the device. */
	hdSetDoublev(HD_CURRENT_FORCE, forceVec);

	/* End haptics frame. */

	/* Check for errors and abort the callback if a scheduler error
	   is detected. */
	if (HD_DEVICE_ERROR(error = hdGetError()))
		hduPrintError(stderr, &error, "BaseGeometryPatch.calcPatch():\n");

		if (hduIsSchedulerError(&error))

	if(phantomToSim != NULL){
		for(int i = 0; i < 16; ++i){
			phantomToSim->matrix[i] = transformMat[i];

	/* Signify that the callback should continue running, i.e. that
	   it will be called again the next scheduler tick. */

Next, the Sim code:

void TargetSphere::environmentCalc(){

	double forces = phantomToSim->targForcesMagnitude[targIndex];
	double sumVec[3];
	double sumMag = 0;
	for(int i = 0; i < 3; ++i){
		constraintAnchorPos[i] = 0;
		sumVec[i] = 0;
	for(int i = 0; i < SimToPhantom::NUM_SENSORS; ++i){
		constraintAnchorPos[0] += sensorPos[i][0];
		constraintAnchorPos[1] += sensorPos[i][1];
		constraintAnchorPos[2] += sensorPos[i][2];

		double force = phantomToSim->targForceMagnitude[targIndex][i];
		sumMag += force;
		double forceVec[3];
		forceVec[0] = phantomToSim->targForceVec[targIndex][i][0];
		forceVec[1] = phantomToSim->targForceVec[targIndex][i][1];
		forceVec[2] = phantomToSim->targForceVec[targIndex][i][2];
		sumVec[0] += forceVec[0];
		sumVec[1] += forceVec[1];
		sumVec[2] += forceVec[2];

		//Dprint::add("targ[%d] sens[%d] forceVec = (%.2f., %.2f, %.2f) force = %.2f, forces = %.2f",
		//	targIndex, i, forceVec[0], forceVec[1], forceVec[2], force, forces);

	constraintAnchorPos[0] = constraintAnchorPos[0]/SimToPhantom::NUM_SENSORS;
	constraintAnchorPos[1] = constraintAnchorPos[1]/SimToPhantom::NUM_SENSORS;
	constraintAnchorPos[2] = constraintAnchorPos[2]/SimToPhantom::NUM_SENSORS;

	//double mag = m3dGetMagnitude3(sumVec);
	//Dprint::add("sumVec (%.2f., %.2f, %.2f) Mag = %.2f, sumForce = %.2f", sumVec[0], sumVec[1], sumVec[2], mag, forces);
	double ratio = 1.0;
	if(sumMag >0){
		ratio = forces/sumMag;
		if(ratio > 0.5){
			double velocityScalar = 1.0; // should be time-based
			for(int i = 0; i < 3; ++i){
				velocityVec[i] += (-sumVec[i])*velocityScalar;
				position[i] += velocityVec[i];
				if(velocityVec[i] > 0.1){
					velocityVec[i] -= 0.1;
					velocityVec[i] = 0;
			for(int i = 0; i < 3; ++i){
				velocityVec[i] = 0;
				position[i] = constraintAnchorPos[i];
	Dprint::add("sumMag = %.2f, sumForce = %.2f, ratio = %.2f", sumMag, forces, ratio);


And yet more…

Got the wiring cleaned up.

Integrating collision response with the targetSphere. The math is looking reasonably good.

Added multi-target capability.

Added adjustable sensitivity to the pressure sensors. The pushing directly on the speakers is causing artifacts. I think I need to build small c-section angle that decouples the squeezing force from the Vibroacoustic feedback.

More refining.

Working on constraint code. Got the framework done, but didn’t have enough sleep to be able to do the math involved. So instead I…

Got the actuators mounted on the Phantom! Aside from having one of the force sensors break during mounting, it went pretty smoothly. I may have to adjust the sensitivity of teh sensors so that you don’t have to press so hard on them. At the current setting the voice coils aren’t behaving at higher grip forces. But the ergonomics feel pretty good, so that’s nice.


What you get when you combine FLTK, OpenGL, DirectX, OpenHaptics and shared memory

Wow, the title sounds like a laundry list 🙂

Building a two-fingered gripper

Going to add sound class to SimpleSphere so that we know what sounds are coming from what collision. Didn’t do that’ but I’m associating the sounds by index, which is good enough for now

Need to calculate individual forces for each sphere in the Phantom and return them. Done.

To keep the oscillations at a minimum, I’m passing the offsets from the origin. That way the loop uses the device position as the basis for calculations within the haptic loop.
Here’s the result of today’s work:

Flailing, but productive flailing.

Basically spent the whole day figuring out how the 4×4 phantom matrix equates to the rendering matrix (I would have said OpenGL, but that’s not true anymore. I am using the lovely math libraries from the OpenGL SuperBible 5th Edition, which makes it kinda look like the OGL of Yore.

Initially I thought I’d just use the vector components of the rotation 3×3 from the Phantom to get the orientation of the tip, but for some reason, parts of the matrix appear inverted. So instead of using them directly, I multiply the modelviewmatrix by the phantom matrix, Amazingly, this works perfectly.

To make sure that this works, I rendered a sphere at the +X, +Y and +Z axis in the local coordinate frame. Everything tracks. So now I can create my gripper class and get the positions of the end effectors from the class. And since the position is in the global coordinate frame, it kind of comes along for free.

Here’s a picture of everything working:
Tomorrow, I’ll build the gripper class and start feeding that to the Phantom. The issue will be to sum the force vectors from all the end effectors in a reasonable way.

Some Assembly Required

Integrating all the pieces into one test platform. The test could be to move a collection of physically-based spheres (easy collision detect) from one area to another. Time would be recorded from the indication of a start and stop (spacebar, something in the sim, etc). Variations would be:

  • Open loop: Measure position and pressure, but no feedback
  • Force Feedback (Phantom) only
  • Vibrotactile feedback only
  • Both feedbacks

Probably only use two actuators for the simplicity of the test rig. It would bean that I could use the laptop’s headphone output. Need to test this by wiring up the actuators to a micro stereo plug. Radio Shack tonight.

Got two-way communication running between Phantom and sim.

Have force magnitude adjusting a volume.

Added a SimpleSphere class for most of the testing.