Programmable Stiffness Joint - Revision history

EricN: /* Stiffness Theory */

2008-12-12T04:42:54Z

Stiffness Theory

← Older revision		Revision as of 23:42, 11 December 2008
Line 93:		Line 93:
	The code is heavily commented and is intended to be used either stand-alone or in conjunction with the [[Rotational Stiffness]] page. The plots produced are internally formatted and ready for viewing upon running the code. The code computes and plots the location of the sliding insertion point on the rotating member relative to the stationary insertion point on the base. It also computes and plots the amount of spring stretch experienced for a given combination of rotation and insertion distance ratios, assuming that the spring is given slack so that the neutral angle is consistent at -20 degrees (or -pi/9 radians). Finally, it computes the amount of tension force actually being used to produce torque as well as the respective moment arm, and from that plots the amount of torque required to achieve the rotation at different insertion distance ratios.		The code is heavily commented and is intended to be used either stand-alone or in conjunction with the [[Rotational Stiffness]] page. The plots produced are internally formatted and ready for viewing upon running the code. The code computes and plots the location of the sliding insertion point on the rotating member relative to the stationary insertion point on the base. It also computes and plots the amount of spring stretch experienced for a given combination of rotation and insertion distance ratios, assuming that the spring is given slack so that the neutral angle is consistent at -20 degrees (or -pi/9 radians). Finally, it computes the amount of tension force actually being used to produce torque as well as the respective moment arm, and from that plots the amount of torque required to achieve the rotation at different insertion distance ratios.

	True rotational stiffness would be the incremental change in torque needed to produce a small change in angle, however the code does not ~~preform~~ this computation. From the plots, over the range of angles used for this application the torque vs angle curves are close to linear, and therefore we assumed a linear relationship for the sake of simplicity and ignored the differential stiffness. If the joint were to incorporate a larger range of motion or were to be required to maintain a specific stiffness, computing the actual stiffnesses over the range of angles and insertion distance ratios would be necessary, however this project did not require that.		True rotational stiffness would be the incremental change in torque needed to produce a small change in angle, however the code does not perform this computation. From the plots, over the range of angles used for this application the torque vs angle curves are close to linear, and therefore we assumed a linear relationship for the sake of simplicity and ignored the differential stiffness. If the joint were to incorporate a larger range of motion or were to be required to maintain a specific stiffness, computing the actual stiffnesses over the range of angles and insertion distance ratios would be necessary, however this project did not require that.

	==Mechanical Design==		==Mechanical Design==

JamesYeung: /* Electrical Design */

2008-03-24T12:44:01Z

Electrical Design

← Older revision		Revision as of 07:44, 24 March 2008
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	==Electrical Design==		==Electrical Design==

	[[Image:ProgStiffJointCircuit.jpg\|right\|Photo of circuit board\|thumb\|~~500px~~]]		[[Image:ProgStiffJointCircuit.jpg\|right\|Photo of circuit board\|thumb\|300px]]

	===Component List===		===Component List===

Lynch: /* Future Directions */

2008-03-23T21:31:58Z

Future Directions

← Older revision		Revision as of 16:31, 23 March 2008
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	The actual stiffness of the joint is not constant over the range of motion. For this limited range of motion, a linear approximation is valid, however more precise computations accounting for the non-linearity could be of use.		The actual stiffness of the joint is not constant over the range of motion. For this limited range of motion, a linear approximation is valid, however more precise computations accounting for the non-linearity could be of use.


	This device could be modified in design to incorporate more powerful motors to drive the slider faster and even possibly during loading to achieve a stiffness which can change during the gait cycle to adapt to conditions or simply better conform to natural gait kinetics.		This device could be modified in design to incorporate more powerful motors to drive the slider faster and even possibly during loading to achieve a stiffness which can change during the gait cycle to adapt to conditions or simply better conform to natural gait kinetics.


	Following this device with a model incorporating programmable damping would be another step toward differentiating between the elastic stiffness and damping properties of the ankle joint during walking.		Following this device with a model incorporating programmable damping would be another step toward differentiating between the elastic stiffness and damping properties of the ankle joint during walking.

EricNickel: /* MATLAB Code */

2008-03-21T17:07:51Z

MATLAB Code

← Older revision		Revision as of 12:07, 21 March 2008
Line 91:		Line 91:
	[[media:stiffnesstheory.m\|stiffnesstheory.m]]		[[media:stiffnesstheory.m\|stiffnesstheory.m]]

	The code is heavily commented and is intended to be used either stand-alone or in conjunction with the [[Rotational Stiffness]] page. The plots produced are internally formatted and ready for viewing upon running the code. The code computes and plots the location of the sliding insertion point on the rotating member relative to the stationary insertion point on the base. It also computes and plots the amount of spring stretch experienced for a given combination of rotation and insertion distance ratios, assuming that the spring is given slack so that the neutral angle is consistent. Finally, it computes the amount of tension force actually being used to produce torque as well as the respective moment arm, and from that plots the amount of torque required to achieve the rotation at different insertion distance ratios.		The code is heavily commented and is intended to be used either stand-alone or in conjunction with the [[Rotational Stiffness]] page. The plots produced are internally formatted and ready for viewing upon running the code. The code computes and plots the location of the sliding insertion point on the rotating member relative to the stationary insertion point on the base. It also computes and plots the amount of spring stretch experienced for a given combination of rotation and insertion distance ratios, assuming that the spring is given slack so that the neutral angle is consistent at -20 degrees (or -pi/9 radians). Finally, it computes the amount of tension force actually being used to produce torque as well as the respective moment arm, and from that plots the amount of torque required to achieve the rotation at different insertion distance ratios.

	True rotational stiffness would be the incremental change in torque needed to produce a small change in angle, however the code does not preform this computation. From the plots, over the range of angles used for this application the torque vs angle curves are close to linear, and therefore we assumed a linear relationship for the sake of simplicity and ignored the differential stiffness. If the joint were to incorporate a larger range of motion or were to be required to maintain a specific stiffness, computing the actual stiffnesses over the range of angles and insertion distance ratios would be necessary, however this project did not require that.		True rotational stiffness would be the incremental change in torque needed to produce a small change in angle, however the code does not preform this computation. From the plots, over the range of angles used for this application the torque vs angle curves are close to linear, and therefore we assumed a linear relationship for the sake of simplicity and ignored the differential stiffness. If the joint were to incorporate a larger range of motion or were to be required to maintain a specific stiffness, computing the actual stiffnesses over the range of angles and insertion distance ratios would be necessary, however this project did not require that.

EricNickel: /* Stiffness Theory */

2008-03-21T17:06:15Z

Stiffness Theory

← Older revision		Revision as of 12:06, 21 March 2008
Line 69:		Line 69:
	This all condenses into the following torque formula in terms of the variables from the conceptual diagram:		This all condenses into the following torque formula in terms of the variables from the conceptual diagram:

	~~<math>~~T = k * ( (L2cos(theta))^2 + (L1+L2sin(theta))^2 )^~~0.5~~ * sin(beta) * L2~~</math>~~		T = k * ( (L2cos(theta))^2 + (L1+L2sin(theta))^2 )^1/2 * sin(beta) * L2

	<math>beta = pi/2 - theta - arctan(h/a)</math>		<math>beta = pi/2 - theta - arctan(h/a)</math>

EricNickel: /* Stiffness Theory */

2008-03-21T17:05:50Z

Stiffness Theory

← Older revision		Revision as of 12:05, 21 March 2008
Line 69:		Line 69:
	This all condenses into the following torque formula in terms of the variables from the conceptual diagram:		This all condenses into the following torque formula in terms of the variables from the conceptual diagram:

	<math>T = k * ( (L2cos(theta))^2 + (L1+L2sin(theta))^2 )^~~1/2~~ * sin(beta) * L2</math>		<math>T = k * ( (L2cos(theta))^2 + (L1+L2sin(theta))^2 )^0.5 * sin(beta) * L2</math>

	<math>beta = pi/2 - theta - arctan(h/a)</math>		<math>beta = pi/2 - theta - arctan(h/a)</math>

EricNickel: /* Stiffness Theory */

2008-03-21T17:05:28Z

Stiffness Theory

← Older revision		Revision as of 12:05, 21 March 2008
Line 69:		Line 69:
	This all condenses into the following torque formula in terms of the variables from the conceptual diagram:		This all condenses into the following torque formula in terms of the variables from the conceptual diagram:

	<math>T = k * ( (L2cos(theta))^2 + (L1+L2sin(theta))^2 )^1^/^2 * sin(beta) * L2</math>		<math>T = k * ( (L2cos(theta))^2 + (L1+L2sin(theta))^2 )^1/2 * sin(beta) * L2</math>

	<math>beta = pi/2 - theta - arctan(h/a)</math>		<math>beta = pi/2 - theta - arctan(h/a)</math>

EricNickel: /* Stiffness Theory */

2008-03-21T17:04:47Z

Stiffness Theory

← Older revision		Revision as of 12:04, 21 March 2008
Line 69:		Line 69:
	This all condenses into the following torque formula in terms of the variables from the conceptual diagram:		This all condenses into the following torque formula in terms of the variables from the conceptual diagram:

	<math>T = k * ( (L2cos(theta))^2 + (L1+L2sin(theta))^2 )^(1/2) * sin(beta) * L2</math>		<math>T = k * ( (L2cos(theta))^2 + (L1+L2sin(theta))^2 )^1^/^2 * sin(beta) * L2</math>

	<math>beta = pi/2 - theta - arctan(h/a)</math>		<math>beta = pi/2 - theta - arctan(h/a)</math>

EricNickel: /* Stiffness Theory */

2008-03-21T17:04:15Z

Stiffness Theory

← Older revision		Revision as of 12:04, 21 March 2008
Line 69:		Line 69:
	This all condenses into the following torque formula in terms of the variables from the conceptual diagram:		This all condenses into the following torque formula in terms of the variables from the conceptual diagram:

	<math>T = k * ( (L2cos(theta))^2 + (L1+L2sin(theta))^2 )^1/2 * sin(beta) * L2</math>		<math>T = k * ( (L2cos(theta))^2 + (L1+L2sin(theta))^2 )^(1/2) * sin(beta) * L2</math>

	<math>beta = pi/2 - theta - arctan(h/a)</math>		<math>beta = pi/2 - theta - arctan(h/a)</math>

JamesYeung: /* Circuit Diagram */

2008-03-21T07:32:07Z

Circuit Diagram

← Older revision		Revision as of 02:32, 21 March 2008
Line 149:		Line 149:
	===Circuit Diagram===		===Circuit Diagram===

	Here's a detailed drawing of the circuit. The interface with the PIC microcontroller has been ignored but is more information about how to put one together is available [http://hades.mech.northwestern.edu/wiki/index.php/Main_Page#PIC_18F4520_prototyping_board here].		Here's a detailed drawing of the circuit. The interface with the PIC microcontroller has been ignored but more information about how to put one together is available [http://hades.mech.northwestern.edu/wiki/index.php/Main_Page#PIC_18F4520_prototyping_board here].
	<br>		<br>
	[[Image:SteelToeCircuit.gif\|Detailed drawing of circuit\|800px]] <br>		[[Image:SteelToeCircuit.gif\|Detailed drawing of circuit\|800px]] <br>