John E. Speich

A Well-Behaved Revolute Flexure Joint for Compliant Mechanism Design

This paper describes the design of a unique revolute flexure joint, called a split-tube flexure, that enables (lumped compliance) compliant mechanism design with a considerably larger range-of-motion than a conventional thin beam flexure, and additionally provides significantly better multi-axis revolute joint characteristics. Conventional flexure joints utilize bending as the primary mechanism of deformation. In contrast, the split-tube flexure joint incorporates torsion as the primary mode of deformation, and contrasts the torsional properties of a thin-walled open-section member with the bending properties of that member to obtain desirable joint behavior. The development of this joint enables the development of compliant mechanisms that are quite compliant along kinematic axes, extremely stiff along structural axes, and are capable of kinematically well-behaved large motions.

Transparency and Stability Robustness in Two-Channel Bilateral Telemanipulation

This paper presents a two-channel architecture and design approach that enables a simultaneous increase in the transparency and stability robustness of a bilateral teleoperation system, and additionally provides a high degree of transparency robustness to uncertainty in the operator and environment dynamics. The former is provided by the use of a loop-shaping filter incorporated on the master-to-slave motion command, and the latter by local feedback loops around both the master and slave manipulators. The proposed architecture and design approach are illustrated on a single-degree-of-freedom example with and without a communication channel time delay. Finally, the implications of scaling on the stability of the teleoperator loop are discussed. @DOI: 10.1115/1.1387018#

A compliant-mechanism-based three degree-of-freedom manipulator for small-scale manipulation

This paper describes the design of a small-scale three degree-of-freedom compliant-mechanism-based manipulator with an approximately 2 cm×2 cm×2 cm cubic workspace. The manipulator exhibits a significantly larger range of motion and better spatial structural properties than a conventional compliant mechanism, due primarily to a unique flexure joint developed by the authors. A brief description of the mechanics of the flexure joint is followed by a description of the design of the manipulator. Following the mechanical description, the design of the low-level manipulator controller is discussed. Finally, data is presented that demonstrates manipulator performance.

Low-Cost IR Reflective Sensors for Submicrolevel Position Measurement and Control

This paper investigates the feasibility of using commercially available, low-cost IR reflective sensors for micro- to sub- microscale position measurement and control. These sensors are typically used as optical switches; however, their application for detecting fine motion, such as the movement of a piezoactuator, has not been investigated. Five IR sensors were evaluated to determine their range, resolution, linear distortion, noise characteristics, and bandwidth. Experimental results show that the performance of the IR sensors compares well with a commercial inductive sensor that costs significantly more. For example, the measured resolution was within several hundred nanometers over a plusmn200 mum range and the linear distortion was significantly lower than the inductive sensor. A selected IR sensor was used in the design of a state-feedback control system to compensate for hysteresis and creep in an experimental piezopositioner. Compared to the open-loop system, by using the IR sensor in feedback, the output hysteresis was reduced by over 95 %. These results show the potential of such sensors in the design of low-cost microprecision mechatronic positioning systems.

Adaptation of the length-active tension relationship in rabbit detrusor

Studies have shown that the length-tension (L-T) relationships in airway and vascular smooth muscles are dynamic and can adapt to length changes over a period of time. Our prior studies have shown that the passive L-T relationship in rabbit detrusor smooth muscle (DSM) is also dynamic and that DSM exhibits adjustable passive stiffness (APS) characterized by a passive L-T curve that can shift along the length axis as a function of strain history and activation history. The present study demonstrates that the active L-T curve for DSM is also dynamic and that the peak active tension produced at a particular muscle length is a function of both strain and activation history. More specifically, this study reveals that the active L-T relationship, or curve, does not have a unique peak tension value with a single ascending and descending limb, but instead reveals that multiple ascending and descending limbs can be exhibited in the same DSM strip. This study also demonstrates that for DSM strips not stretched far enough to reveal a descending limb, the peak active tension produced by a maximal KCl-induced contraction at a short, passively slack muscle length of 3 mm was reduced by 58.6 +/- 4.1% (n = 15) following stretches to and contractions at threefold the original muscle length, 9 mm. Moreover, five subsequent contractions at the short muscle length displayed increasingly greater tension; active tension produced by the sixth contraction was 91.5 +/- 9.1% of that produced by the prestretch contraction at that length. Together, these findings indicate for the first time that DSM exhibits length adaptation, similar to vascular and airway smooth muscles. In addition, our findings demonstrate that preconditioning, APS and adaptation of the active L-T curve can each impact the maximum total tension observed at a particular DSM length.

Stimulated calcium entry and constitutive RhoA kinase activity cause stretch-induced detrusor contraction.

Urinary bladder wall muscle (i.e., detrusor smooth muscle; DSM) contracts in response to a quick-stretch, but this response is neither fully characterized, nor completely understood at the subcellular level. Strips of rabbit DSM were quick-stretched (5 ms) and held isometric for 10 s to measure the resulting peak quick-stretch contractile response (PQSR). The ability of selective Ca(2+) channel blockers and kinase inhibitors to alter the PQSR was measured, and the phosphorylation levels of myosin light chain (MLC) and myosin phosphatase targeting regulatory subunit (MYPT1) were recorded. DSM responded to a quick-stretch with a biphasic response consisting of an initial contraction peaking at 0.24+/-0.02-fold the maximum KCl-induced contraction (F(o)) by 1.48+/-0.17 s (PQSR) before falling to a weaker tonic (10 s) level (0.12+/-0.03-fold F(o)). The PQSR was dependent on the rate and degree of muscle stretch, displayed a refractory period, and was converted to a sustained response in the presence of muscarinic receptor stimulation. The PQSR was inhibited by nifedipine, 2-aminoethoxydiphenyl borate (2-APB), 100 microM gadolinium and Y-27632, but not by atropine, 10 microM gadolinium, LOE-908, cyclopiazonic acid, or GF-109203X. Y-27632 and nifedipine abolished the increase in MLC phosphorylation induced by a quick-stretch. Y-27632, but not nifedipine, inhibited basal MYPT1 phosphorylation, and a quick-stretch failed to increase phosphorylation of this rhoA kinase (ROCK) substrate above the basal level. These data support the hypothesis that constitutive ROCK activity is required for a quick-stretch to activate Ca(2+) entry and cause a myogenic contraction of DSM.

Evidence that actomyosin cross bridges contribute to "passive" tension in detrusor smooth muscle.

Contraction of detrusor smooth muscle (DSM) at short muscle lengths generates a stiffness component we termed adjustable passive stiffness (APS) that is retained in tissues incubated in a Ca(2+)-free solution, shifts the DSM length-passive tension curve up and to the left, and is softened by muscle strain and release (strain softened). In the present study, we tested the hypothesis that APS is due to slowly cycling actomyosin cross bridges. APS and active tension produced by the stimulus, KCl, displayed similar length dependencies with identical optimum length values. The myosin II inhibitor blebbistatin relaxed active tension maintained during a KCl-induced contraction and the passive tension maintained during stress-relaxation induced by muscle stretch in a Ca(2+)-free solution. Passive tension was attributed to tension maintaining rather than tension developing cross bridges because tension did not recover after a rapid 10% stretch and release as it did during a KCl-induced contraction. APS generated by a KCl-induced contraction in intact tissues was preserved in tissues permeabilized with Triton X-100. Blebbistatin and the actin polymerization inhibitor latrunculin-B reduced the degree of APS generated by a KCl-induced contraction. The degree of APS generated by KCl was inhibited to a greater degree than was the peak KCl-induced tension by rhoA kinase and cyclooxygenase inhibitors. These data support the hypothesis that APS is due to slowly cycling actomyosin cross bridges and suggest that cross bridges may play a novel role in DSM that uniquely serves to ensure proper contractile function over an extreme working length range.

A method for simultaneously increasing transparency and stability robustness in bilateral telemanipulation

Describes a design technique for simultaneously increasing the transparency bandwidth and stability robustness of a two-channel position-force bilateral teleoperation architecture. Specifically, the stability and performance enhancements are obtained by introducing a dynamic compensator into the system to shape the frequency-domain properties of the human-teleoperator-environment loop. This design technique is demonstrated in a single degree-of-freedom numerical example.

An implementation of loop-shaping compensation for multidegree-of-freedom macro-microscaled telemanipulation

This brief describes the implementation of a telemanipulation control architecture on a three degree-of-freedom (3-DOF) scaled master-slave telemanipulation system. Specifically, feedback linearization enables the use of loop-shaping compensators to increase the transparency bandwidth of a 3-DOF macro-micro telemanipulator pair, while the stability robustness of the system is maintained. Experimental results contrast the transparency and stability robustness of the compensated with the uncompensated system. The enhanced performance of the former demonstrates the utility of the approach.

Active tension adaptation at a shortened arterial muscle length: inhibition by cytochalasin-D

Unlike the static length-tension curve of striated muscle, airway and urinary bladder smooth muscles display a dynamic length-tension curve. Much less is known about the plasticity of the length-tension curve of vascular smooth muscle. The present study demonstrates that there were significant increases of ∼15% in the phasic phase and ∼10% in the tonic phase of a third KCl-induced contraction of a rabbit femoral artery ring relative to the first contraction after a 20% decrease in length from an optimal muscle length (L(0)) to 0.8-fold L(0). Typically, three repeated contractions were necessary for full length adaptation to occur. The tonic phase of a third KCl-induced contraction was increased by ∼50% after the release of tissues from 1.25-fold to 0.75-fold L(o). The mechanism for this phenomenon did not appear to lie in thick filament regulation because there was no increase in myosin light chain (MLC) phosphorylation to support the increase in tension nor was length adaptation abolished when Ca(2+) entry was limited by nifedipine and when Rho kinase (ROCK) was blocked by H-1152. However, length adaptation of both the phasic and tonic phases was abolished when actin polymerization was inhibited through blockade of the plus end of actin by cytochalasin-D. Interestingly, inhibition of actin polymerization when G-actin monomers were sequestered by latrunculin-B increased the phasic phase and had no effect on the tonic phase of contraction during length adaptation. These data suggest that for a given level of cytosolic free Ca(2+), active tension in the femoral artery can be sensitized not only by regulation of MLC phosphatase via ROCK and protein kinase C, as has been reported by others, but also by a nonmyosin regulatory mechanism involving actin polymerization. Dysregulation of this form of active tension modulation may provide insight into alterations of large artery stiffness in hypertension.