Lever Systems Research Articles

Кинематический анализ рычажных систем лесных и строительных манипуляторов

Кинематический анализ рычажных систем лесных и строительных манипуляторов

LEVERS AND LINKAGES: MECHANICAL TRADE-OFFS IN A POWER-AMPLIFIED SYSTEM

Mechanical redundancy within a biomechanical system (e.g., many-to-one mapping) allows morphologically divergent organisms to maintain equivalent mechanical outputs. However, most organisms depend on the integration of more than one biomechanical system. Here, we test whether coupled mechanical systems follow a pattern of amplification (mechanical changes are congruent and evolve toward the same functional extreme) or independence (mechanisms evolve independently). We examined the correlated evolution and evolutionary pathways of the coupled four-bar linkage and lever systems in mantis shrimp (Stomatopoda) ultrafast raptorial appendages. We examined models of character evolution in the framework of two divergent groups of stomatopods-"smashers" (hammer-shaped appendages) and "spearers" (bladed appendages). Smashers tended to evolve toward force amplification, whereas spearers evolved toward displacement amplification. These findings show that coupled biomechanical systems can evolve synergistically, thereby resulting in functional amplification rather than mechanical redundancy.

MUSCLE TRADE-OFFS IN A POWER-AMPLIFIED PREY CAPTURE SYSTEM

Should animals operating at great speeds and accelerations use fast or slow muscles? The answer hinges on a fundamental trade-off: muscles can be maximally fast or forceful, but not both. Direct lever systems offer a straightforward manifestation of this trade-off, yet the fastest organisms use power amplification, not direct lever action. Power-amplified systems typically use slow, forceful muscles to preload springs, which then rapidly release elastic potential energy to generate high speeds and accelerations. However, a fast response to a stimulus may necessitate fast spring-loading. Across 22 mantis shrimp species (Stomatopoda), this study examined how muscle anatomy correlates with spring mechanics and appendage type. We found that muscle force is maximized through physiological cross-sectional area, but not through sarcomere length. Sit-and-wait predators (spearers) had the shortest sarcomere lengths (fastest contractions) and the slowest strike speeds. The species that crush shells (smashers) had the fastest speeds, most forceful springs, and longest sarcomeres. The origin of the smasher clade yielded dazzlingly high accelerations, perhaps due to the release from fast spring-loading for evasive prey capture. This study offers a new window into the dynamics of force-speed trade-offs in muscles in the biomechanical, comparative evolutionary framework of power-amplified systems.

Musculoskeletal determinants of pelvic sucker function in hawaiian stream gobiid fishes: Interspecific comparisons and allometric scaling

Gobiid fishes possess a distinctive ventral sucker, formed from fusion of the pelvic fins. This sucker is used to adhere to a wide range of substrates including, in some species, the vertical cliffs of waterfalls that are climbed during upstream migrations. Previous studies of waterfall-climbing goby species have found that pressure differentials and adhesive forces generated by the sucker increase with positive allometry as fish grow in size, despite isometry or negative allometry of sucker area. To produce such scaling patterns for pressure differential and adhesive force, waterfall-climbing gobies might exhibit allometry for other muscular or skeletal components of the pelvic sucker that contribute to its adhesive function. In this study, we used anatomical dissections and modeling to evaluate the potential for allometric growth in the cross-sectional area, effective mechanical advantage (EMA), and force generating capacity of major protractor and retractor muscles of the pelvic sucker (m. protractor ischii and m. retractor ischii) that help to expand the sealed volume of the sucker to produce pressure differentials and adhesive force. We compared patterns for three Hawaiian gobiid species: a nonclimber (Stenogobius hawaiiensis), an ontogenetically limited climber (Awaous guamensis), and a proficient climber (Sicyopterus stimpsoni). Scaling patterns were relatively similar for all three species, typically exhibiting isometric or negatively allometric scaling for the muscles and lever systems examined. Although these scaling patterns do not help to explain the positive allometry of pressure differentials and adhesive force as climbing gobies grow, the best climber among the species we compared, S. stimpsoni, does exhibit the highest calculated estimates of EMA, muscular input force, and output force for pelvic sucker retraction at any body size, potentially facilitating its adhesive ability.

A compact nano manipulator based on an atomic force microscope coupling with a scanning electron microscope or an inverted optical microscope

In this paper, we describe a novel nano manipulator based on an atomic force microscope (AFM). The body of the manipulator is enough compact to be operated inside the sample chamber of a scanning electron microscope (SEM). In order to realize the compact body, we employed a self-detection type cantilever for AFM observation. The cantilever includes strain resistance element, which can easily detect a deflection signal of the cantilever without other sensing devices such as optical lever systems. It is possible to observe the manipulation situation in the real time observation by using the SEM. The AFM manipulator is coupled with a haptic device for human interface. Thus, by using this system, the operator can move the AFM probe at any position on the surface with feeling the interaction force detected by the cantilever on the sample surface according to the cantilever deflection. As a performance of the system, biological samples were controllably manipulated under the SEM observation. Furthermore, in order to deal with biological samples in liquid condition, the manipulator can be coupled with an inverted optical microscope. By using the system, we successfully demonstrated manipulation of biological samples in liquid condition. Two AFM manipulators could be used for dissection of biological samples like a knife and fork.

When Skeletons Are Geared for Speed: The Morphology, Biomechanics, and Energetics of Rapid Animal Motion

A skeleton amplifies the minute contractions of muscles to animate the body of an animal. The degree that a muscular contraction displaces an appendage is determined by the gearing provided by the joints of a skeleton. Species that move rapidly commonly possess joints with relatively high gears that produce a large output displacement. However, the speed of an appendage can depend on dynamics that obscure how this motion is influenced by the skeleton. The aim of this review is to resolve mechanical principles that govern the relationship between the gearing and speed of skeletal joints. Forward dynamic models of three rapid force-transmission systems were examined with simulations that varied the gearing of a joint. The leg of a locust, the raptorial appendage of a mantis shrimp, and the jaw of a toad are all driven by the conversion of stored elastic energy into kinetic energy. A locust achieves this conversion with high efficiency when it kicks and thereby applies nearly all stored energy into fast movement. This conversion is unaffected by differences in the leverage of the knee joint, as demonstrated by a maximum kicking speed that was found to be independent of gearing. In contrast, the mantis shrimp creates drag as it strikes toward a prey and thereby loses energy. As a consequence, high gears displace the raptorial appendage relatively far and yield slower motion than do low gears. The muscle that opens a toad's jaw also dissipates energy during ballistic capture of prey. This loss of energy is reduced when jaw opening occurs from the slower muscle contraction produced by a high gear within the jaw. Therefore, the speed of these lever systems is dictated by how gearing affects the efficiency of the conversion of potential energy into kinetic energy. In this way, the energetics of force transmission mediate the relationship between the gearing of a skeletal joint and the maximum speed of its motion.

There is no trade-off between speed and force in a dynamic lever system.

Lever systems within a skeleton transmit force with a capacity determined by the mechanical advantage, A. A is the distance from input force to a joint, divided by the distance from the joint to the output force. A lever with a relatively high A in static equilibrium has a great capacity to generate force but moves a load over a small distance. Therefore, the geometry of a skeletal lever presents a trade-off between force and speed under quasi-static conditions. The present study considers skeletal dynamics that do not assume static equilibrium by modelling kicking by a locust leg, which is powered by stored elastic energy. This model predicts that the output force of this lever is proportional to A, but its maximum speed is independent of A. Therefore, no trade-off between force and velocity exists in a lever system with spring-mass dynamics. This demonstrates that the motion of a skeleton depends on the major forces that govern its dynamics and cannot be inferred from skeletal geometry alone.

Running backwards: soft landing–hard takeoff, a less efficient rebound

Human running at low and intermediate speeds is characterized by a greater average force exerted after 'landing', when muscle-tendon units are stretched ('hard landing'), and a lower average force exerted before 'takeoff', when muscle-tendon units shorten ('soft takeoff'). This landing-takeoff asymmetry is consistent with the force-velocity relation of the 'motor' (i.e. with the basic property of muscle to resist stretching with a force greater than that developed during shortening), but it may also be due to the 'machine' (e.g. to the asymmetric lever system of the foot operating during stance). Hard landing and soft takeoff-never the reverse-were found in running, hopping and trotting animals using diverse lever systems, suggesting that the different machines evolved to comply with the basic force-velocity relation of the motor. Here we measure the mechanical energy of the centre of mass of the body in backward running, an exercise where the normal coupling between motor and machine is voluntarily disrupted, in order to see the relevance of the motor-machine interplay in human running. We find that the landing-takeoff asymmetry is reversed. The resulting 'soft landing' and 'hard takeoff' are associated with a reduced efficiency of positive work production. We conclude that the landing-takeoff asymmetry found in running, hopping and trotting is the expression of a convenient interplay between motor and machine. More metabolic energy must be spent in the opposite case when muscle is forced to work against its basic property (i.e. when it must exert a greater force during shortening and a lower force during stretching).

Comparative rates of lower jaw diversification in cichlid adaptive radiations

The lower jaw (LJ) provides an ideal trophic phenotype to compare rates and patterns of macroevolution among cichlid radiations. Using a novel phylogeny of four genes (ND2, dlx2, mitfb, and s7), we examined the evolutionary relationships among two of the most phylogenetically disparate cichlid radiations: (i) the Central America Heroines; and (ii) the East African Lake Malawi flock. To quantify jaw morphology, we measured two LJ lever systems in approximately 40 species from each lineage. Using geologic calibrations, we generated a chronogram for both groups and examined the rates of jaw evolution in the two radiations. The most rapidly evolving components of the LJ differed between the two radiations. However, the Lake Malawi flock exhibited a much faster rate of evolution in several components of the LJ. This rapid rate of divergence is consistent with natural selection, promoting unparalleled trophic diversification in Lake Malawi cichlids.

The bounce of the body in hopping, running and trotting: different machines with the same motor

The bouncing mechanism of human running is characterized by a shorter duration of the brake after ‘landing’ compared with a longer duration of the push before ‘takeoff’. This landing–takeoff asymmetry has been thought to be a consequence of the force–velocity relation of the muscle, resulting in a greater force exerted during stretching after landing and a lower force developed during shortening before takeoff. However, the asymmetric lever system of the human foot during stance may also be the cause. Here, we measure the landing–takeoff asymmetry in bouncing steps of running, hopping and trotting animals using diverse lever systems. We find that the duration of the push exceeds that of the brake in all the animals, indicating that the different lever systems comply with the basic property of muscle to resist stretching with a force greater than that developed during shortening. In addition, results show both the landing–takeoff asymmetry and the mass-specific vertical stiffness to be greater in small animals than in large animals. We suggest that the landing–takeoff asymmetry is an index of a lack of elasticity, which increases with increasing the role of muscle relative to that of tendon within muscle–tendon units.

Attitudes and opinions of railway signallers and related staff, using the Rail Ergonomics Questionnaire (REQUEST)

REQUEST, the Rail Ergonomics Questionnaire, has been designed to survey attitudes and opinions of railway signallers and those in associated roles on a range of human factors such as job satisfaction, the workplace, culture or stress. The development of the survey instrument has been described in Ryan et al. [2008. Developing a rail ergonomics questionnaire (REQUEST). Appl. Ergon., doi:10.1016/j.apergo.2008.04.006.]. The present paper presents an overview of findings from this national survey which achieved a sample size of 3889 and a response rate of 83%. Findings are compared by different roles (e.g. signaller, controller) on a range of main scales and responses to additional questions in the survey. Ratings from the largest of the occupational groups, the signaller at 83.1% of the overall population, have been compared according to different types of signalling system used, identifying different characteristics in the use of lever, panel and VDU signalling systems. Comparisons of signallers’ ratings by geographical location have produced findings of interest at different layers of management of the organisation, identifying locations with high or low ratings on a range of scales. The findings provide valuable information for the client organisation, using direct input from frontline staff on a range of human factors issues. This was a large survey, one of the largest ever civilian human factors surveys, involving lengthy, often repetitive and frequently complex analyses. Lessons learned within the administration of the survey, the analysis of the data and dissemination of the findings will be of interest to researchers. An overview of the scope of analyses of the database is introduced, in addition to proposals for further development of the survey instrument.

Optimal gear ratios of drives

One of the most complex problems in the design of practically any mechanism or machine is to select the gear ratio of an electric drive, on the basis of scientific, engineering, and economic principles. There is an extensive literature on this subject, dating mainly to the period from the 1940s to the 1960s. In current economic conditions, however, this problem is important, first, in connection with the need to find hidden reserves in existing technological equipment and, second, on account of the computerization of design systems (the availability of CAD systems) and the wide introduction of high-speed microprocessor control systems, which considerably increase production efficiency. In my view, information technologies and microprocessor control systems for electric drives, with elements of artificial intelligence and self-diagnostics, may soon permit the replacement (at least partial) of large, metalheavy, labor-intensive mechanical transmissions and gear systems. For example, the creation of microprocessor-based speed-adjustment systems and power (torque) converters seems possible even today. In addition, in real-time microprocessor control, the speed and dynamic parameters of the drive may be varied within certain limits, so as to operate as closely as possible to the optimal gear ratio or transfer function (the gear ratio as a function of the angle of rotation for lever systems). As a result, hidden reserves of the equipment may be implemented, with a perceptible economic benefit. In most research devoted to selecting the optimal gear ratio of a drive, the optimum is assumed to correspond to maximum speed of the executive mechanism or to minimum heat losses in the armature circuit of the independent-excitation dc motor, when the necessary displacement and processing time are specified. In the present work, we consider the search for the optimal gear ratio using Pontryagin’s maximum principle (from the mathematical theory of optimal processes) for both of these criteria and also for the case of minimum heat losses in the motor’s armature circuit [1]. The results obtained may be regarded to some extent as a generalization of existing research on optimal gear ratios.

Why chads? Determinants of voting equipment use in the United States

This paper provides an empirical study of the determinants of voting equipment choice in the United States. We document that, in contrast to widespread belief, voting machines of older types, such as lever and punchcard systems, are not used in counties with lower income – and newer machines, such as optical scanners and electronic machines, are not used in – richer counties. We provide an economic explanation for this and other regularities of voting equipment usage in the United States. In our economic framework (a) the adoption of a new technology is more likely in richer and larger counties, but (b) the adoption of a new technology is less likely the more advanced is the technology already adopted in the county. The adoption of more advanced optical and electronic machines in the 1980s and 1990s was less likely in richer and larger counties that had already mechanized and computerized in previous decades than in poorer and smaller – and hence not yet computerized counties. Estimates of historical determinants of voting equipment choice support our hypothesis. In particular, the probability of using punchcard machines in the 1990s is positively related to a county’s income in the 1960s, when punchcard machines were first introduced. When the effect of past income is controlled for, the effect of more recent levels of income on the probability of using punchcard machines becomes negative.

An Ergonomic Analysis of Scale-Pits

Much of the scale industry involves weighing large amounts of a product. The main method is the truck or railroad scale. These require pits to hold the lever systems necessary to weigh the truck or railroad car. However, these pits are designed with no thought for the safety of the technicians who maintain the scales. in this paper, four problems with current pit design were examined using data on the physical dimensions and the types of injuries possible. Three experiments were conducted to examine the risks of falling due to loss of balance, problems caused by moving around in the pit, and the effect of poor lighting. Using this data, suggestions are made to improve the safety of the scale pits for the technicians who work in them.

Morphological basis of kinematic diversity in feeding sunfishes

The effects of differences among species in the scaling of lower jaw levers on the scaling of prey-capture kinematics are explored in three species of centrarchid fishes. We consider the jaw opening and closing lever systems and calculate the consequences of differences in the scaling of the in-levers for the scaling of the time taken to open the mouth (T(o)) and the time taken to close the mouth (T(c)) during prey capture. Predictions of T(o) and T(c), based on differences in the scaling of jaw in-levers, are compared with the observed scaling of T(o) and T(c) in three centrarchid fishes. Video recordings (200 and 400 images s(-)(1)) were made of prey capture in largemouth bass Micropterus salmoides (33-206 mm standard length, SL), spotted sunfish Lepomis punctatus (24-145 mm SL) and bluegill sunfish Lepomis macrochirus (24-220 mm SL), and the fastest values of T(o) and T(c) were taken from the fastest recorded feeding event for each fish. The scaling exponents of T(o) and T(c) regressed on fish SL for largemouth bass were 0.592 and 0.572, respectively. Exponents observed for sunfishes were not significantly different from predicted values, based on scaling exponents in largemouth bass and interspecific differences in jaw lever proportions. Two conclusions are emphasized. First, between 25 and 220 mm SL, the time taken to open and close the mouth during the strike increases with body size in all three species, suggesting a general pattern for this family. Second, evolutionary changes in jaw lever mechanics are a major determinant of the diversity of prey-capture kinematics in this sample of centrarchid fishes.

Two basic mechanisms in insect wing folding

Detailed comparison of patterns of folding in insect wings has shown that all those which fold transversely can be referred to two basic mechanisms, each consisting of four panels rotating hingewise about four folding lines, intersecting at a single point. The mechanisms, which have one degree of freedom, are in effect lever systems, whose velocity ratios change non-linearly as they operate. They are designated as ‘Internal9 (INT) and ‘External’ (EXT), and further specified by a plus or minus sign, derived from the convex or concave orientation of the folding lines. There are hence four possible combinations: INT-, INT+, EXT- and EXT+. The two types are kinematically distinct. As INT unfolds, the effector panels move slowly at first and accelerate towards the end of the movement, whereas in EXT the effector panels move fast initially, then decelerate rapidly to their their final position. Furthermore INT operates reversibly, whereas EXT usually needs to be closed elastically, or by an extraneous force. The principles of the two mechanisms are applicable to many other folding structures.

Biomechanics of cranial kinesis in birds: Testing linkage models in the white-throated sparrow (Zonotrichia albicollis).

Cranial kinesis in sparrows refers to the rotation of the upper jaw around its kinetic joint with the braincase. Avian jaw mechanics may involve the coupled motions of upper and lower jaws, in which the postorbital ligament transfers forces from the lower jaw, through the quadrate, pterygoid, and jugal bones, to the upper jaw. Alternatively, jaw motions may be uncoupled, with the upper jaw moving independently of the lower jaw. We tested hypotheses of cranial kinesis through the use of quantitative computer models. We present a biomechanical model of avian jaw kinetics that predicts the motions of the jaws under assumptions of both a coupled and an uncoupled mechanism. In addition, the model predicts jaw motions under conditions of force transfer by either the jugal or the pterygoid bones. Thus four alternative models may be tested using the proposed model (coupled jugal, coupled pterygoid, uncoupled jugal, uncoupled pterygoid). All models are based on the mechanics of four-bar linkages and lever systems and use morphometric data on cranial structure as the basis for predicting cranial movements. Predictions of cranial motions are tested by comparison to kinematics of white-throated sparrows (Zonotrichia albicollis) during singing. The predicted relations between jaw motions for the coupled model are significantly different from video observations. We conclude that the upper and lower jaws are not coupled in white-throated sparrows. The range of jaw motions during song is consistent with a model in which independent contractions of upper and lower jaw muscles control beak motion. © 1996 Wiley-Liss, Inc.

Morphological constraints in the digging apparatus of pocket gophers (Mammalia: Geomyidae)

The digging apparatus of pocket gophers offers a unique opportunity to examine morphological constraints within a historical context because relationships among extant taxa are well resolved and the features enhancing digging performance are relatively well understood. Structural and functional considerations suggest that the muscles associated with tooth- and claw-digging in pocket gophers are subjected to contrasting levels of morphological constraints. To assess this hypothesis, we analysed the bones and muscles of the jaws and forelimbs in four genera comprising five species of pocket gophers. Morphometric analyses were performed on 12 osteological measurements selected to reflect overall skull size, variation in rostral shape and procumbency, differences in overall length of the forelimbs and processes relating to the function of lever systems used in claw-digging. In addition, dissections were made of the jaw, hyoid, neck and all of the forelimb muscles excluding the intrinsic muscles of the manus. Results of our morphometric analyses corroborate the recent suggestion that pocket gophers encompass a wide range of morphological variation extending from claw-diggers to tooth-diggers. Myologically, however, we found structural variation only in the forelimb muscles, some of which may be advantageous for digging. No changes in jaw, neck and hyoid muscles, other than differences in muscle mass or those concordant with differences in rostral shape, were noted. These results support our hypothesis that constrasting levels of morphological constraint exist between the jaw and forelimb muscles of pocket gophers. We present a discussion of the structural and functional constraints on jaws and forelimbs in gophers as well as an analysis of historical constraints acting on this group, and perhaps on mammals in general.

Force-Velocity Relationship of Human Elbow Flexors in Voluntary Isotonic Contraction under Heavy Loads

The force-velocity relationships of the human elbow flexors as one muscle in maximal voluntary contraction were determined using isotonic lever systems for seven men (19-38 yrs). The external loads used for the contraction weighed 0%, 20%, 40% 60%, 80% and 90% of maximum voluntary isometric force (Fo). The force and velocity were determined at an elbow angle of 90 degrees. The effect of the inertia of the forearm on the force was corrected using the angular acceleration of the forearm during an elbow flexion. The effect of muscular fatigue on the velocity during an elbow flexion was minimized by adjusting the initial elbow angle at the onset of the elbow flexion to the size of the load and reducing the time duration of the elbow flexion with a heavy load. Hill equation fitted fairly well to the force-velocity data observed in the experiments up to 90% Fo. The maximum isometric force predicted using Hill equation was larger by 6% (mean) than that observed in the experiments.

Adduction Levers And Adductor Muscle Function in the Mandibular System of the Shore Crab Carcinus Maenas

ABSTRACT The lever systems, and structure and function of the adductor muscles, of the mandibles of large male Carcinus maenas (L.) were investigated. The functional mechanical advantage (FMA) of the external adductor muscles, measured at the middle of the biting edge of the mandible, was 1·53 ± 0·01; the ideal mechanical advantage (IMA), calculated from measured lever lengths, was 1·78 ± 0·03 (mean ± S.E.). The FMA of the internal adductor muscles was 0·53 ± 0·01 and the IMA was 0·62 ±0·02 When slowly loaded, the external adductor system broke at 3·09 ± 0·16 N; when rapidly loaded, the system broke at 7·16 ± 0·79 N. Short duration loading at 2·0 N or more was found to result in histologically detectable damage at the pivot. When slowly loaded, the internal adductor system broke at 0·68 ± 0·05 N. When a load of 0·39 N was applied to the internal adductor system, the failure point on slow loading of the external adductor system was not significantly increased. The mean maximum force of contraction of the external adductor muscles on electrical stimulation was 0·98 ± 0·03 N, with a stress of 627 kN m-2 in the fibres. The internal adductors contracted with a mean maximum force of 0·33 ± 0·01 N. The total maximum bite force is therefore about 3·3 N, only 10% being contributed by the internal adductors. The safety factor of both internal and external systems is about 2. The mean sarcomere length of half-contracted fibres of the external adductor muscles was 11· 62 ± 0·11 μm.