Rubber Hammer Research Articles

Resonant frequencies of multi-layer building constructions: Estimation by measurement of acceleration amplitudes

The Austrian building regulation requirements for impact sound insulation are based on the weighted standardized impact sound pressure level as single-number specification. In recent years, it has become apparent that not only the single-number specification, but the extended frequency range and frequency characteristics of impact sound insulation of constructions can have noticeable influence on the perceived acoustic performance of a construction. Therefore, the Austrian Classification Standard ÖNORM B 8115-5: 2021-04 includes extended requirements on impact sound insulation. It provides two ways for verification of the sound insulation classes A to C. One way is the verification via the resonance frequency of multi-layer constructions. However, there exist as yet no standardized measurement methods for the estimation of the resonance frequency of multi-layer building constructions. In response, in course of this study a new measurement method for the estimation of the resonance frequencies of multi-layer constructions was developed. For this development acceleration measurements were carried out on both surfaces of particularly double-layer building constructions, that were excited with a rubber hammer. From these measurement results, in conjunction with an analytical model, it was possible to derive a measurement method for estimating the resonant frequency via the frequency characteristics of the acceleration amplitudes.

Feasibility of using a vibrating machine for laying ceramic tiles

Inadequate practices are still present in the day-to-day of the works when performing the ceramic tile laying service. The coating laying machine comes as a proposal to improve the execution process of this service, guaranteeing higher quality. The general objective of this work is to verify the quality of the ceramic tile laying service using a vibrating laying machine. Eight pieces of porcelain tiles measuring 60x120 cm were laid in order to verify the differences in the quality of laying the pieces using the vibrating machine and the rubber hammer. The quality was verified following two requirements, mortar compaction and the adherence resistance of the pieces. The use of a vibrating machine for installing ceramic tiles improves the quality of the service, as well as makes its application viable in laying coatings. The mortar compaction was better in the pieces settled using the vibrating machine. Adherence to the pieces laid using the vibrating machine was, on average, twice that stipulated by the regulatory standard, whether using one or two layers of mortar. It is noteworthy that there were no cases of rejected values. The use of the vibrating machine proved to be high compared to the traditional laying method, which makes it legitimate to lay pieces with surface area dimensions greater than 900 cm², using only a single layer of mortar. Adherence to the pieces laid using the vibrating machine was, on average, twice that stipulated by the regulatory standard, whether using one or two layers of mortar. It is noteworthy that there were no cases of rejected values. The use of the vibrating machine proved to be high compared to the traditional laying method, which makes it legitimate to lay pieces with surface area dimensions greater than 900 cm², using only a single layer of mortar. Adherence to the pieces laid using the vibrating machine was, on average, twice that stipulated by the regulatory standard, whether using one or two layers of mortar. It is noteworthy that there were no cases of rejected values. The use of a vibrating machine proved to be high compared to the traditional laying method, which makes it legitimate to lay pieces with surface area dimensions greater than 900 cm², using only a single layer of mortar.

Design of Amplifier Circuit of Optical Fiber Sensor and Its Application in Cloud Computing of Mechanical Vibration Fault

Photoelectric detection technology has been widely used in industry, agriculture, medicine, and other fields. The signal collected by photoelectric signal detection equipment is weak and vulnerable to noise interference. Therefore, a preamplifier circuit with good performance is needed to amplify the original signal effectively. Firstly, considering that a single-mode fiber coupler is more sensitive to the length of the coupling region, a coupled optical fiber vibration sensor is designed. Secondly, the appropriate operational amplifier (Op-amp) is chosen based on the photodetector. By listing and selecting the OPA656 Op-amp produced by TI Company, the basic current and voltage conversion circuit of photoelectric detection equipment is analyzed. In addition, a basic trans-impedance circuit with a phase compensation function is proposed and the calculation method of optimal phase compensation capacitance is derived. Finally, in the process of monitoring the vibration data of equipment, cloud computing technology (fuzzy C-means clustering algorithm+MapReduce model) is used for distributed processing of mechanical vibration data. In the test, the coupled optical fiber vibration sensor designed with an amplifier circuit and moving coil vibration sensor are placed on the ship equipment at the same time, and the rubber hammer is employed to hit the surface of the ship machinery. The test results of the two sensors are the same, which proves that the optical fiber sensor designed in this study meets the requirements of vibration measurement.

Funny How? Sketch Comedy and the Art of Humor

Funny How? seeks to demonstrate what makes a great sketch funny. The simplicity of the book’s main goal is its great virtue and informs its best part: its summaries of a dozen and more sketches performed by a wide variety of comedians. Guided by a broad sense of what constitutes sketch comedy, Clayton picked these sketches because he loves them. This makes good sense, since the point of the book is to talk straightforwardly about what makes things funny, and not, for instance, to provide a scholarly history of the genre. This simplicity comes with a price, though, insofar as the book does not enter into a dialogue with contemporary humor scholarship or with current theories. If readers want to hear what the author has to say about specific sketches or be introduced to a method for summarizing sketches, this book may be of interest to them.The book includes a relatively long first chapter that seeks to articulate an approach to humor theory that stresses how humor is “irreducibly compound.” On this approach, humor “will therefore most fruitfully yield to a form of analysis that is receptive to the multiplicity of factors in its construction and sensitive to the ways they meld and combine” (47). The summaries of sketches that follow, then, are demonstrations of this approach. The idea that humor cannot be reduced to one factor and that any approach should account for many factors while avoiding unnecessary universalism is, however, common to most contemporary humor scholarship, and so the book’s demonstration of how reductive approaches are inadequate not unsurprisingly takes the form of simplistic takedowns of famous “postulates” (34) about humor from Hobbes to Kant, Bergson, and Schopenhauer. There are almost no references to any twenty-first century theories, such as Alenka Zupančič’s The Odd One In: On Comedy or John Limon’s Stand-up Comedy in Theory, or, Abjection in America, just as there are almost no references to humor scholarship, including scholarship on sketch comedy. The book’s contributions are not to be found in such scholarly conversation.The book’s subsequent chapters provide summaries of sketches generally grouped together by themes, including parodies, what-ifs, music, and rivalry. For the most part, the focus is on UK and US film and television sketches, with one notable exception being the toilet party scene in Luis Buñuel’s The Phantom of Liberty. The introduction opens with a summary of the famous parrot sketch by Monty Python and the Flying Circus, providing a good example of what follows throughout the book. The work here challenges us, compelling us to think through what makes the sketch funny and to consider how it might have been done differently. This strategy offers a useful way to think about humor and also a useful way to teach (one gets the impression Clayton is a fine teacher of humor). How would the sketch have been different if instead of being about a parrot being returned to a pet store, it had instead been about “a rubber hammer being returned to a hardware store?” (2). Or what if the pet had not been a parrot but another animal, such as a dog? (3) The provisional conclusion as to the sketch-comedy value of the parrot is that parrots “are not so compassionate that the death of an unknown parrot could be felt tragic, but also not so simply decorative as to make it an impersonal matter of return-and-replace” (3). It’s impossible to summarize adequately here the account Clayton provides because its value is in its attention to the details of the scene. If we are going to talk about what makes things funny in sketch comedy then we do need to get down to the details. A later summary of a mock advertisement for the Tim and Eric Awesome Show, Great Job! is another fine example of what Clayton’s approach has to offer in its careful attention to detail (113–18).The book concludes with a suggestion that Aristotle’s famous three modes of persuasion—ethos, pathos, and logos—might be instructively applied to theorizing how sketches persuade us to laugh (128). While this is an interesting suggestion, it would have made more sense to have introduced it at the beginning of the book and then to have tried it out during the summaries of sketches that are the substance of the book. This method would have been consistent with the simple approach of the book and perhaps provided a light illustration of how to think through comedy, which is what this book has to offer readers interested in sketch comedy and humor in general.

An Experimental Study on the Performance of a Damper Fabricated by Dual Rubber Springs

In this paper several experimental investigations have been studied on the dynamic behavior of a damper using dual pre-compressed rubber springs to validate the performance of this damper in practical applications. For this aim, three specimens of the same dual polyurethane rubber spring are prepared to evaluate their mechanical behavior under fatigue and vibration tests. Hysteretic force–displacement of the quasi-static and dynamic tests after cycling loading are compared with those of the initial tests. Considering a suspended cantilever steel pipe, the dynamic properties of the system before and after installing the damper are investigated. To find the effect of damper on the natural frequency of the system, the rubber hammer impact tests are conducted in both lateral and vertical directions. Moreover, while increasing the frequency through the vibration test the acceleration and displacement amplitude of the system before and after installing the damper are compared. Furthermore, this damper is employed in a factory in the field of power generation and power piping system to dissipate the water hammer effect and provide sufficient deformation in the dual rubber spring damper.

Sealant Delamination Detection of Structural Sealant Glazing Systems Based on Driving-Point Accelerance

The structural sealant glazing system is widely used in glass curtain wall worldwide. However, due to the aging of the sealants, cracking may form along the sides of the glass. If the panel of curtain wall arises, delamination may occur and induce failure or loss of the system. In order to detect the delamination of the sealant, in this paper, a new vibration-based damage identification method is proposed by using the difference between the predamage and postdamage driving-point accelerance (DA). This detection method would require only one acceleration sensor on a glass panel and a rubber hammer, which operates very conveniently. When the rubber hammer taps the glass panel near the acceleration sensor, the glass curtain wall panel would generate acceleration response which can be measured by the acceleration sensor. The measured acceleration responses will be used to calculate the DA and lead to a new delamination index, called relative accumulative difference of DA, which will give indications on the potential delamination of the sealant. In addition, the influence of the acceleration sensor installation position was analysed by the finite element method, and the optimal sensor location was determined to be at the intersection of the long-side quarter and the short-side quarter. Nine cases on various delamination severities were identified by the new method, as well as the natural frequency reduction and modal assurance criterion. The laboratory experiments showed that the relative accumulative difference of DA is extremely sensitive to sealant delamination. Even if delamination severity was only 6.39%, the relative accumulative difference of DA would be larger than 18%. As the delamination of the sealant progresses, the relative accumulative difference of DA increases, resulting in an effective detection method for sealant delamination of the structural sealant glazing system. The fundamental frequency reduction is suitable to identify relatively large delamination, and the modal assurance criterion of higher modes is also sensitive to sealant delamination.

Engineering application of a safety-state evaluation model for hidden frame-supported glass curtain walls based on remote vibration

Laser doppler vibrometer (LDV), which has measurement advantages such as being remote and non-contact, accurate, and having rapid dynamic response, is a useful assessment tool for the safety-state evaluation of hidden frame-supported glass curtain walls (HFSGCW). The engineering application influence factors of a LDV safety-state evaluation model for HFSGCW were analyzed and the vibration frequency for practical cases was tested in this paper. Results show that the first order peak frequency from a frequency spectrum obtained by LDV can be selected as the safety-state evaluation index for HFSGCW caused by structural sealant failure. A rubber hammer is an effective way to excite glass panels to obtain an accurate vibration frequency spectrum. The middle of glass panels is advisable to be selected as the measurement point to obtain an accurate dynamic frequency. The frequency spectrum of a glass panel edge point can be used to determine structural sealant failure position. Binoculars are suggested to be added in order to improve working efficiency of LDV for measurement distance greater than 10 m. Pasting reflective film is an effective way to increase LDV test signal accuracy. The glass panel safety-state of a commercial center building in Guangdong (China) is accurately evaluated by LDV, and those test results provide guidance for real-time monitoring and repair of HFSGCW.

Tree Health Analyzing of Malvaceae Collections in Bogor Botanical Gardens

Center for Plant Conservation Botanic Gardens (Bogor Botanical Gardens) is an ex-situ conservation center in Indonesia which has ± 13,000 plants specimens collection in shrubs, herbs, lianas and trees. The collection is classified in 218 families, which one is Malvaceae. Most of Malvaceae collections at Bogor Botanical Gardens is tree shaped. Trees have risk of fracture, failure or death which can cause harm. The aim of this research is determining the health condition of Malvaceae collection to predict the occurrence of damage (broken, failure, dead etc.) and as a consideration for collection collections treatment. The method which used are combination of visual observation methods and sound waves using arborsonic. Total samples measured are 7 trees which have criteria such as being in a location with high visitor accessibility, large diameter, old tree and visible disease or pest attack. Each sample was done visually and checked with arborsonic basically using sound wave. The point of measuring on the tree is depend on initial identification of damage using a rubber hammer. In this research can be concluded, there are 2 trees which high risk of damage and become first priority handling because has percentage of damage above 60%, 5 trees have medium risk with second priority (30-60%).

Effect of Clamping Torque on Large Deflection Static and Dynamic Response of a Cantilever Beam: An Experimental Study

The present paper reports an experimental study on the effect of finite clamping on static and dynamic characteristics of cantilever beam. The experiment is carried out with two different beams, each of which is clamped at two different locations resulting in two different geometry settings. Under each of these four settings, specimen is clamped under two different torque ratings giving rise to different finite clamping effect. Under the eight settings, coordinates of tip point under static loading are measured directly using scales and plumb at each load step; whereas, complete deflection profiles of loaded beam under each static load step are obtained through post-processing of images captured during experimentation. Such image processing is carried out manually using AutoCAD® and in-built AutoLISP® software. Strain measurements at each static load step are carried out by using strain gauge, a universal data acquisition system and the associated Catman Easy® software. To obtain loaded free vibration characteristics, loaded beam under each setting is disturbed by a rubber hammer and its dynamic response is recorded from strain gauge signal through Catman Easy® software. These dynamic strain readings of loaded beam are post-processed and FFT plots are generated in MATLAB® software and first two loaded natural frequencies of beam under each setting are obtained. Finally, effects of clamping torques on the static strain and deflection results and loaded natural frequencies for beam settings with the four different thickness to length ratios are reported in a suitable manner. The result reported may be useful as ready reference to develop a theoretical model of clamped beam like structures incorporating the effect of finite clamping.

Effect of Clamping Torque on Large Deflection Static and Dynamic Response of a Cantilever Beam: An Experimental Study

The present paper reports an experimental study on the effect of finite clamping on static and dynamic characteristics of cantilever beam. The experiment is carried out with two different beams, each of which is clamped at two different locations resulting in two different geometry settings. Under each of these four settings, specimen is clamped under two different torque ratings giving rise to different finite clamping effect. Under the eight settings, coordinates of tip point under static loading are measured directly using scales and plumb at each load step; whereas, complete deflection profiles of loaded beam under each static load step are obtained through post-processing of images captured during experimentation. Such image processing is carried out manually using AutoCAD®and in-built AutoLISP®software. Strain measurements at each static load step are carried out by using strain gauge, a universal data acquisition system and the associated Catman Easy®software. To obtain loaded free vibration characteristics, loaded beam under each setting is disturbed by a rubber hammer and its dynamic response is recorded from strain gauge signal through Catman Easy®software. These dynamic strain readings of loaded beam are post-processed and FFT plots are generated in MATLAB®software and first two loaded natural frequencies of beam under each setting are obtained. Finally, effects of clamping torques on the static strain and deflection results and loaded natural frequencies for beam settings with the four different thickness to length ratios are reported in a suitable manner. The result reported may be useful as ready reference to develop a theoretical model of clamped beam like structures incorporating the effect of finite clamping.

Tree health assessment of Agathis borneensis Warb. in Bogor Botanical Garden using arborsonic

Bogor Botanical Garden has ± 14,000 living plant collections including shrubs, herbs, climber and trees. Tree collections exhibit different characteristics, larger dimensional shapes and can reach old ages. However, trees collections possess some flaws that could result in materials harm and other losses. The aim of this research was to define health condition of Agathis borneensis trees, as a base of determining treatment in Bogor Botanical Gardens. The method used was a combination of visual and sound waves assessment using arborsonic. Targeted trees were selected based on accessibility, tree diameter and age, and pest attack. Each tree was assessed with high risk by visual assessment and assessed using arborsonic on main stem. The height level of measurement point was based on sound, which was produced by rubber hammer tapping. This study concluded that there were 32 Agathis borneensis trees observed, where 4 trees were chosen as first priorities due to their decay level of above 60%, whereas the other 11 trees turned as the second priorities (30-60% decay level) and the last 17 trees became the third priorities (<30% decay level).

THE BARGAIN

1 5 6 Y T H E B A R G A I N S T E V E N G E H R K E Together, they were the good pig, always checking locks, vats of water boiling in their fireplace, and still he came, pale and thinly bearded, drawn to the taste of moon inside their daughter’s room, her colic evicting them from sleep, the two rising to find their brickedtogether shelter turned a lighthouse to an aimless ship, that nameless, likely homeless, man pounding at their door past two most nights, her quickly on the phone to the police, him trying to dislodge the man, hoping a tide of passing cars would lift him from their fast-eroding shore. The cops, when they arrived, suggested they might pay him o√, tape a few dollars to their door, but they were too zombie, too fretful and sleep-deprived, too far from empathy, to see anything but a stray who, once fed, would add their house to the clots of blood on the map inside of his head. When he wasn’t there, they’d hear that knocking in the bathroom window’s broken latch, sense him wandering but closing in, like an electric pulse mazing through the grid. In bed, they’d lay awake waiting for the first knock to fall like a rubber hammer to the knee, wondering what secret open sesame this 1 5 7 R stranger might possess, thinking he might unscrew their hinges with a fingernail, lift a key from underneath his tongue, their anxiety reshaping him until they almost believed he was their own private Rumpelstiltskin, there to remind them that gold can always be restrawed, that their daughter could be recalled, perhaps not just by chance or their incompetence, but by that subtle bargain they had struck, the promise that, to keep her safe, they would love each other just a sliver less. Which might be why, once, when their nightly dose of trespass was delivered, the husband started dumbly knocking back, not out of anger or any simple wanting-out, but as if to say that they didn’t need this easy prophecy, didn’t need a scru√y Hermes in disguise, as if to say, this door can knock itself, because our house was already ringing on its own – wasn’t it? – the ladder swiped from beneath the belfry we had climbed, the two of us waiting for the echo of who-we’d-been to finally refund, but hearing only are and soon enough become. ...

Experimental study on condition assessment of reinforced concrete structure using a dynamics response approach

Purpose – Condition assessment on reinforced concrete (RC) structures is one of the critical issues as a result of structure degradation due to aging in many developed countries. The purpose of this paper is to examine the sensitivity and reliability of the conventional dynamic response approaches, which are currently applied in the RC structures. The key indicators include: natural frequency and damping ratio. To deal with the non-linear characteristics of RC, the concept of random decrement is applied to analyze time domain data and a non-linear damping curve could be constructed to reflect the condition of RC structure. Design/methodology/approach – A full-scale RC structure was tested under ambient vibration and the impact from a rubber hammer. Time history data were collected to analyze dynamics parameters such as natural frequency and damping ratio. Findings – The research demonstrated that the measured natural frequency is not a good indicator for integrity assessment. Similarly, it was revealed that the traditional theory of viscous damping performed poorly for the RC with non-linear characteristics. To address this problem, a non-linear curve is constructed using random decrement and it can be used to retrieve the condition of the RC structure in a scientific manner. Originality/value – The time domain analysis using random decrement can be used to construct a non-linear damping curve. The results from this study revealed that the damage of structure can be reflected from the changes in the damping curves. The non-linear damping curve is a powerful tool for assessing the health condition of RC structures in terms of sensitivity and reliability.

1P1-N04 神経-筋制御系の理解を支援する膝ロボットの開発(医療ロボティクス・メカトロニクス(1))

In order to recover functional disorder, suitable rehabilitation and trained excellent physical therapists is required. Therefore, we developed the knee robot for understanding neuromuscular control system. The robot imitates patient's motions and human body model. The robot extends its lower thigh immediately after tapping its ligament below the patella with a small rubber hammer. The robot has a pneumatic artificial muscle for pulling up the lower thigh. It was selected by reference to the knee-jerk data of some healthy people which was measured in previous work. In this paper, we compared the angular velocity and the angle alternation of the knee robot with human data.

Bird strike event monitoring in a composite UAV wing using high speed optical fiber sensing system

In this study, high speed bird strikes on a composite structure were successfully monitored using optical fiber sensors. Four multiplexed optical fiber sensors in a single cable were surface-bonded on the leading edge of a composite UAV wing box. In order to acquire those high frequency signals, a newly developed interrogation system was used to process strain signals from four sensors simultaneously at a sampling frequency of 100kHz. Before the bird strike tests, pre-impact tests using a rubber hammer were performed to verify the suitability of the FBG signal acquisitions. The pre-test data were used in the neural network training procedures to estimate the bird strike locations. Then, the bird strike tests were accomplished using dummy projectiles and a pneumatic gun. The one-pound dummy birds, made of gelatin, hit the leading edge with a maximum speed of 201km/h. The impact signals were successfully recorded during the tests and their frequency characteristics were then analyzed. Finally, the strike locations were estimated with the neural network which was trained through the pre-tests. The average error was 33.6mm.

When I Got a Word From a Steinbeck Novel Tattooed on My Arm

I almost laugh. Parental reflex. Years have passed since I've spent more than a sporadic week or two at home, but still, even now, when he hears the word tattoo, it falls on his knee like a rubber hammer, and he kicks. I know that it's involuntary and, perhaps more importantly, benign, because despite the threat behind his question Are you prepared to deal with the consequences? consequences are not forthcoming: my father is not going to spank me or ground me or send me to my room without dessert. Graduated from college, living on my own, with rent checks and phone bills and bank statements all in my own name, I am no longer his to punish. I see that realization fall on his face even as he is asking the question, so I do laugh, and say, Okay. Sure, Dad. Goodnight.

Automated Part Centering With Impulse Actuation

Centering a part on a spindle for precision machining is a tedious, time-consuming task. Currently, a skilled operator must measure the run-out of a part using a displacement gauge, then tap the part into place using a plastic or rubber hammer. This paper describes a method to automatically center a part on a vacuum chuck with initial run-out as large as 2.5 mm. The method involves measuring the magnitude and direction of the radial run-out and then actuating the part until the part and spindle centerlines are within 5 μm of each other. The run-out can be measured with either a touch probe mounted to a machine axis or an electronic gauge. The part is tapped into place with a linear actuator driven by a voice coil motor. This paper includes an analysis of run-out measurement uncertainty as well as the design, performance modeling, and testing of the alignment actuator. This actuator was employed for part realignment and successfully positioned a hemispherical part with an initial run-out of 1–2.5 mm to within 5 μm of the spindle centerline. This capability shows that the run-out of a part manually placed on flat vacuum chuck can be automatically corrected.

Intramedullary Canal Pressure Distribution: An Experimental Parametric Study

Intramedullary instrument/device insertion during total joint replacement can generate high intramedullary pressures, with potential for clinical fat embolism syndrome. We evaluated effects of process parameters on intramedullary pressure generated when hammering an implant into a simulated femur analogue. Lower implant insertion speed, lower hammering force, a rubber- compared with steel-tipped hammer and a larger synthetic bone-to-implant radial gap reduced intramedullary pressure generated. Number of hammer strikes required to insert an implant increased with increasing marrow viscosity, whereas intramedullary pressure decreased with increasing viscosity. Significant intramedullary pressure reduction is obtained by applying more strikes of lower peak force using a rubber hammer tip, as opposed to fewer larger strikes. Caution should be exercised when instrumenting the distal femur, where viscosity is low and very high intramedullary pressures can be generated.

Depression of an inhibitory reflex, the masseteric silent period, in recovering alcoholics.

Because inhibitory deficits may contribute to motor incoordination of alcoholics, we proposed that the duration of the masseteric silent period (SP), an inhibitory reflex, might be shorter in alcoholics (ALs) than in nonalcoholics (NAs). To test this hypothesis, we measured the SP in a racially mixed group of 12 ALs and 12 NAs matched for age (31-49 years) and sex. All subjects were normotensive, had full dentition, and reported no major medical problems. Sensory and motor conduction velocities of the anterior tibialis, ulnar, and medial nerves were measured for each subject, and were not different in ALs and NAs. Jaw jerk and SP were evoked by tapping the chin manually with a rubber hammer containing a circuit to trigger the oscilloscope display of the masseter EMGs. Averaged mean latencies and durations of the SPs were not significantly different between the right and left masseters. SP latencies were significantly (0.7 msec) shorter in ALs than NAs (p < 0.01). The mean SP duration for ALs (13.9 +/- 1.6 msec) was also significantly shorter than that of the NAs (24.4 +/- 2.4 msec; p < 0.001). Results support the hypothesis that chronic alcoholism may interfere with inhibitory mechanisms in the CNS.

The vestibulo-ocular reflex during human saccadic eye movements.

Eye and head movements were recorded in normal humans during rapid refixations with the head still (saccades) or moving (gaze saccades) to determine if the vestibulo-ocular reflex was operating at such times. Subjects made self-electrooculogram for large saccades and with the eyecoil/magnetic field method for smaller movements. The putative function of the vestibulo-ocular reflex during a gaze saccade is to adjust the movement of the eye for the movement of the head by adding the saccadic command and the vestibular signal. This action, referred to here as linear summation, would maintain gaze-saccade accuracy by making gaze velocity (eye in space) independent of head velocity. It would also preserve the duration of the eye saccades of about 200 deg. When a subject increased his head velocity voluntarily, for example, from 420 to 805 deg/s, mean gaze velocity rose from 540 to 820 deg/s and duration dropped from 380 to 250 ms. Linear summation did not occur. By means of a yoke clenched in the teeth, the subject's head could be momentarily and unexpectedly slowed by collision of the yoke with a lead weight during a 180 deg gaze saccade. The perturbation decreased head velocity by about 150-200 deg/s, decreased gaze velocity by about the same amount and did not change eye velocity (in the head); another indication that the vestibulo-ocular reflex was not working. Nevertheless, gaze-saccade duration was automatically increased so that the over-all accuracy of the movement was not changed. Subjects made saccades between targets at +/- 20 deg without attempted head movements. Simultaneously the experimenter struck the yoke, clenched in the subject's teeth, with a rubber hammer. The hammer blow caused a transient head velocity of about 70 deg/s. Gaze velocity transiently rose or fell, depending on the direction of the blow, by similar amounts and a quantitative analysis suggested that the vestibulo-ocular reflex was essentially absent. Again, duration was automatically altered so that saccade accuracy was not changed. Subjects looked back and forth between targets 20, 40 and 60 deg apart as their head turned through the straight ahead position, actively or passively, at velocities up to 600 deg/s (active) or 300 deg/s (passive).(ABSTRACT TRUNCATED AT 400 WORDS)