Pneumatic Screwdrivers Research Articles

Exhaust Noise Reduction by Application of Expanded Collecting System in Pneumatic Tools and Machines

In this paper, we demonstrate how to reduce the noise level of expanded air from pneumatic tools. Instead of a muffler, we propose the expanded collecting system, where the air expands through the pneumatic tube and expansion collector. We have elaborated a mathematical model which illustrates the dynamics of the air flow, as well as the acoustic pressure at the end of the tube. The computational results were compared with experimental data to check the air dynamics and sound pressure. Moreover, the study presents the methodology of noise measurement generated in a pneumatic screwdriver in a quiet back room and on a window-fitting stand in a production hall. In addition, we have performed noise measurements for the pneumatic screwdriver and the pneumatic screwdriver on an industrial scale. These measurements prove the noise reduction of the pneumatic tools when the expanded collecting system is used. When the expanded collecting system was applied to the screwdriver, the measured Sound Pressure Level (SPL) decreased from 87 to 80 dB(A).

Ergonomics assessment of passive upper-limb exoskeletons in an automotive assembly plant

Over the years, the industry’s interest in using external support devices, such as exoskeletons, is increasing. They are introduced as a new technique for improving the conditions of workers and for reducing the risk of musculoskeletal injuries. An investigation of muscle activity, Jonsson’s (Jonsson, 1982) ergonomic acceptance ranges, and shoulder range of motion was conducted with a sample of 12 workers using an upper extremity exoskeleton in an automotive assembly line. The operators performed continuous cycles of dynamic overhead work consisting of the assembly of the car body at the underside of the car making use of pneumatic screwdrivers. The EMGs (anterior part of deltoid, trapezius, latissimus dorsi and erector spinae) were measured for the muscle activity analysis on the one hand, and for the ergonomics study on the other hand. The latter consisted of an approach based on Jonsson’s work, that establishes acceptance thresholds of cumulative percentage of maximum voluntary contraction of muscle activity (%MVC) in a work cycle. The joint angles motion capture was carried out by measuring the angles of the neck, back, and arms joints. All measurements were performed during experimental sessions with and without an exoskeleton. The key findings show reductions of 34% and 18% of the deltoid and the trapezius muscular activities, respectively, which in turn could lead to a reduction of discomfort and fatigue. The erector spinae and latissimus dorsi muscles were not significantly affected by exoskeleton. The values of muscular activity were also represented over Jonsson’s acceptance areas. Referring to the posture, some differences were found in the range of movement of back, neck, and arms owing to the use of the exoskeleton; however, the differences were smaller than 5% in all cases.

Extraction of angle deterministic signals in the presence of stationary speed fluctuations with cyclostationary blind source separation

This paper addresses the use of a cyclostationary blind source separation algorithm (namely RRCR) to extract angle deterministic signals from mechanical rotating machines in presence of stationary speed fluctuations. This means that only phase fluctuations while machine is running in steady-state conditions are considered while run-up or run-down speed variations are not taken into account. The machine is also supposed to run in idle conditions so non-stationary phenomena due to the load are not considered. It is theoretically assessed that in such operating conditions the deterministic (periodic) signal in the angle domain becomes cyclostationary at first and second orders in the time domain. This fact justifies the use of the RRCR algorithm, which is able to directly extract the angle deterministic signal from the time domain without performing any kind of interpolation. This is particularly valuable when angular resampling fails because of uncontrolled speed fluctuations. The capability of the proposed approach is verified by means of simulated and actual vibration signals captured on a pneumatic screwdriver handle. In this particular case not only the extraction of the angle deterministic part can be performed but also the separation of the main sources of excitation (i.e. motor shaft imbalance, epyciloidal gear meshing and air pressure forces) affecting the user hand during operations.

Dynamic modeling of compressors illustrated by an oil-flooded twin helical screw compressor

Compressed air is a basic energy source in several industrial areas. The energy of pressurized air is used during manufacturing processes, commonly as driving force for actuating pneumatic cylinders and in power tools such as pneumatic screwdrivers. The widespread use of this energy source justifies efforts to reduce losses within the compressed air infrastructure. One of the main energy consumers in the network is the production of compressed air. Thus, one problem area is generation with compressors of different kinds and sizes. Another problem affects the transmission through piping networks with non-negligible leakage effects adding to energy losses within the pneumatic infrastructure. This paper focuses on the process of compressing air and describes a dynamic simulation model of an oil-flooded screw compressor. A single compressor block, part of an overall compressor station, is split into four subsystems which are presented as mathematical models. Simulation results are compared to physical measurements and studied with respect to energy losses. The presented model is detailed enough to account for dynamic effects in real machines. But it is also abstract enough to be integrated in further simulations with more components. Future work will be done on optimizing compressor station design with respect to the reduction of energy losses.

Forces associated with pneumatic power screwdriver operation: statics and dynamics

The statics and dynamics of pneumatic power screwdriver operation were investigated in the context of predicting forces acting against the human operator. A static force model is described in the paper, based on tool geometry, mass, orientation in space, feed force, torque build up, and stall torque. Three common power hand tool shapes are considered, including pistol grip, right angle, and in-line. The static model estimates handle force needed to support a power nutrunner when it acts against the tightened fastener with a constant torque. A system of equations for static force and moment equilibrium conditions are established, and the resultant handle force (resolved in orthogonal directions) is calculated in matrix form. A dynamic model is formulated to describe pneumatic motor torque build-up characteristics dependent on threaded fastener joint hardness. Six pneumatic tools were tested to validate the deterministic model. The average torque prediction error was 6.6% (SD = 5.4%) and the average handle force prediction error was 6.7% (SD = 6.4%) for a medium-soft threaded fastener joint. The average torque prediction error was 5.2% (SD = 5.3%) and the average handle force prediction error was 3.6% (SD = 3.2%) for a hard threaded fastener joint. Use of these equations for estimating handle forces based on passive mechanical elements representing the human operator is also described. These models together should be useful for considering tool handle force in the selection and design of power screwdrivers, particularly for minimizing handle forces in the prevention of injuries and work related musculoskeletal disorders.

Evaluating the effects of activation mode, torque and horizontal operating distance on hand–arm response while operating pneumatic screwdrivers

The objective of this study is to evaluate the influences of activation mode, torque and horizontal operating distance on hand–arm response while operating in-line pneumatic screwdrivers. Hand–arm response was investigated in terms of finger force exertion, flexor digitorum electromyography, and hand-transmitted vibration. Two activation modes (push-to-start, and trigger-to-start), two torque levels (low, and high) and three horizontal operating distance (far, middle, and near) were evaluated. Thirteen healthy male subjects drove screws into an iron plate with pre-tapped screw holes using in-line pneumatic screwdrivers in randomly ordered experimental conditions. The results indicate that the use of push-to-start mode, not only required a greater holding force involving forearm muscular exertion and middle, ring and small finger forces, but also incurred a greater hand-transmitted vibration than the use of trigger-to-start mode. Higher torque caused a greater hand-transmitted vibration and required a firmer grip than lower torque. A middle distance level (18–30 cm away from the table edge) is recommended as it is found to have the least hand-transmitted vibration and requires less finger force exertion. Relevance to industry The findings on the evaluation of the influence of activation mode, torque, and horizontal operating distance on hand–arm response can provide useful information for the design of assembly tasks using pneumatic screwdrivers as well as the design of powered hand tools.

Evaluating the effects of wearing gloves and wrist support on hand–arm response while operating an in-line pneumatic screwdriver

The objective of this study is to evaluate the effects of wearing a glove and wrist support on hand–arm response while operating an in-line pneumatic screwdriver. Hand–arm response was investigated in terms of triggering finger force, flexor digitorum EMG and hand-transmitted vibration. Four glove levels (barehanded, cotton, nylon and open-finger), and two wrist support levels (wearing, and not wearing) were evaluated. Thirteen healthy male subjects drove screws into a horizontally mounted iron plate with pre-tapped screw holes using an in-line pneumatic screwdriver in the randomly ordered experimental conditions. The results indicate that wearing a nylon glove and not using a wrist support is the best combination among the eight evaluated experimental conditions. Wearing a nylon glove reduced 18.2% of the triggering force as compared with the barehanded condition. In addition, wearing a nylon glove had comparatively low forearm muscular exertion, and reduced 16% and 15% of hand-transmitted vibration in the z-axis and the sum of 3-axes as compared with the barehanded condition. The use of a wrist support required a greater triggering force and a 9.9% greater hand-transmitted vibration in the y-axis than when not using a wrist support. Relevance to industry The results of this study can be applied to the design of assembly tasks in the electronic industry to reduce the risk of incurring upper extremity cumulative trauma disorders.

Effects of pneumatic screwdrivers and workstations on inexperienced and experienced operator performance

This study investigated the effects of pneumatic screwdriver characteristics and workpiece orientation on operator productivity. Operators used four pneumatic screwdrivers (two pistol and two straight grip) representing two different clutch types (positive and automatic air shut-off). The two grip types represented both fast (1700 RPM) and slow (1000 RPM) motor speeds. The pneumatic screwdrivers were used at each of three different workstations representing different workpiece orientations (horizontal workpiece at a fixed height, horizontal workpiece with an adjustable height, and angled workpiece with adjustable height). In the first phase of the study, 18 university students (inexperienced operators) participated in a simulated furniture assembly operation. In the second phase, 16 experienced employees of a furniture manufacturing facility participated in an actual furniture assembly operation. The results of the study indicate that operators took longer to complete the required tasks and made more errors when the straight grip screwdrivers were used than when the pistol grip screwdrivers were used. These differences were more pronounced at the end of the task than at the beginning of the task. No strong performance differences were found among the three different workstations used.

Psychophysical Assessment of Simulated Assembly Line Work: Combinations of Transferring and Screw Driving Tasks

Upper extremity cumulative trauma disorders have been linked to the repeated and/or forceful exertions and/or awkward postures sometimes required by upper extremity intensive work. The combined effect of these physical stressors can be evaluated using psychophysical methods. The purpose of this study was to examine different combinations of repetitive upper extremity work using established psychophysical methods to determine design recommendations for upper extremity tasks. The tasks studied simulated assembly line type work where a part is transferred from a storage bin and attached with a pneumatic tool to another larger part. Twenty-four experienced industrial workers performed five combination tasks of transferring an object along a conveyor and screw driving using a pistol shaped pneumatic screwdriver: 100% transfer; 75% transfer and 25% screw drive; 50% transfer and 50% screw drive; 25% transfer and 75% screw drive; and 100% screw drive. The cycle time was 24 seconds. Each combination task was performed for an hour. Overall, transferring, and screw driving perceived exertions were measured using 10 cm visual analog scales (VAS) with verbal descriptions at the endpoints. The left and right sides corresponded to “Easiest imaginable work” at 0 cm, and “Hardest imaginable work” at 10 cm, respectively. Body part discomfort surveys were utilized to assess discomfort from each of the tasks. The overall perceived exertion (VAS) rating increased, as the task utilized more of one upper extremity than the other and involved more of either the transferring or screw driving tasks. The mean overall VAS ratings were 5.3, 4.3, 3.5, 4.4, and 5.3 for the five combination tasks, respectively. As the transferring (or screw driving) proportion of the task increased, the transferring (or screw driving) VAS increased. A repeated measures ANOVA showed that the combination task effect was significant (p<0.01). This psychophysical data can provide guidance in the analysis and design of upper extremity work. Since less varied work which utilized more of one upper extremity than the other had greater overall perceived exertion, upper extremity tasks should be designed as varied as possible utilizing as many body parts as possible. Body part discomfort surveys verified that this decreased discomfort severity and distributed the discomfort more evenly throughout the different body parts. This study provides evidence of the positive effects of work enlargement.

‘Effect of pneumatic screwdrivers and workstations on operator body posture’ : Schulze, L J H, Koppa, R J, Congleton, J J and Whiteley, J DInt J Ind Ergon Vol 8 No 1 (1991) pp 17–31 (28 refs)

‘Effect of pneumatic screwdrivers and workstations on operator body posture’ : Schulze, L J H, Koppa, R J, Congleton, J J and Whiteley, J DInt J Ind Ergon Vol 8 No 1 (1991) pp 17–31 (28 refs)

Effect of pneumatic screwdrivers and workstations on operator body posture

Four pneumatic screwdrivers, representing two different motor speeds and grip types, were used by both inexperienced (college student) and experienced male and female operators in a simulated and actual furniture assembly operation, respectively. All screwdrivers were used to set screws in furniture desk tops configured in three different orientations. The workstation/workpiece orientations were chosen to assess both ideal and non-ideal upperarm-forearm, wrist, shoulder and body postures assumed by operators during the assembly task. The results of this study indicate that less deviation of the upperarm-forearm and wrist was assumed by male operators. The female operators, necessarily disadvantaged by strength and stature, assumed postures representing greater body part abduction and deviation from neutral points. No differences were found between inexperienced and experienced operators.

Powered screwdriver design and use: Tool, task, and operator effects

The study investigated three primary factors related to the ergonomic aspects of pneumatic screwdriver design and use. These factors were: (1) tool grip diameter, (2) tool weight, and (3) shut-off (reactive) torque. The study consisted of a simulated industrial assembly task, that was representative of many of today's industrial operations. The results of the study indicate that, for vertical hanging tools, the weight of the tool has very little effect on the operator and that higher shut-off torques require significantly more gripping force by the operator. Contrary to the popular industrial assumption, the larger grip diameters reduce the amount of gripping effort required at higher torques. However, at low torque levels, the grip diameter has much less effect. The implications for occupational safety, product quality and productivity are discussed. The results of the study are important to both manufacturers and users of powered screwdrivers.

Assessment of Hand Vibration Exposure on an Assembly Line

This paper describes a study undertaken to evaluate and control vibration exposure associated with pneumatic screwdrivers used in an electrical appliance assembly plant. The study was motivated by management's concern about reports of cumulative trauma disorders in the upper extremities of workers who used pneumatic screwdrivers. Vibration exposure from power hand tools on an assembly line is difficult to predict due to highly variable conditions and techniques used between operators. Vibration exposure was measured using observation samples of tool vibration obtained on the assembly line for individual assembly tasks. Typical tool one-third octave band acceleration spectra estimated from laboratory measurements were used in conjunction with the measured exposure times to compare workers' risk of exposure to the hazards associated with operating vibrating hand tools. Characteristic vibration produced by the tools during phases of operation were separated and analyzed individually to identify and control the source.