The Experts below are selected from a list of 4776 Experts worldwide ranked by ideXlab platform
Roland S. Johansson - One of the best experts on this subject based on the ideXlab platform.
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Control of Forces Applied by Individual Fingers Engaged in Restraint of an Active Object
Journal of neurophysiology, 1997Co-Authors: Magnus K. O. Burstedt, Ingvars Birznieks, Benoni B. Edin, Roland S. JohanssonAbstract:We investigated the coordination of fingertip forces in subjects who used the tips of two fingers to restrain an instrumented manipulandum with horizontally oriented grip surfaces. The grip surfaces were subjected to tangential pulling forces in the distal direction in relation to the fingers. The subjects used either the right index and middle fingers (unimanual grasp) or both index fingers (bimanual grasp) to restrain the manipulandum. To change the Frictional Condition at the digit-object interfaces, either both grip surfaces were covered with sandpaper or one was covered with sandpaper and the other with rayon. The forces applied normally and tangentially to the grip surfaces were measured separately at each plate along with the position of the plates. Subjects could have performed the present task successfully with many different force distributions between the digits. However, they partitioned the load in a manner that reflected the Frictional Condition at the local digit-object interfaces. When both digits contacted sandpaper, they typically partitioned the load symmetrically, but when one digit made contact with rayon and the other with sandpaper, the digit contacting the less slippery material (sandpaper) took up a larger part of the load. The normal forces were also influenced by the Frictional Condition, but they reflected the average friction at the two contact sites rather than the local friction. That is, when friction was low at one of the digit-object interfaces, only the applied normal forces increased at both digits. Thus sensory information related to the local Frictional Condition at the respective digit-object interfaces controlled the normal force at both digits. The normal:tangential force ratio at each digit appeared to be a controlled variable. It was adjusted independently at each digit to the minimum ratio required to prevent Frictional slippage, keeping an adequate safety margin against slippage. This was accomplished by the scaling of the normal forces to the average friction and by partitioning of the load according to Frictional differences between the digit-object interfaces. In conclusion, by adjusting the normal:tangential force ratios to the local Frictional Condition, subjects avoided excessive normal forces at the individual digit-object interfaces, and by partitioning the load according the Frictional difference, subjects avoided high normal forces. Thus the local Frictional Condition at the separate digit-object interfaces is one factor that can strongly influence the distribution of forces across digits engaged in a manipulative act.
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Development of human precision grip. IV. Tactile adaptation of isometric finger forces to the Frictional Condition.
Experimental brain research, 1995Co-Authors: Hans Forssberg, Ann-christin Eliasson, H. Kinoshita, G. Westling, Roland S. JohanssonAbstract:The adaptation of the grip forces to the Frictional Condition between the digits and an object relies on feedforward sensorimotor mechanisms that use tactile afferent input to intermittently update a sensorimotor memory that controls the force coordination, i.e., the ratio between grip force (normal to the grip surface) and load force (tangential to the grip surface). The present study addressed the development of these mechanisms. Eighty-nine children and 15 adults lifted an instrumented object with exchangeable grip surfaces measuring the grip and load forces. Particularly in trials with high friction (sandpaper), the youngest children used a high grip force to load force ratio. Although this large safety margin against slips indicated an immature capacity to adapt to the Frictional Condition, higher grip forces were produced for more slippery material (silk versus sandpaper). The safety margin decreased during the first 5 years of age, in parallel with a lower variability in the grip force and a better adaptation to the current Frictional Condition. The youngest children (18 months) could adapt the grip force to load force ratio to the Frictional Condition in a series of lifts when the same surface structure was presented in blocks of trials, but failed when the surface structure was unpredictably changed between subsequent lifts. The need for repetitive presentation suggests a poor capacity to form a sensorimotor memory representation of the friction or an immature capacity to control the employed ratio from this representation. The memory effects, reflected by the influences of the Frictional Condition in the previous trial, gradually increased with age. Older children required a few lifts and adults only one lift to update their force coordination to a new friction. Hence, the present finding suggests that young children use excessive grip force, a strategy to avoid Frictional slips, to compensate for an immature tactile control of the precision grip.
C.f. Cheung - One of the best experts on this subject based on the ideXlab platform.
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A mesoplasticitiy analysis of cutting friction in ultra-precision machining
Journal of Materials Processing Technology, 2003Co-Authors: Bun Lee, C.f. CheungAbstract:Abstract The control and minimization of cutting force variation is of prime importance in obtaining a consistent surface finish and form accuracy of a machined workpiece in ultra-precision machining. However, most continuum theories do not take into account the effect of crystallographic anisotropy that causes variation in the shear plane at the grain level and hence of the cutting force. The periodicity of the fluctuation of cutting forces is found to be dependent on the Frictional Condition during cutting. However, investigation of the in situ relationships among the cutting friction, the crystallographic orientation of workpiece and the periodic fluctuation of cutting forces has received relatively little attention. In this paper, a mesoplasticity approach is proposed to access the crystallographic and Frictional effect on the fluctuation of micro-cutting forces in diamond turning of crystalline materials. The predictions were able to explain the experimental results based on the power spectrum analysis of the cutting force variation. The research findings throw light on the possibility of an indirect in situ assessment of the Frictional Condition in ultra-precision machining.
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A mesoplasticitiy analysis of cutting friction in ultra-precision machining
Journal of Materials Processing Technology, 2003Co-Authors: W.b. Lee, C.f. CheungAbstract:The control and minimization of cutting force variation is of prime importance in obtaining a consistent surface finish and form accuracy of a machined workpiece in ultra-precision machining. However, most continuum theories do not take into account the effect of crystallographic anisotropy that causes variation in the shear plane at the grain level and hence of the cutting force. The periodicity of the fluctuation of cutting forces is found to be dependent on the Frictional Condition during cutting. However, investigation of the in situ relationships among the cutting friction, the crystallographic orientation of workpiece and the periodic fluctuation of cutting forces has received relatively little attention. In this paper, a mesoplasticity approach is proposed to access the crystallographic and Frictional effect on the fluctuation of micro-cutting forces in diamond turning of crystalline materials. The predictions were able to explain the experimental results based on the power spectrum analysis of the cutting force variation. The research findings throw light on the possibility of an indirect in situ assessment of the Frictional Condition in ultra-precision machining.Department of Industrial and Systems Engineerin
Ingvars Birznieks - One of the best experts on this subject based on the ideXlab platform.
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EuroHaptics (1) - Classification of Texture and Frictional Condition at Initial Contact by Tactile Afferent Responses
Haptics: Neuroscience Devices Modeling and Applications, 2014Co-Authors: Heba Khamis, Stephen J Redmond, Vaughan G Macefield, Ingvars BirznieksAbstract:Adjustments to friction are crucial for precision object handling in both humans and robotic manipulators. The aim of this work was to investigate the ability of machine learning to disentangle concurrent stimulus parameters, such as normal force ramp rate, texture and friction, from the responses of tactile afferents at the point of initial contact with the human finger pad. Three textured stimulation surfaces were tested under two Frictional Conditions each, with a 4 N normal force applied at three ramp rates. During stimulation, the responses of fourteen afferents (5 SA-I, 2 SA-II, 5 FA-I, 2 FA-II) were recorded. A Parzen window classifier was used to classify ramp rate, texture and Frictional Condition using spike count, first spike latency or peak frequency from each afferent. This is the first study to show that ramp rate, texture and Frictional Condition could be classified concurrently with over 90 % accuracy using a small number of tactile sensory units.
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classification of texture and Frictional Condition at initial contact by tactile afferent responses
International Conference on Human Haptic Sensing and Touch Enabled Computer Applications, 2014Co-Authors: Heba Khamis, Stephen J Redmond, Vaughan G Macefield, Ingvars BirznieksAbstract:Adjustments to friction are crucial for precision object handling in both humans and robotic manipulators. The aim of this work was to investigate the ability of machine learning to disentangle concurrent stimulus parameters, such as normal force ramp rate, texture and friction, from the responses of tactile afferents at the point of initial contact with the human finger pad. Three textured stimulation surfaces were tested under two Frictional Conditions each, with a 4 N normal force applied at three ramp rates. During stimulation, the responses of fourteen afferents (5 SA-I, 2 SA-II, 5 FA-I, 2 FA-II) were recorded. A Parzen window classifier was used to classify ramp rate, texture and Frictional Condition using spike count, first spike latency or peak frequency from each afferent. This is the first study to show that ramp rate, texture and Frictional Condition could be classified concurrently with over 90 % accuracy using a small number of tactile sensory units.
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Control of Forces Applied by Individual Fingers Engaged in Restraint of an Active Object
Journal of neurophysiology, 1997Co-Authors: Magnus K. O. Burstedt, Ingvars Birznieks, Benoni B. Edin, Roland S. JohanssonAbstract:We investigated the coordination of fingertip forces in subjects who used the tips of two fingers to restrain an instrumented manipulandum with horizontally oriented grip surfaces. The grip surfaces were subjected to tangential pulling forces in the distal direction in relation to the fingers. The subjects used either the right index and middle fingers (unimanual grasp) or both index fingers (bimanual grasp) to restrain the manipulandum. To change the Frictional Condition at the digit-object interfaces, either both grip surfaces were covered with sandpaper or one was covered with sandpaper and the other with rayon. The forces applied normally and tangentially to the grip surfaces were measured separately at each plate along with the position of the plates. Subjects could have performed the present task successfully with many different force distributions between the digits. However, they partitioned the load in a manner that reflected the Frictional Condition at the local digit-object interfaces. When both digits contacted sandpaper, they typically partitioned the load symmetrically, but when one digit made contact with rayon and the other with sandpaper, the digit contacting the less slippery material (sandpaper) took up a larger part of the load. The normal forces were also influenced by the Frictional Condition, but they reflected the average friction at the two contact sites rather than the local friction. That is, when friction was low at one of the digit-object interfaces, only the applied normal forces increased at both digits. Thus sensory information related to the local Frictional Condition at the respective digit-object interfaces controlled the normal force at both digits. The normal:tangential force ratio at each digit appeared to be a controlled variable. It was adjusted independently at each digit to the minimum ratio required to prevent Frictional slippage, keeping an adequate safety margin against slippage. This was accomplished by the scaling of the normal forces to the average friction and by partitioning of the load according to Frictional differences between the digit-object interfaces. In conclusion, by adjusting the normal:tangential force ratios to the local Frictional Condition, subjects avoided excessive normal forces at the individual digit-object interfaces, and by partitioning the load according the Frictional difference, subjects avoided high normal forces. Thus the local Frictional Condition at the separate digit-object interfaces is one factor that can strongly influence the distribution of forces across digits engaged in a manipulative act.
Hans Forssberg - One of the best experts on this subject based on the ideXlab platform.
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Development of human precision grip. IV. Tactile adaptation of isometric finger forces to the Frictional Condition.
Experimental brain research, 1995Co-Authors: Hans Forssberg, Ann-christin Eliasson, H. Kinoshita, G. Westling, Roland S. JohanssonAbstract:The adaptation of the grip forces to the Frictional Condition between the digits and an object relies on feedforward sensorimotor mechanisms that use tactile afferent input to intermittently update a sensorimotor memory that controls the force coordination, i.e., the ratio between grip force (normal to the grip surface) and load force (tangential to the grip surface). The present study addressed the development of these mechanisms. Eighty-nine children and 15 adults lifted an instrumented object with exchangeable grip surfaces measuring the grip and load forces. Particularly in trials with high friction (sandpaper), the youngest children used a high grip force to load force ratio. Although this large safety margin against slips indicated an immature capacity to adapt to the Frictional Condition, higher grip forces were produced for more slippery material (silk versus sandpaper). The safety margin decreased during the first 5 years of age, in parallel with a lower variability in the grip force and a better adaptation to the current Frictional Condition. The youngest children (18 months) could adapt the grip force to load force ratio to the Frictional Condition in a series of lifts when the same surface structure was presented in blocks of trials, but failed when the surface structure was unpredictably changed between subsequent lifts. The need for repetitive presentation suggests a poor capacity to form a sensorimotor memory representation of the friction or an immature capacity to control the employed ratio from this representation. The memory effects, reflected by the influences of the Frictional Condition in the previous trial, gradually increased with age. Older children required a few lifts and adults only one lift to update their force coordination to a new friction. Hence, the present finding suggests that young children use excessive grip force, a strategy to avoid Frictional slips, to compensate for an immature tactile control of the precision grip.
Jongjin Park - One of the best experts on this subject based on the ideXlab platform.
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development of severe plastic deformation by various asymmetric rolling processes
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: Y H Ji, Jongjin ParkAbstract:Rolling is the most appropriate process to produce a severe plastic deformation in the sheet or plate type of materials. Compared to symmetric rolling, asymmetric rolling is more efficient in producing plastic deformation since it develops additional shear strain for a given reduction in thickness. In the present investigation, various asymmetric rolling processes were analyzed by the rigid-viscoplastic finite element method. The results of the analyses were compared to each other in terms of plastic deformation: effects of asymmetries due to the differences in size, rotational speed and Frictional Condition between upper and lower rolls. Rolling pressure distribution, rolling force and rolling torque were also compared.
