title: Clinical Implications of Landing Distance on Landing Error Scoring System Scores

authors: Hanzlíková, Ivana

subjects: Science & Technology

abstract: Context: The Landing Error Scoring System (LESS) screens for the risk of non-contact anterior cruciate ligament injury. The LESS requires individuals to jump forward from a 30-cm box to a distance of 50% of their body height. However, different landing distances have been cited in the scientific literature.

Objective: To examine whether landing distance influences LESS outcomes.

Design: Cross-sectional study.

Setting: Laboratory.

Participants or Other Participants: Seventy young active individuals (34 males, 36 females).

Intervention(s): Participants performed 33 30-cm jump landing tasks under 2 landing conditions in randomized order: (1) 50% of body height (d50%), (2) self-selected distance (dss).

Main Outcome Measure(s): Mean LESS scores, proportions of individuals categorized at high (LESS: 5 errors) and low (LESS: <5 errors) injury risk, and landing distances were compared between conditions using generalized estimating equations. Consistency of risk categorization was examined using odds ratios (ORs) and McNemar tests. McNemar and Wilcoxon signed rank tests were used to compare the occurrence of specific LESS errors.

Results: Participants landed closer to the box under the dss condition (difference = 23.28 [95% CI = 20.73, 25.81]%, P < .001). Group mean LESS scores (difference = 0.01 [95% CI = 0.59, 0.57] error, P = .969) and risk categorization (OR = 0.94 [95% CI = 0.47, 1.88], P = .859) were similar between conditions. However, individual-level risk categorization was inconsistent in 33% of participants, as was the occurrence of specific errors.

Conclusions: Using dss during the LESS might lead to different LESS errors and risk categorizations at an individual level than using d50%. Given that individual LESS scores are of primary interest in clinical and sport settings and the injury-risk threshold has not been validated for dss, we recommend the use of the original LESS protocol. When only group mean LESS scores or proportions of at-risk individuals are of interest, using dss is feasible to facilitate the testing of large cohorts.

text: Clinical Implications of Landing Distance on Landing Error Scoring System Scores Context: The Landing Error Scoring System (LESS) screens for the risk of non-contact anterior cruciate ligament injury. The LESS requires individuals to jump forward from a 30-cm box to a distance of 50% of their body height. However, different landing distances have been cited in the scientific literature.

Objective: To examine whether landing distance influences LESS outcomes.

Design: Cross-sectional study.

Setting: Laboratory.

Participants or Other Participants: Seventy young active individuals (34 males, 36 females).

Intervention(s): Participants performed 33 30-cm jump landing tasks under 2 landing conditions in randomized order: (1) 50% of body height (d50%), (2) self-selected distance (dss).

Main Outcome Measure(s): Mean LESS scores, proportions of individuals categorized at high (LESS: 5 errors) and low (LESS: <5 errors) injury risk, and landing distances were compared between conditions using generalized estimating equations. Consistency of risk categorization was examined using odds ratios (ORs) and McNemar tests. McNemar and Wilcoxon signed rank tests were used to compare the occurrence of specific LESS errors.

Results: Participants landed closer to the box under the dss condition (difference = 23.28 [95% CI = 20.73, 25.81]%, P < .001). Group mean LESS scores (difference = 0.01 [95% CI = 0.59, 0.57] error, P = .969) and risk categorization (OR = 0.94 [95% CI = 0.47, 1.88], P = .859) were similar between conditions. However, individual-level risk categorization was inconsistent in 33% of participants, as was the occurrence of specific errors.

Conclusions: Using dss during the LESS might lead to different LESS errors and risk categorizations at an individual level than using d50%. Given that individual LESS scores are of primary interest in clinical and sport settings and the injury-risk threshold has not been validated for dss, we recommend the use of the original LESS protocol. When only group mean LESS scores or proportions of at-risk individuals are of interest, using dss is feasible to facilitate the testing of large cohorts.

year: 2021-06-01

title: Incorporating contact area in soft finger grasp models

authors: Fernandez-Ritchie, Tara

subjects: Grasp

abstract: The ability to grasp is a significant function of many robotic hands, whether it be for fruit-picking or manufacturing tasks. Two major theories often used in conjunction to model grasping are Nguyen’s theorem and Coulomb’s friction law. Both theories model the contact between the fingers and the object in grasp as at a point. This runs true when the fingers and the object in grasp are made of hard materials. However, when the fingers or the object are soft, they deform around each other and result in a contact area between the objects rather than a contact point. This contact area means that soft-fingered grasps can apply an additional moment to balance any external moments, of which hard fingers cannot. To account for this, the soft-fingered grasp is often modelled as a point contact with a moment about the normal direction. However, in scenarios where there is no external moment both soft and hard fingers would exert a moment of 0 Nm and their grasps are modelled identically using Nguyen’s theorem and Coulomb’s law. Since soft-fingered grasping has been used extensively due to its superiority to hard-fingered grasping it does give rise to the question of whether the soft fingered grasp should be modelled identically to the hard fingered grasp in this case.  

This research expands the current grasp models to better showcase the differences between soft and hard finger grasps. The approach taken to achieve this was to incorporate the contact area of soft fingered grasping into the contact model so as to highlight the differences between soft and hard fingers when grasping an object. The research utilised this expansion in the contact model employing Nguyen’s theorem and Coulomb’s friction law. Nguyen’s theorem is a condition that must be met for a grasp to be in force closure, while Coulomb’s friction model limits the forces that can be applied by a finger onto an object to being within a friction cone at a point for no slipping to occur. Both Nguyen’s and Coulomb’s theories model the friction cone of the soft finger at the centre-point of the area of contact. A set-of-cones theory was proposed, where the area of contact is comprised of many friction cones corresponding to the points that make up the contact area instead of a single friction cone. 

An experiment was devised for a two-fingered symmetrical grasp of a cylinder, where the maximum angle of contact above the horizontal before slipping was investigated. The set-of-cones approach was made into a resultant friction cone model. The resultant cone model and the original centre-point cone model were used to predict the forces due to Coulomb’s theory at the maximum angle of contact. The predictions were compared to the data obtained from the experiment. It was found that the resultant cone contact model predicted the normal force applied at the maximum angle before slipping more accurately than the centre-point contact model for both soft finger materials being investigated in this research. 

When the resultant cone model was translated for use in the prediction of a force closure grasp by using Nguyen’s theorem, the range of positions where the object was grasped in force closure increased as compared to when using the centre-point contact model. If further verified, the resultant cone model would be used for soft fingers while the centre-point model would be used for hard fingers. This extends the modelling of soft finger contact so as to illustrate the differences in the stability of a grasp between hard and soft finger contact.

text: Incorporating contact area in soft finger grasp models The ability to grasp is a significant function of many robotic hands, whether it be for fruit-picking or manufacturing tasks. Two major theories often used in conjunction to model grasping are Nguyen’s theorem and Coulomb’s friction law. Both theories model the contact between the fingers and the object in grasp as at a point. This runs true when the fingers and the object in grasp are made of hard materials. However, when the fingers or the object are soft, they deform around each other and result in a contact area between the objects rather than a contact point. This contact area means that soft-fingered grasps can apply an additional moment to balance any external moments, of which hard fingers cannot. To account for this, the soft-fingered grasp is often modelled as a point contact with a moment about the normal direction. However, in scenarios where there is no external moment both soft and hard fingers would exert a moment of 0 Nm and their grasps are modelled identically using Nguyen’s theorem and Coulomb’s law. Since soft-fingered grasping has been used extensively due to its superiority to hard-fingered grasping it does give rise to the question of whether the soft fingered grasp should be modelled identically to the hard fingered grasp in this case.  

This research expands the current grasp models to better showcase the differences between soft and hard finger grasps. The approach taken to achieve this was to incorporate the contact area of soft fingered grasping into the contact model so as to highlight the differences between soft and hard fingers when grasping an object. The research utilised this expansion in the contact model employing Nguyen’s theorem and Coulomb’s friction law. Nguyen’s theorem is a condition that must be met for a grasp to be in force closure, while Coulomb’s friction model limits the forces that can be applied by a finger onto an object to being within a friction cone at a point for no slipping to occur. Both Nguyen’s and Coulomb’s theories model the friction cone of the soft finger at the centre-point of the area of contact. A set-of-cones theory was proposed, where the area of contact is comprised of many friction cones corresponding to the points that make up the contact area instead of a single friction cone. 

An experiment was devised for a two-fingered symmetrical grasp of a cylinder, where the maximum angle of contact above the horizontal before slipping was investigated. The set-of-cones approach was made into a resultant friction cone model. The resultant cone model and the original centre-point cone model were used to predict the forces due to Coulomb’s theory at the maximum angle of contact. The predictions were compared to the data obtained from the experiment. It was found that the resultant cone contact model predicted the normal force applied at the maximum angle before slipping more accurately than the centre-point contact model for both soft finger materials being investigated in this research. 

When the resultant cone model was translated for use in the prediction of a force closure grasp by using Nguyen’s theorem, the range of positions where the object was grasped in force closure increased as compared to when using the centre-point contact model. If further verified, the resultant cone model would be used for soft fingers while the centre-point model would be used for hard fingers. This extends the modelling of soft finger contact so as to illustrate the differences in the stability of a grasp between hard and soft finger contact.

year: 2021

title: Te Ika Huirua o Te Mate

authors: Maxwell, Te Kahautu

abstract: This composition is a lament to two staesman of the Māori world Apira Mahuika of Ngāti Porou and Tama Huata of Ngāti Kahungunu. Both men were giants in their respective areas, governance, tribal politics cultral revival language revitalisation, Treaty settlements they both died within days of each other. This compostion also talks about how Pākeha law clashes with Māori lore with the James Takamore case where his whanau took his body and returned it to James ancestral home Whakatohea and the widow laid charges to have her husbands remains dug up and returned to Christchuch. I thought it appropriate to protest about this being the Te Matatini World Championship Kapa Haka Competition was held in Christchurch March 2015. This composition was performed by Ōpōtiki Mai Tawhiti.

text: Te Ika Huirua o Te Mate This composition is a lament to two staesman of the Māori world Apira Mahuika of Ngāti Porou and Tama Huata of Ngāti Kahungunu. Both men were giants in their respective areas, governance, tribal politics cultral revival language revitalisation, Treaty settlements they both died within days of each other. This compostion also talks about how Pākeha law clashes with Māori lore with the James Takamore case where his whanau took his body and returned it to James ancestral home Whakatohea and the widow laid charges to have her husbands remains dug up and returned to Christchuch. I thought it appropriate to protest about this being the Te Matatini World Championship Kapa Haka Competition was held in Christchurch March 2015. This composition was performed by Ōpōtiki Mai Tawhiti.

year: 2015-02-12