Vision and Radar Steering Reduces Agricultural Sprayer Operator Stress without Compromising Steering Performance

Self-propelled agricultural sprayer operators work an average of 15 h d-1 in peak season, and steering is the task that causes the operator the most stress because of the large number of stimuli involved. Automatic guidance systems help reduce stress and fatigue for operators by allowing them to focus on tasks other than steering. Physiological signals like skin conductance (electrodermal activity, EDA) change with stress and can be used to identify stressful events. The objective of this study was to determine if using a commercially available vision and radar guidance system (VSN®, Raven Industries) reduces agricultural sprayer operators’ stress compared to when they are steering manually. Four male professional sprayer operators participated in this study. Each operator performed his job duties normally in GPS-guidance-planted fields, at his self-selected speed, except to drive some passes manually and others with VSN in the same field. EDA was measured with an Empatica E4 wristband, and stressful events were quantified. Machine data (e.g., speed, RTK-GPS, and VSN metrics) were collected from each sprayer via CAN logs. The steering type, stress rate (e.g., stressful events min-1), and steering performance (crosstrack error standard deviation, XTE SD) were determined for each pass. In total, 51 passes (23 manual, 28 VSN) in six fields were analyzed. Operators using VSN had a significant reduction (48% lower, p \u3c 0.001) in their stress rate compared to when they were steering manually. There was no significant difference in the XTE SD for the steering type. The use of an automatic guidance system such as VSN could have a dramatic positive effect on the health of sprayer operators, especially during the long workdays of the peak spraying season, and could reduce the negative effects that stress and fatigue have on steering performance, mistakes, and accidents

Initial Fixation of a Femoral Knee Component: An In vitro and Finite Element Study

Loosening is the primary cause of total knee arthroplasty implant failure; therefore, to investigate this failure mode, femoral knee components were implanted in vitro on three cadaveric femurs. Bone-implant finite element (FE) models were created to predict the initial fixation of the interface of each femur. Initial fixation of the femoral knee component was successfully measured with the strain-gauged implants. Specimen-specific FE models were calibrated using the in vitro strain measurements and used to assess initial fixation. Initial fixation was shown to increase with bone density. The geometry of the implant causes the distal femur to deform plastically. It also causes higher stresses in the lateral side and higher pressures on the lateral surfaces. The implementation of plasticity in the bone material model in the FE model decreased these strains and pressures considerably from a purely elastic model, which demonstrated the importance of including plasticity

Session 2: \u3cem\u3eThe Effect of Boom Leveling on Spray Dispersion\u3c/em\u3e

Self-propelled sprayers are commonly used in agriculture to disperse agrichemicals. These sprayers commonly have two boom wings with dozens of nozzles that disperse the chemicals. Automatic boom height systems reduce the variability of agricultural sprayer boom height, which is important to reduce uneven spray dispersion if the boom is not at the target height. A computational model was created to simulate the spray dispersion under the following conditions: a) one stationary nozzle based on the measured spray pattern from one nozzle, b) one stationary model due to an angled boom, c) superposition of multiple stationary nozzles due an angled boom, and d) superposition of multiple nozzles given the inputs of measured boom heights and the position of the sprayer over a field in time. The effect of boom leveling on spray dispersion was compared for three boom leveling systems on two sprayers (Systems A and B on a John Deere R4045, Systems B and C on an AGCO RoGator 1100C). For each boom leveling system, the measured boom height and sprayer position in time for one run was used (medium terrain course at 26 kph (16 mph)) [Burgers et al. Appl. Eng. Agric. 2021]. For each run, a coverage map was calculated with the measured boom heights and a reference level boom; the spray application error was calculated as the difference between them. The area for which the application error was less than 10% was 34.4 and 56.6% for Systems A and B on the R4045, respectively, and 45.0 and 59.3% for Systems C and B on the RoGator, respectively. This model can be used to quantify and compare coverage maps from boom leveling systems

Comparison of Three Commercial Automatic Boom Height Systems for Agricultural Sprayers

Automatic boom height systems reduce the variability of agricultural sprayer boom height. Consistent boom height is important for three key reasons: to reduce uneven spray dispersion if the boom is too low, to reduce spray droplet drift if the boom is too high, and to reduce damage to the boom or crop if the boom is too low. No data is available comparing commercial boom height systems. Three leading North American automatic boom height systems were compared: John Deere BoomTrac Pro (System A), Raven AutoBoom® XRT (System B), and Norac UC5TM Passive Roll (System C) on a John Deere R4045 (Systems A and B) and RoGator 1100C (Systems B and C). Each system was evaluated with three test runs for at least three speeds over each of a mild, medium, and rough terrain course. Boom heights at the left and right outside sensors were measured with the AutoBoom XRT sensors. The accuracy of the automatic boom height systems was quantified with root mean squared deviation (RMSD), the Herbst-modified Hockley Index, and the fraction of points within 10 and 25 cm of target (f10 and f\u3c25). With four exceptions out of 216 comparisons, System B significantly outperformed System A on the R4045 and System C on the RoGator for each metric, at each sensor location, at each speed, on each terrain. At 26 km/h on medium terrain, the RMSD for Systems A and C was 174% and 107% larger than System B, respectively. At 26 km/h on medium terrain, the fraction of points within 25 cm (f\u3c25) was 56% and 21% higher for System B than Systems A and C, respectively. These results indicate System B kept the boom significantly closer to target with significantly less height variability

Compressive Properties of Trabecular Bone in the Distal Femur

Early loosening and implant migration are two problems that lead to failures in cementless (press-fit) femoral knee components of total knee replacements. To begin to address these early failures, this study determined the anterior–posterior mechanical properties from four locations in the human distal femur. Thirty-three cylindrical specimens were removed perpendicular to the press-fit surface after the surgical cuts on 10 human cadaveric femurs (age 71.5 ± 14.2 years) had been made. Compression testing was performed that utilized methods to reduce the effects of end-artifacts. The bone mineral apparent density (BMAD), apparent modulus of elasticity, yield and ultimate stress, and yield and ultimate strain were measured for 28 cylindrical specimens. The apparent modulus, yield and ultimate stress, and yield and ultimate strain each significantly differed (p\u3c0.05) in the superior and inferior locations. Linear and power law relationships between superior and inferior mechanical properties and BMAD were determined. The inferior apparent modulus and stresses were higher than those in the superior locations. These results show that the press-fit fixation characteristics of the femoral knee component differ on the anterior shield and posterior condyles. This information will be useful in the assignment of mechanical properties in finite element models for further investigations of femoral knee components. The property–density relations also have applications for implant design and preoperative assessment of bone strength using clinically available tools

Time Dependent Fixation and Implantation Forces for a Femoral Knee Component: An In Vitro Study

Implant survival rate is a primary concern for individuals receiving a primary total knee arthroplasty. Loosening is the primary reason for revision surgery and was therefore the focus of the current study. To better understand the mechanics of implant fixation, the time-dependent fixation of a femoral knee component was measured in vitro on three cadaveric femurs. The fixation of each femoral knee component was measured with strain gauged implants for at least 10 minutes on each femoral component. Additionally, impaction forces were measured during the implantation of each component. These forces were 2–6 times less than previously reported. The implantation impact forces were higher for the bones with higher bone density. Power law regressions were fit to the absolute value of the principal strains measured on the components over time to quantify the relaxation of the bone. The average power coefficient value for the three bones was lower for the bones with higher bone density. The average power coefficient value for the maximum principal strains was significantly higher than that of the minimum principal strains in each bone. The results were extrapolated to approximate the fixation strength at nine months after implantation. In this time period the strain was predicted to decrease to between 78 and 91% of the strain one second after implantation where those with lower bone density will have decreased fixation strength

Repair of Full-scale Timber Bridge Chord members by Shear Spiking

The addition of vertically-oriented shear spikes (fiberglass reinforced polymer rods) was shown to increase the effective stiffness of the stringers of a full-scale timber bridge chord specimen. Results found from the flexural load testing of a full-scale timber bridge chord laboratory specimen are presented. Reinforcement was provided with 19 mm diameter shear spikes bonded to the wood by an epoxy resin. The bridge chord specimen was intentionally damaged to simulate degradation. Shear spikes were then installed from the top of the member into pre‑drilled holes to provide horizontal shear resistance and to improve the flexural effective stiffness. Results from the testing showed that with the insertion of five sets of shear spikes the average flexural effective stiffness recovered in the four stringers of the chord was 91.6%

Biomechanical Evaluation of fracture Fixation Constructs using a Variable-angle Locked Periprosthetic Femur Plate System

BackgroundIn the United States there are more than 230,000 total hip replacements annually, and periprosthetic femoral fractures occur in 0.1–4.5% of those patients. The majority of these fractures occur at the tip of the stem (Vancouver type B1). The purpose of this study was to compare the biomechanically stability and strength of three fixation constructs and identify the most desirable construct.MethodsFifteen medium adult synthetic femurs were implanted with a hip prosthesis and were osteotomized in an oblique plane at the level of the implant tip to simulate a Vancouver type B1 periprosthetic fracture. Fractures were fixed with a non-contact bridging periprosthetic proximal femur plate (Zimmer, Inc., Warsaw, IN). Three proximal fixation methods were used: Group 1, bicortical screws; Group 2, unicortical screws and one cerclage cable; and Group 3, three cerclage cables. Distally, all groups had bicortical screws. Biomechanical testing was performed using an axial-torsional testing machine in three different loading modalities (axial compression, lateral bending, and torsional/sagittal bending), next in axial cyclic loading to 10,000 cycles, again in the three loading modalities, and finally to failure in torsional/sagittal bending.ResultsGroup 1 had significantly greater load to failure and was significantly stiffer in torsional/sagittal bending than Groups 2 and 3. After cyclic loading, Group 2 had significantly greater axial stiffness than Groups 1 and 3. There was no difference between the three groups in lateral bending stiffness. The average energy absorbed during cyclic loading was significantly lower in Group 2 than in Groups 1 and 3.ConclusionsBicortical screw placement achieved the highest load to failure and the highest torsional/sagittal bending stiffness. Additional unicortical screws improved axial stiffness when using cable fixation. Lateral bending was not influenced by differences in proximal fixation.Clinical RelevanceTo treat periprosthetic fractures, bicortical screw placement should be attempted to maximize load to failure and torsional/sagittal bending stiffness

Post-yield Relaxation Behavior of Bovine Cancellous Bone

Relaxation studies were conducted on specimens of bovine cancellous bone at post-yield strains. Stress and strain were measured for 1000 s and the relaxation modulus was determined. Fifteen cylindrical, cancellous bone specimens were removed from one bovine femur in the anterior–posterior direction. The relaxation modulus was found to be a function of strain. Therefore cancellous bone is non-linearly viscoelastic/viscoplastic in the plastic region. A power law regression was fit to the relaxation modulus data. The multiplicative constant was found to be statistically related through a power law relationship to both strain (p \u3c 0.0005) and apparent density (p \u3c 0.0005) while the power coefficient was found to be related through a power law relationship, E(t, ε)= A(ε)t-n(ε), to strain (p \u3c 0.0005), but not apparent density

Mice with a Heterozygous Lrp6 Deletion Have Impaired Fracture Healing

Bone fracture non-unions, the failure of a fracture to heal, occur in 10%–20% of fractures and are a costly and debilitating clinical problem. The Wnt/β-catenin pathway is critical in bone development and fracture healing. Polymorphisms of linking low-density lipoprotein receptor-related protein 6 (LRP6), a Wnt-binding receptor, have been associated with decreased bone mineral density and fragility fractures, although this remains controversial. Mice with a homozygous deletion of Lrp6 have severe skeletal abnormalities and are not viable, whereas mice with a heterozygous deletion have a combinatory effect with Lrp5 to decrease bone mineral density. As fracture healing closely models embryonic skeletal development, we investigated the process of fracture healing in mice heterozygous for Lrp6 (Lrp6+/−) and hypothesized that the heterozygous deletion of Lrp6 would impair fracture healing. Mid-diaphyseal femur fractures were induced in Lrp6+/− mice and wild-type controls (Lrp6+/+). Fractures were analyzed using micro-computed tomography (μCT) scans, biomechanical testing, and histological analysis. Lrp6+/− mice had significantly decreased stiffness and strength at 28 days post fracture (PF) and significantly decreased BV/TV, total density, immature bone density, and mature area within the callus on day-14 and -21 PF; they had significantly increased empty callus area at days 14 and 21 PF. Our results demonstrate that the heterozygous deletion of Lrp6 impairs fracture healing, which suggests that Lrp6 has a role in fracture healing