Load distribution measurement instrument for oscillating follower cam mechanism.

Cam mechanism is widely applied in industry because it can help achieve various complex motions of the follower via the cam contour design. However, its performance is significantly affected by the wear condition. This study proposes a load distribution measurement instrument to assist the study on friction and wear regularities of oscillating follower cam mechanisms through obtaining the normal pressure (F) and friction force (Ff) distributions along the cam profile. In the instrument, F and Ff are automatically calculated via a MATLAB program based on the geometry and the measured rotary resistance torque and rotary angle of the cam. The latter two parameters are obtained through a static torque sensor and a rotary encoder built in servo motor in real time, respectively. An experimental test was conducted and the cam morphology after service was observed using scanning electron microscopy. Results show that the wear condition of the cam is significantly related to the corresponding F and Ff. Complex load parameters of oscillating follower cam mechanisms can be provided by this instrument, which is crucial in understanding the friction and wear behaviors of cams and finding the vulnerable position.

Influence of clamping stress and duration on the trauma of liver tissue during surgery operation.

BACKGROUND: Tissue grasping damage often occurs in minimally invasive surgery, which would increase the postoperative recovery time and the risk of surgical complications. The purpose of this study was to evaluate the relationship between liver tissue trauma and compression stress magnitude and duration during tissue clamping operation. METHODS: The clamping experiments of liver tissues in vivo were conducted by using a universal soft tissue mechanical testing machine under different clamping stress magnitudes and durations. The rabbit liver was used to simulate human liver. A minimally invasive surgery grasper was used in these tests to simulate the real tissue-surgical operation condition. A pathological grading system was created to quantitatively assess the trauma within the liver tissue. The hyperbolic regression models were utilized to predict the trauma degree of liver tissue. FINDINGS: Obvious hyperemia, hemorrhage, hepatic capsule rupture and inflammatory cell infiltration appeared in the clamping sites of the liver. Assessment results indicated that the trauma degree increased nonlinearly with the increasing clamping stress and duration time. There exist safe thresholds, in which the severe trauma of the studied tissue can be avoided during grasping operation. INTERPRETATION: The results could provide the safety margins and the trauma prediction models for surgeons during grasping and palpation tasks in minimally invasive surgery.

Technical note: An in vitro study of dental microwear formation using the BITE Master II chewing machine.

Dental microwear has been used for decades to reconstruct the diets of fossil hominins and bioarchaeological populations. The basic theory has been that hard-brittle foods (e.g., nuts, bone) require crushing and leave pits as they are pressed between opposing cheek-tooth surfaces, whereas soft-tough foods (e.g., grass blades, meat) require shearing and leave scratches as they are dragged along opposing surfaces that slide past one another. However, recent studies have called into question the efficacy of microwear as an indicator of diet. One issue has been the limited number of in vitro studies providing empirical evidence for associations between microwear pattern and chewing behavior. We here describe a new study using a chewing simulator, the BITE Master II, to examine the effects of angle of approach between opposing teeth and food consistency on microwear surface texture. Results indicate that opposing teeth that approach one another: 1) perpendicular to the occlusal plane (crushing) result in pits; 2) parallel to the occlusal plane (shearing) result in striations in the direction of movement; and 3) oblique to the occlusal plane (45°) result in both striations and pits. Results further suggest that different food types and abrasive loads affect the propensity to accumulate microwear features independent of feature shapes.