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The Electro-Hydrostatic Actuator (EHA) is a self-contained and modular hydraulic actuation system using feedback control. EHAs are being increasingly used in engineering and industrial systems that require high precision and efficiency such as aircrafts (Airbus 380), off-highway hydraulic hybrids and construction machineries. In this research, mathematical models (linear and nonlinear) with different control strategies (that include PID, PID with feedforward compensation, and Sliding Mode Control (SMC)) are developed and experimentally applied to an EHA prototype. These methods are then compared to a new control strategy that is a combination of Interacting Multiple Model concept, Sliding Mode Control (IMM-SMC) and the Smooth Variable Structure Filter (SVSF). The IMM and the SMC strategies are also applied with the Kalman Filter (KF) for comparison. The above mentioned control strategies were implemented on an EHA prototype for position control under a range of fault conditions that were physically simulated. Both simulation and experimental results showed that the new IMM-SMC with SVSF outperformed all the other control strategies in terms of robustness and precision in trajectory tracking. / Thesis / Master of Applied Science (MASc)

Thesis (M. Sc. Agriculture (Crop Science)) -- University of Limpopo, 2008 / Striga control through agronomic practices is the key to maize production predominantly in small holder farmers who cannot afford chemical weed control. Striga has affected maize yield in many areas in Limpopo Province, South Africa. Field experiments were carried out over one season at three sites to determine the effect of weed control method on striga on maize. The experiment was done at Mafarana village (Mopani District) near Tzaneen where striga is a serious problem. It was conducted on three fields, belonging to Mrs. Shingwenyana, Mr. Nyathi and Mr. Mushwana. A randomized complete block design experiment was laid out consisting of two factors; (i) two maize cultivars i.e. Zm 1421 and Zm 423 (ii) three agronomic practices: hand hoeing alone (as the control factor), hand hoeing plus inorganic fertilization using lime ammonium nitrate (LAN-28%N) at the rate of 56kg/ha, and hand hoeing plus inter-row intercropping of maize with cowpea. Cowpea cultivar Bechuana White was used for the experiment. The results indicated that the effect of the method of weed control on the number of striga plants was significant at the 5% level of significance at all locations except at Mushwana’s where at 105 days after planting (DAP) there was no significant effect. Striga numbers were lower in hand hoed plus inorganic fertilizer plots compared to hand hoed alone and hand hoed plus intercropping. At Shingwenyana’s field the results indicated that effect of weed control methods on grain yield was significant and this is where the striga numbers were the highest than at Mushwana and Nyathi’s fields. The effect of weed control methods on grain yield was significant only at Shingwenyana’s field ranging from 2219kg/ha (hand hoeing), 2248kg/ha (hand hoeing plus inorganic fertilizer) to 3928kg/ha (hand hoeing plus intercropping). The effect of weed control method on shelling %, hundred seed weight, number of cobs per plant and lodging % was not significant. The effect of weed control method on number of plants per plot was significant at Mushwana’s field only. There was significant difference of striga numbers among maize varieties at Nyathi’s field at 105 DAP. In hand hoed, striga numbers were 0.075 for Zm 1421 and 0.489 for Zm 423. Plots that were hand hoed plus inorganic fertilizer application striga numbers were 0.075 for Zm 1421 and 0.270 for Zm 423 and finally hand hoed plus intercropped plots with maize and cowpeas had striga numbers of 0.739 for 1421 and 0.850 for ZM 423. It is recommended that farmers improve the fertility status of their soils in order to control striga problem. / Limpopo Department of Agriculture

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An examination into the influence of observed gaze cues on motor output. / Richardson and colleagues (2013) demonstrated oculo-manual spatial interference by finding that the finger trajectory in a vertical tapping task deviated toward the direction of a concurrent saccade. It was proposed that the entrainment of the hand to the eyes was in part a function of generalized motor planning. Human action observation research has shown that cortical motor planning is also active during action observation (e.g. Buccino et al. 2001; Decety et al. 1997), which can lead to other forms of spatial interference (Kilner et al 2003). We hypothesized that because motor planning subserves both observation and execution of action, simply observing the horizontal saccades of another person would cause sufficient recruitment of oculomotor planning structures, that would result in finger tap trajectory deviations toward the direction of the observed saccade (but would not do so in a non-biological observation control condition).19 participants performed 24 trials of vertical finger taps under three different visual conditions. They were required to: a) saccade horizontally between targets; b) fixate on a biological stimulus (i.e. a video of horizontally saccading human eyes); or c) fixate on a non-biological control stimulus (horizontally moving black dots) while tapping their finger to an auditory metronome beat presented at a 750ms intervals. Results from the saccading condition replicate Richardson et al’s (2013) entrainment effect. That is, finger taps deviated to the left when participants saccaded left, and to the right when executed with a rightward saccade. Contrary to expectations however, there was no entrainment induced by observing either the biological stimulus or the control stimulus. This suggests that competing motor plans (eyes and hands) are necessary to induce interference. Further, simply observing eye movements do not recruit the same oculomotor planning networks as action execution. / Thesis / Master of Science in Kinesiology

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