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Materials and methods 48 4.3 Physical prototype of the hoeing tool 4.3.1 Selection of the drive for the hoeing tool Preferably, a hydro engine system would be chosen for controlling the hoeing tool as a tractor implement. Although the hydraulic system can fulfil the requirements, for the high accuracy and dynamics expected from the intra-row weeding tool a hi-pressure servo-hydraulic solution will be necessary. Such a solution would significantly increase the costs of the experiments and after consideration of the required parameters an electrical servo drive able to provide same performance like a hydro system was choosen. 4.3.1.1 Electrical servo drive A servo motor, or servo drive, is a system which combines a motor with a controller and positioning device to precisely regulate the speed or position of a load. Such a system allows controlling of the load, concerning different parameters such as speed, torque or position or direction. Its basic components are an interface panel which sends a command signal, a positioning controller which receives the signal, a servo control amplifier which provides power to the servo motor, and a feedback device which relays information about position or velocity of the motor and load. The servo can be controlled through semiconductors, such as silicon controller rectifiers (SCR). Used alone, an SCR is effective but does not provide compete control (Baldor Electric company 2007). Power from the SCR comes in discrete pulses, thus instant acceleration and maintaining of the steady state are feasible, but when the motor must be slowed down the SCR can only be turned off. In such a case there is no direct control of the motor and the deceleration of the load is affected by inertial force. With additional electronics a transport delay in the load response can be introduced to provide more uniform speed changes, but this often introduces too much system inertia and is not suitable for applications requiring rapid modification of the speed. Transistors can be used to create a more linear power response which is delivered constantly rather than in discrete pulses like the SCR alone. Other techniques exist as well, including pulse width modulation (PWM) and pulse frequency modulation
Materials and methods (PFM). As the names imply, either the width of constant frequency pulse signals or the frequency of constant width pulse signals can tell the motor to apply more or less power at any given time. The actual motor combined with a servo drive can theoretically be of any type. Earlier, direct current (DC) motors were generally combined with a servo drive because the only type of control for large currents was through SCRs. However, alternating current (AC) motors, the most commonly used motors in industrial applications, become used more often as transistors became capable of controlling large currents and switching the large currents at high frequencies. If a motor is intended to be used as a servo motor it needs to be able to operate at range of speeds without overheating, to operate at zero speed and retain sufficient torque to hold a load in position and to operate at very low speed for long periods of time without overheating. In stepper motors, a reasonable alternative to servo motors, the drive receives low-level signals from the indexer or control system and converts them into electrical (step) pulses to run the motor. A stepper drive is a typical example of an open loop system. Generally, stepper motors are limited to small torque and speed requirements. The permanent magnet DC (PMDC) motor is the best and predominantly used motor for start-stop, servo device applications. The permanent magnets produce a constant field flux at all speeds and therefore a linear speed torque curve. Other advantages are high starting torque, small frame, light weight, and linear and predictable behaviour. A unique aspect of a servo motor is its feedback control, closed loop function. Motors controlled in open loop, comprising most simple motors including stepper motors, operate under the assumption that motion has taken place once the control signal has been sent. In case the motor’s move is disabled, for example due to jamming, the controlling unit of the open loop system does not receive information about the problem and cannot make any correction. Closed loop systems contain a feedback device that can detect whether the desired effect on the load has taken place, and subsequently alert the control device to 49
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Institut für Landtechnik der Rhein
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Development of a novel mechatronic
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Kurzfassung Entwicklung eines neuar
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Acknowledgements Acknowledgements M
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Table of contents Table of contents
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Glossary of abbreviations and symbo
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Symbol Unit Description Mmmax Nm Ma
Page 15 and 16: Symbol Unit Description Glossary of
Page 17: ωold ωout rad s -2 Latest rotatio
Page 20 and 21: Introduction The most frequently us
Page 22 and 23: Introduction application that had p
Page 24 and 25: Introduction be to go from a system
Page 26 and 27: Introduction limited and environmen
Page 28 and 29: Introduction than 40 years before g
Page 30 and 31: Introduction techniques. It is know
Page 32 and 33: Introduction Sowing and planting al
Page 34 and 35: Introduction Inter-row weeding syst
Page 36 and 37: Introduction 18 Figure 1.3 Inter-ro
Page 38 and 39: State of the art 20 Figure 2.1 a) F
Page 40 and 41: State of the art cylinder rotates a
Page 42 and 43: State of the art 1998). This device
Page 44 and 45: State of the art 26 2.2 Detection o
Page 46 and 47: State of the art The fluorescence s
Page 48 and 49: Definition of the problem and resea
Page 51 and 52: 4 Materials and methods 4.1 Detecti
Page 53 and 54: Materials and methods Figure 4.1 a)
Page 55 and 56: Materials and methods Figure 4.3 a)
Page 57 and 58: 4.1.2 Data acquisition 4.1.2.1 Hard
Page 59 and 60: 4.1.4 Test objects Materials and me
Page 61 and 62: Materials and methods become a poss
Page 63 and 64: Materials and methods environments
Page 65: Materials and methods dimensions ne
Page 69 and 70: Materials and methods A command sig
Page 71 and 72: Materials and methods The drive con
Page 73: Materials and methods Another tool
Page 76 and 77: Results and discussion 58 Figure 5.
Page 82 and 83: Results and discussion objects. Acc
Page 84 and 85: Results and discussion Plant positi
Page 86 and 87: Results and discussion Plant positi
Page 88 and 89: Results and discussion 70 5.1.4 Dis
Page 92 and 93: Results and discussion Connection b
Page 94 and 95: Results and discussion 76 5.2.1 Opt
Page 96 and 97: Results and discussion xmi1 = ( RLA
Page 98 and 99: Results and discussion With the inv
Page 100 and 101: Results and discussion 82 Horizonta
Page 102 and 103: Results and discussion 84 5.2.4 Sel
Page 104 and 105: Results and discussion 86 5.2.5 Dis
Page 106 and 107: Results and discussion Conventional
Page 108 and 109: Results and discussion Since the fi
Page 110 and 111: Results and discussion To avoid con
Page 112 and 113: Results and discussion As the size
Page 114 and 115: Results and discussion 96 5.3.4 Alg
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Results and discussion 98 V = zc( t
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Results and discussion corresponds
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Results and discussion 102 5.3.6 Me
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Results and discussion hoeing accur
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Results and discussion between the
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Results and discussion distance fro
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Results and discussion Distribution
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Results and discussion cuts are ran
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Results and discussion Forward spee
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Results and discussion x [mm] Distr
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Results and discussion The experime
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6 Summary Summary Neither a mechani
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Summary The third part of the work
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7 Conclusions Conclusions The prese
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8 References References Agrios, G.
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References in California's Sacramen
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References Johnson, W C and Mullini
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References Schans, D. v. d. et al.
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List of figures List of figures Fig
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List of figures Figure 5.24 Scheme
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Plant position 9 Appendix Table 9.1
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Plant position Table 9.3 Detection
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Personal data Education About the a
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