Asymptotically Stable Walking of a Five-Link Underactuated 3D Bipedal Robot

This paper presents three feedback controllers that achieve an asymptotically stable, periodic, and fast walking gait for a 3D (spatial) bipedal robot consisting of a torso, two legs, and passive (unactuated) point feet. The contact between the robot and the walking surface is assumed to inhibit yaw rotation. The studied robot has 8 DOF in the single support phase and 6 actuators. The interest of studying robots with point feet is that the robot's natural dynamics must be explicitly taken into account to achieve balance while walking. We use an extension of the method of virtual constraints and hybrid zero dynamics, in order to simultaneously compute a periodic orbit and an autonomous feedback controller that realizes the orbit. This method allows the computations to be carried out on a 2-DOF subsystem of the 8-DOF robot model. The stability of the walking gait under closed-loop control is evaluated with the linearization of the restricted Poincar\'e map of the hybrid zero dynamics. Three strategies are explored. The first strategy consists of imposing a stability condition during the search of a periodic gait by optimization. The second strategy uses an event-based controller. In the third approach, the effect of output selection is discussed and a pertinent choice of outputs is proposed, leading to stabilization without the use of a supplemental event-based controller

DDR5 클락 버퍼를 위한 LC PLL의 설계

학위논문(석사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2022. 8. 정덕균.This thesis describes a wide-range, fast-locking LC PLL for DDR5 clock buffer application. To operate LC PLL at wide range of input frequency, proposed PLL uses LC VCO with 28GHz center frequency and calculates appropriate division ratio of programmable divider for certain input frequen-cy at transient state. Calculating division ratio is achieved by using integer counter and fractional counter, detecting frequency of input clock at transient state. After calculating division ratio, proposed PLL operates as 3rd order charge pump PLL with optimum current value to lock fast. Proposed PLL is described with Systemverilog and simulation results shows that proposed LC PLL operates at 1 ~ 4.2GHz input frequency, while successfully acquires to lock at under 1μs. Also, LC-VCO is designed in a 40nm CMOS and simulation results shows that tuning range of VCO is ±9.25% with respect to center frequency of 28.2GHz, and VCO dissipates 26.4mW and phase noise is –104.86dBc/Hz at 1MHz offset, operating at center fre-quency with 1.1V supply voltage.본 논문은 DDR5 Clock Buffer를 위한, 넓은 범위에서 빠르게 락을 하는 LC PLL에 대해서 설명한다. 넓은 범위의 입력 주파수에서 LC PLL을 동작하기 위해, 제안한 PLL은 28GHz가 중심 주파수인 LC VCO을 사용하여, 과도 상태에서 특정 입력 주파수에 알맞는 프로그램 가능한divider의 제수를 계산한다. 제수의 계산은 과도 상태에서 입력 클락의 주파수를 감지하는 정수 카운터와 소수 카운터를 통해 이루어진다. 제수의 계산 이후, 제안한 PLL은 빠르게 락을 하기 위한 최적의 전류 값으로 3차의 Charge pump PLL로 동작한다. 제안한 PLL은 systemverilog로 기술되었고 시뮬레이션 결과 제안한 LC PLL은 1 ~ 4.2GHz의 입력주파수에서 동작하며, 1us 이내에서 성공적으로 락을 한다. 또한, LC-VCO가 40nm CMOS 공정에서 설계되었고, 시뮬레이션 결과 VCO의 튜닝 범위가 중심 주파수 28.2GHz을 기준으로 ±9.25%이고, 중심 주파수와 1.1V 공급 전압에서 26.4mW의 전력을 소모하고, phase noise가 1MHz 오프셋에서 -104.86dBc/Hz임을 확인할 수 있었다.CHAPTER 1 INTRODUCTION 1 1.1 MOTIVATION 1 1.2 THESIS ORGANIZATION 3 CHAPTER 2 BACKGROUND ON LC PLL 4 2.1 BASIS OF PLL 4 2.2 FREQUENCY RANGE AND LOCK TIME OF PLL 11 2.2.1 FREQUENCY RANGE 11 2.2.2 LOCK TIME 13 2.3 BASIS OF LC VCO 15 CHAPTER 3 DESIGN OF LC PLL FOR DDR5 CLOCK BUFFER 18 3.1 DESIGN CONSIDERATION 18 3.2 OVERALL ARCHITECTURE 20 3.3 OPERATION PRINCIPLE 24 3.4 IMPLEMENTATION OF LC VCO 33 3.5 ALTERNATIVE DESIGN CHOICE OF LC PLL FOR DDR5 CLOCK BUFFER 35 CHAPTER 4 SIMULATION RESULT 37 4.1 PLL 37 4.2 LC VCO 42 CHAPTER 5 CONCLUSION 46 BIBLIOGRAPHY 47 초 록 49석

Design and control of a clutch for a minimally-actuated biped based on the passive-dynamic simple walker

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (leaf 41).Passive-dynamic walking robots are remarkable mechanical devices capable of maintaining dynamically stable walking gaits with no actuation or control. These systems, however, depend on ideal environmental conditions for stability. Robustness and control capabilities are increased with actuation, but so is the power consumption. Such actuated robots are designed to minimize the actuation requirement by exploiting the system natural dynamics system, but still need actuation to compensate for energy dissipated by friction and collision events, as well as for more control capabilities. A simple clutch mechanism is developed for such systems to allow intermittent control of otherwise passive joints, allowing controllers to exploit the passive or actuated control when desired. The clutch is tested on a hip actuated simple 3D walker to evaluate the performance capabilities of clutched control. Preliminary tests of several control strategies suggest the clutched actuation may provide good performance at a higher efficiency compared to fully actuated systems. This paper describes the development of the clutch device and the hip-actuated biped on with which the clutch is tested, and evaluates the performance of intermittent clutch-control for several control strategies.by Arlis Reynolds.S.B

Model-based powertrain design and control system development for the ideal all-wheel drive electric vehicle

The transfer case based all-wheel drive electric vehicle (TCAWDEV) and dual-axle AWDEV have been investigated to balance concerns about energy consumption, drivability and stability of vehicles. However, the mentioned powertrain architectures have the torque windup issue or the wheel skidding issue. The torque windup is an inherent issue of mechanical linked all-wheel drive systems. The hydraulic motor-based or the electric motor-based ideal all-wheel drive powertrain can provide feasible solutions to the mentioned issues. An ideal AWDEV (IAWDEV) powertrain architecture and its control schemes were proposed by this research; the architecture has four independent driving motors in powertrain. The IAWDEV gives more control freedoms to implement active torque controls and traction mode controls. In essence, this research came up with the distributed powertrain concept, and developed control schemes of the distributed powertrain to replace the transfer case and differential devices. The study investigated the dual-loop motor control, the hybrid sliding mode control (HSMC) and the neural network predictive control to reduce energy consumption and achieve better drivability and stability by optimizing the torque allocation of each dependent wheel. The mentioned control schemes were respectively developed for the anti-slip, differential and yaw stability functionalities of the IAWDEV powertrain. This study also investigated the sizing method that the battery capacity was estimated by using cruise performance at 3% road grade. In addition, the model-based verification was employed to evaluate the proposed powertrain design and control schemes. The verification shows that the design and controls can fulfill drivability requirements and minimize the existing issues, including torque windup and chattering of the slipping wheel. In addition, the verification shows that the IAWDEV can harvest around two times more energy while the vehicle is running on slippery roads than the TCAWDEV and the dual-axle AWDEV; the traction control can achieve better drivability and lower energy consumption than mentioned powertrains; the mode control can reduce 3% of battery charge depleting during the highway driving test. It also provides compelling evidences that the functionalities achieved by complicated and costly mechanical devices can be carried out by control schemes of the IAWDEV; the active torque controls can solve the inherent issues of mechanical linked powertrains; the sizing method is credible to estimate the operation envelop of powertrain components, even though there is some controllable over-sizing

Development of an electronic control unit for the T63 gas turbine

Includes bibliographical references.Fundamental research has been undertaken at the SASOL Advanced Fuels Laboratory to investigate the effects of the chemistry and physical properties of both conventional and synthetic jet fuels on threshold combustion. This research was undertaken using a purpose built low pressure continuous combustion test facility. Researchers at the laboratory now wish to examine these effects on an aviation gas turbine in service for which “off-map” scheduling of fuel to the engine would be required. A two phase project was thus proposed to develop this capability; the work of this thesis embodies Phase I of that project

DESIGN OF AN ANTI-JERK CONTROLLER FOR BOTH LOCKED AND SLIPPING TORQUE CONVERTER CONDITIONS IN A VEHICLE

With the advancement in the automotive technologies, the customer scrutiny on the ride comfort of automobiles has come to light. Vehicle drivability is one of the important aspects that defines the ride comfort for a vehicle. Drivability of a vehicle is a qualitative measure and may differ from person to person, however, researches have come up to highlight a few parameters that can categorize the drivability performance of a vehicle into good or bad for a majority of the targeted audience. One of those parameters include shuffle, which is defined as the longitudinal oscillations that occurs in the drivetrain when a sudden demand for torque rise or drop is made. Another such parameter is the sluggishness in the delivery of torque at wheels against the requested torque by the driver. This can exist due to the shift in the dynamics during the drivetrain operation from locked torque converter clutch to slipping torque converter clutch. This work addresses both the drivability related issues, namely, shuffle and torque lag mentioned in the preceding para. Initially, the shuffle oscillations generated in a vehicle are analyzed when subjected to a sudden positive to positive driver torque tip-in request. Further, a pre-compensator and feedback controller based control scheme is designed to damp those shuffle oscillations while keeping the torque delivery response fast. This control approach shapes the actuator torque (i.e., an engine or an e-motor) in such a way that the desired response is achieved. Next, the problem of sluggish torque response at wheels due to slipping of the torque converter clutch is addressed. Initially, a model-based feedforward and feedback controller is developed to control the actuator torque such that when the torque converter slips, an extra compensatory torque from the actuator is applied. This compensation torque ensures that the torque response at the turbine and succeeding driveline components up till the wheels is maintained as desired. However, the actuator has some physical limitations in terms of the maximum magnitude and rate of the torque delivery. So, at some instances, the torque request generated by the controller may not be feasible for the actuator to follow. This problem is addressed when another controller, based on model predictive control approach, is proposed. This controller is based on the approach that continuously updates the controller of the torque delivery of the actuator. The controller solves an optimisation problem over the defined constraints of the actuator and plant, and further finds the most feasible response for the actuator to follow within its defined operating range. Later, A comparison between the two controllers showed model predictive controller to be 15.3% better in terms of the propeller shaft torque response than the feedforward and feedback controller, for the problem under discussion