For hydraulic hybrid excavators (HEEs), two recoverable energy sources for power hybridization ar... more For hydraulic hybrid excavators (HEEs), two recoverable energy sources for power hybridization are from engine optimization and actuator energy regeneration. This paper presents a hydraulic hybrid system that integrates with these two sources using engine torque coupling and boom energy regeneration, thus to further explore the fuel economy potential of HHE. Their different characteristics are analyzed first to perform specialized system design. Then an optimal control problem is formulated and solved for system sizing. The effectiveness of the proposed system and its energy saving performance will be assessed, as well as the contributions of engine torque coupling and boom ERS, respectively.
For a compressed air energy storage (CAES) system to be competitive for the electrical grid, the ... more For a compressed air energy storage (CAES) system to be competitive for the electrical grid, the air compressor/expander must be capable of high pressure, efficient and power dense. However, there is a trade-off between efficiency and power density mediated by heat transfer, such that as the process time increases, efficiency increases at the expense of decreasing power. This trade-off can be mitigated in a liquid (water) piston aircompressor/expander with enhanced heat transfer. However, in the past, dry air has been assumed in the design and analysis of the compression/expansion process. This paper investigates the effect of moisture on the compression efficiency and power. Evaporation and condensation of water play contradictory roles-while evaporation absorbs latent heat enhancing cooling, the tiny water droplets that form as water condenses also increase the apparent heat capacity. To investigate the effect of moisture, a 0-D numerical model that takes into account the water evaporation/condensation and water droplets have been developed. Results show that inclusion of moisture improves the efficiencypower trade-off minimally at lower flow rates, high efficiency cases, and more significantly at higher flow rates, lower efficiency cases. The improvement is primarily attributed to the increase in apparent heat capacity due to the increased propensity of water to evaporate.
In recent years several novel hydraulic architectures have been proposed with the intention of si... more In recent years several novel hydraulic architectures have been proposed with the intention of significantly increasing system efficiency. Two of these architectures, Steigerung der Energieefflzienz in der Arbeitshydraulik mobiler Arbeitsmaschinen (STEAM), and the Hybrid Hydraulic-Electric Architecture (HHEA), use a system of multiple common pressure rails (CPRs) to serve the multiple degrees-of-freedom of the machine. The key difference is that STEAM throttles hydraulic power from these rails while HHEA combines electric and hydraulic power to meet actuator demands. As a throttle-less architecture, HHEA is expected to save more energy than STEAM at the expense of added complexity. Therefore, it is useful to quantify this additional energy saving. Both systems have discrete operational choices corresponding to how the CPRs are utilized for each actuator. It is necessary to determine optimal operation for each of these architectures for analysis and fair comparison. Techniques for optimal operation of the HHEA have been developed previously from the Langrange multiplier method. Applying the same optimal control method to STEAM encountered some technical challenge leading to the optimal control algorithm not being able to satisfy certain constraints. The issue is analyzed and solved by adding noise to the optimization. Using this proposed algorithm, case studies are performed to compare the energy-saving potentials of STEAM and HHEA for two sizes of excavators and a wheel-loader performing representative duty cycles. The baseline is a standard load-sensing architecture. Results show that STEAM and HHEA can reduce energy consumption between 35–65% and 50–80% respectively.
The hydraulic human power amplifier (HPA) is a tool similar to exoskeleton that uses hydraulic ac... more The hydraulic human power amplifier (HPA) is a tool similar to exoskeleton that uses hydraulic actuation to amplify the applied human force. The control objective is to make the system behave like a passive mechanical tool that interacts with the human and the environment passively with a specified power scaling factor. In our previous work, a virtual velocity coordination approach recasts the single degree-of-freedom human power amplifier control problem into a velocity coordination with a fictitious reference mechanical system. Force amplification becomes a natural consequence of the velocity coordination. In this paper, this control approach is extended for fully coupled multi-DoF systems. A passivity based control approach that uses the natural energy storage of the hydraulic actuator to take full account of the nonlinear pressure dynamics is used to define the flow requirement. Additional passive assistance dynamics are designed and implemented to enable the user to perform specific tasks more easily. Guidance is achieved using a passive velocity field controller (PVFC), and obstacle avoidance is achieved using a potential field. Experimental results demonstrate good performance on a 2-DoF Human Power Amplifier. * Fredrik Eskilsson was an international exchange student at the University of Minnesota.
In the AHS architecture of the California PATH program traffic is organized into platoons of clos... more In the AHS architecture of the California PATH program traffic is organized into platoons of closely spaced vehicles. Whenever platoons are formed or broken up, the large relative motion between platoons, increases the risk of high relative velocity collisions. In this paper we derive a safety region for the relative velocity between two platoons. By guaranteeing that the relative velocity between platoons remains in this region, impacts of high relative velocity can be avoided. For each one of the four control laws that a platoon leader can perform in normal operation, a desired velocity profile for the platoon that satisfies safety and time-optimality requirements is derived. A nonlinear velocity controller is designed to track the desired velocity profile within a given error bound. When safety is not compromised, this controller keeps the acceleration and jerk of the vehicles in the platoon within comfort limits.
A hydro-mechanical transmission (HMT) transmits power both mechanically and hydraulically allowin... more A hydro-mechanical transmission (HMT) transmits power both mechanically and hydraulically allowing continuously variable transmission ratios and more efficient transmission than hydrostatic transmission. A conventional HMT tends to be costly and bulky since it has a hydrostatic transmission in parallel with a mechanical transmission. An alternative is a compact inline configuration that utilizes a two-shafted pump that is mechanically and hydraulically connected to a motor. This avoids the need for a planetary gear set while providing the HMT functionality. When the pump/motor displacement is zero, all of the power is transmitted mechanically and the transmission ratio is unity, a condition referred to as lock-up that is expected to be very efficient. Previous research however has shown significant losses at this operating condition in experiments. This is thought to be caused primarily by compressibility losses due to the repeated unnecessary opening and closing of the distributor valves. This paper first models the Hondamatic in simulations to confirm that compressibility losses contribute to the low efficiency at lock-up. Second, the paper proposes a solution to reduce these compressibility losses by means of a second cam mode that closes the distributor valves to prevent flow between the piston and the high and low pressure volumes. The performance of the existing inline HMT and the proposed solution at lock-up are modeled in simulations and compared. The results indicate a 10% increase in efficiency at lock-up.
Hydraulic systems, as power source and transmission, offer many advantages over electromechanical... more Hydraulic systems, as power source and transmission, offer many advantages over electromechanical or purely mechanical counterparts in terms of power density, flexibility and portability. Many hydraulic systems require touching and contacting the physical environments; and many of these systems are directly controlled by human. If hydraulic systems are passive, they would be safer to interact with, and easier for human to control. In this paper, we describe our current research in developing bilateral passive teleoperated hydraulic machines which a human operator controls via a force feedback joystick. Two key developments are 1) methodologies to passify the electrohydraulic valves as a two-port device, and 2) the passive teleoperation controllers.
Linköping electronic conference proceedings, Dec 20, 2017
A hardware-in-the-loop (HIL) testbed for testing and evaluating experimental hydraulic transforme... more A hardware-in-the-loop (HIL) testbed for testing and evaluating experimental hydraulic transformers has been developed. The testbed is capable of emulating a variety of loading conditions specified by the desired work cycle operation of various hydraulic machines, such as humanoid robots or excavators. The HIL testbed is a useful research tool as it allows studying the dynamics of many desired loading conditions without having to obtain and reconfigure the said physical hardware for each case. This paper discusses the background, construction, and control of the HIL testbed with the experimental results. Preliminary results demonstrating the functionality of an experimental switch mode hydraulic transformers are also presented.
This paper propose an approach to extract the most significant color information that takes into ... more This paper propose an approach to extract the most significant color information that takes into account 1) the inherent sensitivity of the Human Visual System (HVS) to color variations and 2) the sensitivity of the HVS to specific colors of a given image. By giving higher importance to the significant colors in the stabilization control formulation, it is possible to retain the consistency of only the most significant colors to a human viewer. Such restriction is critical due to the limited actuation authorities of typical xerographic color printing process. To account for color-specific sensitivity, we make use of the CIE L*a*b* color formulation. To account for the image-specific sensitivity, we make use of the fact that the HVS have lower sensitivity to high frequency components (detail) of high chrominance image. Moreover, typically “smooth” images are visually more irrelevant compared to textured and detailed images. These effects in the color and spatial domain are taken into account to reduce the redundancy in the image representation by following similar procedure to that used in wavelet transform coding decomposition. Introduction The color reproduction characteristics(CRC) function describes how a printer maps the desired colors into actual printed colors. These printed colors vary with time due to printer dynamics as well as environmental and material variations, resulting in inconsistent color prints. In our current and previous works [1, 2, 3, 4], we have looked into control and sensing issues of maintaining tone and color consistency. The key control challenge is the high dimensional print-map (in that a color printer can reproduced high numbers of colors) with limited actuation authorities. This means that it is not possible to maintain the consistency of all the printed colors. In this paper, we developed a technique to stabilize only colors that are significant to a human viewer. Specifically there are two main redundancies of a printed image. The first is the inherent sensitivity of the Human Visual System (HVS) to color variations. In fact it is well known that human does not differentiate two colors with a ∆E∗ 94 < 1 [5]. The second redundancy can be found on the printed color image itself. For a color image, the redundancies can be found in the color and spatial representation of the image. Human visual system (HVS) has lower sensitivity to high frequency components (details) of high chrominance image. Moreover, typically “smooth” images are visually more irrelevant compared to textured and detailed images. These effects in the color and spatial domain are taken into account to reduce the redundancy in the image representation by following similar procedure to that used in wavelet transform coding [6]. The multi-resolution properties of wavelet decomposition is particularly well suited to the characteristics of the HVS because psycho-visual studies show that the human visual system can be modeled using multiple perceptual channels, which are octavewise spread over the spatial frequency range. From one octave to the next, the summation area (area of the retina contributing to the perceived signal) also changes by a factor of four. This behavior match that of the dyadic structure of the discrete wavelet transform. Problem Formulation In both sensing and control for maintaining color consistency, it is convenient to take the input colorspace as the CMY colorspace and the output colorspace as the CIE L∗a∗b∗ colorspace [1]. Uniformly discretizing the CMY colorspace domain, by M1, M2 and M3 points in each of the C, M, Y coordinates respectively, the CRC can be adequately approximated by its response at a finite number of Mt = M1M2M3 color combinations. Let L∗ i a ∗ i b ∗ i (k) denotes the i-th values of the Mt discretized points time-varying output color gamut of the printer. In this context, the time dependent error vector, ē(k) ∈R3Mt of discretized output of the spatial signal is given by: ē(k)= [ ∆L∗ 1(k), . . . ,∆L ∗ Mt (k),∆a ∗ 1(k), . . . ,∆a ∗ Mt (k),∆b ∗ 1(k), . . . ,∆b ∗ Mt (k) ] (1) where ∆L∗ i (k) := L ∗ i (k)−L∗∗ i , ∆ai (k) := ai (k)− a∗∗ i , ∆bi (k) := bi (k)− b∗∗ i . L∗∗ i a∗∗ i b∗∗ i gives the i-th value of the nominal color gamut. In the color stabilization control formulation [1], we can then specify the relative importance of the CRC errors at different colors for their stabilization given by the performance index term: J(k) = ēT (k)Weē(k) ∈R (2) where the error weighting is given by We ∈ R3Mt×3Mt . The error weighting matrix is made up of the color and image specific weightings i.e.:
For hydraulic hybrid excavators (HEEs), two recoverable energy sources for power hybridization ar... more For hydraulic hybrid excavators (HEEs), two recoverable energy sources for power hybridization are from engine optimization and actuator energy regeneration. This paper presents a hydraulic hybrid system that integrates with these two sources using engine torque coupling and boom energy regeneration, thus to further explore the fuel economy potential of HHE. Their different characteristics are analyzed first to perform specialized system design. Then an optimal control problem is formulated and solved for system sizing. The effectiveness of the proposed system and its energy saving performance will be assessed, as well as the contributions of engine torque coupling and boom ERS, respectively.
For a compressed air energy storage (CAES) system to be competitive for the electrical grid, the ... more For a compressed air energy storage (CAES) system to be competitive for the electrical grid, the air compressor/expander must be capable of high pressure, efficient and power dense. However, there is a trade-off between efficiency and power density mediated by heat transfer, such that as the process time increases, efficiency increases at the expense of decreasing power. This trade-off can be mitigated in a liquid (water) piston aircompressor/expander with enhanced heat transfer. However, in the past, dry air has been assumed in the design and analysis of the compression/expansion process. This paper investigates the effect of moisture on the compression efficiency and power. Evaporation and condensation of water play contradictory roles-while evaporation absorbs latent heat enhancing cooling, the tiny water droplets that form as water condenses also increase the apparent heat capacity. To investigate the effect of moisture, a 0-D numerical model that takes into account the water evaporation/condensation and water droplets have been developed. Results show that inclusion of moisture improves the efficiencypower trade-off minimally at lower flow rates, high efficiency cases, and more significantly at higher flow rates, lower efficiency cases. The improvement is primarily attributed to the increase in apparent heat capacity due to the increased propensity of water to evaporate.
In recent years several novel hydraulic architectures have been proposed with the intention of si... more In recent years several novel hydraulic architectures have been proposed with the intention of significantly increasing system efficiency. Two of these architectures, Steigerung der Energieefflzienz in der Arbeitshydraulik mobiler Arbeitsmaschinen (STEAM), and the Hybrid Hydraulic-Electric Architecture (HHEA), use a system of multiple common pressure rails (CPRs) to serve the multiple degrees-of-freedom of the machine. The key difference is that STEAM throttles hydraulic power from these rails while HHEA combines electric and hydraulic power to meet actuator demands. As a throttle-less architecture, HHEA is expected to save more energy than STEAM at the expense of added complexity. Therefore, it is useful to quantify this additional energy saving. Both systems have discrete operational choices corresponding to how the CPRs are utilized for each actuator. It is necessary to determine optimal operation for each of these architectures for analysis and fair comparison. Techniques for optimal operation of the HHEA have been developed previously from the Langrange multiplier method. Applying the same optimal control method to STEAM encountered some technical challenge leading to the optimal control algorithm not being able to satisfy certain constraints. The issue is analyzed and solved by adding noise to the optimization. Using this proposed algorithm, case studies are performed to compare the energy-saving potentials of STEAM and HHEA for two sizes of excavators and a wheel-loader performing representative duty cycles. The baseline is a standard load-sensing architecture. Results show that STEAM and HHEA can reduce energy consumption between 35–65% and 50–80% respectively.
The hydraulic human power amplifier (HPA) is a tool similar to exoskeleton that uses hydraulic ac... more The hydraulic human power amplifier (HPA) is a tool similar to exoskeleton that uses hydraulic actuation to amplify the applied human force. The control objective is to make the system behave like a passive mechanical tool that interacts with the human and the environment passively with a specified power scaling factor. In our previous work, a virtual velocity coordination approach recasts the single degree-of-freedom human power amplifier control problem into a velocity coordination with a fictitious reference mechanical system. Force amplification becomes a natural consequence of the velocity coordination. In this paper, this control approach is extended for fully coupled multi-DoF systems. A passivity based control approach that uses the natural energy storage of the hydraulic actuator to take full account of the nonlinear pressure dynamics is used to define the flow requirement. Additional passive assistance dynamics are designed and implemented to enable the user to perform specific tasks more easily. Guidance is achieved using a passive velocity field controller (PVFC), and obstacle avoidance is achieved using a potential field. Experimental results demonstrate good performance on a 2-DoF Human Power Amplifier. * Fredrik Eskilsson was an international exchange student at the University of Minnesota.
In the AHS architecture of the California PATH program traffic is organized into platoons of clos... more In the AHS architecture of the California PATH program traffic is organized into platoons of closely spaced vehicles. Whenever platoons are formed or broken up, the large relative motion between platoons, increases the risk of high relative velocity collisions. In this paper we derive a safety region for the relative velocity between two platoons. By guaranteeing that the relative velocity between platoons remains in this region, impacts of high relative velocity can be avoided. For each one of the four control laws that a platoon leader can perform in normal operation, a desired velocity profile for the platoon that satisfies safety and time-optimality requirements is derived. A nonlinear velocity controller is designed to track the desired velocity profile within a given error bound. When safety is not compromised, this controller keeps the acceleration and jerk of the vehicles in the platoon within comfort limits.
A hydro-mechanical transmission (HMT) transmits power both mechanically and hydraulically allowin... more A hydro-mechanical transmission (HMT) transmits power both mechanically and hydraulically allowing continuously variable transmission ratios and more efficient transmission than hydrostatic transmission. A conventional HMT tends to be costly and bulky since it has a hydrostatic transmission in parallel with a mechanical transmission. An alternative is a compact inline configuration that utilizes a two-shafted pump that is mechanically and hydraulically connected to a motor. This avoids the need for a planetary gear set while providing the HMT functionality. When the pump/motor displacement is zero, all of the power is transmitted mechanically and the transmission ratio is unity, a condition referred to as lock-up that is expected to be very efficient. Previous research however has shown significant losses at this operating condition in experiments. This is thought to be caused primarily by compressibility losses due to the repeated unnecessary opening and closing of the distributor valves. This paper first models the Hondamatic in simulations to confirm that compressibility losses contribute to the low efficiency at lock-up. Second, the paper proposes a solution to reduce these compressibility losses by means of a second cam mode that closes the distributor valves to prevent flow between the piston and the high and low pressure volumes. The performance of the existing inline HMT and the proposed solution at lock-up are modeled in simulations and compared. The results indicate a 10% increase in efficiency at lock-up.
Hydraulic systems, as power source and transmission, offer many advantages over electromechanical... more Hydraulic systems, as power source and transmission, offer many advantages over electromechanical or purely mechanical counterparts in terms of power density, flexibility and portability. Many hydraulic systems require touching and contacting the physical environments; and many of these systems are directly controlled by human. If hydraulic systems are passive, they would be safer to interact with, and easier for human to control. In this paper, we describe our current research in developing bilateral passive teleoperated hydraulic machines which a human operator controls via a force feedback joystick. Two key developments are 1) methodologies to passify the electrohydraulic valves as a two-port device, and 2) the passive teleoperation controllers.
Linköping electronic conference proceedings, Dec 20, 2017
A hardware-in-the-loop (HIL) testbed for testing and evaluating experimental hydraulic transforme... more A hardware-in-the-loop (HIL) testbed for testing and evaluating experimental hydraulic transformers has been developed. The testbed is capable of emulating a variety of loading conditions specified by the desired work cycle operation of various hydraulic machines, such as humanoid robots or excavators. The HIL testbed is a useful research tool as it allows studying the dynamics of many desired loading conditions without having to obtain and reconfigure the said physical hardware for each case. This paper discusses the background, construction, and control of the HIL testbed with the experimental results. Preliminary results demonstrating the functionality of an experimental switch mode hydraulic transformers are also presented.
This paper propose an approach to extract the most significant color information that takes into ... more This paper propose an approach to extract the most significant color information that takes into account 1) the inherent sensitivity of the Human Visual System (HVS) to color variations and 2) the sensitivity of the HVS to specific colors of a given image. By giving higher importance to the significant colors in the stabilization control formulation, it is possible to retain the consistency of only the most significant colors to a human viewer. Such restriction is critical due to the limited actuation authorities of typical xerographic color printing process. To account for color-specific sensitivity, we make use of the CIE L*a*b* color formulation. To account for the image-specific sensitivity, we make use of the fact that the HVS have lower sensitivity to high frequency components (detail) of high chrominance image. Moreover, typically “smooth” images are visually more irrelevant compared to textured and detailed images. These effects in the color and spatial domain are taken into account to reduce the redundancy in the image representation by following similar procedure to that used in wavelet transform coding decomposition. Introduction The color reproduction characteristics(CRC) function describes how a printer maps the desired colors into actual printed colors. These printed colors vary with time due to printer dynamics as well as environmental and material variations, resulting in inconsistent color prints. In our current and previous works [1, 2, 3, 4], we have looked into control and sensing issues of maintaining tone and color consistency. The key control challenge is the high dimensional print-map (in that a color printer can reproduced high numbers of colors) with limited actuation authorities. This means that it is not possible to maintain the consistency of all the printed colors. In this paper, we developed a technique to stabilize only colors that are significant to a human viewer. Specifically there are two main redundancies of a printed image. The first is the inherent sensitivity of the Human Visual System (HVS) to color variations. In fact it is well known that human does not differentiate two colors with a ∆E∗ 94 < 1 [5]. The second redundancy can be found on the printed color image itself. For a color image, the redundancies can be found in the color and spatial representation of the image. Human visual system (HVS) has lower sensitivity to high frequency components (details) of high chrominance image. Moreover, typically “smooth” images are visually more irrelevant compared to textured and detailed images. These effects in the color and spatial domain are taken into account to reduce the redundancy in the image representation by following similar procedure to that used in wavelet transform coding [6]. The multi-resolution properties of wavelet decomposition is particularly well suited to the characteristics of the HVS because psycho-visual studies show that the human visual system can be modeled using multiple perceptual channels, which are octavewise spread over the spatial frequency range. From one octave to the next, the summation area (area of the retina contributing to the perceived signal) also changes by a factor of four. This behavior match that of the dyadic structure of the discrete wavelet transform. Problem Formulation In both sensing and control for maintaining color consistency, it is convenient to take the input colorspace as the CMY colorspace and the output colorspace as the CIE L∗a∗b∗ colorspace [1]. Uniformly discretizing the CMY colorspace domain, by M1, M2 and M3 points in each of the C, M, Y coordinates respectively, the CRC can be adequately approximated by its response at a finite number of Mt = M1M2M3 color combinations. Let L∗ i a ∗ i b ∗ i (k) denotes the i-th values of the Mt discretized points time-varying output color gamut of the printer. In this context, the time dependent error vector, ē(k) ∈R3Mt of discretized output of the spatial signal is given by: ē(k)= [ ∆L∗ 1(k), . . . ,∆L ∗ Mt (k),∆a ∗ 1(k), . . . ,∆a ∗ Mt (k),∆b ∗ 1(k), . . . ,∆b ∗ Mt (k) ] (1) where ∆L∗ i (k) := L ∗ i (k)−L∗∗ i , ∆ai (k) := ai (k)− a∗∗ i , ∆bi (k) := bi (k)− b∗∗ i . L∗∗ i a∗∗ i b∗∗ i gives the i-th value of the nominal color gamut. In the color stabilization control formulation [1], we can then specify the relative importance of the CRC errors at different colors for their stabilization given by the performance index term: J(k) = ēT (k)Weē(k) ∈R (2) where the error weighting is given by We ∈ R3Mt×3Mt . The error weighting matrix is made up of the color and image specific weightings i.e.:
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