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Relations between size and gear ratio in spur and planetary gear trains
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
2005 (English)Report (Other academic)
Abstract [en]

In this report equations for the minimum gear sizes necessary to drive a given load are derived. The equations are based on the Swedish standards for spur gear dimensioning:SS 1863 and SS1871. Minimum size equations for both spur gear pairs and three-wheel planetary gears are presented. Furthermore, expressions for the gear weight and inertiaas function of gear ratio, load torque and gear shape are derived.For a given load torque and gear material, it is possible to retrieve the necessary gearsize, weight and inertia as function of gear ratio. This is useful for gear optimization,but also for optimization of a complete drive system, where the gear size, inertia and weight may affect the requirements on the other parts of the drive system.The results indicate that the Hertzian flank pressure limits the gear size in most cases.The teeth root bending stress is only limiting for very hard steels. Furthermore, then ecessary sizes, weights and inertias are shown to be smaller for planetary gears than for the equivalent pinion and gear configuration. Both these results are consistent with state of practice; planetary gears are commonly known to be compact and to have low inertia.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. no 1, 35 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2005:01
National Category
Reliability and Maintenance
Identifiers
URN: urn:nbn:se:kth:diva-7409OAI: oai:DiVA.org:kth-7409DiVA: diva2:12428
Note
QC 20100816. Uppdaterad från Artikel till Rapport 20100816.Available from: 2007-08-23 Created: 2007-08-23 Last updated: 2010-12-20Bibliographically approved
In thesis
1. On design methods for mechatronics: servo motor and gearhead
Open this publication in new window or tab >>On design methods for mechatronics: servo motor and gearhead
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The number of electric powered sub-systems in road-vehicles is increasing fast. This development is primarily driven by the new and improved functionality that can be implemented with electro-mechanical sub-systems, but it is also necessary for the transition to electric and hybrid-electric drive trains.

An electromechanical sub-system can be implemented as a physically integrated mechatronic module: controller, power electronics, electric motor, transmission and sensors, all integrated into one component. A mechatronic module, spans, as all mechatronic systems, over several closely coupled engineering disciplines: mechanics, electronics, electro-mechanics, control theory and computer science. In order to design and optimize a mechatronic system it is therefore desirable to design the system within all domains concurrently. Optimizing each domain or component separately will not result in the optimal system design. Furthermore, the very large production volumes of automotive sub-systems increase the freedom in the mechatronics design process. Instead of being limited to the selection from off-the shelf components, application specific components may be designed.

The research presented in this thesis aims at development of an integrated design and optimization methodology for mechatronic modules. The target of the methodology is the conceptual design phase, where the number of design parameters is relatively small. So far, the focus has been on design methods for the electric motor and gearhead, two of the most important components in an actuation module. The thesis presents two methods for design and optimization of motor and gearhead in mechatronic applications. One discrete method, intended for the selection of off-the-shelf components, and one method mainly intended for high volume applications where new application specific components may be designed. Both methods can handle any type of load combination, which is important in mechatronic systems, where the load seldom can be classified as pure inertial or constant speed.

Furthermore, design models relating spur gear weight, size and inertia to output torque and gear ratio are presented. It is shown that a gearhead has significantly lower inertia and weight than a motor. The results indicate that it almost always is favorable from a weight and size perspective to use a gearhead. A direct drive configuration may only be lighter for very high speed applications. The main contribution of this thesis is however the motor/gear ratio sizing methods that can be applied to any electromechanical actuation system that requires rotational motion.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. ix, 13 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2005:02
Keyword
Applied mechanics, mechatronics design methodology, servo systems, electric motors, gears, auxiliary systems, Teknisk mekanik
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-167 (URN)
Presentation
2005-02-01, B442, KTH, Brinellvägen 83, Stockholm, 10:00
Supervisors
Note
QC 20101220Available from: 2005-04-15 Created: 2005-04-15 Last updated: 2010-12-20Bibliographically approved
2. Towards a methodology for integrated design of mechatronic servo systems
Open this publication in new window or tab >>Towards a methodology for integrated design of mechatronic servo systems
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Traditional methods for mechatronics design are often based on a sequential approach, where the mechanical structure is designed first, and then fitted with off-the-shelf electric motors, drive electronics, gearheads and sensors. Finally a control system is designed and optimized for the already existing physical system. Such a design method, that doesn’t consider aspects from a control point of view during the design of the physical system, is unlikely to result in a system with optimal control performance. Furthermore, to separately design and optimize each of the physical components will, from a global perspective, generally not result in a system that is optimal from a weight, size or cost perspective.

In order to reach the optimal design of an integrated mechatronic system (mechatronic module) it is necessary to treat the system as a whole, considering aspects from all involved engineering domains concurrently. In this thesis such an approach to integrated design of mechatronic servo systems is presented. A design methodology that considers the simultaneous design of the electric machine, gearhead, machine driver and control system, and therefore enables global optimization, has been developed. The target of the design methodology is conceptual design and evaluation. It is assumed that the load to be driven by the servo system is known and well defined, a load profile describing the wanted load motion and the corresponding torque, is required as input. The methodology can then be used to derive the lightest or smallest possible system that can drive the specified load. Furthermore, the control performance is evaluated and optimized, such that the physical system design and the controller design are integrated.

The methodology is based on modelling and simulation. Two types of component models have been developed, static and dynamic models. The static models describe relations between the parameters of the physical components, for example a component’s torque rating as function of its size. The static models are based on traditional design rules and are used to optimize the physical parts of the system. The dynamic models describe the behaviour of the components and are used for control system design and performance optimization.

The gear ratio is identified to be the most central design variable when designing and optimizing electromechanical servo systems. The gear ratio directly affects the required size of the gearhead, electric machine and the machine driver. But it has also large influences on the system’s control performance. It is concluded that high gear ratios generally are better from a control point of view than low ratios. A consequence of this is that it is possible, without compromising the control performance, to use less expensive (less accurate) sensors and microprocessors in high gear ratio servo systems, while low gear ratio systems require more expensive hardware. It is also concluded that it is essential to include all performance limiting phenomena, linear as well as non-linear, in this type of integrated analysis. Using for example a linearized system description for controller design, means that many of the most important couplings between control system and physical system design are overlooked.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. viii, 106 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2007:07
Keyword
Mechatronics, Servo Systems, Design Methodology, Integrated Design
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-4473 (URN)
Public defence
2007-09-14, Sydvästra galleriet, KTH main library, Osquars backe 31, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100816Available from: 2007-08-23 Created: 2007-08-23 Last updated: 2010-08-16Bibliographically approved

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