Simplified strategy of the dynamic model of a 6-UPS parallel kinematic machine for real-time control

Closed-loop parallel kinematic machines (PKMs) have been proposed to improve precision and operation speed over conventional machine tools and robots. However, an embarrassing dilemma is that most of the existing PKMs achieve very lower precision in contrast to equivalent serial machine tools or robots, which are competitive to same tasks. Limited works have been conducted to evaluate errors thus improve precision of machine in real-time control. It becomes necessary to explore the relation of the motion error with the dynamics of a PKM. In this paper, the new model of the error evaluation has been proposed; three major sources of error under consideration are the deformations of the components under dynamic loads, the deformations at joint contacts, and the clearances of passive joints. To illustrate the modeling procedure, the dynamic model of machine is developed to determine internal forces among components and locations of joint contacts. Errors caused by machine dynamics are evaluated analytically in real time; in particular, the errors happened at the contacts of passive joints are estimated based on Hertz theory. The developed error models can be applied to compensate the motion errors of tool tip in real-time. The Exechon parallel kinematic machine is used as a case study, the results from simulation has been compared with the test data.

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An Inverse Dynamic Model of Over-Constrained Parallel Kinematic Machine Based on Newton–Euler Formulation

Journal of Dynamic Systems Measurement and Control ◽

10.1115/1.4026533 ◽

2014 ◽

Vol 136 (4) ◽

Cited By ~ 24

Author(s):

Z. M. Bi ◽

Bongsu Kang

Keyword(s):

Dynamic Model ◽

Dynamic Performance ◽

Clear Understanding ◽

Real Time Control ◽

Inverse Dynamic ◽

Redundant Constraints ◽

Quality Of Control ◽

Time Control ◽

Parallel Kinematic ◽

First Time

It has been known that redundant constrains in a mechanism can improve the rigidity and stiffness of the mechanism. Some Parallel Kinematic Machines (PKMs) have adopted redundant constraints to enhance their performance and stability. However, limited studies have been conducted on the dynamics of over-constrained mechanisms. While a dynamic model is not essential to machine control, a clear understanding of the dynamic behavior of the system can be useful in identifying the weakest components, optimizing the overall structure, and improving the quality of control. In this paper, the dynamic characteristics of an over-constrained PKM are investigated for the first time. The Newton–Euler formulation is extended to develop the dynamic model of the machine. It is shown that the compliance of deformations of the redundant constraints needs to be taken into account to build a complete and solvable dynamic model since the number of equations derived from the force and moment equilibrium of the PKM components is insufficient to determine all unknown variables. The proposed approach is generic in sense that it can be applied to model dynamic behaviors of other over-constrained machines with a combination of the Newton–Euler formulation and compliance conditions. Its effectiveness has been verified by the dynamic model established for Exechon PKM. The developed dynamic model has its potential to be integrated with control systems to improve accuracy and dynamic performance of real-time control.

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A Real Time Control Architecture for Continuously Managing Patients in a Care Unit

Methods of Information in Medicine ◽

10.1055/s-0038-1634619 ◽

1995 ◽

Vol 34 (05) ◽

pp. 475-488

Author(s):

B. Seroussi ◽

J. F. Boisvieux ◽

V. Morice

Keyword(s):

Real Time ◽

Linear Time ◽

Treatment Plan ◽

Control Architecture ◽

Real Time Control ◽

Time Representation ◽

Time Control ◽

Continuous Support ◽

Definition Of ◽

Computerized System

Abstract:The monitoring and treatment of patients in a care unit is a complex task in which even the most experienced clinicians can make errors. A hemato-oncology department in which patients undergo chemotherapy asked for a computerized system able to provide intelligent and continuous support in this task. One issue in building such a system is the definition of a control architecture able to manage, in real time, a treatment plan containing prescriptions and protocols in which temporal constraints are expressed in various ways, that is, which supervises the treatment, including controlling the timely execution of prescriptions and suggesting modifications to the plan according to the patient’s evolving condition. The system to solve these issues, called SEPIA, has to manage the dynamic, processes involved in patient care. Its role is to generate, in real time, commands for the patient’s care (execution of tests, administration of drugs) from a plan, and to monitor the patient’s state so that it may propose actions updating the plan. The necessity of an explicit time representation is shown. We propose using a linear time structure towards the past, with precise and absolute dates, open towards the future, and with imprecise and relative dates. Temporal relative scales are introduced to facilitate knowledge representation and access.

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