Some influences about the regenerative energy effect in the optimal functioning of the linear actuators.

Nasui, Vasile ; Lobontiu, Mircea ; Banica, Mihai 等

1. INTRODUCTION

The technical and technological evolution towards the integration in mechatronic included the stages of development of the module of linear acting of the actuator type marked by the integration of the microprocessors. The development of the mechatronic technology within this context contributed to the development of the actuators as elements of execution capable with this which have besides the cinematic chain, energetic and informational material. In the dynamic study of the actuators we have to consider the whole actuators, in spite of the effects the transitory functional regime (Catrina & Constantin, 2002).

Thus results the necessity of the analysis of the influence of the energy regenerated in the system as a consequence of the periods of deceleration in the functioning on all the mechanic, electrical, electronically components (Dumitru et al., 2004). Suppose there is a form of kinetic energy recovery system which is considerably less efficient at gathering energy and using it again, particularly at high peak power and energy flow levels. The optimization problem for the actuator is formulated with material, packaging, and performance constraints. Since loads are continuously being accelerated and decelerated, actuators absorb energy as frequently as they output energy, but power is required from the supply regardless of the direction of power flow in the actuator. The absorbed power is simply dissipated in the actuator or power supply (Boiangiu, 2003).

2. THE ECONOMIC WORKING REGIME

The correct definition of the economic functioning regime of an electro mechanic linear actuator must take into account, on one hand, the clues that characterize the economic regime. The main component parts of an actuator (fig. 1), including the electric engine of acting, the transmission itself, the filling and the control devices. The parameters which characterize the economic regime are the training electric power and the efficiency of all the structural components. (Nasui, 1993).

[FIGURE 1 OMITTED]

Saving the electric energy can be done by important measures in the whole chain of the actuator system starting from the filling point, passing to the control one or the regulating one and going on with the acting engine and the cinematic transmission.

The basic problem in order to obtain a profitable regime is to correctly establish the nominal power according to the efficiency, the transmission report, the increase or decrease in the speed and the cinematic moment. In the situation of the actuators, to establish acting power is very important owing to the conditions of transitory regime of work.

The opportunity of the research results from the fact that the authors are in general for real functioning situations with under load power. When calculating the overall efficiency of the actuator s transmission we approximate taking into consideration the only losses that occur while the friction within the mechanism, neglecting these depending among others on the degree of covering as well (Nasui, 2006).

To take into consideration all the losses we write the relation of the overall efficiency according to the total / overall moment [M.sub.t] and to that clue to the constant [DELTA][M.sub.c] and variable [DELTA][M.sub.a] mechanical losses as it follows:

[[eta].sub.t] = [M.sub.t]/[M.sub.t] + [DELTA][M.sub.c] + [DELTA][M.sub.a] (1)

If we define: the loading coefficient, [K.sub.i] = [M.sub.t]/[M.sub.n] and the loss coefficient, [K.sub.p] = [DELTA][M.sub.t]/[M.sub.t], using the relation (1) results:

[[eta].sub.t] = [[eta].sub.n]/1 - [[eta].sub.n] [K.sub.p] (1 - 1/[K.sub.i]) (2)

For this, we make real assessment of the value of the efficiency of the actuator s transmission considering the overall of the power losses within the actuator and for partial loading. For the transitory regimes of functioning, the efficiency can be calculated deterring the two components of the moment of losses within the transmission according to the relation (2) including the dynamic moment (Dumitru et al., 2008).

The experimental determination of power losses specific to the mechanical transmission of an actuator has shown its dependence according to the degree of loading and functioning regime. The minimal value of these losses represents 2 - 6 % out of the transmission power, load nearly to the nominal one but not exceeding it.

Establishing the loading coefficient is necessary in view of the choice of the acting engine and of the calculation of the overall efficiency of the mechanical transmission of the actuator.

Thus results the great importance of the correct establishment of the functioning in this functioning regime by mathematical modeling of these influences (Maties et al., 2000).

3. THE REGENERATED ENERGY IN THE ACTUATOR AND ITS EFFECTS

This regenerated energy in the system results from the weight by amplifications from the energy supplier. At the actuators, in order to reduce the stopping time of the acting system, it is frequently applied the dynamic braking or recuperative braking in continuous power regime. The electric machine in this case functions as a generator transforming the rotation kinetic energy or the potential energy of the working machine into electric energy debit ate dons the braking resistance. The whole of the kinetic energy of the weights in movement is transformed in electric power which in its turn is dissipated on the circuit, being controlled in this way.

The catching up braking is similar to the dynamic braking with the difference that the electric engine generates in the continuous power flux. The potential energy is transformed by the engine in electric energy recuperating by itself and being used by other consumers.

The pattern of dynamic control is shown in figure 2. At the actuators with asynchrony engines in recuperating energy regime, the braking is obtained for speeds of the superior's rotor, the speed of the rotator field, generating within the net of active power, but continuing to obtain reactive power.

Because the actuators have a significant control, the recuperative energy has a major part which can influence the optimum functioning of the whole system. Regenerative energy is transferred from the motor load through the amplifier to the power supply during deceleration. If this energy is not managed it will boost the voltage which may damage the driver.

Since the electrical energy stored within the motor is small, it usually can be neglected. However, the driver must be able to handle the motor and load mechanical energy [E.sub.R] = 1/2 x J x [[omega].sup.2], less the energy dissipated by the cable and motor, [E.sub.R] = [I.sup.2] x R x t

x

E = 1/2 x J x [[omega].sup.2](4,2 x [10.sup.5]) - [I.sup.2] x R x t (3)

t = J x [omega]/[M.sub.T] x I [2 x [pi]/60] (4)

where:

E--amplifier regenerative energy capacity;

J--inertia of motor plus load;

[omega]--velocity load;

I--current limit setting of driver;

R--resistance of cable and motor;

t--deceleration time, [sec.];

[M.sub.T]--motor torque constant.

The energy handling capacity of the driver power supply must beat least the value calculated. (Aerotech, 1990) suggests a 50% margin on this value. Also, give consideration to simultaneous deceleration in multi-axis systems. The actual systems focus on the energy recovery by dynamic or regenerative braking and less on the direct recovery of kinetic energy and on its rendering at the appropriate moment.

The first systems produce heat which is then internally or externally dissipated and they are not energetically efficient. Regenerative recovery depends on the use of appropriate batteries, non ecological.

Also these systems of electronic regulation require regulation equipment, compatible with the type of acting electric engines. All these make the kinetic systems performances of recovery successful as their weight is smaller and smaller.

[FIGURE 2 OMITTED]

4. SUMMARY AND CONCLUSION

The research focuses on the improvement of the energetic performances, such as superior efficiency and the achievement of structural changes especially regarding the solutions for transmission mechanisms of movement, and its control. We propose original innovative solutions from this point of view with new mechanism actuator of movement (Nasui, 1993).

The development perspectives aim optimum solutions equipped with mechanisms of transmission and transformation of the movement with high efficiency and fiability. The problem consists in solving an incompatibility among the functional and constructive of the components of the system actuator.

The conception and its manufacture assisted on the computer has as application field the assembly of the process of developing new products, covering the conception aspects, manufacture and the link between them. The control of the movement of the system actuator is the key factor on which depend the capacity and their availability. Owing to the dynamic regime particular to the functioning of the actuators, it is necessary to know the influence of the regenerated energy in the system in order to take the technical measures most appropriate as far as the performances of the control equipment of the actuators are concerned.

When designing a linear motion system, it is necessary to consider the effect of the variables operation will have on performance. In the future the researches can continue for the development of new applications on other types of mechanical transmission using this method and different modular control laboratory.

5. REFERENCES

Boiangiu, T. (2003). Advanced Robot Motion Control, Editura AGIR, ISBN 973-8130-98-0, Bucuresti.

Catrina, D., & Constantin, G. (2002). Evolution of Some Kinematics Parameters of the Feed Kinematics Chain at High Slide Speeds in CNC Machine Tools, Proceedings of the International Conference on Manufacturing Systems, pp. 97-100, ISSN 0035-4074, October 2002, Editura Academiei Romane, Bucuresti.

Dumitru, D. & Strajescu, E. (2004). Performant Optimization of Feed Driving at CNC Machine Tools, Proceedings of the International Conference Optimization on Manufacturing Systems, pp. 175-178, ISBN 973-27-1102-7, October 2004, Editura Academiei Romane, Bucuresti.

Maties, V., Mandru, D., Tatar, O. & Maties, M. (2000). Actuatori in mecatronica, Actuators for Mechatronics, Editura Mediamira, ISBN 973-9358-16-0, Cluj-Napoca.

Nasui, V. (2006). Actuatori liniari electromecanici, Linear Electromechanic Actuators, Editura Risoprint, ISBN 973656-813-X, Cluj Napoca.

Nasui, V. (1993). Patent RO 106.284. B1.

*** AEROTECH (1990). Motion Control Product Guide, Aerotech, Inc., USA