FR2490037A1 - Electrically operated moulding press - has motor windings connected in star and triangle pattern during operating cycle to provide higher approach speed and greater force at low s - Google Patents

Abstract

The moulding press has a vertical sliding piston moving through a height of approx. 200 mm to mould a workpiece in a component. The sliding piston approaches the workpiece at a first speed, but actually comes into contact with it at a reduced speed. A microswitch is provided to change from one phase to the next. The final stage of the moulding is achieved at a still lower speed, and a second microswitch detects the point at which to make the changeover. In order to save energy during the moulding process, the electrical connections to the motor windings are changed during the cycle of operation. During the first stage of relatively rapid movement the windings are connected in a star pattern, whilst during the second low speed stage they are connected in a triangle pattern to provide the greater force but lower speed which is required.

Description

 This invention relates to a method for achieving electrical energy savings in machines equipped with electric motors and in particular in presses.

 According to this invention, the known star-triangle coupling is applied to such machines, this coupling being carried out with conventional devices. The originality of the present invention lies in the fact that these star-triangle couplings are applied during the course of the cycle without it being necessary to complicate this cycle or to add information to that already existing on the machine to give coupling orders; this invention further making it possible to use standard asynchronous conventional motors if necessary.

 Consequently, the subject of this invention is a method for saving electrical energy in machines, for example presses, equipped with one or more electric motors, this method being characterized in that one uses for the motor or motors electric, star-delta coupling, the motor (s) operating in star connection during periods of starting and no-load operation and in triangle connection during periods of actual work.

 According to a characteristic of this invention, the transition from the star connection to the triangle connection takes place before the request for maximum torque occurs.

 Other characteristics and advantages of this invention will emerge from the description given below with reference to the accompanying drawings which illustrate an embodiment given by way of example without any limiting character.

On the drawings
- Figure 1 is a very schematic side elevation view
rale of a press to which the present invention is applied
- Figure 2 is a diagram illustrating the function cycle
operation of the press shown in Figure 1
- Figure 3 is a diagram illustrating the intensity absorbed
by a star-coupled motor during the entire operating cycle
- Figure 4 is a diagram illustrating the absorbed intensity
bee by the same motor but coupled in star, and
- Figure 5 is a diagram of the phases of the voltages of a
motor respectively triangle and star torque, this
diagram showing the energy savings achieved by
the invention.

 We first refer to Figures 1 and 2.

 FIG. 1 represents a press to which the invention is applied and FIG. 2 represents the operating cycle of this press.

In the nonlimiting example chosen, the press must fit a part 1 into a part 2. The total stroke of the slide is represented by the height AD which in this example is 200 mm. The slide must come into contact with part 1 at reduced speed. To this end, a microswitch 4 is provided, placed on the path of the slide stroke and which controls the change from fast approach speed to slow working speed;
The working stroke is used effortlessly from B to C, in this example over a height of 10 mm, then from C to D with the effort necessary to ensure the fitting of part 1 into part 2. In this example the maximum torque stroke
CD is 20mm. The effort is maintained thanks to a micro-switch 5 triggering the time delay at the bottom of the stroke (phase DE).

Then from E to G, the press ram slides up without work, the EF phase being a decompression period.

 If we examine the cycle shown in Figure 2, we see that the periods AB, EG and GA '(A' being the starting point of a new operating cycle) require only the minimum power necessary to operate when empty , or at low load, the electrical, mechanical and hydraulic components of the press. Only the BE phase requires maximum power, which in the cycle illustrated in Figure 2 represents only about 1/3 of the cycle time.

 The method according to the invention therefore consists in operating the press motor in star connection during phase AB of the cycle (approach stroke of the slide) then in triangle connection during phase BE, corresponding to the working stroke and finally in star connection from the end of work delay (point E) of the next cycle to micro-contact 4 which again gives the triangle coupling order for the next work phase BE. It will be noted that the transition from star coupling to triangle coupling takes place at point B before the request for the maximum cut occurs (point C).

 FIGS. 3 and 4 show the diagrams of the measurements of the apparent intensities absorbed by a motor of a press according to FIG. 1, respectively the triangle and star torque.

 In the diagram in FIG. 3, a motor with a power of 5.5 kW connected to the three-phase 220 V network is coupled in a triangle. During the so-called empty period (descent of the slide H and return of the latter L) the absorbed intensity I # is approximately 13 A. The intensity under load Ic, during the periods of operation with actual work (during the time pressure maintenance P, that is to say from the pressure increase K until the start of the return stroke of the slide L, this period corresponding to phase BE of the diagram in FIG. 2), is equal to about. 27 A.

 The same motor, on the same press and under identical conditions but running in a star (Figure 4) has an absorbed intensity of 4.6 A. During this test it was observed that the speed of rotation was maintained from coupling, triangle to coupling canvas. The power is actually sufficient to compensate for losses and work in the so-called no-load periods, by connecting this star engine.

 Reference is now made to FIG. 5 which illustrates the nature of these electrical energy savings made according to the measurements illustrated in FIGS. 3 and 4.

These energy savings are of two types 1- in active power, that is to say in power expressed in watts 2- in reactive power, that is to say in power expressed in
volts amps.

 In the example illustrated by FIG. 3, the real cos t of the no-load motor is cos t = 0.3.

A. Coupling in triangle the motor connected in triangle and running at no load, we get
- Apparent intensity OB = 13 A
- active intensity O Aa = OB. cos
= 13 x 0.3 = 3.9 A - Reactive current O C. # = OB # sin #
= 13 x 0.95 = 12.35 A r. Star coupling the motor connected in star and running at no load we have
- Apparent intensity OB1 = 4.6 A.

- active intensity OA + = O BA. cos
= 4.6 x 0.3 = 1.38 A
- Reactive current OC \ = OB. sin t
= 4.6 x 0, G5 = 4.37 A
The expressior. of the three-phase alternating current power whether the motor is connected in star or in triangle is always
P = UI 6 cos f
The active power in watts is therefore
a) for triangle connection P - 3.9 x 220 x V) x 0.3
b) for star connection
P = 1.38 x 220 x ï3 x 0,) # 157.70 W
The reactive power in volts-amps will be
a) for the triangle connection
P '= 12.35 x 220 x 6 x 0.3 ~ 4411 VA

 b) for star connection P '= 4.37 x 220 x # 3 x 0.3 # 499.5 V.A.

 We see that the savings in both active and reactive power represent about 2/3 of normal consumption and this, for about 2/3 of the normal operating time of the press in cycle, more if cycles are more spaced in time.

 The systematic use of the method of the invention obviously brings the advantages already sought in the use of star-delta starts especially the reduction in starting intensities hence a reduction in the sections of the supply conductors, in addition it offers the advantage, resulting from the considerable economy which it generates, of allowing a generalized application to engines of weak power on which the only star-delta starting material could not be amortized until now because of the weak gain brought in only during the start-up period.

 It goes without saying that this invention is not limited to the example of embodiment and application described and shown here, but that it encompasses all variants thereof. In particular, the method according to the invention can be applied to any other type of cycle than that described above, having periods of operation when empty and under load.

Claims (3)

 1.- Method for saving electrical energy in machines, in particular presses, equipped with one or more electric motors, characterized in that a star-delta coupling is used for the motors, the motor or motors operating in star connection during periods of starting and no-load operation and triangle connection during periods of actual work.  2.- Method according to claim i, characterized in that the transition from the star connection to the triangle connection takes place before the request for maximum torque occurs.  3.- Method according to one of the preceding claims, characterized in that the star-triangle coupling is carried out using conventional means, a micro-contact (4) giving the triangle coupling order for the corresponding phase during periods of actual work.