USE of ASSEMBLY Maxon Motor 399505 WITH SET МСВ-04

In frame of improving procedures of training sets our company «NPF Mechatronica-Pro» has received for testing the dc drive components manufactured by Maxon Motors. The electric drive consists of:

• DC motor - RE-max 24 Part Number(PN) 222053

• Planetary-gear reducer - GP 22 C PN 143979

• Quadrature encoder – MR type ML PN 201940

Assembly of these components is aggregate 399505, which is ready to connection to set МСВ-04, whose parameters are shown in table 1.

Table 1

Standard set МСВ-04 has specification listed in table 2, which show that available power and control cards of the set can be used to control the assembly 399505 manufactured by Maxon Motors.

Table 2

Since the assembly is compatible with the set, let’s connect them. To do so, connect the output ribbon cable of the assembly according to connection circuit (Fig. 1) to the set into corresponding connector, as it is shown in fig.

Fig. 1 Circuit of the assembly connection

Fig. 2 Connection to the set , 1 – Encoder connectors, 2 – Power connectors, 3 – Tested assembly

After connection of the assembly to the set let’s do several starts in direct an inverse directions to check the correctness of the connection.

To develop the control system of the motor let’s create a project under MexBIOS Development studio environment for embedded system software development.

Fig. 3 Basic project under MexBIOS Development Studio environment

Parameters of blocks and their functions are listed in table 3.

Table 3

After setting the corresponding blocks let’s connect to the set and load the project into RAM. Pushing BUTTON after begin of refreshing causes lighting-on green LED PWM in control card, however the shaft of the assembly does not move, since the reference for duty factor in block TRACKBAR is equal to zero. By changing the scrolling in the box, make sure that the motor speed is changed both in value and in direction. Thereafter let’s tune the controllers.

In general the structure of the subordinate control system is shown in block diagram in fig. 4

Fig. 4 Block diagram of control system

This diagram takes into consideration parameters of the assembly motor only, since its mechanical parameters are by an order of magnitude greater than the parameters of encoder and reduced, therefore they can be neglected.

As you can see from the structure for the operation of the control loops the corresponding feedbacks are needed, which come from outputs of sensors. Dealing the sensor outputs is function of formula Driver, whose structure is shown in Fig. 5, and the parameters of the blocks are listed in table 4.

Fig. 5 Structure of block Driver

Table 4

. The scaling factor can be determined in the following way:

1. Insert into armature circuit a multimeter t measure the armature current
2. Start the motor and register the mean value of the current in steady-state
3. Determine the scaling factor from reading of label LCurrent (block Label) by dividing the real current by reading from AD module and by entering the resulted value as parameter GainA of block fOffset.

Tuning of the subordination control system is carried out according to known methods of loop tuning. First let’s tune the inner current loop to the modular optimum:

Let’s determine parameters of the current loop controller:

To check quality of the loop tuning we need to assemble a circuit, which provides instantaneous reversing. To achieve it let’s add to the circuit that was assembled earlier in formula PWM the blocks that are shown in table 5 and in Fig. 6.

Fig. 6 Structure of block PWM for tuning the current loop

Table 5

Start of this circuit allows us visually to estimate the speed of the drive response to the sign change of the current reference.

Fig. 7 Current loop operation in reversing mode of the current reference

Let’s insert the calculated parameters in block of PID-controller and carry out the same study of the response speed. Reversing after parameter inserting should be fulfilled with the same response speed, as in previous experiment.

After successful tuning if the current loop let’s tune the speed loop:

It should be noted that tuning of motors with very fast response because of small moment of inertia, the formulas for determining tuning parameters of symmetrical optimum slightly differ from the standard ones.

Let’s add the circuit from Fig. 6 by second loop as it is shown in Fig. 8

Fig. 8 Structure of block PWM при for tuning the speed loop

Table 6

Fig. 9 Results of the speed loop operation

Let’s implement the outer loop of the system – position loop to get position servo-drive – an electric drive that moves the output shaft to required angle without compliance to a motion curve.

A feature of such systems is supposed to be slightly oscillatory character of the speed in steady-state operation due to some neglecting in calculations. One of simple methods to reduce the influence of these phenomena under MexBIOS environment is to decrease the calculation frequency of individual component or of the group of components, this method allows in our case to call the position controller calculation with smaller frequency, which causes the oscillation decrease without change in static error. However you should not set very low frequency of the block calling, optimum value would be scaling frequency ratio, whose value is in range 5..100 as a function of the motor response speed.

The algorithm can be realized in the following way:

In the first place you need to make alterations in the main body of the program as it is shown in Fig. 10 and table 7

Fig. 10 Main program for the drive operation with three control loops

Table 7

Thereafter let’s go into formula Driver and add the teleport labels and blocks of frequency scaling, as it is shown in Fig. 11

Fig. 11 Formula Driver for position loop

Table 8

Next let’s go into formula Pos_Loop that contains the position controller block. Fig. 12.

Fig. 12 Position loop

Таблица 9

The tuning parameters (factors) of the position controller can be calculated in terms of formulae:

Next let’s go into block PWM to change it according to Fig. 13

Fig. 13 Block PWM for position loop

Table 10

Finally we developed a control system of the servo drive, where the reference of angular displacement in form of number of counts of encoder is set in block In. Results of the position drive operation are shown in Fig. 14, Fig. 15.

Fig. 14 Motor shaft speed transient for positioning to required rotation angle

Fig. 15 Rotor position transient

References

• http://www.aviton.spb.ru/
• http://www.maxonmotor.com/maxon/view/content/index
• http://mechatronica-pro.com/