KE-750_MAINTE.pdf - 第131页

- 128 - memorizes the stop position at the st art time but the deviation counter reads 0. (3) When LM628 analyzes the data above, and profile of the motor drive is complete, ① command voltage is gradually applied to the …

page), both the speed control and the positioning control are controlled with

the rotary encoder of the motor. Therefore, if there is a mechanical

positioning offset in the drive system, it is difficult to accurately control the

left and right positioning.

To assure a high positioning accuracy (high resolution and accuracy), the

fully closed loop system is better. When a long ball screw is used in the

semi-closed loop system, the error among the lead pitches of the ball

screws shall be corrected for every machine. This correction value must

be stored as a parameter in the program, and this makes adjustment

troublesome.

(2) Control system of Z/θ axes

For KE series, a semi-closed loop system is used to control the motor of the

Z/θ axes. The following explains the theory of operation.

Figure 6.2 shows the fully closed system for the Z axis. And, the example

shows that the Z axis is moved by +5 mm from the origin.

① + Command

voltage

Z/θ servo control board AC servo driver

Power for the U, V, W phase driver

Control

circuit

Control circuit

Speed control

Deviation

counter

Motor

LM628

② Speed detection and e position detection

Rotary encoder

Counter

(Stores the

current position.)

Figure 6.1 Semi-closed loop system

(1) The SUB CPU1 board of the control unit sets the data such as moving

distance, acceleration/deceleration, and maximum speed of the Z axis

to the Z/θ control board, and issues a start command.

(2) The motor controller IC, LM628, a dedicated IC for positioning control

and motor drive, and it has the deviation counter and the positioning

counter for the current position. However, the AC servo driver

dedicated to the speed control does not have the deviation counter for

positioning control. Therefore, the AC servo driver controls the speed,

and LM628 controls the position. The current position counter

- 127 -

- 128 -

memorizes the stop position at the start time but the deviation counter

(3) When LM628 analyzes the data above, and profile of the motor drive is

complete,① command voltage is gradually applied to the AC servo

driver. The AC servo driver then controls the rotation speed of the

motor according to the voltage being applied. (The range of the

command voltage is ±10 V.)

(4) The AC servo driver counts the number of pulses from the rotary

encoder (1 pulse = 10 µm), and detects (② speed detection) the

rotating speed of the motor. On the other hand, the counted pulse is

input to both the current position counter and the deviation counter

(DOWN side) of LM628. As a result, the reading of the current

position counter increases, and that of the deviation counter decreases.

(③ position detection)

(5) The deviation counter performs a computation, (command pulse) -

(position pulse), and when the Z axis approaches the target position

plus 5 mm, the command voltage goes near 0 V to decelerate the

motor. As a result, when the Z axis reaches at +5 mm position, the

deviation counter reads 0, and the command voltage is set 0 V to stop

the motor. The operation of stop and acceleration/deceleration may

largely change depending on the gain setting of the AC servo driver.

Therefore, an appropriate gain setting value must be found and set for

the system.

(6) When the motor stops, the absolute counter of LM628 reads the position

at the start plus 500.

As described above, in the semi-closed loop system, both the speed control

and the positioning control are performed together with the rotary encoder

directly coupled to the motor. Therefore, if there is a defect in the

mechanical system before the motor shaft (overload, loose screw, etc.), the

stop position of the ball screw may be offset even when the rotating position

of the motor is normal.

- 129 -

7. TROUBLESHOOTING

7.1 Part Mount

Part mount offset can be classified in an offset of XY, θ, or XYθ. And, it can

also be classified by causes as follows:

1. Bond (adhesive) or cream solder

2. Mount program entered

3. Cramp state of the board on the board carriage

4. Mount head

5. Vacuum or blow pressure when mount

6. XY axes

7. MS parameters entered

1. Problems caused by dispenser or cream solder

The adhesive and cream solder are main causes of trouble. On a

double-sided tape, it is necessary to be mounted correctly.

Symptom Cause Remedy

There is an

offset in XY and

θ axes when

mounting using

adhesive. (In

particular, for

small-sized parts

such as

2125/3216

capacitors, Melf,

and SOT)

With adhesive, there is an offset mainly in

θ axis, and this is affected by the amount

and position of adhesive. In particular,

2125/3216 capacitors, Melf, and SOT are

affected by the amount of adhesive. For

capacitors, the body is raised with respect

to its edges, and if little adhesive is applied

the body does not touch the adhesive. In

addition to this, if adhesive displacement

occurs, it is fixed by 1 point, and the part is

largely affected. This applies also to

SOT. The body is raised with respect to

the leads. Melf is likely to roll because of

its shape, and it can be largely affected by

the amount of adhesive.

In general, the amount of adhesive

increases, a stable mount is performed.

Check that there is no adhesive

displacement on the board to which

the adhesive is applied, using

position tracking. For the amount

of adhesive, check on the board

which the parts are mounted so that

the adhesive adequately touches

the parts. If there is problem with

the placement and amount of

adhesive, make corrections on the

application conditions of the

dispenser for the specific part type,

or for all part types.