Optimizing acceleration parameters

It is advisable to optimize acceleration parameters with the maximum permis-sible load. Optimization with a smaller load may result in reduced cycle times.

However, no greater load can then be moved without first carrying out optimi-zation again.

Fig. 7-9: $LG_PTP=1.4

Fig. 7-10: $LG_PTP=0.8

长沙工控帮教育科技有限公司

7.4.3.1 Optimizing $RAISE_TIME

Description $RAISE_TIME defines the time in which an axis is accelerated to rated speed.

The aim of the optimization is to move the axes as fast as possible without ex-ceeding the maximum permissible current.

 Too high a value leads to slow accelerations and unnecessarily long cycle times.

 Too low a value leads to fast accelerations so that the axis goes into cur-rent limitation. This results in overshoot and following errors.

The required system-specific or customer-specific acceleration and decelera-tion times must be checked for feasibility. If no value is specified, it is advisable to commence optimization with a start value of 500 ms. This is a feasible value for most kinematic systems.

For optimization, $RAISE_TIME must be reduced in increments in the ma-chine data. During testing of the axis motion, the current must not exceed 90%

of the maximum value.

Example Data for $RAISE_TIME for a 10-axis industrial robot

In the case of very large kinematic systems, a start value of 500 ms may be too low. In this case, the value for the optimization must be increased in increments. Suitable values for most kinematic systems range from 150 to 1,000 ms.

Fig. 7-11: $RAISE_TIME=500

REAL $RAISE_TIME[12]

$RAISE_TIME[1]=350.0

$RAISE_TIME[2]=750.0

$RAISE_TIME[3]=300.0

$RAISE_TIME[4]=250.0

$RAISE_TIME[5]=180.0

$RAISE_TIME[6]=240.0

$RAISE_TIME[7]=400.0

$RAISE_TIME[8]=150.0

$RAISE_TIME[9]=250.0

$RAISE_TIME[10]=200.0

$RAISE_TIME[11]=0.0

$RAISE_TIME[12]=0.0

长沙工控帮教育科技有限公司

7.4.3.2 Optimizing $RED_ACC_EMX

Description $RED_ACC_EMX is used to define a braking ramp for the path-maintaining EMERGENCY STOP. $RED_ACC_EMX is specified as a percentage and re-fers to $RAISE_TIME, e.g. a value of 200% means that the EMERGENCY STOP braking ramp is twice as steep as the acceleration ramp.

The aim of the optimization is to brake the axes as quickly as possible in the event of an EMERGENCY STOP, without exceeding the maximum permissi-ble current.

 If the braking ramp is too shallow, path-maintaining braking is ensured, but the braking distance is too long for an EMERGENCY STOP.

 If the braking ramp is too steep, the axis goes into current limitation and path-maintaining braking is lost, i.e. the programmed path is left in the case of an EMERGENCY STOP.

The required system-specific or customer-specific deceleration times must be checked for feasibility. If no value is specified, it is advisable to commence op-timization with a start value of 100%.

For optimization, $RED_ACC_EMX must be increased in increments in the machine data. When an EMERGENCY STOP button is pressed, the current must not exceed 90% of the maximum value.

Example Data for $RED_ACC_EMX for a 10-axis industrial robot Fig. 7-12: $RED_ACC_EMX=100

INT $RED_ACC_EMX[12]

$RED_ACC_EMX[1]=190

$RED_ACC_EMX[2]=300

$RED_ACC_EMX[3]=300

$RED_ACC_EMX[4]=250

$RED_ACC_EMX[5]=250

$RED_ACC_EMX[6]=250

$RED_ACC_EMX[7]=300

$RED_ACC_EMX[8]=1000

$RED_ACC_EMX[9]=300

$RED_ACC_EMX[10]=150

$RED_ACC_EMX[11]=100

$RED_ACC_EMX[12]=100

长沙工控帮教育科技有限公司

7.4.3.3 Optimizing $DECEL_MB

Description $DECEL_MB is used to define a braking ramp for path-oriented maximum braking. The axes are stopped in the time defined in $DECEL_MB, with the axis speed being reduced from maximum to zero.

In the case of maximum braking, the current actual speed value is taken as the command speed and linearly reduced to zero using the set ramp. The ramp prevents the command speed from falling too quickly and causing the current controller to go into limitation, which in turn would prevent the robot from being braked in a controlled manner.

The ramp is calculated for each axis using the optimized values for

$RAISE_TIME and $RED_ACC_EMX:

$DECEL_MB = $RAISE_TIME * 100% / $RED_ACC_EMX

Example Data for $DECEL_MB for a 10-axis industrial robot

7.4.3.4 Configuration examples

Non-optimized The axes of most kinematic systems can follow the programming without any problem using the non-optimized start values, but they are moved too slowly.

Parameters:

 $RAISE_TIME=500

 $RED_ACC_EMX=100

 $DECEL_MB=500

Following optimization, the acceleration parameters are independent of one another. $DECEL_MB must be at least 180 ms, even if the cal-culation gives a smaller value.

REAL $DECEL_MB[12]

$DECEL_MB[1]=211.0

$DECEL_MB[2]=267.0

$DECEL_MB[3]=180.0

$DECEL_MB[4]=200.0

$DECEL_MB[5]=200.0

$DECEL_MB[6]=200.0

$DECEL_MB[7]=500.0

$DECEL_MB[8]=200.0

$DECEL_MB[9]=200.0

$DECEL_MB[10]=200.0

$DECEL_MB[11]=0.0

$DECEL_MB[12]=0.0

长沙工控帮教育科技有限公司

Only part of the torque is used (current approx. 8 A) to accelerate the axis to the rated speed. In the event of an EMERGENCY STOP, the axis does not brake with the maximum possible torque. The braking distance is long.

Over-optimized With over-optimized values, the axes move at maximum velocity, but can no longer follow the programming. During acceleration or braking, the axes leave the programmed path and the setpoint speeds of the motors exceed the val-ues actually reached. In the oscilloscope trace, the axis overshoot and the fol-lowing errors become visible.

Parameters:

 $RAISE_TIME=100

 $RED_ACC_EMX=300

 $DECEL_MB=180 (minimum permissible value) Fig. 7-13: Non-optimized basic setting

1 Current limitation: 16 A

2 E-STOP

Fig. 7-14: Over-optimized setting 1 Current limitation: 16 A

长沙工控帮教育科技有限公司

The axis attempts to follow the setpoint speed. The actual speed deviates from the setpoint speed because of current limitation; the following error is large.

Optimized With optimized values, the axes are accelerated and braked with their maxi-mum values, without leaving the programmed path.

Parameters:

 $RAISE_TIME=250

 $RED_ACC_EMX=250

 $DECEL_MB=180 (minimum permissible value)

The maximum torque is used (current approx. 14 A) to accelerate the axis to the rated speed. In the event of an EMERGENCY STOP, the axis brakes with the maximum possible torque. The actual speed is virtually identical to the set-point speed; the following error is virtually zero.