WEIGHT and INERTIA Settings
The WEIGHT and INERTIA commands are for setting the load parameters of the Manipulator. These settings optimize the Manipulator motion.
- WEIGHT Setting
The WEIGHT command is for setting the load weight. The more the load weight increases, the more the speed and acceleration/deceleration are reduced. - INERTIA Setting
The INERTIA command is for setting the inertia moment and the eccentricity of the load. The more the inertia moment increases, the more the acceleration and deceleration of the Arm #6 are reduced. The more the eccentricity increases, the more the acceleration and deceleration for the Manipulator movement are reduced.
To ensure that the Manipulator is functioning properly, keep the load (the sum of the weights of the hand and workpiece) and the moment of inertia of the load within the rated values, and do not allow for eccentricity from the center of the Arm #6. If the load or the inertia moment exceeds the ratings or if the load becomes eccentric, follow the steps below to set parameters.
Setting parameters makes the operation of the Manipulator optimal, reduces vibration to shorten the operating time, and improves the capacity for larger loads. This also works to curb any persistent vibration that may occur when the hand and workpiece have a large moment of inertia.
You can also perform settings using the "Weight, Inertia, and Eccentricity/Offset Measurement Utility."
For details, refer to the following manual.
"Epson RC+ User's Guide - Weight, Inertia, and Eccentricity/Offset Measurement Utility"
The allowable load for C12 series Manipulators is up to 12 kg.
Due to the limitations of the moment and moment of inertia shown in the table below, the load (hand + workpiece) should also meet these conditions.
Allowable Load
| Joint | Allowable moment | (GD2/4) Allowable Moment of Inertia |
|---|---|---|
| Joint #4 | 25.0 N·m (2.55 kgf·m) | 0.70 kg·m2 |
| Joint #5 | 25.0 N·m (2.55 kgf·m) | 0.70 kg·m2 |
| Joint #6 | 9.8 N·m (1.0 kgf·m) | 0.20 kg·m2 |
Moment
The moment indicates amount of torque applied on the joint in order to support the gravity on the load hand + workpiece). The moment increases as weight of the load and amount of eccentricity increase. As this also increases the load applied on the joint, make sure to keep the moment within the allowable value.
Moment of inertia
The moment of inertia indicates how difficult the load (hand + workpiece) to rotate when the Manipulator joint starts to rotate (amount of inertia). The moment of inertia increases as weight of the load and amount of eccentricity increase. As this also increases the load applied on the joint, make sure to keep the moment within the allowable value.
The moment M (Nm) and moment of inertia I (kgm2) when the volume of the load (hand + workpiece) is small can be obtained by the following formula.
M (Nm) = m (kg) × L (m) × g (m/s2)
I (kgm2) = m (kg) × L2 (m)
- m: Weight of load (kg)
- L: Eccentricity of load (m)
- g: Gravitational acceleration (m/s2)
The figure below shows distribution of the center of gravity when the volume of the load (hand + workpiece) is small. Design the hand so that the center of gravity is within the allowable moment. If the volume of the load is large, calculate the moment and inertia moment by referring to the following section.
"INERTIA Setting - Calculating the Moment of Inertia"
| Symbol | Description |
|---|---|
| a | Distance from the center of Arm #* rotation [mm] |
| b | Center of gravity of load from the Arm #* rotation center [mm] |
Max. Eccentricity of Load (Distance between the joint rotation center and the load’s center of gravity)
| Joint | 1 kg | 3 kg | 5 kg | 8 kg | 10 kg | 12 kg |
|---|---|---|---|---|---|---|
| #4 | 300 mm | 300 mm | 300 mm | 296 mm | 255 mm | 213 mm |
| #5 | 300 mm | 300 mm | 300 mm | 296 mm | 255 mm | 213 mm |
| #6 | 300 mm | 258 mm | 200 mm | 125 mm | 100 mm | 83 mm |
When calculating the critical dimension of the load using the allowable moment and inertia moment, the calculated value represents a distance from the Arm #6 rotation center, not the distance from the flange. To calculate the distance from the flange to the load’s center of gravity, subtract the distance from the center of the Arm #5 rotation center to the flange (=80 mm) as shown in the example below.
Example: Calculation of the critical dimension of the load (A) when the load is 12 kg.
Center of gravity by the allowable moment control: 25.0 N·m/(12 kg × 9.8 m/s2) = 0.212 m = 212 mm
Center of gravity by the allowable inertia moment control: (0.70 kgm2/12 kg)1/2 = 0.241 m = 241 mm
Due to the allowable moment control, center of gravity for the load limit is 212 mm from the Arm #5 rotation center.
Distance from the flange to the center of gravity for the load limit A = 212 mm - 80 mm = 132 mm
Critical Dimension of Load
(Units: mm)
| Symbol | Description |
|---|---|
| a | Load center of gravity position |
| b | Arm #6 rotation center |
| c | Flange |
| d | Arm #5 rotation center |