The soft landing force control function aims to control the force during the contact between the actuator and the workpiece, preventing damage to the device or other problems caused by pressure.
To achieve precise force control, a systematic design is required. Force control is divided into open-loop force control and closed-loop force control. Open-loop force control is where the driver controls the force simply by judging the motor current. Closed-loop force control combines an end pressure sensor to form a closed loop, so that the force control mode will only end when the force set by the sensor is reached at any position.
Force control method introduction
1. Open-loop force control:
Open-loop force control places high demands on mechanical structure and motor. However, the overall structural design is relatively simple. It requires the overall structure to form a linear relationship between current and thrust. The motor acts directly on the machined part through rigid components, without any flexible or elastic links in between, so that the motor current can be directly converted into the end-effector thrust. For example, the structure of a voice coil motor is generally to act directly on the machined part. Moreover, the current linearity of the voice coil motor is superior to other motors, making it the preferred motor type.
2. Closed-loop force control:
Closed-loop force control builds upon the open-loop structure by adding a pressure sensor at the motor's end. When the driver detects a pressure change (typically an analog signal) from the sensor, it performs closed-loop calculations, achieving simultaneous control and detection. However, because closed-loop force control adds external loop calculations, its response time is slower than open-loop force control. Therefore, it is not the optimal choice for scenarios requiring high-response force control.
Advantages of ISMC Force Control Algorithm
1. Three-stage force control algorithm
Through continuous engineering iterations, the ISMC force control method has achieved a force control effect of 1g +/-0.1g in practical applications, as shown in the force control curve below. The following figure shows the data curve collected by the sensor.
As explained earlier, the more precise the force control requirements, the more stringent the requirements for the structure and motor. To achieve a force control of 1g, a zero-friction guide rail, such as an air-bearing guide rail, is required, and the motor's current linearity must be high.
2. Force control parameters can be edited in real time.
Many force control actuators on the market are programmed internally, but they cannot change the force control parameters in real time via a higher-level control unit. This makes them inflexible and unable to achieve force control functionality under different operating conditions on the same device.
ISMC's open parameter configuration allows for online parameter changes via EtherCAT bus and Modbus commands, enabling configuration of the distance, speed, and force magnitude of the three segments.
ISMC Force Control Application Case
1. Application of Placement Equipment
Currently, in camera mounting equipment, because many components on a camera are very precise and fragile, such as CMOS chips and glass lenses, precise force control is required, ranging from 30 to 200g, depending on the actual needs of different products.
2. Battery production line testing
During battery production, various charge-discharge tests are required. If a battery has defects, it may bulge or other defects during overcharging and discharging. A force-controlled method is used; when the required pressure is reached, the current position is detected to determine if the battery dimensions meet the requirements. The advantage of this method is that even if the battery is defective and bulging, it can be accurately detected without causing the battery to explode.
3. Mounting of optical chips
High-throughput chips on the market are mostly imported, and the unit price of these products is high. If the pressure control during the mounting process is not up to standard, it will damage the chips. In this application, the customer's acceptance standard is 1g +/- 0.1g, while the actual processing requires 3g of pressure.
4. ZR module compatibility
As the localization of equipment in the semiconductor industry continues to advance, breakthroughs are also being made in ZR modules used in semiconductors. Domestic partners have made considerable progress in products that achieve both precise force control and high-frequency short-distance motion. ISMC accompanies its partners in continuous improvement, achieving precise Z-axis force control. The spring-loaded Z-axis structure can achieve a pressure effect of 3-5g, while the R-axis meets high-precision positioning requirements, ensuring fast and stable positioning.
