Robots perform specific pre-planned tasks such as assembly line work, surgical assistance, warehouse pickup/retrieval, and even hazardous tasks such as landmine removal Today's robots are capable of handling not only highly repetitive tasks, but also complex functions that require flexibility in direction and movement. As technology advances, speed and dexterity increase, and costs decrease, robots will gradually be widely adopted. The cost advantage of being lower than labor also gives us a glimpse of the robotics industry. In addition, advances in machine vision, computing power, and networking will also drive the popularization of robot applications, and these high-performance machine
The realization of the human is due to the following aspects of the enhancement:
1. Complex sensors
2. Computing power and algorithms that enable real-time decision-making and movement.
3. Motors that quickly and precisely progress mechanical power to realize complex tasks!
When specifically selecting a motor type and model, the designer has to consider three primary factors the designer has to consider.
1. The minimum and maximum speed (and acceleration) of the motor.
2. The maximum torque the motor can deliver, and the relationship between torque and speed curves.
3. the accuracy and repeatability of motor operation (without sensors and closed-loop control); of course, there are many other important factors to consider when selecting a motor, such as size, weight, and cost. For almost all small to mid-sized robotic actuators, the choice of drive motors is usually between brushed DC motors, brushless DC motors (BLDC) and stepper motors. (However, in some cases hydraulic vs. pneumatic presses are the best choice.)
Brushed DC motors are the oldest DC motor technology, the simplest and least expensive. The rotation of the motor's rotor switches (commutates) the magnetic field of the windings around the rotor due to the contact between the brushes and the rotor. The speed of the motor is a function of the applied voltage, so drive requirements are modest, but managing torque is difficult. There are also reliability issues when operating due to factors such as brushes wearing out, needing to be cleaned and maintained, and potentially being a source of electronic noise (electromagnetic interference). As a result of these issues, brushed DC motors are, for the most part, the least attractive option for robot design.
Brushless DC motors appeared in the 1860s and benefited from two developments: the emergence of robust, small, low-cost permanent magnets; and the emergence of small, efficient electronic switches (usually MOSFETs) to switch the current flow to the windings." Electronic commutation" replaces the mechanical commutation of the brush motor to control the switching of the magnetic field, the interaction between the fixed switching coil around and the magnets on the rotating core replaces the mechanical commutation of the brush motor, i.e., it utilizes the interaction between the magnetic field and the electric field. By changing the switching frequency of the MOFSET, the motor speed can thus be controlled. In addition, its motor controller can better control the motor performance compared to brushed motors.
Even better, advanced algorithms such as PID (Proportional-Integral-Differential) correction algorithms or FOC (Field Oriented Control, sometimes called Vector Control) control algorithms can be solidified into the motor controller. This allows ideal motor operation to be matched to actual loads and load variations, resulting in more robust and accurate motor performance. For example, motor control algorithms/programs can take into account relevant factors such as rotor inertia and enable the motor drive to adapt and gradually reduce errors due to mechanical factors. Such algorithms make it possible to precisely control acceleration and torque.
Brushless motors (BLDC) require more complex control circuits but can exhibit better performance than brushed motors. Typically, BLDC motors need to be equipped with a position feedback sensor, such as a Hall effect sensor, an optical encoder, or a reverse potential detection device.
Another type of BLDC motor commonly used in robots is the stepper motor, where a switching electromagnet is used, located next to the central core of the permanent magnet ring. Stepper motors do not "rotate" in a conventional way; instead, they gradually increase their speed with the help of a constantly rotating shaft, thus allowing for a certain angle of rotation or continuous rotation. Stepper motors have repeatable motion control: they can be returned to the previous position when required.
Stepping angles range from 1.8° (200 steps/revolution) to 30° (12 steps/revolution). The stepping angle or number of steps depends on the number of permanent magnets the motor has, but values outside this range are also possible.
With stepper motors, if power is applied but no steps are pointed, they will remain in their original position; stepper motors provide high torque at low rpm. The most direct way to get a stepper motor to rotate is to energize and de-energize the solenoid in an orderly fashion, but this can introduce jitter or vibration. Brushless motors and stepper motors have partially overlapping application areas. Stepper motors are better suited for applications that require precise in-and-out motions (such as pick and place) rather than long periods of sustained rotation, as well as for smaller applications that do not require high torque or speed from the motor. In addition, stepper motors have lower energy efficiency requirements than brushless DC motors. In addition to the motors listed here, there are many other types available. The motor families are numerous and complex, with many subdivisions. For example, the permanent magnet synchronous motor (PMSM) is a combination of a brushless DC motor (with respect to the rotor) and an AC induction motor (with respect to the stator structure). It is characterized by high energy efficiency, high relative density per unit of small volume, torque-to-weight ratio, fast response time, and relative ease of control, but it is also relatively expensive.
The robot motion system involves more than just motors; it includes three main functional modules.
1.Real-time controller, manifested in the following three forms.
Fast computational processors for general purpose, running motion-control firmware.
DSP-oriented FPGAs for control applications.
Specialized controller IC circuits with hardwiring and built-in algorithms.
2. One or more driver layers cascaded to take low-level signals out of the controller outputs and output the high voltage/current needed to turn the control electronics on/off.
3.MOSFET (or other switching devices, such as IGBT or bipolar transistors), which controls the current flow to the motor windings specific
MOSFET selection depends mainly on the motor and the windings of the required current and voltage size. MOSFET model to determine down to select the driver after the MOSFET driver selection by the MOSFET rating: sometimes may require a series of ascending repulsion driver, the specific decision to determine the driver. Sometimes a series of boost drivers may be required, depending on the size of the MOSFETs.
4. Problems that may be encountered when selecting a controller
Controller model selection is also very strategic and requires a decision to be made before selecting a specific vendor and model. There are many trade-offs when choosing whether to use a general-purpose processor for motor control only, an FPGA with local computational power, or a specialized control IC circuit (usually from a specific motor control vendor). Designers need to consider factors such as.
What complexity of control algorithm do you need, and how many I/0 ports?
Who will provide the control algorithm and code: the IC supplier, a third-party partner, or an unrelated third-party developer? How will they verify and validate the performance of the motor and its application?
How much user programming capability do you need? Even dedicated, non-programmable controllers will require the user to select the type of algorithm, closed-loop control mode (position, velocity, or acceleration), and will need to set a number of operating parameters. Does the motor and application have unique properties to set? If the answer is yes, then it would be better to choose programmable I. Conversely, if there is no need to modify the algorithms, a dedicated IC with hardwired, solidified algorithms is preferable to a fully programmable IC. Does the controller need to support multiple motor types? Even if it is the same type, does the controller need to support only one size of motor in that model, or a range of sizes?
What level of technical support does the vendor provide? What hands-on motor development experience do they have? Will they provide specific reference designs that have been built and validated, including interface circuitry between the control IC and the MOSFET driver?
Are there any regulatory issues to be aware of? For example, authorized energy efficiency evaluations
(many motor applications must now meet various "green" environmental requirements). If so, does the supplier understand these issues and do their components and algorithms meet these requirements?
5. Development Kits Demonstrate Controller and Interface Performance
For many engineers, bringing all the pieces together - controllers, drivers, MOSFETs, etc. with solidified or separate algorithms - is a multi-disciplinary task, one that they don't want to "start from scratch". For this reason, many vendors offer evaluation boards or even complete kits with sample controller algorithms, drivers and MOSFETs. For example, the Freescale MTRCKTSPNZVM128 three-phase sensorless PMSM kit uses sensorless motor control technology to drive a three-phase BLDC or PMSM motor, and is designed for rapid prototyping and evaluation using inverse potentials supported by the integrated ADC module with the aid of a microcontroller. In addition, this kit (featuring the MC9S12ZVML12 microcontroller) can also be configured for sensor-based evaluation of operation using Hall sensors or resolvers. The future of robotics is also very promising as advances in technology, including precision actuation through improved motor control and sensing, will create new opportunities. Revolutions in the key areas of sensing, control and motors will continue to influence changes in robotics.