A direct drive system connects a direct drive motor (linear motor or torque motor) directly to the load under the control of a drive system, thus directly driving the load. This article summarizes several common problems encountered in the application of direct drive systems, hoping to provide helpful assistance to users.
How does a linear motor work?
A linear motor is a transmission device that directly converts electrical energy into linear motion mechanical energy without any intermediate mechanisms. It can be viewed as a rotary motor radially sliced and unfolded into a plane. The side derived from the stator is called the primary; the side derived from the rotor is called the secondary. In practical applications, the primary and secondary are manufactured with different lengths to ensure that the coupling between them remains constant within the required stroke range. Linear motors can have either a short primary and long secondary, or a long primary and short secondary. Considering current manufacturing and operating costs, the short primary and long secondary configuration is currently the most common.
It can be observed that the working principle of a linear motor is quite similar to that of a rotary motor. Taking a linear induction motor as an example: when an AC power supply is applied to the primary winding, a traveling wave magnetic field is generated in the air gap. Under the cutting of the traveling wave magnetic field, the secondary winding induces an electromotive force and generates a current. This current interacts with the magnetic field in the air gap to produce an electromagnetic thrust. Assuming the primary winding is in a fixed state, the secondary winding will move linearly under the action of the thrust; conversely, the primary winding will move linearly.
The principle of a linear motor is actually not complicated. Imagine cutting a rotating induction motor along its radius and flattening it; this forms a linear induction motor. In a linear motor, the part equivalent to the stator of a rotating motor is called the primary, and the part equivalent to the rotor is called the secondary. Alternating current is passed through the primary, and the secondary moves linearly along the primary under the influence of electromagnetic force. The primary needs to be relatively long, extending to the required position, while the secondary does not need to be as long. In fact, linear motors can have both a very long primary and a very long secondary; they can have a fixed primary and a movable secondary, or vice versa, achieving the effect of switching between them at will, real-time processing, and are very convenient and simple.
What are some of the commonly used structural patterns for linear modules?
Synchronous belt-slide structure
Speed reduction mechanism: Increases the output thrust of the slide table and saves overall space of the slide table.
High-strength steel wire synchronous belt: low dust generation, high tension.
Fully enclosed sliding frame: reliable strength and beautiful appearance.
Precision linear guides: ensure the straightness and parallelism of sliding operation.
Sensor cable tray: Allows for the internal storage of sensor cables, preventing damage to the sensors and cables.
Ball screw-slide structure
Split-type motor connector: Excellent interchangeability facilitates the installation of couplings and motors.
Seals: prevent grease from leaking out and dust from entering.
Fully enclosed sliding frame: reliable strength and beautiful appearance.
Precision linear guides: ensure the straightness and parallelism of sliding operation.
Sensor cable tray: Allows for the internal storage of sensor cables, preventing damage to the sensors and cables.
Precision ball screws: C5 and C7 are optional.
Diverse input connection methods
Without changing the length of the mechanical body, various connection methods can be achieved for the input end of the robot, making it highly interchangeable.
Characteristics of cleanroom robotic arms
Vacuum tube connector: In a dust-free environment, a vacuum tube can be connected to extract trace amounts of dust generated by mechanical friction inside the module.
Sealing strip: Rubber magnets attract the steel strip, preventing the steel strip from deforming and bulging, thus achieving an effective seal.
Cleanroom environment robotic arm (standard configuration does not include sealing strips; installing sealing strips would generate trace amounts of dust in a cleanroom environment, so they are generally not installed. If required by the customer, please specify before ordering.)
Steel belt and rubber rollers: Wear-resistant rubber rollers are used at the contact points between the robot slide and the steel belt to achieve rolling friction between the slide and the steel belt, reduce the resistance between the slide and the steel belt, prevent the generation of friction dust, and reduce noise.
What are the differences between linear motors and ball screw modules?
Linear motors, as high-precision linear transmission devices, play an important role in printing, medical, industrial, and CNC applications. Typically, a linear motor's maximum load capacity is only 20KG, but its stroke can reach four meters. Furthermore, using gratings, its accuracy can reach ±5µm. Depending on the thrust, the mover and stator will vary. During assembly, workshop technicians will straighten the linear guide rails to achieve a straightness of ±2µm. Therefore, customers with light loads, long strokes, and high precision requirements generally choose linear motors. Customization can be provided to meet the needs of a wide range of customers.
Ball screw linear modules, also known as single-axis manipulators or single-axis robots, are widely used in industries such as lithium batteries, solar energy, and new energy. A typical 200mm wide linear module can handle a maximum load of 130kg, with a stroke of 2.5 meters and an accuracy of ±2µm. For higher customer requirements, ground ball screws can be used, achieving an accuracy of ±5µm. Currently, Hisek primarily uses Delta and Panasonic servo motors, providing customers with more options for selection and configuration.
Of course, the linear module mentioned here is mainly equipped with lead screws and guide rails. If the customer's precision requirements are not high and the budget is not so sufficient, a synchronous pulley (belt) module can also be used. Generally, this type has a longer main stroke, moderate load-bearing capacity, and low precision requirements, so it can be selected. It is also a good choice for cost control.
What are the typical load performance characteristics of linear modules?
1. Reference values for the flatness and straightness of the slide table
Flatness standard: The parallelism between the mounting reference surface of the main body and the reference surface of the slide block is less than ±0.05mm/M.
Straightness standard: The parallelism between the slide reference surface and the external straightness reference gauge is less than ±0.05mm/M.
Flatness testing methods: flatness, granite platform
Straightness testing methods: Straightness, granite platform
Cross-sectional view of the electric slide table: slide base reference surface, slide base, slider, slide rail, and body mounting reference surface.
2. Inertia Calculation
Generally, machining tools and workpieces are not of a single shape, making calculations difficult. Calculations often involve breaking them down into the inertia of several single shapes and then summing up the inertia.
3. Load arm length
The load arm length represents the maximum distance the slide can extend. If the load arm extending from the slide on the electric slide exceeds the allowable value, it will cause abnormal vibration and increase the settling time. Therefore, please be sure to comply with the load arm length limit.
The length of the slide determines the length of the load arm. If the load arm exceeds the allowable value, it will cause abnormal vibration and increase the settling time. Therefore, please be sure to comply with the load arm length limit.
4. Allowable load torque
The allowable load torque represents the maximum load torque that the slide block can withstand, calculated based on the service life of the existing slide rail. The MP, MY, and MR torques (in all three directions) vary for different specifications of electric slide rails. Using the linear slide rail beyond its allowable value will reduce its lifespan. If it cannot be used within the allowable range, be sure to install an external auxiliary linear slide rail.
What precautions should be taken when using linear motor modules?
When purchasing, the applicable environment should be checked with the manufacturer's sales personnel. Do not use in corrosive environments such as those containing sulfur or sulfide gases, as these can lead to circuit breakage or poor contact. During model selection, the usage requirements and motor parameters must also be checked with the sales personnel to ensure proper application.
Linear motor modules are precision mechanical parts and widely used in the machinery industry. Please ensure that only qualified and experienced technicians operate them. Always follow the product's operating instructions. If there are special requirements regarding the application environment, such as cable or motor installation methods, please contact sales personnel for confirmation to prevent accidents and avoid unnecessary losses. Never plug or unplug any terminals while the power is on to prevent damage to the motor and driver. Ensure the motor ground wire is properly grounded. Do not store control signal lines and power lines (main power lines, motor power lines, etc.) in the same conduit or bundle them together. Do not touch any moving parts of the motor while it is running.
When storing equipment, please note the following: temperature control should be within -20℃ to +60℃; humidity: below 85%; place in a dust-free, clean environment free of corrosive gases, abrasive liquids, metal powders, and oil. Before moving, wiring, maintaining, or inspecting the equipment, please disconnect the power supply for at least 3 minutes. Even after disconnecting the power supply for approximately 2-3 minutes, residual voltage may remain on the power lines; do not touch the equipment hastily. Frequent power disconnection/on/off can degrade the main circuit components. After disconnecting the power supply, please reconnect it after at least one minute, and limit the frequency of power switching to no more than "2 times/3 minutes". During use, the linear guide rails should be lubricated and maintained regularly.
What are the advantages of using a direct-drive torque motor?
Taking the Hisense RMA series new direct-drive torque motor as an example, compared with traditional motors, it has advantages such as ultra-low vibration, ultra-quiet operation, high cleaning power, energy saving, and long lifespan, which can comprehensively improve the performance of washing machines. Traditional washing machines consume a large amount of electrical energy due to the numerous components in their drive system. Washing machines using DD motor technology change the traditional transmission method of using belts and pulleys to drive the washing device, instead using a motor to directly drive the washing device, making the motor efficiency 2-3 times that of ordinary washing machines.
The direct drive torque motor product structure mainly consists of the following parts: fixed part, rotating part (worktable), mounting hole, hollow shaft, positioning pin hole, motor cable, and encoder cable.
The RMA series direct-drive torque motors connect directly to the customer's load, eliminating the need for continuous mechanisms such as reducers and gearboxes. This results in a compact, reliable, and low-noise overall mechanism. Furthermore, the high-resolution circular grating significantly improves the overall mechanism's precision. Therefore, the RMA series motors offer advantages such as high precision, high response, and accurate positioning, making them widely used in industries such as inspection and machine tools. Applicable fields include: machine tools (machining centers, lathes, milling machines, drilling machines); semiconductor manufacturing equipment (wire bonding machines, electronic component insertion machines); industrial robots (Cartesian coordinate type, cylindrical coordinate type); and other devices (injection molding machines, coordinate measuring machines).
(Source: Dongguan Hisek Transmission Technology Co., Ltd.)
