Robot Joints RDrive

Drive Your Business Effectively
Do you need a powerful tool for own robot production? Or adjustable spare parts for your CNC robotic arm? Then have a look at the RDrive robot joints by Rozum Robotics.

RDrive

Robot joint

RDrive is a robot joint with an increased integration level, optimized size and weight. Despite that, it doesn’t lower efficiency and torque. RDrive is a suitable option for the spheres where careful use of space and consumables, as well as detailed control and accuracy, matter the most.

How does a robot joint work?

Like the bones in a human arm, movable segments in a robot are linked up with robotic joints. And just like with a human body, every single part is a complicated system that consists of numerous tightly connected smaller parts. A closed-looped RDrive structure includes a motor, a control system, a feedback system, and a gear:

How does a robot joint work?

Like the bones in a human arm, movable segments in a robot are linked up with robotic joints. And just like with a human body, every single part is a complicated system that consists of numerous tightly connected smaller parts. A closed-looped RDrive structure includes a motor, a control system, a feedback system, and a gear:

Step 1

A controller gets a command from a control device and creates a profile of motion.

Step 2

Relying on this profile, the controller generates signals for the motor. It sets the speed and trajectory of the movement.

Step 3

Gears increase the output torque.

Step 4

The encoder monitors the process and sends the message back to the controller.

Step 5

The controller analyses the signal from the encoder. If there is an error, the controller adjusts the moves to the settled parameters.

The components’ characteristics influence the performance of a robot. Let’s have a look at the key components in the RDrive robot joints:

AC Servo Motor. Drive it.

The engine for a robot should meet several requirements to make sure your robotic arm rocks. It should be compact and ensure a high force output at the same time. The most suitable and reliable decisions here are AC or DC servo motors. They are different from regular motors as they are based on feedback control and move only after receiving a signal. For RDrive we use an AC servo motor. The table below illustrates the advantages of AC motors for robotics.

AC and DC servo motor differences

Weigh & Size
AC

Lighter and smaller

DC

Heavier and larger

Speed & Torque
AC

The frequency of the applied voltage and the number of magnetic poles determine the speed Adaptable to high torque

DC

The supply voltage with a constant load is proportional to the speed. Less adaptable to high torque

Stability
AC

More stable

DC

Less stable

Control
AC

More sophisticated control

DC

Easy control

Price
AC

More expensive

DC

Less expensive

Application
AC

More Servo systems with no extra requirements (CNC)

DC

Servo systems where extra-high precision and repetition are mandatory. (robotics)

Noise
AC

Pretty noisy

DC

Less noisy

Parameter AC DC
Weigh & Size Lighter and smaller Heavier and larger
Speed & Torque The frequency of the applied voltage and the number of magnetic poles determine the speed Adaptable to high torque The supply voltage with a constant load is proportional to the speed. Less adaptable to high torque
Stability More stable Less stable
Control More sophisticated control Easy control
Price More expensive Less expensive
Application More Servo systems with no extra requirements (CNC) Servo systems where extra-high precision and repetition are mandatory. (robotics)
Noise Pretty noisy Less noisy

Torque is a core efficiency characteristic of a servomotor. How much force can be generated? What is the maximum load for a servo? It depends on numerous factors – motion type, gearheads, supply voltage, shaft speed, motor size, etc.

We created 6 types of AC servomotors to meet our clients’ needs:

Model RDrive 50 RDrive 60 RDrive 70 RDrive 85 RDrive 110
Rated power 65 W 225 W 155 W 450 W 450 W
Rated rotation speed 55 rpm 55 rpm 30 rpm 40 rpm 20 rpm
Supply voltage 48 V 48 V 48 V 48 V 48 V
RMS Current 1,6 A 3,1 A 5 A 8,8 A 9 A
Operating Temperature 0...35 °C 0...35 °C 0...35 °C 0...35 °C 0...35 °C
Rated torque 11 Nm 39 Nm 49 Nm 108 Nm 216 Nm
RMS Current 28 Nm 54 Nm 82 Nm 157 Nm 333 Nm

Integrated controller.
Rule it.

While a motor is a muscle, the control circuit is the brain of a robotic joint. It is usually based on a control loop feedback system: A controller transfers the command to the motor, compares the actual results to the inputted, and, if needed, adjusts movements, speed, and trajectory. The closer the motor is to the desired position, the slower it moves. When it reaches the point, the power supply is stopped.

These controllers are both small and efficient which allows to integrate them into compact servo motor housing. Smart design saves space, prevents additional connectors, and reduces EMC (electromagnetic compatibility).

Integrated controller.
Rule it.

While a motor is a muscle, the control circuit is the brain of a robotic joint. It is usually based on a control loop feedback system: A controller transfers the command to the motor, compares the actual results to the inputted, and, if needed, adjusts movements, speed, and trajectory. The closer the motor is to the desired position, the slower it moves. When it reaches the point, the power supply is stopped.

These controllers are both small and efficient which allows to integrate them into compact servo motor housing. Smart design saves space, prevents additional connectors, and reduces EMC (electromagnetic compatibility).

Built-in encoders.
Understand the feedback.

In the robotic joint, an encoder is like a receptor or a feedback sensor of a robot. It detects the mechanical motion of the motor, and how it changes its position in space and time. Then the encoder translates this information into an electrical impulse and sends it to the controller.

Transducers are divided into two big ‘species’ - incremental and absolute. The main difference is their tracking approach. An incremental encoder needs a reference point to start with. In other words, every time power is supplied to the sensor, the encoder is not able to report the current position and starts counting from zero unless there is a reference point. An absolute encoder generates a unique code for the motor position using a special scale and doesn’t need any calibration. Generally, incremental encoders are cheaper than absolute ones, but the latter have a benefit that is hard to beat. An absolute encoder isn’t influenced by blackouts and doesn’t lose track of positioning even when the battery runs out.

When choosing an encoder, it’s also highly recommended to consider the environment in which you plan to use a robotic joint. Optical sensors are resistant to electromagnetic influence, unlike magnetic ones, but they are dramatically affected by excessive dust, moisture or vibration.

Magnetic encoders used in RDrive are resistant to high temperatures, vibrations, and non-ferromagnetic particles. The combination of two encoders increases the accuracy and speed of the whole process. While one encoder monitors the motion and speed of the output shaft, the other reports on the positions and speed of the rotor to the controller. Communication with the controller goes through the CAN network.

Gears. Turn it.

The main trend in industrial robotics is to create small but powerful tools. A small motor can spin fast but doesn’t give high torque. And here gears do their main job – they turn the high output speed into high torque, and, as a result, increase the efficiency of the whole mechanism. In the RDrive robot joints, a gear ratio is 1:100. So if a servomotor generates 2 N·m input torque, the output torque will be 200 N·m.

Some servomotors do not include a gearbox, therefore, it should be extra integrated. It increases the risk of coupling failures, mismatching of parts, and lower efficiency. Therefore, such servomotors are not the best choice for your robot.

RDrive has integrated gearheads. Integration allowed reducing the size of the RDrive robot joint and guaranteed the symbiosis of all the parts. We also addressed the backlash problem. The distance between gears’ teeth often results in lost motion, decreased speed, and not precise positioning. To keep RDrive robot joints fast and accurate, a zero-backlash harmonic gearbox is used. Strain wave or harmonic gearbox consists of an outer fixed ring, an inner flexible ring, and an elliptical wave generator with steel ball bearings. This construction allows reaching a minimal backlash with precise motion control and high torque at the same time. In RDrive, the backlash is 0.3 arcmin.

So, to sum up. Why RDrive?

All-in-one

RDrive has gearboxes, encoder, and controller as incorporated parts. Such integration:

- Improves the dimensions of the robot joint
- Guarantees perfect coupling between the motor, gear, controlling box and the computer
- Minimizes the failure and imbalances risks
- Reduces production costs and, therefore, the price for the final user

Place an Order

RDrive compact design reduces the footprint of your robots. Choose a size that suits your aims the most:

- RDrive 50 / is only 88 mm length / weighs 0.55 kg
- RDrive 60 / is only 88 mm length / weighs 0.89 kg
- RDrive 70 / is only 88 mm length / weighs 0.91 kg
- RDrive 85 / is only 88 mm length / weighs 2.1 kg
- RDrive 110 / is only 88 mm length / weighs 3.9 kg

Efficient and accurate

Every detail of RDrive was designed keeping in mind the main idea of robotics: high accuracy at smaller sizes.

- Peak Torque (depending on model) 28 -333 Nm
- Two built-in encoders
- Integrated harmonic gearbox
- 0,3 arcmin backlash
- Gear ratio of 1:100

Reliable and friendly

RDrive is a system that is simple to integrate. It’s like a high-tech puzzle that you can use to start own robot production or to upgrade the existing one.

- Absolute encoder
- IP Rating 21
- Compliance with ISO standards
- Strict suppliers policy

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