When choosing a robot for machining tasks, you've got options. The four main types are Articulated, Cartesian, SCARA, and Parallel robots. All of these options are called 'robot arms' in the industry, but when you picture a robot arm, you're likely just thinking of an Articulated robot.
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In choosing a robot, pay particular attention to the working area available in your shop and the size of the parts you require it to work with. Articulated and SCARA robots work best for small parts and tight cells. Cartesian and Parallel robots can handle larger, heavier parts but often require more setup, such as ceiling tracks and are therefore less adaptable. Precision and speed are key for machining, so you'll want to look out for the robot's 'repeatability' ' how accurately it can return to a position over and over again.
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With your robot chosen, the next important choice is the end-of-arm-tooling. These 'end-effectors' are what allow your robot to interact with the environment around it and dictate the types of tasks your robot can undertake. Here are a few of the most common options for machining:
If you need to pick and place parts or manipulate objects, a multi-fingered gripper end-effector is a good choice. Grippers can grasp parts of various shapes and sizes. Basic grippers will look much like a workbench clamp or a human hand. More advanced examples include Vacuum grippers which use suction to pick up smooth, non-porous parts. Magnetic grippers are ideal for handling ferrous metal parts, while Needle grippers can pierce and move fabric.
For welding applications, a welding torch end-effector can be attached to a Machining robot. The robot can then perform arc welding, spot welding, laser welding and more. The welding torch may need to be customized based on the specific welding process and a higher payload robot is often required to handle heavy cables for shielding gas and electrodes.
To cut, grind, deburr, polish or sand parts, a Machining robot can be fitted with rotary cutting tools like saws, grinders, sanders and deburring tools. The spindle speed and power need to match the requirements of the cutting tool. A coolant system is often necessary to prevent overheating, and you may consider an end-effector with a built-in vacuum to reduce mess or a grit-changer to reduce human intervention.
For assembly tasks like drilling, screwing, riveting or inserting fasteners, the appropriate driver bit or drill chuck can be attached to the robot arm. These include nut drivers, screwdrivers, drill chucks, and riveting tools. You'll want an end-effector with a built-in torque or force sensor to ensure your robots don't over-tighten fastenings.
End-of-arm-tooling exists for almost any application you can think of. If there's a tool which can be manipulated by a human, then a robotic adaption almost certainly exists. End-effectors exist for chiseling, gluing, nail-gunning, and even cutting materials with scissors. If you're looking for a particularly niche end-effector, your robot's manufacturer will be able to point you in the right direction.
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When choosing a Machining robot, there are several factors you should consider to determine which type is right for your manufacturing shop. We've already considered the specific types of robots you should look at and the importance of end-effectors. But you'll also want to consider the work envelope, speed, safety factors, and cost.
A robot's work envelope refers to the area it can reach. A larger envelope means a bigger range of motion to access your parts or move them around. This does often come at the cost of precision and even more often, speed. Think about the sizes of parts you need to handle and the tightness of workspaces.
Speed is also an important factor. This is both inherent in the type of robot you choose such as a SCARA robot which has fewer joints to individually move than an Articulated arm and therefore can generally move faster. The RO1 by Standard Bots can outpace most robots with a joint rotation speed of 435 degrees per second.
While small differences in speed can seem trivial, higher joint movement means faster cycle times, which translates to more output from your robots and a higher ROI.
Safety is your next consideration if you're going to operate a fast-moving robot equipped with a sharp tool. You'll want to consider a 'Collaborative Robot' ' that is, a robot equipped with built-in safety sensors and collision detection for safely working alongside humans.
For more dangerous situations, like lifting heavy payloads or equipping a robot with a cutting device, your risk assessment may necessitate additional safety equipment like a fence, proximity sensor or emergency-stop buttons.
Your budget is another important factor to consider. Machining robots can cost anywhere from $35,000 to $400,000 or more depending on the type, brand, and accessories. While cost is always a factor, choosing a robot that can't perform the necessary tasks efficiently will cost more in the long run. You'll want to consider additional costs depending on your choice of robot and process, such as retooling or programming costs, which can vary wildly depending on the robot.
When it comes to choosing a robot for your machining needs, you have several reputable manufacturers to consider. Here are some of the top players in the field and what they offer.
ABB is a Swiss pioneer in robotics and automation, with over 300,000 robots installed worldwide. They offer a wide range of Articulated, SCARA, and Cartesian coordinate robots suitable for machining applications like welding, cutting, deburring, grinding, and polishing. Their higher payload robots like the IRB or IRB are well-suited for heavy machining tasks.
FANUC is one of the largest Japanese robotics companies, with over 4 million CNC's and 400,000 robots installed globally. They provide highly reliable robots for machining, including their FANUC M-710iC/50H and M-20iA/12L models. These Six-Axis, high-speed robots can perform precision machining operations like deburring, grinding, polishing, and dispensing sealants.
Standard Bots are a US-based robotics company with a manufacturing facility based out of New York. Their flagship Articulated Arm RO1 possesses the largest payload at 18 kg in its class, with the fastest joint movement and most accurate repeatability amongst competing robots. RO1 can integrate particularly easily with OnRobot machining end-effectors and pricing begins at $5 per hour of operation.
Yaskawa Motoman produces innovative Industrial robots for various machining applications like spot welding, arc welding, cutting, and dispensing. Their high-speed, space-saving robots like the Motoman GP8 and GP12 are well-suited for machine tending and parts transfer. They also offer the Motoman MH24, a heavy-duty robot designed for demanding welding and cutting operations.
No matter the manufacturer you choose, each will be able to help you figure out your full robotics solution, including the most suitable robot type, compatible end-effectors, appropriate accessories like conveyors and safety features like proximity sensors.
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So there you have it, the basics of choosing a Machining robot for your factory floor. Do your own exploring, and think about what kinds of parts and materials you want to work with first and how quickly you need to produce them. With your budget in mind, you can narrow down your options and find a robot that will help streamline your processes, reduce costs in the long run, and boost your productivity and profits. With so many options available now for even the smallest of operations, getting automated is more feasible than ever.
Interested in bringing robotic Machining to your own business? RO1 by Standard Bots is the best choice for machine shops large and small:
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Speak to our solutions team today to organize a free, 30-day onsite trial and get expert advice on everything you need to deploy your first robot.
Today's robot joints have highly integrated motors, encoders, gearing solutions, and sometimes brakes. It is common to use a direct drive frameless torque motor kit coupled to a precision high ratio gear system. While these two terms 'direct drive' and 'precision gear' tend to conflict, the combination is successful in optimizing for size and performance.
The five tips below focus on how to select a direct drive frameless torque motor kit and provide system engineering requirements for the drive motor selection.
Selection of control methods, feedback requirements, and mechanical attributes really drive the selection of the motor.
a. The most common motorized joint includes a brushless permanent magnet frameless torque motor kit, an absolute encoder kit, and a high ratio zero backlash gear.
b. In most cases, a high precision absolute encoder is also required on the output of the gear to handle any lost motion and wind-up due to the low stiffness and lost motion in the gear systems.
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c. System voltage levels tend to be in the low voltage range < 50volts. This drives low impedance motor characteristics and defines the input speed range. d. Field oriented control sinusoidal servo drives with proper safety functionality and serial communication interfaces, such as EtherCat, are being used. Drives are getting smaller and located closer to the motor. e. Force and torque sensors may be necessary if the robot is used in a collaborative environment.
f. If the robot needs to hold a pose, fail-safe power-off brakes may be required.
The most important attributes in a frameless motor kit are mechanical form factor, motor constant (Km), and torque vs. speed characteristics when operating within the power limits. Do your homework, know what motor constant, Km, you need.
a. There are no standards in the industry regarding motor form factor, i.e. Diameter, Length and through hole size.
b. Motor Constant, Km, is the only true indicator of a motor's ability to output torque under thermal constraints. Km is a calculation = Kt/sqrt(R), where Kt is the torque constant NM/Amp, and R is the resistance in Ohms. Take care in making sure units are consistent and always calculate this because datasheets are notoriously lacking.
c. Cogging torque can greatly impact smoothness of operation. Cogging torque is not normally shown in a motor datasheet. The absolute value and the frequency of this cogging torque is important to the dynamics. Less is always better in this case, zero is preferred.
d. Sinusoidal torque versus angle curves and phase balance are critical to smooth motion. These two items are not shown in datasheets. It is only through experience and testing a problem will be uncovered. Ask for this data from the supplier.
e. Thermal resistance and thermal time constant are also important to know. Again, not always provided in a datasheet, and often assume unrealistic test conditions. Some robots have very specific temperature requirements almost disconnected from how motors are typically rated.
f. Electrical time constant is usually overlooked during selection. However, servo system response and servo driver PWM frequency play a large role in system performance. A low inductance motor, (typically a result of smaller size, zero cogging, weight optimized, low voltage motor kits), requires higher driver PWM frequency to minimize current ripple. Current ripple can cause electrical noise as well as additional heating.
Integrating a frameless motor kit into a mechanical joint is a complex mechanical design, with rotating mechanics, dynamics, and thermal considerations.
a. Joint size reduction is achieved by a high level of mechanical integration. Simplifying the number of bearings, eliminating couplings, and sharing rotating shafts and housings. This is the best way to improve reliability and reduce components.
b. Direct drive brushless frameless torque motors provide the highest Km, and therefore the highest torque output within the thermal budget. Torque requirements are not always known, if in doubt, look for the highest Km motor you can find for the available space. Supplier ratings for continuous torque are for reference only due to thermal conditions. A high Km motor will allow flexibility in electrical, mechanical and thermal attributes.
c. Motor Km increases with diameter faster than it increases with axial length. Always select the largest diameter frameless motor kit available with the shortest length to achieve the Km required.
d. Large diameter, high Km motors also typically have a large through hole. This through hole can be used for mechanical integration with bearings, or it can be used to house a holding brake coaxial to the motor. This will reduce the axial length of the joint.
e. Radial and axial magnetic forces are present in all motors. Again, not shown in datasheets, so you need to ask the supplier.
f. Cogging torque is undesired in all cases for a robot joint. Find the lowest cogging or zero cogging and it will eliminate much of the down stream diagnostic and vibration issues. Cogging frequency is also very important, a high frequency is generally better than a lower frequency and can be more easily tuned out. You will need to ask for this data.
a. The thermal resistance of a motor when mounting into a robot joint is unknown. This means that whatever the datasheet says for torque output isn't really relevant to the robot joint. Getting the highest Km in the size available will allow the most flexibility.
b. If a power off brake (mostly the case for safety reasons) is required and integrated, the brake is heating when the motor is moving. This heat reduces the available thermal budget for the motor.
c. A thermal model is necessary to predict heating for all sources and consider the available thermal budget for each joint. Each joint needs to be highly engineered.
d. In most cases the motor will have to be sized to perform under less than optimal thermal conditions essentially derating the motor from what it could produce.
a. Well, everyone wants to use 'off the shelf' standard product' right? They are readily available and lower cost'sounds good. Realistically, if you are designing a precision robot to be manufactured in a highly controlled quality system, off the shelf may not be the best solution.
b. Tight control of design and revisions directly conflicts with the 'off the shelf' supplier mentality. Buying off the shelf means that the supplier can change whatever they want at any time, especially if there are no industry standards controlling design and interface compatibility. Without control, internal materials, design, or form factor can change without notice. Forcing a supplier to control the design and changes, turns the product into a custom product that is not 'off the shelf' any longer.
c. Some low-cost hobby motors from global distributors posing as manufacturers are finding their way into advanced systems. In this case, it is unknown who the actual manufacturer is, and there are no controls in place to guarantee that materials and design will not change on the next delivery.
d. Buy from a reputable supplier with an open book policy allowing factory visits, sub-supplier identification, and customer included change control. At minimum, purchase a modified standard product, where the modifications include control/approval over design revisions.
e. If volumes approach a few hundred units per year, a custom designed solution may be the best option. It gives complete control over the design, materials, and manufacturing process. It will get you to the center of the requirements spectrum in Figure 1 below.
Figure 1 ' Design Spectrum for a robot Joint, axes converge on the center
A traditional frameless motor is shown below. The motor shown in Figure 2 is a slotless LS Series motor from ThinGap. These motors have zero cogging and a large through hole. Km of these motors rivals some traditional slotted (or toothed) brushless permanent magnet motors.
Figure 2 ' Slotless Frameless Torque Motor Example
Figure 3 below is a compact integrated Robot Joint. It uses a frameless torque motor kit, high resolution medium accuracy absolute encoder on the input. It has a high ration zero backlash precision gear and a high accuracy absolute encoder on its output.
Figure 3 ' Highly integrated Robot Joint
Figure 4 below is a Robot Joint with Tradition Servo Motor. It is more than 2X longer for exact same performance. It is also less reliable with more components including a coupling. It has more adjustments and connections than the compact joint above. It does not have a through hole in the shaft.
Figure 4 ' Traditional Robot joint with exposed servo motor
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