Page 20 - Industrial Technology EXTRA 26th October 2020

l Torque-to-diameter ratio – robots are normally the size of the brake itself is less critical. In some
constrained by the space they operate in, which cases such as torque motors or hollow shaft motors,
means the torque-to-diameter ratio is a key the brakes will have to be mounted separately.
consideration. In general, OEMs should look for the However, size of the brake is still important for all
highest possible ratio, particularly for the brakes applications.
used at the base of the robot arm.
l Response time – power-off brakes are typically Maximum and minimum torque
used as safety brakes that engage when power fails. In medical units such as a surgical operating arm,
In this case, response time is particularly important. the brake can also act as the clutch. The brake
PM brakes tend to have the faster response times holds the robot arm in place but if the maximum
and so are often the prefeered choice in safety- torque limit is reached, the unit can be moved (ie
critical applications. pushed out of the way) but still held safely. Often,
l Resolution – robots provide highly controlled the friction material can affect or control this, which
motion and so resolution is always important. Both is a good safety aspect.
PM brakes and spring-applied brakes offer infinite
resolution. Other common options
l Cost – spring-applied friction brakes tend to be Other features can be added to brakes used in
the most economical solution, offering effective compact robotic applications. These include:
performance in a wide range of applications. PM l Reduced holding voltage – after being released
friction brakes are next in terms of cost, followed by at nominal voltage, some manufacturers of spring
spring-applied tooth brakes – the most costly due to applied brakes can drop to a holding voltage of 50%
the precision manufacturing required. nominal. This is very advantageous for an AGV,
forklift truck or other mobile robotic application
Low profile brake designs where the power supply is a battery, as power
Recent advancements have enabled robotic arms consumption is significantly reduced. This will also
and mechatronic systems to shrink in size. This reduce heat generated from the brake coil. This is
reduction in footprint often requires low profile or typically achieved with PWM (Pulse Width
‘pancake’ style brake technology. KEB has Modulation) controlled by the customer.
recognised the increasing demand for compact l Cable assembly and connectors – some
spring applied brakes and has successfully designed suppliers can provide brakes complete with heat
custom low profile brakes. shrink tubing, wire jackets, pig tailed leads, cable
This style of brake is functionally identical to the labels, etc. Along with added connectors or plugs.
standard spring applied brake but achieves the This eliminates the need for customers to add cable
same rated torque in approximately two-thirds the assembly to their process and provides a ‘plug-and-
thickness, which allows for highly compressed drive play’ ready solution.
system braking in robotic joints, AGV’s, forklift l Custom coil voltages – some batteries and
trucks, etc. Magnetic simulation software can also control systems operate at voltages outside of the
be used to design custom brakes that meet common standard offerings (24, 48, 105,
customer-specific design envelope constraints. 205VDC). Some suppliers can design and wind a
Not all robotic applications require the brake to coil to suit any desired voltage.
be incorporated into the robot arm, which means www.keb.co.uk

October 2020 • INDUSTRIAL TECHNOLOGY EXTRA • p20