In surgical robot applications a motion solution that delivers high power density in a small package is a common requirement .
Ensuring the lifetime of a DC gearmotor with systematic reliability testing
Utpal Rabha , Lead Engineer , Portescap , explains the RDT procedure
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From industrial power tools to surgical robots , through to applications in aerospace and defence , a motion solution that delivers high power density in a small package is a common requirement . However , integrating a gearmotor means an assurance of reliability is crucial . When operational life exceeds the duration allowable for testing , a systematic approach to Reliability Demonstration Testing ( RDT ) can provide OEMs with 95 % certainty that the gearmotors will meet or exceed their required run time .
DC gearmotors are designed to meet the torque requirements of specific tasks while ensuring compact dimensions . With an assembly of a brush or brushless DC motor , the device combines a gearbox that optimises torque , speed , and efficiency requirements . This enables a gearmotor to reduce output speed while increasing torque to the required level , achieving this with a more compact diameter compared to using a higherrated individual motor alone .
With the additional gearbox mechanism , it ’ s imperative that the design of the gearmotor is sufficiently reliable for the duration of its required use . To ensure resilience for real-world conditions , Reliability Demonstration Testing ( RDT ) is required .
RDT stages The first task of the planning stage is to establish the reliability objective , which is required to set the RDT parameters . Typical gearmotor characteristics subject to RDT include voltage , current , speed , temperature , noise , and physical integrity . The test models can then be selected to calculate sample size , as well as the test time required . The preference depends on whether the test duration differs from the expected service life ; it is needed for a device that operates long-term , compared to a device that might just require single-shot operation . An accepted test tolerance level must also be set .
Ideally , testing should take place under actual application conditions , and be continued for the full duration of the intended operational period . However , if time to market requirements don ’ t allow this , such as for long life expectancy gearmotors that might operate for 10 years , an accelerated test method can be used . In this case we would calculate the B10 life , the time at which devices have a 90 % probability or more of survival .