An alternative is here put forward to counterbalance the present-day preoccupation with series-actuated robot-arms. A systematic study of robots and manipulators, now concentrating on “in-parallel” actuator-arrangements, reveals many geometries applicable either to entire robot-arms or to parts of otherwise series-actuated arms. No survey of this kind is possible without drawing heavily on the theory of screw systems. Having established a means of enumerating possible geometries, screw theory is again invoked to highlight, in broad terms, the patterns considered to be most promising. Criteria for avoiding undesirable robot-arm-configurations are touched upon, and certain aspects of the performance of in-parallel-actuated robot-arms are compared and contrasted with those of series-actuated arms. Within the bounds here set (thought to be realistic) the survey on its own is intended to be exhaustive, but many details remain to be investigated. This paper aims to do no more than edge open the door a little further towards in-parallel actuation in robot-arms; others may then consider that further study could be productive.

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