Evolution of an Integrated Actuation Mechanism for Planetary Exploration Using Dual-Reciprocating Drilling By Craig Pitcher, Surrey Space Centre Prof. Yang Gao, Surrey Space Centre & Dr. Lutz Richter, OHB System AG Surrey Space Centre, University of Surrey, UK 13 th Symposium on Advanced Space Technologies in Robotics and Automation (ASTRA) ESA-ESTEC, Noordwijk, The Netherlands, 11-13 th May 2015
Overview Introduction Summary of Dual-Reciprocating Drilling Presence of Lateral Forces Internal Actuation Mechanism Dual Mechanism Concept Trade-Off Quadruple Cam Design Experimental Set-Up
Introduction Rotary and percussive drills Rotary drills require large overhead force, exacerbated by low-gravity environment Percussive drills have limited penetration depth Rotary-percussive drills are heavy, complex systems Percussive moles penetrate regolith only Dual-Reciprocating Drill (DRD) Self-contained, low mass system Requires low overhead force
Wood Wasp Ovipositor Drills into wood using two-valve reciprocating motion Backwards-facing teeth of receding half grip substrate Tensile force generated is converted to compressive force
Dual-Reciprocating Drill Prototype tested in low-strength rocks Custom-built drill heads and test bench Allowed testing of various operational parameters and drill head designs in regolith Drills deeper than static penetration High levels of slippage observed (>95%) Receding drill half moves upwards instead of gripping surrounding substrate
Presence of Lateral Forces Small sideways movements of drill heads observed Forces acting on DRD measured using mono-block drill head experiments Traction forces generated by teeth one to two orders of magnitude lower than penetration forces Increased penetration due to sideways movements of DRD creating significant lateral forces
Presence of Lateral Forces Several experiments experienced significant bending of the drill stem This consistently caused an increase in drilling depth and speed Additional compression of surrounding regolith produces large horizontal resistance
Internal Actuation System is transferring from proof of concept test bench to integrated prototype Reciprocating mechanism fitted inside hollow drill heads Cam wheels mechanically linked to conventional motor Drive shafts convert rotary motion to linear reciprocation
Dual Mechanism New internal actuation mechanism design First demonstration of a fully integrated system Active control of lateral movement New drilling motions available Reciprocating-only drilling Simultaneous reciprocating and lateral motion, creating a burrowing motion Allows comparison of drilling and burrowing performance Fully investigate effects of lateral motion
Concept Designs Five concepts based upon original design 90 Cam and Gearing Shaft Base Third Cam Tilted Cam Tilted Cam With Linear Actuator Quadruple Cam
Trade-off Study Performance Criteria Ease of Changing Between Motions Number of Parts Ease of Implementation Overall Drill Diameter Even Distribution of Force Coupling of the Motions Weight 2 2.5 3 3 4.5 5 Emphasis placed on studying performance of different drilling motions
Quadruple Cam Independent variation of reciprocation and lateral amplitudes Force distributed throughout drill 4 drive rails 14 connection points Complex design Three possible drilling motions Reciprocation-only Circular Diagonal
Circular Motion Non-sinusoidal piston movement creates a squashed circular motion Reducing one amplitude only creates an elliptical path
Diagonal Motion Changing of cam set-up allows diagonal drilling motion Reducing one amplitude only creates a slightly curved path
Experiment Set-Up 21 possible drilling motions Tension-compression load cell inside drill head measures forces Support plate held on guiding rails Tests in poured martian regolith to a maximum depth of 22cm Aim to determine the optimal burrowing mechanism required in different regoliths
Summary DRD is a low-mass alternative to traditional drilling techniques Sideways movements of the drill heads have a significant effect on drilling performance The system is moving from a proof of concept to a first fully integrated system prototype Quadruple Cam design chosen for its ability to perform wide range of drilling motions Experiments will determine the benefit of lateral motions and the optimal set-up