A conveyor system comprising: a first conveyor including: a conveyor belt arranged to advance forward along a conveying path at a belt speed in a first direction and including: a first side and a second side defining the width of the conveyor belt; and a plurality of belt rollers rotatable on axes of rotation oblique to the first direction and arranged in columns extending longitudinally in the first direction and spaced apart laterally across the width of the conveyor belt a distance d; a roller-engagement mechanism underlying the conveyor belt along a portion of the conveying path to form a roller-engagement zone, wherein the roller- engagement mechanism includes: a plurality of parallel first belt support surfaces extending longitudinally and spaced apart laterally the same distance d as the columns of belt rollers; a motor driving the first belt support surfaces so that they advance in the first direction at the belt speed; an actuator coupled to the first belt support surfaces to move the first belt support surfaces between a first position in which the first belt support surfaces are in contact with the belt rollers and a second position in which the first belt support surfaces are out of contact with the belt rollers; wherein, in the first position, the first belt support surfaces advance in the first direction at the belt speed to inhibit the rotation of the belt rollers passing through the roller-engagement zone. a conveyor belt arranged to advance forward along a conveying path at a belt speed in a first direction and including: a first side and a second side defining the width of the conveyor belt; and a plurality of belt rollers rotatable on axes of rotation oblique to the first direction and arranged in columns extending longitudinally in the first direction and spaced apart laterally across the width of the conveyor belt a distance d; a first side and a second side defining the width of the conveyor belt; and a plurality of belt rollers rotatable on axes of rotation oblique to the first direction and arranged in columns extending longitudinally in the first direction and spaced apart laterally across the width of the conveyor belt a distance d; a roller-engagement mechanism underlying the conveyor belt along a portion of the conveying path to form a roller-engagement zone, wherein the roller- engagement mechanism includes: a plurality of parallel first belt support surfaces extending longitudinally and spaced apart laterally the same distance d as the columns of belt rollers; a motor driving the first belt support surfaces so that they advance in the first direction at the belt speed; an actuator coupled to the first belt support surfaces to move the first belt support surfaces between a first position in which the first belt support surfaces are in contact with the belt rollers and a second position in which the first belt support surfaces are out of contact with the belt rollers; a plurality of parallel first belt support surfaces extending longitudinally and spaced apart laterally the same distance d as the columns of belt rollers; a motor driving the first belt support surfaces so that they advance in the first direction at the belt speed; an actuator coupled to the first belt support surfaces to move the first belt support surfaces between a first position in which the first belt support surfaces are in contact with the belt rollers and a second position in which the first belt support surfaces are out of contact with the belt rollers; wherein, in the first position, the first belt support surfaces advance in the first direction at the belt speed to inhibit the rotation of the belt rollers passing through the roller-engagement zone.