A conveyor comprising: a rail having an array of permanent magnets embedded in and extending along the length of the rail to form a permanent-magnet stator creating a magnetic field; a tray supported on the rail and having a top article-supporting surface and having a series of commutated drive coils as a forcer coacting with the permanent-magnet stator to form a brushless linear dc motor to propel the tray along the rail ; a tray conveyor segment extending from a first end to a second end in a conveying direction and including: a pair of the rails closely spaced and separated by a slot and having tops , each of the rails including such an array of permanent magnets creating a magnetic field across the slot ; wherein the tray includes: a platform forming the top article-supporting surface and a bottom surface supported on the tops of the rails ; a blade extending downward from the bottom surface and in the conveying direction to ride in the slot and housing the series of commutated drive coils ; a tray controller driving the drive coils to produce a traveling electromagnetic wave that interacts with the magnetic field to propel the tray in the conveying direction ; wherein the slot widens at the tops of the rails and the tops of the rails are convexly curved. a rail having an array of permanent magnets embedded in and extending along the length of the rail to form a permanent-magnet stator creating a magnetic field; a tray supported on the rail and having a top article-supporting surface and having a series of commutated drive coils as a forcer coacting with the permanent-magnet stator to form a brushless linear dc motor to propel the tray along the rail ; a tray conveyor segment extending from a first end to a second end in a conveying direction and including: a pair of the rails closely spaced and separated by a slot and having tops , each of the rails including such an array of permanent magnets creating a magnetic field across the slot ; wherein the tray includes: a platform forming the top article-supporting surface and a bottom surface supported on the tops of the rails ; a blade extending downward from the bottom surface and in the conveying direction to ride in the slot and housing the series of commutated drive coils ; a tray controller driving the drive coils to produce a traveling electromagnetic wave that interacts with the magnetic field to propel the tray in the conveying direction ; wherein the slot widens at the tops of the rails and the tops of the rails are convexly curved. a pair of the rails closely spaced and separated by a slot and having tops , each of the rails including such an array of permanent magnets creating a magnetic field across the slot ; wherein the tray includes: a platform forming the top article-supporting surface and a bottom surface supported on the tops of the rails ; a blade extending downward from the bottom surface and in the conveying direction to ride in the slot and housing the series of commutated drive coils ; a tray controller driving the drive coils to produce a traveling electromagnetic wave that interacts with the magnetic field to propel the tray in the conveying direction ; wherein the slot widens at the tops of the rails and the tops of the rails are convexly curved. a platform forming the top article-supporting surface and a bottom surface supported on the tops of the rails ; a blade extending downward from the bottom surface and in the conveying direction to ride in the slot and housing the series of commutated drive coils ; a tray controller driving the drive coils to produce a traveling electromagnetic wave that interacts with the magnetic field to propel the tray in the conveying direction ; wherein the slot widens at the tops of the rails and the tops of the rails are convexly curved. <EOS>